The magic of a clear night sky filled with stars has inspired many creative souls. Now, through a collaboration between science and art, a stainless steel sculpture installed at the Australian National University in Canberra brings new depth to the connection between ourselves and the stars above.

The 4 metre diameter, mirror-polished stainless steel sphere (called UNA), which sits in the science precinct at ANU, is so much more than first meets the eye. Designed by UK artist Wolfgang Buttress, UNA features 9,100 laser-cut perforations, which were mapped in collaboration with ANU astrophysicist Dr Daniel Bayliss.

The holes match the 9,100 stars that we can see with the naked eye from Earth and vary in size according to the brightness of the stars in the night sky (the brighter the star, the larger the hole).

Inside the sphere sits a second, two metre diameter mirror polished, stainless steel sphere. When viewed through one of the outer perforations, the internal sphere reflects small points of light from the outer sphere, creating, according to Mr Buttress, a microcosm of our perceived night sky.

“One makes connections to one self and the stars above. We are all made from stardust,” he said.

The magic enters a different realm at night, thanks to the fibre optic lights that sit in the centre of the two spheres, casting a glow through the perforations.

Mr Buttress said the use of stainless steel and high quality fabrication were integral to the success of the project.

Aside from the ability to be mirror polished, he said stainless steel was specified due to its strength, resilience and, if maintained properly, the fact that it will look as good in 50 years as it does now.

The spheres incorporate around 2000kg of 4mm 316L, 2B finish stainless steel, which was supplied in 24 pieces by ASSDA Major Sponsor Sandvik Materials Technology (now Vulcan Stainless). The pieces were laser cut to shape in-house on one of Sandvik’s four laser machines. Sandvik VIC/TAS State Manager Stephen Orridge said each hole was unique in its shape and the work involved about 40 hours of programming.

The sheet was pressed by Dished & Flanged Ends to create the curved forms for both the inner and outer spheres. ASSDA Member and Accredited Fabricator NRG Piping then joined and welded each segment with only 1mm tolerance, followed by polishing. NRG Piping co-ordinated the fabrication, transport and installation of UNA.

Mr Buttress said the welding had to be done carefully to minimise distortion as all would be seen when it was mirror polished. “There is nowhere to hide. NRG Piping are amazing fabricators as they totally understand the properties and essence of stainless steel,” he said.

Because the inner sphere had to be positioned inside the outer sphere during the fabrication process, a 600mm hole at the base allowed enough room for a welder to get access inside to polish out the internal welds.

The end result is one of the artist’s favourite pieces that he has created. “By day, the inner world is revealed on close inspection and at night it has a different character as light pours out of her like a beacon. It works on a micro and macro level, at day and by night. It was a great marriage between art, architecture and engineering,” Mr Buttress said.

Images courtesy of Ben Wrigley.

This article is featured in Australian Stainless magazine issue 54, Spring 2014.

The normal state for stainless

Stainless steels resist corrosion because they have a self-repairing “passive” oxide film on the surface. As long as there is sufficient oxygen to maintain this film and provided that the level of corrosives is below the steel’s capacity of the particular material to repair itself, no corrosion occurs. If there is too high a level of (say) chlorides, pitting occurs. As an example, 316 works well in tap water (<250 ppm) all over Australia, but will rapidly corrode in seawater because seawater has very high chloride levels (20,000 ppm).

If there is not enough oxygen and the local corrosives are not high enough to cause pitting, then general corrosion can occur. This might happen in a crevice (which has very limited oxygen) or in a strong, reducing acid (such as mid concentrations of sulphuric acid). General corrosion can occur when there are stray currents flowing from stainless steel to ground. This can happen in mineral extraction if the bonding arrangements are inadequate during electrowinning. General corrosion may also occur from galvanic effects, e.g. if a conductive carbon gasket is used on stainless steel in an aggressive environment.

QUANTIFYING CORROSION RESISTANCE
For circumstances where general corrosion is expected, graphs are available called iso-corrosion curves. They plot the effect of a single chemical and corrosion rate for temperature against concentration. An example is the graph below of a 42% nickel alloy 825 in pure sulphuric acid with air access. This graph shows that the corrosion rate increases with temperature and that provided the temperature is less than ~45 °C and a corrosion rate of 0.13 mm/year is acceptable, alloy 825 would be suitable for any concentration of pure sulphuric acid. The boiling point curve is often included to show the limits of data at atmospheric pressure.

 

 

Most of the following graphs are from the Outokumpu Corrosion Handbook. The specific alloy compositions are tabulated in that Handbook and in the Appendix of the ASSDA Technical FAQ 8.

However, a series of graphs each showing the results for one material over the full range of concentrations and temperatures is cumbersome and so multi-material plots are used for the initial material selection. Titanium is frequently included because of the widespread expectation that it is the “super” solution – although the data shows this is not always correct.

The two graphs below show data for austenitic and duplex stainless grades in pure sulphuric acid. However, only the 0.1 mm/year lines are drawn for each alloy because it is assumed that a loss of 0.1 mm/year would be acceptable for continuous exposure during 365 days per year. This assumption may not be acceptable if, for example, the process using the acid required very low iron levels. For each material, the temperature and concentrations of pure sulphuric acid that are below the line would mean a corrosion rate of less than 0.1 mm/year.

 

WHAT ABOUT IMPURITIES OR ADDITIVES?
The graphs below show (and note the temperature scale changes from earlier graphs) the dramatic reduction in corrosion resistance when 200 mg/L of chlorides are added to sulphuric acid or ten times that amount, i.e. 2,000 mg/L. The heavily reducing range from about 40% to 60% acid concentration  defeats even the high nickel 904L and 254/654 grades.

Nevertheless, a number of grades are potentially suitable for concentrations below 20% sulphuric even with significant chlorides.  However, the graphs also show that at the other end of the concentration scale, the oxidising conditions, which occur for sulphuric acid above about 90%, are extremely aggressive if the acid is impure.

 

 

Some additives act as inhibitors to corrosion and this can be critical in selecting suitable materials for mineral extraction processes. For example, the graph below shows that adding iron ions to sulphuric acid improves the resistance of 316. Adding oxidising cupric ions has a similar effect but as with any inhibitor, attack can occur in crevices where the inhibitors may be used up. And despite the requirement for oxidising conditions to ensure  stability of the stainless steel’s passive layer, it is possible to add too much oxidant as shown by the positive effect of small additions of chromic acid followed by a reduction in corrosion resistance if more chromic acid is added. It is relatively common to refer to the redox potential (rather than concentrations of oxidising ions) if the chemistry is not simple.

 

The data in this section is intended to show that while these iso-corrosion graphs are useful in predicting corrosion rates for specific pure compounds, the addition of aggressive ions, oxidisers or crevice conditions require more detailed consideration.

MATERIALS SELECTION FOR OTHER CHEMICALS
A very common chemical is phosphoric acid, which is used in cleaning, pre-treatments, food preparation and a host of other applications.  It requires increasing chemical resistance with high temperatures and concentrations. For pure phosphoric acid, the iso-corrosion curves show a progression from ferritic 444, through the austenitic 304, 316, 317 to 904L. This is not an oxidising acid so although it removes iron contamination, it does not strengthen the passive film on stainless steels.

Phosphoric acid is frequently associated with chloride or fluoride ions especially in production from rock phosphate. The variation in composition in this wet process acid (WPA) means that iso-corrosion plots are of limited use. However, with thermally produced acid and various impurities, a plot of corrosion rate vs. contaminant ion concentration may be used instead of an iso-corrosion graph – in this case chlorides with the 2.5% molybdenum version of 316. This data is for exposure 24 hours a day, 365 days a year. Note that while the two graphs do not overlap, the trends of these different experimental plots do not exactly match, i.e. iso-corrosion curves provide trend data and not precise values.

 

 

ACIDS FOR CLEANING STAINLESS STEELS

Both the chelating oxalic and citric acids, and the oxidising nitric acid, are widely used on stainless steels both for cleaning and passivation as shown in ASTM A380 and A967. Nitric acid can be used at elevated temperatures and low to medium concentrations without concern for the standard austenitics. However, at high concentrations and above ambient temperatures, they can suffer intergranular attack, unless a low carbon grade is used. In the same environment, molybdenum-containing grades may suffer intergranular attack of the intermetallic phases such as sigma.

 

ALKALIS
As shown by the plot, austenitic stainless steels are resistant to general corrosion for all concentrations of sodium hydroxide and, for high concentrations, the usual problem is lack of solubility. However, at near boiling temperatures, austenitic stainless steels (and especially those with extensive chromium carbide precipitates) are susceptible to cracking as shown by the shaded area.

 

 

SUMMARY
If you intend to use a stainless steel with a new, relatively pure chemical, iso-corrosion curves offer an initial guide to the temperature and concentration limits against general attack. If there are contaminants or oxidants present, then the corrosion susceptibility can increase or decrease significantly and specialist advice should be obtained.

This technical article is featured in Australian Stainless magazine issue 54, Spring 2014.

Brisbane's New Farm Riverwalk is one of the city's beloved icons. Originally constructed in 2003, the Riverwalk was used daily by over 3000 cyclists, pedestrians and runners before it was washed away during the 2011 floods.

After a construction period of nearly 18 months, Brisbane City Council’s re-imagined New Farm Riverwalk has now opened to the public, connecting New Farm to the Brisbane City via the Howard Smith Wharf Precinct.

Engineered by Arup, the Riverwalk has a design life of 100 years and sits 3.4m above mean sea level on robust piles.

Critical to its design and life expectancy is the extensive use of stainless steel for both structural and aesthetic purposes.

Brisbane City Council’s two key objectives of the project were to achieve a low maintenance, durable structure while achieving high aesthetic qualities. Stainless steel was deemed suitable to achieve both objectives while also providing the necessary strength required.

Key design elements featuring stainless steel include balustrades, skate stops, help point enclosures, light posts, signage, electrical enclosures, deck furniture and bins at the node structures. For additional durability, stainless steel reinforcement conforming to BS10088 and BS 6744:2001 was used in the soffit of the precast concrete girders where the structure could be subject to wetting and chloride contamination in the future.

Constructed by John Holland, the project involved a high level of collaboration between multiple suppliers and fabricators to meet the exacting demands of the specification.

John Holland Project Engineer Cameron Pahor said one challenge was programming works in accordance with project specifications to reduce contamination between carbon steel and stainless steel, both of which were used within the precast concrete girders incorporated into the Riverwalk.

Modelling of the reinforcing in 3D by Vectors Computer Aided Drafting also meant exact dimensions were ascertained, reducing waste of stainless steel reinforcing.

ASSDA Sponsor Valbruna Australia Pty Ltd’s Queensland construction division was contracted to supply 385 tonnes of stainless steel reinforcing bar, with The Australian Reinforcing Company (ARC) sub-contracted to schedule, cut and bend the rebar in a specifically prepared quarantine location to prevent processing and storage contamination issues.

Valbruna Special Products Manager Scott Ford said the majority of the rebar (in diameters ranging from 12mm to 40mm) was produced to precise precast tolerances predominantly using Reval® special Grade AISI 2304 (1.4362). Grades 2205, 316L and 304L were also used due to the unexpected increase in tonnage required: nearly 40% more than original project calculations was required, making the Riverwalk the largest use of stainless steel rebar in Australia to date.

Mr Ford said stainless steel rebar ensured the Riverwalk met the required 100 years life cycle, while minimising ongoing maintenance costs.

“Using stainless steel rebar ensures that a landmark structure such as the Riverwalk is kept open to the public rather than lengthy maintenance closures due to corrosion issues,” he said.

Down time was also minimised during construction, with Valbruna holding extensive stocks on the floor in both Italy and Australia of stainless Reval® rebar, enabling delivery to site within 48-72 hours of final approval of drawings. Manual templates were produced for many of the bars to ensure the accuracy of the bends and eliminate site down time.

Minimising maintenance for the visual elements of the Riverwalk was also a priority. To this end, ASSDA Sponsor Midway Metals supplied 275 tonnes of grade 316 stainless steel and two tonnes of welding consumables for the construction of around 1900m of balustrading. Midway also supplied 100 litres of Avesta pickling gel that was used to passivate all welds on the balustrades.

Midway Metals Brisbane Branch Manager Sean Lewsam said some of the specified handrail sizes were not available in Australia (e.g. 150x50x6mm rectangular hollow section or RHS) and had to be air freighted in to meet strict deadlines.

Midway supplied the project with 3,522 metres of RHS, 14,500 metres of round bar, 1,924 metres of HRAP (hot rolled, annealed, pickled) flat bar, 1,500 metres of flat bar from their slitting and flat bar machines, and 2,000 metres of mirror tube, storing the material in a dedicated holding area for the duration of the project.

Specific-sized Grade 316 plates were acquired (132 tonnes in total ranging from 10mm to 16mm) to minimise off cuts and wastage during the plasma cutting of stiffener plates, 1500 base plates and 1000 staunchions for the balustrades. Around 26 tonnes of laser cut profile plates ranging from 5mm to 20mm were also supplied.

ASSDA Member Southern Stainless was contracted to fabricate and install three different types of balustrading (solid uprights, mesh wire and glass infill), as well as the other visible stainless steel elements of the project using the stainless steel and welding consumables supplied by Midway Metals.

Southern Stainless General Manager Matthew Brown said all stainless steel components were manually polished to a 600 grit finish prior to assembly and welded in compliance with AS1554.6. After fabrication, the 960 balustrades panels (each weighing between 180 and 220kg) were electropolished in-house to R_a<0.5 and then hand polished with silicone-based polish prior to being wrapped and delivered to site for installation. The end product is both visually appealing and certain to stand the test of time.

Strength testing was undertaken for the balustrade/girder connections to ensure the stainless steel couplers, bolts and ferules (supplied by ASSDA Member Ancon Building Products) would not damage the cast-in items during a flood occurrence.

Riverwalk’s robust design makes it resilient to future flood events. The opening span has been relocated to reduce the likelihood of debris getting caught on the structure, and some elements have been designed to collapse in extreme events (rather than withstand the flood waters), reducing the force on the piles.

With the re-imagined Riverwalk now a fixture on the Brisbane’s riverscape once again, residents and visitors can look forward to enjoying the unique experience that Riverwalk offers well into the future.

This article is featured in Australian Stainless magazine issue 54, Spring 2014.

A grand ballroom demands high impact aesthetics combined with maximum functionality, both of which have been supplied in spades at the recently refurbished RACV Royal Pines on Queensland's Gold Coast

Central to Stage 1 of the award-winning refurbishment is a 55 metre long and 5 metre high floor-to-ceiling glass wall anchored and framed by nearly a tonne of stainless steel wire rope and fittings. The wall ensures an impressive visual impact, as well as enabling a flood of natural light, a stunning view, and flexible exhibition options.

Designed by Joseph Pang Design Consultants and project managed by Schiavello Constructions, ASSDA Member Structural Dynamics (Australia) Pty Ltd (Strudyna - an entity under the Arcus Wire Group) was contracted to work with Queensland Glass to meet the demanding needs of the wall’s design.

Strudyna Architectural Manager Ross Munro said the installation was extremely complex, as well as being the team’s first retrofit glass façade project involving engineering, supply and installation.

The client requested a vertical cable truss, internal glass façade and mirror polished fittings to ensure a high-end finish to compliment the refurbishment.

Mr Munro said the retrofit installation meant there were many challenges associated with working with an existing engineered structure.

“The suspended concrete floor had been built to a specific load capability and included post-tension cables within the concrete floor that had to be accommodated. This affected the loads that could be applied to the cable truss to keep the structure rigid, while considering slab deflection with loads from occupancy,” he said.

The cable truss façade featured frameless hinged doors that were also emergency exit doors, so there were no horizontal cable elements to stabilise the  trusses.

Around 926kg of grade 316 stainless steel were used in the job, including fittings/castings and 8mm and 12mm Hamma X-Strand. Hamma X-Strand is stainless steel wire strand with a high quality shine finish manufactured by KOS in South Korea to Arcus Wire Group’s specifications, including annealing, pre-forming of wires and finished lay length, which significantly improves performance.

Electro bath polishing was used on the wire rope and floor and head tension plate brackets, while the spyders, rotules and compression posts were hand mirror polished.

In addition to the glass wall fixtures, other elements of stainless steel in the refurbished space included a staircase and handrail constructed by Arden Architectural Staircases and around 60 metres of 38mm grade 316 curved handrail fabricated and installed on an existing staircase by ASSDA Accredited Fabricator and Member Stainless Aesthetics.

Stainless Aesthetics Director Mike Mooney said his team also installed grade 316 capping on about 50 metres of 20mm glass balustrade, as well as further handrail and mirror-finish capping in the refurbishment of the resort’s health and fitness centre, which formed Stage 2 of the project.

With just 10 weeks to meet the venue’s fixed re-opening date of Stage 1, this challenging project required a high level of co-operation between trades and resulted in a classic marriage of form and function.

In a nod to the outstanding work carried out by all those involved, the RACV Royal Pines refurbishment was recently awarded the 2014 Queensland Master Builders Association’s Gold Coast Construction Award for Refurbishment/Renovation costing $5-$10 million.

This article is featured in Australian Stainless magazine issue 54, Spring 2014.

ASSDA member Australian Pickling & Passivation Service (APAPS) and ASSDA sponsor Sandvik Mining & Construction have been central to the expansion of a coal export port in North Queensland.

With Queensland coal exports forecast to increase to 250mtpa by 2015, the strength and durability of the state’s expanding coal transport infrastructure and rail systems is critical to ensuring export capacity.

This recent expansion required the manufacture of 300 three-piece conveyor frames using 40 tonnes of 316 grade stainless steel, specified to foil the port’s exposure to wind, rain, salt spray and abrasive dust.

Sandvik Mining & Construction manufactured the conveyor frames for the project, and APAPS pickled the frames before delivery to the terminal.

Stainless steel can corrode in service if there is contamination of the surface. Pickling involves the removal by chemical means of any high-temperature scale and any adjacent low chromium layer of metal from the surface of stainless steel.

The client requested that the stainless steel conveyor frames were pickled to achieve a product that would not rust. According to APAPS’s Director Richard Raper, ‘Pickling stainless steel removes all traces of burnt chromium caused by heat from welding and any iron contamination caused by handling and processing during fabrication.’ He added that several variables must be considered when pickling stainless steel, including the grade, surface finish, the size and shape of the structure and bath temperature.

Transported by road on B-double trucks from Mackay to the APAPS workshop in Newcastle, the conveyor frames arrived a dull grey colour and heavily soiled from anti-spatter and other contaminants. Pre-cleaning of the stainless steel was required prior to pickling as contamination on the surface can reduce the effect of pickling. The frames were sprayed using an Avesta 401 Cleaner and Callington Haven Brite Wash and left for 30 minutes before being high-pressure washed with hot water.

The immersion pickling method was used to pickle the conveyor frames. They were immersed in a nitric and hydrofluoric acid bath for approximately 1.5 hours, which APAPS’s own pickling technician determined following a number of inspections. Avesta Pickling Bath 302 was used at a temperature between 25-30°C. The frames were lifted from the bath and allowed to drain for 15 minutes before being washed down using high-pressure water.

APAPS’s pickling of the stainless steel by was central to ensuring the performance and durability of the conveyor frames and maximising their corrosion resistance. The treatment also produced a consistent and smooth finish with aesthetic appeal.

After the pickling treatment, the conveyor frames were strapped together in batches of five, with timber placed between the stainless steel and strapping. They were then transferred and loaded using a forklift with stainless steel slippers [covers] to protect the frames from cross-contamination. Due to the physical nature of the conveyor frames, only one layer of frames at a time could be placed on the truck deck, and these were tied down with web straps. Transportation took an average of 3 days between Newcastle and Mackay.

The project was completed in 10 weeks and delivered back to Mackay in stages. The APAPS team worked two shifts a day to complete the work on time for Sandvik.

Richard Raper says the project was a testament to APAPS’s membership of ASSDA, as it was the Association’s referral that won him the job.

‘This is a good showcase of how ASSDA members and Accredited fabricators can achieve great outcomes and how clients get what they expect when specifying stainless steel.’

Images courtesy of Australian Pickling & Passivation Service Pty Ltd.
This article is featured in Australian Stainless magazine issue 53, Autumn 2013.

Almost 7 years after former Nickel Institute Director Dr David Jenkinson's 2006 Technical Bulletin, ASSDA's technical expert, Dr Graham Sussex, revisits the CrMn grades of stainless steel.

BACKGROUND
The majority of stainless steel is drawn from the austenitic family because these grades are readily formable, weldable and tough. These chromium-nickel (CrNi) and molybdenum-containing grades were traditionally grouped under the 300 series banner.

However, driven by the increased price of nickel several years ago, there has been renewed interest in lowering the nickel content of austenitic grades while maintaining the austenitic crystal structure. This is achieved by using combinations of higher manganese and nitrogen and even by adding copper.

These high manganese grades - 200 series austenitics - were first developed in the 1930s and were expanded during World War II because of a lack of domestic nickel supplies, especially in the USA.

Many of the new 200 series alloys have proprietary compositions that can vary with manufacturers’ processing. They are not classified or standardised under the ASTM/SAE three-digit codes.

FEATURES OF 200 SERIES
The mechanical, physical and forming properties of the CrMn and CrNi grades are very similar, although the CrMn grades generally have higher tensile strength because of higher nitrogen levels and a higher work-hardening rate because of the nickel level.

The conventional CrMn grades are used in hose clamps or lamp post clamps – thin material heavily cold worked for strength. Proprietary grades are used in galling-resistant applications such as bridge pins or in marine boat shafting, although duplex grades are a strong competitor. A disadvantage of CrMn grades is that the lower nickel content means a higher risk of delayed cracking after deep drawing.

A quirk of the conventional 200 series higher manganese grades is that they do not become magnetic when they are heavily cold worked, hence their suitability for use as end rings in electrical generators.

CORROSION RESISTANCE
The corrosion resistance of the newer CrMn grades is generally inferior to similar CrNi grades. To maintain the austenitic properties, the ferrite forming elements (chromium, molybdenum and silicon) must be in the correct proportions with the austenite formers (nickel, carbon, manganese, nitrogen and copper). If the strong austenite formers such as nickel are reduced, the corrosion-resisting, ferrite-forming elements must also decrease.

SENSITISATION
This occurs when chromium combines with carbon in the steel and forms micron-sized particles of chromium carbide so the chromium is unavailable to form the protective oxide film. The original 200 series increased the carbon level to remain austenitic (see Table 1), but this encouraged sensitisation during welding and is one reason that CrMn grades are not used for fabricated items.

Table 1: Registered 200-series grades

Grade		Chemical composition (wt%)
AISI	UNS	Cr	Ni	Min	N
304	S30400	18.0 - 20.0	8.0 - 10.5	2.0 max	0.10 max
201	S20100	16.0 - 18.0	3.5 - 5.5	5.5 - 7.5	0.25 max
202	S20200	17.0 - 19.0	4.0 - 6.0	7.5 - 10.0	0.25 max
205	S20500	16.5 - 18.0	1.0 - 1.75	14.0 - 15.5	0.32 - 0.40

DURABILITY
The newer grades, such as the Indian-developed J1 and J4 (see Table 2), are intended for use in milder environments. The low nickel content requires a reduction in the chromium content to about 15-16% compared to the 18% industry-standard 304. This is a significant reduction in corrosion resistance, especially for the very low nickel versions, and these small differences in chromium content can have a significant effect on durability.

Table 2: Grades J1 and J4

	Chemical composition (wt%)
Grade	Cr	Ni	Mn	N	Cu
J1	14.5 - 15.5	4.0 - 4.2	7.0 -8.0	0.1 max	1.5 - 2.0
J4	15.0 - 16.0	0.8 - 1.2	8.5 - 10.0	0.2 max	1.5 - 2.0

The newer, low-nickel CrMn grades are successfully used in India, mainly for components such as cookware or mixing bowls that are formed rather than welded. The use of these grades has spread across South-East Asia and especially into China where the increase in capacity for 200 series production was about 3 million tonnes last year - or about 10% of the world’s production.

CONFUSION OF GRADES
The switch in use to CrMn grades (and not just the J1 and J4 grades) has continued despite lower nickel prices because of the perceived benefit of lower price. Unfortunately, the increased use of less corrosion-resistant grades has confused the industry as the CrMn grades are not magnetic and, at least initially, appear to be stainless and are often assumed to be 304 or even 316.

The confusion arose from decades of familiarity with magnetic, lower corrosion resistance ferritic grades such as 430 in contrast to the more corrosion-resistant and non-magnetic 304 or 316. In fact, magnetism has no relationship to corrosion resistance. Grade mix-ups have caused serious corrosion failures in industry and customer dissatisfaction due to less serious corrosion defects like tea staining. This has mainly occurred in Asia but also in Australia.

The variable impurity levels, particularly of sulphur and phosphorous, was a serious issue when there was a significant volume of the new CrMn grades produced by smaller, older mills. The increase in modern production facilities will proportionately reduce this risk. However, the metallurgical necessity to increase carbon levels for austenite stability in specific CrMn alloys means that welded fabrications still require thin sections or rapid cooling to limit sensitisation and the consequent increased corrosion risk.

IDENTIFYING GRADES
It is possible to distinguish between CrMn and CrNi grades by either portable and expensive X-ray fluorescence equipment or, more simply, by drop test kits to detect Mn (CrMn vs CrNi) or Mo (304 vs 316). The kits often use a filter paper and a battery to ensure the test will work rapidly even with cold metal. See ASSDA’s Technical FAQ No. 4 for further details.

QUALITY CONTROL
Users need to ensure they have good quality control systems to avoid installation of a low-level CrMn grade rather than the expected high-level austenitic. The relatively unknown conventional 200 series has a sophisticated niche. However, for cost reasons, clients may push to use the lower CrMn grades instead of the normal CrNi austenitics or, in sheet applications, the ferritics.

SCRAP AND SORTING GRADES
The fabrication scrap and end-of-life scrap from CrMn grades are not readily distinguished from conventional CrNi grade scrap. However, the value is substantially different as the nickel is still the most costly component. This has serious implications for the scrap industry because it is likely to reduce recycling and hence the sustainable and green image of stainless steel. Fabricators will find their total costs will require rejigging as the scrap from offcuts will have lower value, probably decreasing their profitability.

Each grade of stainless steel has its merits for different applications. However, it is vital to purchase from an educated and reputable supplier of quality materials in order to achieve the desired cost and quality outcome.

This technical article is featured in Australian Stainless magazine issue 53, Autumn 2013.

Stainless steel has transformed Perth's historic Forrest Place with a modern, interactive water sculpture.

The ‘Water Labyrinth’ was designed by internationally renowned artist, Jeppe Hein, and is his first permanent installation in Australia.

Launched in mid-November 2012, the $1.3 million sculpture is a major part of the Forrest Place redevelopment initiated by the City of Perth to create a stimulating public space for hundreds of thousands of residents and tourists.

Designed in a grid of nine squares, jets of recycled storm water shoot up into the air, creating 2.3m high water walls that randomly rise and fall. These water walls create up to nine ‘rooms’ that appear and disappear in sequences of 10 seconds before changing configuration.

Visitors of all ages leap from room to room or simply have a splash. The Water Labyrinth enables the interaction of people and art while utilising an important public space flanked by the sandstone inter-war Beaux-Arts style General Post Office and Commonwealth Bank buildings designed by John Smith Murdoch.

Hein says interaction is a distinctive element of the artwork and people play a vital role. ‘The Water Labyrinth activates the space and invites the public to make use of the artwork, either as a space for seclusion and relaxation or the opposite, a place for pure joy and playfulness.’

An impressive feature of the 12m x 12m Water Labyrinth is the 179m of stainless steel grating and drainage. As one of Australia’s largest manufacturers of stainless steel wedge wire grating, ASSDA member and Accredited Fabricator Paige Stainless was chosen to fabricate the water sculpture.

The popular water sculpture features approximately 62m² of PAIGE STAINLESS HEELGUARD® wedge wire and approximately 160m of 30x5mm flat bar in 304-grade stainless steel, supplied by ASSDA Sponsors Atlas Steels and Fagersta Steels.

PAIGE STAINLESS HEELGUARD® wedge wire is at the cutting edge of water drainage technology, overcoming inherent problems of drainage. The purpose-designed wedge shape in the stainless steel grates allows high volumes of water to shoot through the grates while trapping waste material for easy removal and cleaning.

The grating systems were custom made for the Water Labyrinth with a 5mm gap size and a 4mm wire head width, allowing a 50% open area for water flow. Pickling and passivation treatments were performed on the stainless steel grates prior to installation.

Paige Stainless senior design consultant Daniel Manning said a fine toothcomb approach was taken to ensure there were no safety issues in the final structure, as most visitors would be bare foot when experiencing the Water Labyrinth.

Having worked with stainless steel for over 15 years, Hein says stainless steel was the only material offering the required durability and compatibility for chemical treatment necessary for installation. Manning added that stainless steel’s aesthetic and corrosion resistant properties also made it an easy choice for materials specification in water technology.

Manning coordinated the production of the drainage system, which is an essential component of the Water Labyrinth’s design. All stainless steel components of the sculpture were 100% fabricated at Paige Stainless’s workshop in Caboolture, Queensland.

‘The collaboration with Paige Stainless flew smoothly and was very professional,’ says Hein. ‘They were able to produce and deliver quickly and the grids fabricated were of an extremely high quality.’

Main image above courtesy: Johann König, Berlin and 303 Gallery, New York. Photo credits: Jeppe Hein.
This article is featured in issue 53 of Australian Stainless magazine, Autumn 2013.

In the beleaguered Australian manufacturing sector, it's heartening to find ASSDA member Tasman Sinkware is a world-class leader in innovative design and manufacturing. Better still, in addition to supplying the domestic market, Tasman is exporting its products to Canada, the United States, New Zealand, Hong Kong and Singapore.

Tasman began operations in 1948 as a domestic metal fabricator in Adelaide. A move to sink manufacture saw its Oliveri brand pioneer the deep draw process in Australia and introduce precision manufacturing technology to produce high volume sinks.

Sixty-five years later, Tasman is now Australia’s only world-class, production line sink manufacturer, and its premium Oliveri brand is a market leader with a reputation for excellence in design, function and durability.

All Oliveri sinks are manufactured at Tasman Sinkware’s facility in Adelaide from 18/10 304-grade stainless steel supplied by various Australian distributors from reputable overseas mills. Significant capital expenditure over the years has enabled the company to introduce state-of-the-art processing equipment, including pressing, resistance welding, grinding, polishing, cleaning and product assembly equipment, most of which incorporate automation and/or robotic technology.

Tasman Sinkware employs a two-piece manufacturing process. The drainer and bowls are pressed separately then welded together to create bowls that are deep and have straight sides to ensure maximum capacity.

As a result, its stainless steel kitchen and laundry sinks are considered amongst the best in the world and the development of tapware and innovative accessories such as colanders and cutting boards has helped deepen domestic and international market penetration.

The superior design and function of the Oliveri sink range is led by Tasman’s in-house design team in Adelaide. Boasting more than 12 sink ranges and complementary accessories, the Oliveri brand has a strong presence in the building industry with the ability to influence trends.

Tasman Sinkware supplies leading Australian plumbing and electrical merchants and is developing inroads to commercial and residential real estate developments. Oliveri products are sold and distributed overseas through local agents and Tasman Sinkware also has staff on the ground in the USA.

Competition from cheaper Chinese imports is counteracted by Tasman Sinkware’s continued commitment to providing the highest quality products and excellent customer service. Manufucturing manager Steve Warnett says Tasman continues to innovate with new, leading-edge designs for the renovation and building markets. The Oliveri brand also enjoys high market recognition and loyalty amongst consumers and retail outlets.

Stainless steel continues to be the material of choice in laundries and kitchens due to durability, heat resistance, visual appeal and its 100% recyclability.

Grade 304 stainless steel has excellent corrosion properties, is resistant to most food processing environments and organic chemicals, and can be readily cleaned. It also has good oxidisation resistance in intermittent service to 870°C, and in continuous service to 925°C, making grade 304 the most ideal stainless steel grade and material for heat resistance in kitchen accessories.

Tasman Sinkware is Quality Accredited to ISO 9001. All Oliveri sinks are engineered to world standards and manufactured to AS 1756 and laundry tubs are manufactured to AS 1229.

www.oliverisinks.com

Images courtesy of Tasman Sinkware.
This article is featured in Australian Stainless magazine issue 53, Autumn 2013.

When Sydney's Star City Casino emerged from the chrysalis of its construction scaffolding, its metamorphosis included a gleaming 340m² stainless steel-and-glass canopy facing the harbour.

ASSDA Member TripleNine Stainless fabricated and installed the canopy over the main entrance of ‘The Star’, as it is now known, as part of an $850 million redevelopment. This transformation saw Sydney’s only casino swing its orientation 180° from Pyrmont’s fish markets toward the city’s glittering Darling Harbour.

The Star’s façade was designed by Fitzpatrick + Partners and is comprised of 147 flags of clear, low-iron glass supported by two fingers of 20mm and 166mm plate stainless steel. The surfboard-shaped canopy is 40m x 8.5m and made of 300 nominal bore pipe with a lattice effect created by 100 x 50 rectangular hollow sections. All 18 tonnes of stainless steel is 316 grade and was supplied by ASSDA sponsor, Atlas Steels.

Peter Petro, the site architect for the project, says stainless steel was the obvious choice from both a practical and an aesthetic point of view. ‘From a practical perspective, we chose stainless steel because it’s so close to the water and we needed something that was resilient.’

In terms of aesthetics, Petro says they wanted a high-quality finish for the front of the building and stainless steel was a prime choice. ‘We also had a lot of lighting design so we wanted something that would bounce the light around. We were able to give the stainless steel a polish that also matched the glass façade upstairs. This gives it a playfulness at night and a high finish during the day.’

TripleNine’s Director, Justin Brooks, says electropolishing wasn’t an option because of the massive size of the canopy. ‘Instead, it was polished to 400 grit then passivated with an Avesta product.’

Brooks says the project's engineers and designers, Yuanda, employed a Feng Shui expert to sign off on the canopy before
it was built at TripleNine’s purpose-hired workshop. ‘The basic geometry came from the client but we did the design detailing because of all the different shapes and angles,‘ explains Brooks.

The $1.4 million canopy project commenced in August 2010 and was completed in January 2011 with about 15 people assigned to the project. The canopy was built in one piece and transported with a police escort in the dead of the night on the back of a truck with front and rear steering. Installation took only two days, says Brooks.

During the design-detailing phase, TripleNine employed 3-D modelling and Yuanda’s engineers gave careful consideration to expansion and
contraction. ‘Because [the canopy] was so big, we needed to include some bridge building technology,’ says Brooks. ‘We used expansion pads as the canopy was calculated to expand up to 50mm across the total length of it.’

‘The Star’ is a bright, light addition to the harbourside landscape. While the elements of Feng Shui can’t be guaranteed to produce financial fortune in The Star’s casinos, the stainless steel canopy is certain to maintain its appeal for decades to come.

Images courtesy of TripleNine Stainless.

This article is featured in Australian Stainless, issue 52.

Coca-Cola Amatil is reducing the carbon footprint of its 600ml PET bottles by 22% with the help of stainless steel.

Innovation in process technology and the successful application of stainless steel has led to efficiency gains and sustainable outcomes for one of the world's most recognised brands in the food and beverage industry.

In 2011, Coca-Cola Amatil (CCA) announced a $450 million investment in PET bottle self-manufacture, or ‘blowfill’ technology at its production facilities across Australia, New Zealand, Indonesia, Papua New Guinea and Fiji.

Blow-fill technology is a manufacturing technique that allows companies to produce their own PET (polyethylene terephthalate) bottles within their own facility. It allows manufacturers to form, fill and seal bottles in one continuous process at the one location without human intervention. Blow-fill has enabled CCA to make its PET bottles using significantly less PET resin, resulting in production of the lightest-weight bottles in the global Coca-Cola system.

Previously, CCA would buy blow-moulded bottles from a third party supplier, transporting them to its own facility to sterilise and fill with product. CCA’s integration of these three steps into one operation has automated its production lines, creating economies of scale and
optimising efficiencies of operation.

CCA’s Kewdale facility in Perth is one packaging line that recently completed its installation of blow-fill equipment, procured from Krones AG, a German-based process manufacturer.

CCA engaged ASSDA member and Accredited Fabricator TFG Pty Ltd for the installation and fabrication of the stainless steel interconnecting pipework for the facility’s new blow-fill equipment.

Sydney-based ME Engineering detailed the scope of works, and coordinated the process engineering and installation of the new equipment.

Over 6km of 304L and 316L AS1528 standard grade stainless steel tube was supplied by ASSDA sponsor Prochem Pipeline Products, ranging in size from 25mm-200mm diameter.

The TFG team purge TIG welded all stainless steel components on site and internally passivated the stainless steel using citric acid.

ME Engineering’s Project Manager Andrew Meagher said grade 316L was specified for CCA’s Kewdale facility because of the high chloride content of the water supply in Perth.

With spring water one of CCA’s main products, sanitation is key to avoiding microbiologically-influenced corrosion.

Tom Moultrie, General Manager of TFG, said that whilst there are other materials that can be specified for equipment using compressed air, stainless steel provides aesthetic appeal, trusted hygiene and longer life span.

The use of stainess steel has been successful in the output of this project, with CCA’s State Projects Engineer Simon Wall stating that ‘as a beverage manufacturer, food safety aspects of our processes and equipment are critical to ensuring the integrity and quality of our products – an area that stainless steel ensures.’

Kewdale’s new blow-fill line commenced operation in June 2012. It features 14 blowing stations, 108 filling nozzles and 18 capping stations, and has the capacity to produce 26,000 bottles per hour.

Mr Wall said the investment in PET bottle self-manufacture will continue to deliver savings in raw materials - bottles are made using less PET resin and less water is used in the bottling process - and meet future consumer growth and demand.

CCA’s ongoing commitment to innovation and sustainability has maximised production capabilities whilst minimising the use of resources.

By the end of 2012, 10 blow-fill lines will have been deployed across CCA’s production facilities in Australia, bringing self-sufficiency to over 70%. Once all 26 production lines are implemented, CCA estimates a saving of 7000 tonnes of PET resin per year, a 15% reduction in bottle weight and 50,000 truck movements eliminated per year. Overall, this is reducing the carbon footprint of every 600ml bottle by an average of 22%.

Images courtesy of TFG Pty Ltd.

This article is featured in Australian Stainless magazine, issue 52.

Stainless steel is the material of choice to specify for severe weather conditions.

The overhead netting of Perth Zoo's Australian Wetlands and Penguin Plunge Exhibit was badly damaged when a severe hailstorm and winds of up to 128km/h swept through Perth in March 2010.

During the storm, a tree collapsed onto the netting which was made from a nylon material.

The original concept for this major renovation project was to use stainless steel overhead netting and painted or galvanised steel for the cabling and the majority of other supporting infrastructure components.

However, when ASSDA members Structural Dynamics was awarded subcontractor for the supply and installation of the new overhead netting system, it proposed using stainless steel for all components of the structure, including the cable tension system.

Working closely with Slatter Constructions (head contractor), Thinc Projects (project manager) and Pritchard Francis (structural engineers), stainless steel became the clear choice to provide strength and the crucial ability to withstand severe weather conditions.

Structural Dynamics Managing Director Darren Wills said the team agreed that specifying stainless steel would improve performance, product life cycle and reduce the risk of galvanic reaction.

‘Stainless steel materials break down at a much slower rate than galvanised materials,’ Wills said.

In terms of longevity and durability, stainless steel was the better option given the conditions of the local environment and fresh-water animals.

Slatter Constructions’ Project Manager Rob Murrell added that, on top of providing an aesthetic finish and prolonging the life of the enclosure, using stainless steel for the cables negated the need to ensure separation of different metal types.

Perth Zoo was convinced that stainless steel was the better long-term option and proceeded with stainless steel as the majority materials specification. With a life span of up to 20 years when compared with only up to 10 years using galvanised steel, the increased cost of using stainless was outweighed by the longevity of the product.

The new 91m long x 33m wide x 10m high netting and support structure was completed in early 2012, using the following stainless steel materials:

Backstay column support cables

• 440m of 16mm and 19mm HAMMA Pro Stand 1x19 AISI316
• 48 units of 16mm and 19mm Strudyna P2H Adjusters AISI 316

Netting structural support cables

• 720m of 8mm and 10mm HAMMA Pro Stand 1x19 AISI316
• 56 units of 8mm and 10mm Strudyna AM Adjusters AISI316

Netting support cables

• 3900m of 5mm HAMMA x wire rope 7x19 AISI316

Netting

• 5,400sqm of ClearMesh zoological netting AISI316
• 15,200m of 1.6mm seizing wire 1x7 AISI304

Rodent proof barrier

• 300m of 5mm stainless steel angle AISI316 3000m x 150mm x 5mm

Miscellaneous

• 2,400m of 10mm threaded rod AISI316
• 600 units of 10mm eye bolts AISI316
• 600 units of 5mm turnbuckles AISI316

It was pivotal that the new cable structure could cope with extreme one-in-a-hundred year Perth storms, and the high tensile stainless steel structural cable components were ideal for this design parameter. Meeting a range of cable tensions, the HAMMA stainless steel cables installed are rigid to deal with high tensile loads, but also allow for some give to counter the effect of high winds and other harsh weather conditions. Their grade 316 stainless steel construction provides excellent corrosion resistance.

ClearMesh - often used in zoological enclosures globally - was applied to the overhead netting and netting mesh wall that separates the Wetlands from the Penguin Plunge Exhibit within the enclosure. With mesh openings of 2mm, the lightweight and flexible characteristics
of the ClearMesh display a transparent look that complements the landscaped environment and allows for give in case birds fly into the mesh.

Wills said the structure was designed to retain wildlife inside the enclosure and provide a close-to-natural environment for the Australian wetlands wildlife and penguins to thrive in. This resulted in an extremely high level of detail being specified, with stainless steel seizing
wire used every 5mm on the seams of the stainless netting. Over 38,000 hand seizes were performed by the Structural Dynamics team.

As the enclosure was an established site prior to the storm, Perth Zoo required that construction had limited impact on the existing landscaping to assist with animals being reintroduced to their former habitat. Murrell said careful planning between Structural Dynamics and Slatter Constructions ensured the works were completed without harm to the existing vegetation and surrounding areas.

Further construction and landscaping works included a new timber deck walkway for visitors, a limestone block wall and vermin barrier to the perimeter of the wetlands area, an upgraded filtrations system and refurbishment of the existing penguin pool and surrounds.

The renovated enclosure has since survived the June 2012 storm with winds of up to 140km/h, and the cable netting structure and supporting infrastructure today remains as built.

Images courtesy of Structural Dynamics.

This article is featured in Australian Stainless magazine, issue 52.

BACKGROUND

Almost all of the stainless steels in use have 16% chromium or more and have nickel or other additions to make them austenitic and hence formable, tough and readily weldable. However, the formal definition of a stainless steel is that it is an iron- and carbon-based alloy with more than 10.5% chromium. Historically, the corrosion mitigation industry regarded alloys with more than 12% chromium as stainless steels mainly because those alloys did not corrode in mild environments. Because of the perceived problem of high initial price when using stainless steels, alloys that are ‘barely’ stainless (and with low nickel to boot) are more competitive with painted or galvanised carbon steel than higher alloys.

HOW WERE THESE GRADES DEVELOPED?
More than 30 years ago, developments from the 409 grade (used for car exhausts) led to a weldable ferritic that was tough to sub-zero temperatures. Two versions were developed: a stabilised grade for corrosive environments and an unstabilised grade that matched international standards. One issue was that the titanium used for stabilisation was hard on the refractories and caused the surface finish of flat product to be less appealing. However, when end users moved to unstabilised versions, corrosion problems arose in some applications. Research lead to further alloy development and proprietary grades with outstanding resistance to weld sensitisation.

WHAT IS DIFFERENT ABOUT THESE MATERIALS?

• They are ferritic (and attracted to a magnet), and can be bent, formed, cut and electric process welded like carbon steels.
• The balance of their metallurgy limits grain growth when heated. So, unlike ferritics used for cladding, thick sections can be welded without excessive grain growth and embrittlement.
• After welding, they have a duplex ferritic-martensitic microstructure that does not usually require heat treatment.
• As ferritics, their thermal expansion is low (actually less than carbon steel) which reduces distortion risk during welding or furnace operations.
• They have good scaling resistance in air to ~600˚C and reasonable strength at that temperature compared with more expensive austenitics with a scaling limit of ~800˚C in air.
• Like duplex alloys, they do not suffer from chloride stress corrosion cracking.
• They provide excellent and economic resistance in corrosive wear applications compared to hardenable carbon steels, surface-treated materials of highers alloys.

However, there are a few cautions:

• Low chromium, low nitrogen and no molybdenum means they have low corrosion resistance (PRE~11). They will pit in marine environments and in less severe conditions they cannot be used if aesthetic appearance is critical. Painting is a useful option in aggressive environments.
• Neither cold work nor heat treatment will increase their strength, although they are slightly stronger than 300 series stainless steels. Because they do not cold work, they should be less susceptible to galling then austenitic stainless steels.
• While it is nothing to do with the material, supply is mostly limited to sheet or plate, i.e. bar, hot-formed sections, hollow sections and wire and generally unavailable.

WHAT ARE THE ALLOYS?
There is a plethora of proprietary and standardised grades with between 10.5% and 12% chromium. The Ferritic Solution booklet available from the ISSF [www.euro-inox.org/pdf/map/The_ferritic_solution_EN.pdf] lists about a dozen. In Australia, the major proprietary grades are 3Cr12 and 5Cr12 where the ‘3’ and ‘5’ are labels, not compositions, and may include additional letters for other grades in the family. However, these labels cover three different material design decisions – and only those in (A) below are standardised:

A. Low chromium, no molybdenum and low nickel, carbon and nitrogen. There are covered by S40977/1.4003 in ASTM A240/EN10088.2
respectively or S41003 in ASTM A240.

B. As above, but with stabilising titanium or titanium plus niobium. There are several rules for titanium content but 4 (C+N) with a limit of 0.6 is used. The Ti/Nb will lock up C and N and reduce the risk of sensitisation, i.e. it limits corrosion associated with welds.

C. As above, but with lower carbon and nitrogen limits and specific controls on ferrite and austenite stabilising elements. This gives immunity to sensitisation in corrosive environments where there is a risk of fatigue.

REPLACEMENT OF GALVANISED OR COATED CARBON STEEL BY Cr12
The cost of steel that has been galvanised is currently up to 30% less than the cost of a 12Cr utility stainless steel when transport, pickling and other costs are included. When added to the cost of better trained (and hence more expensive) staff required for fabricating stainless steel, it is apparent that on a prime cost basis, even this basic stainless steel will not be cost competitive. However, on a LCC basis, the 12Cr grades have a significant advantage primarily because of durability.

Table 1 shows the relative lifetime of zinc (as a proxy for galvanising) and aluminium vs a 12Cr stainless steel in a medium and low corrosivity environment where the atmospheric corrosion rates for carbon steel are listed averaged over a 20-year exposure. It is clear that the life cycle cost of the 12Cr stainless steel is much better than either of the alternatives listed.

WELDING OF Cr12 STAINLESS STEELS
AS/NZS 1554.6 deals with welding of structural stainless steels and compacts all three branches of the 12Cr grades under ‘1.4003’ for selection of consumables. The recommendation is to use a 309L consumable although 18-8Mn (Note 8) is also prequalified. Heat input should be between 0.5 and 1.5kJ/mm and the interpass temperature should not exceed 150˚C.

As with all stainless steels, contamination by carbon steels must be avoided and any heat tint should be removed prior to exposure to corrosive service. While owners using Cr12 alloys for corrosive abrasion service regard the in-service removal of heat-tint surface layers as sufficient, this is only true if sufficient material is removed to expose the virgin stainless steel before the first rest period with corrodents on the surface could promote pitting.

APPLICATIONS FOR 12Cr STAINLESS STEELS
Applications include piggeries, rail cars, road transport, sugar and mineral industry (especially with corrosive wear), effluent tanks, under pans for conveyors, ducting (including furnaces), BBQ plate, electrical meter boxes, floor plates, gravel screens, railway overhead support towers, etc.

ACKNOWLEDGEMENTS
This paper has been prepared with support from ASSDA colleagues and especially Acerinox, Atlas Steels and Sandvik. Their assistance is gratefully acknowledged.

This technical article is featured in Australian Stainless magazine, issue 52.

This is an abridged version of a story that first appeared under the same title in Stainless Steel Focus No. 07/2012.

The Nickel Institute's director of promotion, Peter Cutler, and consultant Gary Coates, reveal some of the reasons for the continuing popularity of nickel in stainless steels.

Stainless steel is everywhere in our world and contributes to all aspects of our lives. We find stainless steel in our homes, in our buildings and offices, in the vehicles we travel in and in every imaginable industrial sector. Yet the first patents for stainless steel were issued only 100 years ago.

How did this metal become so desirable over the past century that more than 32 million tonnes was produced in 2011? And how does nickel, a vital alloying element in most stainless steel alloys, contribute to the high demand for stainless steel?

THE 'CREATION' OF STAINLESS STEEL
By definition, a ‘stainless’ steel has a minimum level of about 10.5% chromium, so the discovery of chromium in 1799 by Nicolas Louis Vauquelin in France was the first key event in the creation of stainless steel. In 1821 another Frenchman, Pierre Berthier, published research that showed a correlation between increasing chromium content and increasing corrosion resistance, but the high carbon content of his alloys prevented them from showing a true ‘stainless’ behaviour.

Still in France, in 1904 Leon Guillet first published his metallographic work on alloys that today would be classified as ferritic and martensitic stainless steel. In 1906 Guillet published his work on the nickel-containing austenitic stainless steel family, but his studies did not include corrosion resistance. Albert Portevin then continued to build on Guillet’s work.

In 1911, a German scientist named Philip Monnartz reported that as the chromium content neared 12% in a steel with a relatively low carbon content, the alloy exhibited ‘stainless’ properties. Further developments then rapidly occurred in many other countries. In the United States, Elwood Haynes started working with martensitic alloys while Becket and Dantsizen were developing a ferritic stainless steel as lead-in wires for electric light bulbs. In 1912, Great Britain’s Harry Brearley worked on a 13% chromium martensitic alloy, initially for high temperature service in exhaust valves for aeroplane engines.

Meanwhile in Germany, Eduard Maurer and Benno Strauss were testing nickel-containingalloys and, in 1912, two patents were awarded. One of these grades, containing about 20% chromium and 7% nickel, was called V2A, and was found to have exceptional corrosion resistance in nitric acid. That grade had a relatively high carbon content compared to today’s stainless steel, and would be
similar to a Type 302 (EN 1.4317) stainless steel. 100 years later, the most commonly used alloy for nitric acid is 304L (EN 1.4307) with approximately 18.5% chromium and 8.5% nickel, quite similar to the V2A composition other than having a much lower carbon content.

Brearley’s martensitic stainless steel alloy would not rust when wet. He worked with Sheffield cutlery manufacturers to forge it into knife blades and then harden it, replacing the carbon steel blades they were then making. Stainless steel knives rapidly became a common household item. However, for forks and spoons, where high hardness was not so important, the 18-8 (302) composition became the most commonly used alloy.

300 SERIES
We normally think of the austenitic or 300 series family of stainless steels as the ‘nickel stainless steels’, but many other families contain nickel. One of the prime reasons for using nickel in the 300 series alloys is that nickel is an austenite former, but other reasons include:

• Nickel adds corrosion resistance, especially in certain aqueous environments, and in certain high temperature environments.
• Nickel can retard the formation of embrittling intermetallic phases at elevated temperatures, a major downfall of the non-austenitic families.
• The austenitic structure can mean high toughness at cryogenic temperatures.
• The advantages of the 300 series extend to welding and forming operations.

A fuller discussion of these topics can be found in 'The Nickel Advantage - Nickel in Stainless Steels', available on the Nickel Institute website.

200 SERIES
The 200 series stainless steels are also austenitic in structure. The standardised 200 series grades, which have chromium contents close to the level of a 304L alloy (about 18%), have an intermediate level of nickel. The ‘non-standardised’ 200 series not only have lower contents of nickel, but also lower contents of chromium, with the net effect of significantly reduced corrosion resistance, although still an improvement over the 11-13% chromium ferritic stainless steels.

DUPLEX
The duplex (austenitic-ferritic) family of alloys also need some nickel as well as nitrogen to ensure proper austenite formation. Most ‘matching’ duplex filler metals are actually over-alloyed with nickel to ensure that the welds have the required properties.

PRECIPITATION HARDENABLE
The precipitation hardenable (PH) stainless steel family contain nickel, which increases their corrosion resistance, ductility and weldability compared with hardenable non-nickel-containing stainless steel alloys. One of the other major advantages of the PH grades is that, unlike the martensitic grades, they do not need a quenching operation, which considerably reduces risk of distortion. Some of the martensitic grades also contain a small nickel addition. In the higher chromium types, the nickel is needed for the martensitic transition. In all nickel containing martensitic grades, nickel improves their corrosion resistance, ductility and weldability.

Some of the lower alloyed ferritic grades such as UNS S41003 (EN 1.4001) and S40975 contain a small intentional nickel alloying addition that allows for grain size control, which aids especially in welded constructions. A few of the higher alloyed ferritic grades also have a small nickel addition to increase toughness and ductility, which is beneficial during both hot rolling and in their end use.

Clearly, it is important for each specific application to select the appropriate alloy or alloys to give the desired properties.

GROWTH IN DEMAND FOR STAINLESS STEEL
According to the ISSF, 300 series stainless steel still dominates the worldwide production figures, as shown in Figure 1.

The properties of the various 300 series grades - created by the addition of nickel - are clearly valued by users, both in industry and the general public. Upwards of two thirds of all stainless steel produced in 2011 fell within the 300 series and close to three quarters of all stainless steel produced contains nickel.

The growth of worldwide production of stainless steel over the past 100 years has been steady, if not spectacular. This has meant that the demand for new nickel has steadily increased along with the demand for stainless steel, as shown in Figure 2. Recycled stainless steel is also a very important component in the alloy supply chain.

EFFICIENCY AND 'GREEN' CREDENTIALS
Resource efficiency is a recurring theme as the global economy faces economic challenges. Stainless steel not only contributes towards efficiency in many applications, it also shows continuous improvement in the resource efficiency related to stainless steel itself.

There are three important factors:

1. Stainless steel’s long service life, which might average 15 to 20 years, although much longer in prestigious buildings.
2. The extent of recycling: The percentage recovered and recycled at end-of-life - around 90% - is amongst the highest of all materials. Moreover, this recycling can be repeated many times without loss of quality. While the recycled content may appear to be relatively low, this is simply a result of stainless steel’s long service life (15 to 20 years) coupled with much lower global production 15 to 20 years ago.
3. Continual production improvements for stainless steel and its raw materials. For example, whilst the ores being processed today are of lower grade than before, the extraction and recovery processes are more efficient.

THE FUTURE
The history of stainless steel would be incomplete without celebrating the extent to which it has enabled innovation not just in the area of improved performance, but also in the more intangible, aesthetic aspects. From chemical plants to medical equipment to iconic stainless steel-clad buildings, stainless steel has made - and will continue to make - a major contribution to almost every aspect of our lives.

With durability, recyclability, versatility and aesthetic appeal at the core of its appeal, stainless steel - with nickel as one of its trusted alloys - is well placed to continue to innovate and expand its applications.

STAINLESS STEEL IN USE

FOOD AND BEVERAGE INDUSTRY
The popularity of stainless steels in kitchens did not go unnoticed in the food and beverage industry.

If we take milk, we know of an early stainless steel bulk milk tank truck from 1927 in the USA. A paper entitled ‘The Corrosion of Metals by Milk’ from the January 1932 Journal of Dairy Science by Fink and Rohrman states: ‘It has long been known that milk in contact with iron and copper will not only acquire a metallic taste, but corrode these metals readily’. At that time, tin-coated metals were commonly used. It went on to say that ‘High chromium nickel (18-8) iron alloys … are very resistant to corrosion by milk and are satisfactory for dairy equipment …’. The modern milk processing industry is filled with stainless steel equipment, mostly of Type 304 (EN 1.4301) or 304L.

The report also went on to state that some materials that are otherwise suitable for processing of milk ‘…do not stand up well to the action of cleaning compounds that are commonly used in dairies’, but that the 18-8 alloy was suitable for those cleaning compounds. Today, the typical cleaning acids and hypochlorite sanitising compounds that are used not only in the dairy industry but also in most food and beverage plants worldwide, require that same 18-8 alloy as a minimum. A correctly chosen stainless steel alloy will not change the taste or appearance
of the food product. However, it is the ability to withstand repeated use of the sanitising chemicals over the lifetime of the equipment that has led to the widespread use of stainless steel in all sectors of the food and beverage industry. Producers are then able to guarantee the
safety of their food products.

ARCHITECTURE
Another area of quick acceptance was in architecture. The first recorded use for that purpose was in 1929 in London at the Savoy Hotel where a sidewalk canopy and a sign were erected with the 18-8 alloy. These were soon followed by two iconic skyscrapers in New York that used stainless steel as a dominant element on their exteriors: the Chrysler Building in 1930 and the Empire State Building in 1931.

Since then, many prestigious buildings around the world have used stainless steel, including the Petronas Tower in Kuala Lumpur, the Trump Tower in Chicago, and the Jin Mao Tower in Shanghai. Related to architecture is sculpture, and Isamu Noguchi convinced the Associated Press in 1940 to approve stainless steel instead of bronze for his sculpture above the entrance to its building in New York. Since then, artists around the world have been using stainless steel, mostly either 304L or 316L (EN 1.4404), in their works. The St Louis Arch in the USA, Frank Gehry’s Peis (Fish) in Barcelona, Spain, and more recently Genghis Khan in Mongolia are examples of what can be done with stainless steel.

TRANSPORTATION
During the Great Depression in the USA, Edward Budd realised the untapped potential for stainless steels. Although their use in aeroplanes was his first application, his legacy remains the building of more than 10,000 passenger railcars, some of them still in use today.

Around the world, stainless steel is used extensively for passenger rail cars for subways, commuter trains and long distance trains, ensuring safety plus long life and low maintenance costs. In addition, stainless steels are used to transport cargoes such as food products, petroleum products and corrosive chemicals by rail, road, water and even air, both domestically and internationally.

ENERGY
In the broad field of energy, stainless steels have been used to extract oil and gas containing hazardous substances as well as for use in the refining stages. For power plants, stainless steel is used extensively at both low and high temperatures, whether the fuel is coal, oil, gas, uranium or waste products. Hydroelectric stations use stainless steel for dam gates as well as turbines. Many of the established sustainable
energy technologies such as solar and geothermal are using stainless steel, as well as the present biofuels industry with corn or sugar cane as feed stock.

WATER
Fresh water is an essential commodity for mankind, and stainless steel is used extensively in treatment plants for potable water as well as for wastewater. Cost effectively producing fresh water from seawater or brackish water by desalination also requires the use of stainless steel. In some countries, underground stainless steel pipe is used to deliver potable water to homes to prevent leakage, or in other special cases to protect either the environment outside the pipe or the water inside the pipe. Stainless steel plumbing is also common in certain countries and offers a long lasting, low maintenance option.

SURGERY
The first recorded example of an austenitic stainless steel surgical implant is from 1926. Medical instruments are also known from that time period. The ability to easily and repeatedly sterilise components that come in contact with the human body or are used in hospitals and clinics contributed to the early acceptance of stainless steel. Today, there are well-established international specifications for materials used in this industry. For example, stainless steel alloys for implants must meet stringent metallurgical cleanliness requirements and be completely non-magnetic so that the patient can safely undergo diagnosis by Magnetic Resonance Imaging.

FUTURE USES OF STAINLESS STEEL
Strong growth in the use of stainless steel has continued in the past decades despite the rapid and diverse developments in other materials and the more recent economic turmoil. The nickel-containing alloys in the 300 series still account for nearly two thirds of current stainless steel production worldwide, and there is nickel in the 200 series, duplex and precipitation hardening families, as well as in some of the martensitic and ferritic alloys. The reason for this is the great value that is placed on the properties which nickel provides.

Society is rapidly evolving and facing challenges on a global scale. Population is increasing, expectations are growing and resources are limited. Therefore we must use those resources more efficiently. This is particularly apparent for energy where stainless steel, and especially the nickel-containing alloys, already plays a major role in the more difficult to extract fossil fuels. Stainless steel’s corrosion and heat resisting properties are key to more cost-efficient operations. This also applies to the renewable sources that are now being developed, such as wave power and biofuels from new organic sources.

The worldwide need for higher quality, safe food and beverages and water will only increase, especially as food products can come from anywhere in the world. Stainless steel has evolved as the material of choice in this industry, both industrially and domestically, and it is likely to continue to meet the demands of a global population that is predicted to increase to nine billion by 2050.

This growing population, combined with a rapid movement to urbanisation, requires an expanded and more efficient transport infrastructure. The characteristics of stainless steel enable it to deliver lightweight and durable designs, leading to more efficient performance, safety, lower energy requirements and reduced emissions while giving lower life-cycle costs.

Image of Trump Tower (Chicago, USA) pictured above courtesy of C.Houska.

This article is featured in Australian Stainless magazine, issue 52.

The Fibonacci spiral and the intersecting spines of a nautilus shell have inspired an impressive 23m high stainless steel sculpture at Kangaroo Point Park overlooking Brisbane's river.

Designed by UK public space artist Wolfgang Buttress, Venus Rising features 10,790 individual welds and over 7km of grade 316 and 2205 duplex stainless steel tube, pipe and round bar supplied by ASSDA Sponsor, Sandvik.

Having worked with stainless steel for over 25 years, Buttress said that the material’s strength, ability to look good over time with minimal maintenance, and the flexibility of finishes works well both practically and aesthetically.

“The variety of finishes which can be achieved with stainless steel through polishing, glass blasting and heat treatment is great. The material needs to be strong, resilient and look as good in 50 years as it does on installation,” Buttress said.

Initial fabrication works took place in the UK before being transported to Brisbane for final assembly. D&R Stainless, an ASSDA member and Accredited Fabricator, continued the fabrication of the 11.5 tonne spire-like sculpture over a period of six weeks. It used the artistic vision of Buttress, as well as renders and 3D models to guide the assembly of the sculpture.

The central design of the sculpture was to create a piece of artwork that was visibly prominent and exemplified strength, elegance and weightlessness. The sculpture features a criss cross ladder-type construction with heavy wall pipes that gently twist to create a hollow spiral. Visitors can enter the sculpture at the base level and gaze up at the sky through an opening at the top.

“I wanted to make connections between the Brisbane River and the sky above. It was important to me that the sculpture works on an intimate scale as well as being seen from afar,” Buttress said.

“Visually, the most challenging part of the project was to try and maintain harmony between form and sculpture. I wanted the piece to have a delicacy but also be strong.”

The main structure of the sculpture features 2205 duplex stainless with cladding tubes at the bottom of the structure starting at 12mm, ascending to 8mm and 10mm tube through the middle and 6mm and 8mm solid round bar at the top. Tubes were supplied in 6m lengths and welded together to create continuous lines of tubing for the stretch of the sculpture.

12mm thick stainless steel tubes in the skeleton of the structure extend about half way up and were heat treated in a stress relieving oven. This transformed the colour of the steel into a golden hue to create a contrast effect in the sculpture.

“We cut 30 to 40 small lengths of stainless steel at various thicknesses and baked them at different temperatures from 100˚ C up to 400˚ C. After comparing the various shades and hues, I chose the golden colour in the end which required heating to around 300˚ C,” Buttress said.
Grade 316 polished stainless steel tubing was used for the middle cladding on the exterior of the structure.

Stainless steel rings were laser cut from LDX 2101 plate in various thicknesses from 20mm down to 3mm, and welded to the body of the sculpture to create an intricate lace-like effect.

The main structure was bead blasted to create a uniform finish and all tubes were chemically cleaned.

Both TIG and MIG welding processes were used, with both solid wire and flux cord used in the MIG welding technique. Di-penetration testing was conducted offsite on the welding of the body of the sculpture to ensure structural integrity.

D&R Stainless director Karl Manders said that while fabricating stainless steel was familiar territory, the application was different and stimulating.
“We found the project intriguing because while we were producing a delicate structure, the core components of the fabrication were quite complex. Our business focuses on heavy industrial applications, and the materials we used for Venus Rising are those used in the heart of the mining and petrochemical industries,” Manders said.

“The experience of this project was intense but satisfying. We made Wolfgang’s vision come to life.”

Buttress said D&R Stainless was a perfect fit for the project and they will also be on board for an upcoming sculpture for The University of Canberra.

“Their understanding of the properties of stainless steel was second to none and their craftsmanship exemplary. It was great to witness such pride in their workmanship,” Buttress said.

Commissioned by the Queensland Government, Venus Rising was selected in a public vote as the winning design from over 60 submissions and was unveiled in late January 2012.

Photographer: David Sandison. Images courtesy of The State of Queensland, Department of Housing and Public Works.

This article is featured in Australian Stainless magazine, issue 51.

The Go-Between Bridge

With 14,000 vehicles crossing Brisbane's Go-Between Bridge every day, stainless reinforcement is playing a vital structural role on Brisbane's first inner city bridge in over 40 years.

Formerly known as the Hale Street Link, the Go-Between Bridge connects Merivale and Montague Streets in West End to Coronation Drive and the Inner City Bypass in Milton.

Constructed as part of the Brisbane City Council’s TransApex plan, the Go-Between Bridge was designed to improve cross-river accessibility, reduce inner city traffic congestion, increase accessibility to Brisbane’s recreational and cultural precincts and cater for future residential developments in West End and South Brisbane.

The $338 million project commenced in 2008 and was built by the Hale Street Link Alliance (Bouygues Travaux Publics, MacMahon Holdings, Seymour Whyte Holding and Hyder Consulting).

The cantilever, box girder bridge stretches 274 metres over the Brisbane River and was built using stainless steel reinforcement with concrete foundations. Featuring a dedicated pedestrian and cyclist pathway, the Go-Between Bridge is 27 metres wide, with the main span measuring 117 metres.

ASSDA sponsor Valbruna Australia supplied 80 tonnes of grade 316L/1.4462 Reval® stainless steel in 12mm, 16mm, and 24mm reinforcement bar, which was used for the two major pile caps and north abutment of the bridge.

Valbruna Australia’s Managing Director, Ian Moffat, said stainless steel was specified for the critical elements of the bridge to minimise life cycle costs, improve structural integrity and corrosion resistance.

“Particularly being located in a marine environment, Reval® stainless in reinforced concrete is ideal to resist chlorides and pitting corrosion; it has an expected service life of 100 years in concrete,” Moffat said.

By specifying stainless, the designers were able to reduce the area in which stainless rebar was used in the structure because of its tensile strength being higher than carbon steel. In addition, using stainless steel reinforcement in concrete structures is stronger than carbon steel and will prevent material fatigue ensuring longevity for public infrastructure.

Moffat said Valbruna had 30% of stainless rebar already in stock, with the rest of the material having been shipped from their warehouse in Dubai and direct from their mill in Vicenza, Italy.

“Between the three locations, we were able to supply the stainless steel early and well within the specified timeframe,” Moffat said.
All Reval® stainless steel was produced and tested on site at the Acciaierie Valbruna S.p.A mill in Italy and manufactured to ISO 9001:2008 norms as certified by Lloyd’s Register Quality Assurance.

The Reval® stainless rebar was delivered to Neumann Steel in Currumbin for scheduling, cutting and bending.

A cut-to-length shear line machine was used, as well as a level off-coil machine to cut and bend the material into the finished product. All machines were cleaned before use to remove dust and carbon steel residue to avoid contamination of the stainless steel.

Neumann Steel’s Reinforcing Scheduler, Greg Prider, said the project was extremely complex and difficult to schedule.
“As the precast concrete units were manufactured at another site, we had tight tolerances to work with. It was critical to be precise in cutting and bending the stainless rebar to avoid unnecessary additional costs,” Prider said.

Following six weeks of scheduling, the stainless rebar was sent to the Brisbane Barge Berth, where precasting of the concrete units were assembled before transporting the modules direct to site by barge for installation.

Named after iconic Brisbane rock band The Go-Betweens, the Go-Between Bridge was completed and officially opened to traffic in July 2010.

This article is featured in Australian Stainless magazine, issue 51.

Stainless is a key feature in the urban design and revamp of one of the Gold Coast's most iconic and vibrant tourist destinations.

The $25 million Surfers Foreshore Project was commissioned by the Gold Coast City Council (GCCC) to redevelop the beachfront area between Laycock Street and View Avenue in Surfers Paradise.

Aimed at improving infrastructure and visitor recreation, the new promenade features new lifeguard towers, amenity blocks, beach shelters, picnic areas with barbeques, and increased pedestrian and disability access to the beach.

Managing Contractor Abigroup Contractors Pty Ltd appointed ASSDA member and Accredited Fabricator J&T Mechanical Installation to fabricate and install the stainless steel architectural handrails and balustrades across stages 1, 2 and 3.

Trent Todd, J&T Mechanical Installation’s Director, said that with the handrails and balustrades being installed less than 30m from the shoreline, stainless steel was the only choice to withstand the harsh coastal environment to help resist tea staining and ensure long-term durability and performance.

A 2009 GCCC study in affiliation with Griffith University saw the GCCC adopt stainless steel as the default specification for structures with a design life of more than 19 years in foreshore zones.

This followed research results showing the material required lower maintenance and was the most effective in life cycle costs when compared with hot dipped galvanized (HDG) steel, paint systems and duplex systems using both HDG and paint.

At a total cost of approximately $80,000, the stainless steel handrails and balustrades span 1300m across the esplanade that fronts Surfers Paradise Beach.

Grade 316L stainless steel was specified for these elements of the project, which included 36 sheets of 10mm thick plate measuring 1500mm x 3000mm supplied by ASSDA member Allplates. ASSDA Sponsor STM Tube Mills Pty Ltd supplied 1300m of 50.8mm x 1.6mm thick tube. Another 3500m of 1/4” wire was also sourced for the balustrading.

All the flat and tube components including 124 stanchions were laser cut and folded by Allplates.

Stanchions and base plates were machine polished to 600 grit by ASSDA member and Accredited Fabricator Minnis & Samson to give the stainless steel an even polish and the stanchions a square edge. The stanchions were electropolished before being delivered back to J&T Mechanical Installation’s workshop for assembly.

J&T Mechanical Installation fabricated the top (50.8mm x 1.6mm tube) and bottom (folded channel, 4mm thick) rail frames with two vertical 16mm diameter solid round bar intermediate supports. Infill wires at 6.4mm diameter were positioned with swage fittings and lock nuts on each end to construct the vertical balustrades.

On site, J&T Mechanical Installation completed civil works prior to installation, including pre-drilling with the fasteners for the base plates to which the stanchions were then bolted. The rail frames were welded to the stanchions in 2.1m sections.

Following installation, a proprietary stainless steel cleaner was applied to remove any oxides, and a mild cleaner was followed to provide surface protection and inhibit corrosion.

Architectural feature lighting was installed to illuminate the pedestrian walkways at night.

The Surfers Foreshore Project was completed in April 2011 and today continues to thrive as the Gold Coast’s most popular entertainment precinct where city meets the surf.

Images courtesy of Allplates.

This article is featured in Australian Stainless magazine, issue 51.

Stainless steel can provide excellent service underground. It is stronger than polymers and copper and its resistance to chlorides and acidic acids is significantly better than carbon or galvanised steels.

The performance of stainless steel buried in soil depends on the nature of the buried environment. If the soil has a high resistivity and is well drained, performance can be excellent even in conditions where other unprotected materials suffer degradation.

BASIC RULES

The Nickel Institute guidelines for burial of bare stainless steel in soil require:

• No stray currents (see below) or anaerobic bacteria.
• pH greater than 4.5.
• Resistivity greater than 2000 ohm.cm.

Additional recommendations include the absence of oxidising manganese or iron ions, avoidance of carbon-containing materials and ensuring a uniform, well-drained fill. If the guidelines are breached, then either a higher resistivity is required, i.e. measures to lower moisture or salts and ensure resistivity exceeds 10,000 ohm.cm, or else additional protective measures may be required.

In comparison, the piling specification (AS 2159) guidelines for mild steel require a pH greater than 5 and resistivity greater than 5000 ohm.cm for soils to be non-aggressive. It is rare for bare mild steel to be buried, i.e. typical specifications include a wrap or coating possibly with a cathodic protection system.

However, it is well established that even a carbon steel pile driven into undisturbed soil suffers only a few micrometers per year corrosion. This is because of the joint effects of lack of oxygen and the limited diffusion in compacted soil, which means corrosion products cannot escape and therefore stifle corrosion reactions.

SPECIFIC ISSUES

• Uniform soil packing is required as variable compaction can induce differential aeration effects.
• Avoid organic materials in the fill around buried stainless steel as they can encourage microbial attack.
• Avoid carbon-containing ash in contact with metals in soils. Localised galvanic attack of the metal can occur.
• Oxygen access is critical. Having good drainage and sand backfill provides this. A sand-filled trench dug through clay may become a drain and it is not appropriate. Stainless steels generally retain their passive film provided there is a least a few ppb of oxygen, i.e. 1000 times less than the concentration in water exposed to air.
• Chlorides are the most frequent cause of problems with stainless steels. In soils, the level of chlorides vary with location, depth and, in areas with rising salinity, with time. High surface chlorides may also occur with evaporation. This is a problem for all metals although stainless steels are not usually subject to structural failure.

 The general guidelines for immersed service that are in neutral environments at ambient temperatures and without crevices, 304/304L may be used in chloride levels of 200 ppm, 316/316L up to about 1000 ppm chloride and duplex (2205) up to 3600 ppm chloride. The super duplex alloys (PRE>40) and the 6% molybdenum super austenitic stainless steels are resistant to seawater levels of chloride, i.e. approximately 20,000 ppm. These guidelines are easy to apply in aqueous solutions.

Soil tests for chlorides may not exactly match actual exposure conditions in the soil. Actual conditions may be more (or less) severe than shown by the tests. The difference is calculable but in practice, the aqueous limits can be used as general guidelines. More specific recommendations, based on published guidelines, are provided in the table above.

It may seem redundant to asses both chlorides and resistivity. Both are required as the resistivity is primarily affected by water content and if it is low, then quite high chlorides could be tolerated. Despite these recommendations, most Australian practice is to use 316/316L or equivalent, primarily because of variable soils.

• Good drainage and uniform, clean backfill are essential for bare stainless.
• Duplex or super duplex could be replaced with appropriate austenitic and 304/304L could be replaced with a lean duplex.
• Ferritic stainless steels of similar corrosion resistance (usually classified by Pitting Resistance Equivalent [PRE]) could also be used underground.

Potential acid sulphate soils are widespread, particularly in coastal marine areas as described in https://www.qld.gov.au/environment/land/management/soil/acid-sulfate/identified. Once disturbed and drained, which also allows oxygen access, such soils typically become more acidic than pH 4 and will attack metals (although stainless steels will be less readily attacked than other metals). Detailed assessment is required if using metals in such an environment as the effect of other aggressive ions is likely to be more severe at low pH.

    

CASE STUDIES

• Nickel Institute Publication No. 12005 describes a five-year burial exposure in Japan at 25 sites with highly varied corrosivity. After five years in marine sites, horizontal 304 pipes showed no pitting but some crevice attack under vinyl wrap. Only one 316 pipe showed any attack. Vertical 304 pipe suffered attack near the base at some sites apparently due to differential aeration effects. There was also some manganese staining.
• An Idaho study of a 33-year NIST burial found 12% Cr martensitic perforated. The 'lake sand' site had high ground water with pH 4.7 at recovery. Sensitised 304 was attacked worse than annealed but both suffered attack along the rolling direction from edges. 316 was not attacked even if sensitised. Assessment included radiography to ensure the sub-surface pitting and tunnelling was detected despite negligible mass loss.
• A seven-year European study with approximately 800 samples included austenitic and duplex alloys in three marine and five other environments buried either 1.5 m or 0.5 m underground. Creviced samples often corroded in marine environments. Overall alloy type was not relevant for corrosion but chloride content and aeration were critical and, usually for underground, there was some effect from temperature. Resistivity was seen as a proxy for chloride and moisture. No obvious trend was seen from pH, sulphide, sulphate or calcium carbonate levels. Metal potential was not an indicator of corrosion. Full details of the program have been published at EUR 23586.

As noted above, duplex stainless steel of similar corrosion resistance (PRE) to 304 and 316, respectively, are expected to provide similar results when buried.

On a more practical level, there are several common approaches that are used when burying stainless steel:

• Wrap the stainless steel pipe in a protective material, such as a petrolatum tape, prior to burial. If the wrapping is effective (typically an overlap of no less than 55% of the wrap width is specified), then the nature of the external surface of the buried pipe is of no consequence. In this case, stainless steel is only used for its internal corrosion resistance, i.e. its resistance to corrosion by the fluid which the pipe is carrying. Some authorities prohibit this practice because of concerns that damage to the wrap could cause a perforating pit in severe environments.
• Ensure that the soil environment surrounding the buried stainless steel is suitable for this application. In this case, the trench is dug so that it is self-draining, without there being areas where stagnant water can accumulate in contact with the buried pipe. The stainless steel pipe is then placed on a sand or crushed aggregate bed and covered by similar material. Under these circumstances, 316 grade stainless steel can be quite a suitable choice. US practice is to use 304, but Australian soils are quite variable and there have been mixed experiences with 304.
• Above ground sections of pipework are often stainless steel as they are at risk of mechanical damage while underground pipework is polymeric - polyethylene (PE) or fibre reinforced plastic (FRP) - despite the risk of damage due to soil movement.

In all these cases, the assumption is that the stainless steel has been fabricated to best practice. This includes pickling of welds (or mechanical removal of heat tint and chromium depleted layer followed by passivation to dissolve sulphides) and ensuring contamination by carbon steel has been prevented. It is also assumed that the buried stainless steel does not have stickers or heavy markings that could cause crevices and lead to attack.

STRAY CURRENTS

All buried metals, including stainless steels, are at risk if there are stray currents from electrically-driven transport, incorrectly installed or operated cathodic protection systems, or earthing faults in switchboards. Stray current corrosion can be identified as it causes localised general loss rather than pitting. It is also very rapid.

WHAT TEST METHODS ARE USED?

There are Australian and ASTM standards giving basic measurements of resistivity on site with 4 pin Wenner probes or in a soil box in a laboratory. More detailed checking includes water content, chlorides, organic carbon or Biological Oxygen Demand (BOD), pH or redox (or Oxidation Reduction Potential [ORP]) potential - which assess microbial attack risk but also captures the effect of oxidising ions and dissolved oxygen. Most of these test methods are covered in 'Soil Chemical Methods: Australasia' written by George E. Rayment and David J. Lyons and published by CSIRO. 

 

As bottled water continues to gain popularity in Australia, maintaining the quality and purity of the water extracted from natural springs is paramount.

This is just one example within the food and beverage sector where hygiene is vitally important and, therefore, stainless steel continues to be the material of choice for processing and storage facilities.

In 2011, Coca-Cola Amatil (CCA) commissioned ‘Project Flint’ to upgrade three spring water storage tanks for their Moorabbin plant in Victoria plus an additional two tanks for their Thebarton plant in South Australia.

GEA Process Engineering Australia engaged Byford Equipment on behalf of CCA to fabricate and install the five storage tanks.

GEA Engineering’s General Manager Operations, Andrew Fillery, said stainless steel was an important specification as the tanks had to cope with the chemical and thermal rigours of cleaning processes.

“Stainless steel was chosen for process and hygienic reasons, and the vessels needed to withstand the process and cleaning conditions where mild caustic and acid CIP solutions were used,” said Fillery.

Strength and durability was key for the 200,000L capacity silos, which measured 4.7m in diameter by 14.5m high for the Moorabbin site and 5.5m in diameter by 10m high for the Thebarton plant.

ASSDA Sponsor Midway Metals supplied 27 tonnes of grade 304 stainless steel coil with a 2B finish in 2mm, 2.5mm, 3mm and 4mm thicknesses. The coil widths were 1219mm and 1500mm.

With a team of five fabricators on the project, the tanks were welded together using a semi-automatic MIG welding process. The welds were then pickled to restore the chromium oxide layer and abstain from rusting.

Byford Equipment’s Project Manager Geoff Smallwood said coordinating the delivery of the tanks was a challenge, given the logistics of travelling through three states by road.

The delivery of the vessels was critical added Fillery, as there were specific installation windows to work within.

The storage tanks were delivered from Byford’s workshop in New South Wales to Moorabbin in March 2011. The two remaining tanks were delivered to Thebarton a month later for installation. It took one day and one crane to install each tank on site.

The connecting pipework was positioned on site, which was grade 304 polished tube in diameters ranging from 38mm to 150mm and purge welded prior to installation.

Images courtesy of Byford Equipment.

This article is featured in Australian Stainless magazine, issue 51.

Where Strength Meets Style

Innovation in zoo enclosure design is a key feature of the recently completed $7.5 million makeover of the Chimpanzee Sanctuary at Sydney’s Taronga Zoo.

The project brief was to create a chimpanzee habitat akin to their native home that would encourage social interaction and allow the zoo’s primate keepers to manage animal husbandry and the group’s changing demographic. The enclosure’s transparency and the ability to withstand the chimpanzee’s remarkable strength and intelligence were essential.

ASSDA member Ronstan Tensile Architecture was contracted by the builder, the Lipman Group, to be the specialist contractor for the technical design and installation of a mesh enclosure and non-climbable wall. Ronstan’s unique capability in tensile architecture and their technical expertise were a natural fit for this challenging project designed by Jackson Teece Architects.

The Sanctuary features the mesh separation paddock (similar to an aviary), at one end of the main exhibit. A non-climbable wall with a removable curtain, allows both spaces to function as one large paddock. This enables introductions of new chimpanzees into the compound and helps manage the apes’ complex behaviour patterns.

Ronstan Tensile Architecture’s General Manager, Rowan Murray, said the non-climbable wall structure was one of the most the challenging design aspects.

“The architect’s greatest challenge was to separate the chimpanzees physically, but still have them all in view in the paddock. We had to build a wall that was transparent, had openings of no more than 5mm to avoid chimpanzees putting their fingers in and climbing, and could withstand the strength of chimpanzees.” Mr Murray said.

The structural complexity of the non-climbable wall required 3D modelling to analyse design configurations and ensure structural integrity. Test panels of the non-climbable wall were fabricated and assessed in the chimpanzees’ temporary enclosure to determine which would offer the safest containment of the site and minimise visibility.

Mr Murray said the primary structure for the wall consists of a Ronstan supplied tensile cable net that supports semi-transparent perforated stainless steel panels.

“Most materials can be damaged, but the durability of stainless steel panels of certain perforation proved to be the right solution and important in the development of the overall design,” he said.

“The non-climbable wall had been designed with wall panels clamped directly to the enclosure mesh face. In a collaborative effort, we changed this to an independent cable net structure to remove the risk of having the final wall shape differ from that modelled, and in doing so, avoided the risk of panel geometry differing from the complex 10 degree incline necessary for non-climbability. This also ensured uniform set out and fixing methods, more consistent panel shapes and allowed the panel geometry to drive the wall structure rather than this being determined by other elements.”

ASSDA member, Locker Group, supplied the grade 304 stainless steel panels, which were perforated to 50%. A black painted finish was applied before installation.

With stringent performance characteristics to adhere to, including long-term corrosion resistance and aesthetics, Carl Stahl X-Tend stainless steel mesh was specified for the separation enclosure and the removable curtain within the non-climbable wall. The stainless steel mesh was blackened using an electrolytic process to increase transparency of the enclosure.

Trevor Williams, Lead Consultant of Jackson Teece and Project Architect for the development, said materials selection was critical in delivering the aesthetic appeal and longevity of the enclosure.

“We spoke with Ronstan Tensile Architecture for technical design advice in the early stages of the project. There were various other types of meshes that were a possibility but, being a dynamic structure, alternate materials were far too rigid and not as flexible as the Carl Stahl X-Tend stainless steel mesh. I don’t think we could have achieved this outcome with any other mesh,” Mr Williams said.

“The stainless steel will have a longer life in the aggressive south-facing coastal environment. The blackened mesh has a fantastic form and from an architectural point of view, has achieved an organic appearance.”

Ronstan Tensile Architecture’s contribution to the project, including the tensile mesh enclosure and non-climbable wall, cost about $1.2 million and took 16 weeks to construct.

Mr Murray said the stainless steel demonstrates a great mix of strength and transparency, and the end tensile result is very forgiving.

“Achieving the architectural intent involved complex modelling and finite analysis of the mesh form to ensure the surrounding structures could be designed to support the enclosure loads. Ronstan is absolutely rapt with the state-of-the-art structure,” he said.

The paddock was completely re-landscaped and the impressive exhibit also now features several climbing platforms at varying heights of up to 12 metres, and a 180 kilogram hammock for the chimpanzees to enjoy.

The 17 lucky Taronga Zoo chimpanzees moved in to their renovated home in late September 2011.

QUANTITIES AND GRADES OF STAINLESS STEEL USED

›    Mesh enclosure 770m² of 3mm Ø x 60mm blackened stainless steel, grade 316 Carl Stahl X-Tend mesh.
›    Non-climbable wall facade 140m² of grade 304 stainless steel perforated to 50%, with a black painted finish.
›    Cables 1x19 construction 8mm, 12mm and 22mm diameter, grade 316 stainless steel cables. The stainless steel cable end fittings and  components were polished and passivated prior to installation.

Images courtesy of Ronstan Tensile Architecture.

This article features in Australian Stainless magazine - Issue 50, Summer 2011/12.

Fabricating equipment for the chemical sector requires solid high quality materials and superior workmanship. In April 2011, ASSDA member and Accredited Fabricator U-Neek Bending Co Pty Ltd put the finishing touches on a radiant helical coil at their factory in Dandenong, Victoria.

The coil, designed as a heater for Titanium Tetrachloride (TiCl4) production, is 11.4 metres long with a diameter of 3.05 metres and required more than 7 tonnes of high grade Inconel Alloy.

U-Neek’s Business Development Manager, John Lovell, said the client chose to have this material shipped from America.
“At around US$1000 a metre, Inconel Alloy is a very expensive option but it has great heat transfer properties and is completely non-corrosive,” Mr Lovell said.

The Western Australian client, who declined to be named, were looking for a fabricator that, in addition to having a proven record in metal bending, could work to their particular requirements for this critical process componet.

“U-Neek weren’t just competitive in pricing,” said Greg, a project engineer with the client. “They succeeded with all the trial projects we sent them.”

“To ensure total quality control, we provided a comprehensive report that detailed every step of the process, including the names of every person who worked on the individual stages,” Mr Lovell said.

U-Neek Engineer Dale Theobold said the coil was manufactured to exacting tolerances using a range of Inconel Alloy materials.
“We used 150NB Schedule 40 seamless 600 for the pipes and flanges, 366-04 WPNCI-S for the elbows, B168-08 for the plate and 253MA for the high temperature pieces,” he said.

Once completed, the coil then had to undergo a rigorous series of tests. The butt welds were verified with full radiography, the attachment welds were submitted to liquid penetrant inspection (LPI), and a full hydro exam was done on the coil itself.

“The coil was filled with distilled water to test its heating capabilities. Then the coil was pressurised with nitrogen, to a dew point of -12°, to remove all traces of water and moisture prior to transporting,” Mr Lovell said.

The transport frame and mounting jigs were manufactured from mild steel. To ensure no cross contamination, Inconel strips were fitted to the mounting points. The coil was lifted onto the back of a semi-trailer for final transportation to Perth, using U-Neek’s 16 tonne travelling overhead cranes.

Images courtesy of U-Neek Bending Co Pty Ltd.

This article features in Australian Stainless magazine - Issue 50, Summer 2011/12.