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Stainless delivers savings for Sydney Water

Cleaner beaches and major water savings will be the chief benefits of the largest Sydney Water construction project ever undertaken on the New South Wales south coast.

ASSDA Member, Roladuct Spiral Tubing, supplied approximately 60 tonnes of grade 316 and 316L stainless steel tubing and associated fittings for the Wollongong Sewage Treatment Plant.The $197 million Illawarra Wastewater Strategy will see an overhaul of the 40-year-old Wollongong sewage treatment plant (STP) including the construction of a major new water recycling plant, high level (tertiary) treatment processes and ultraviolet disinfection systems.

ASSDA member, Roladuct Spiral Tubing, supplied approximately 60 tonnes of grade 316 and 316L stainless spiral tubing and associated fittings in 2mm to 5mm thicknesses for the project.

These materials were provided to Total Process Services for use throughout the Wollongong STP for the majority of the above-ground process lines.

An additional supply of 35 tonnes of grade 316 stainless tube and pipe fittings were provided by ASSDA Major Sponsor, Atlas Specialty Metals.

Sydney Water’s head contractor for the project is the Walter-Veolia Joint Venture. Walter Construction Group (Walter) is responsible for managing the delivery of the project and undertaking civil infrastructure construction at the treatment plants. Veolia Water Systems Australia (Veolia) is responsible for the process, mechanical and electrical design, supply, installation, commissioning and operational advice.

An additional supply of 35 tonnes of grade 316 stainless tube and pipe fittings were provided by ASSDA Major Sponsor, Atlas Specialty Metals The project’s most dramatic transformations are taking place at the Wollongong sewage treatment plant, where a 21 million litre bioreactor forms the centre-piece of the upgraded plant. Designed to remove organic impurities and nutrients from wastewater, the base of the bioreactor tank was poured over a continuous 15-hour period.

The design approach redirects wastewater from treatment plants at Bellambi and Port Kembla to the Wollongong facility. The Bellambi and Port Kembla plants will be converted to specialised storm-flow treatment facilities which will be used only in extreme wet weather.

The new Wollongong plant will also operate a reuse facility - supplying high quality treated wastewater to BlueScope Steel and cutting demand for fresh water from the local Avon Dam by about 20 percent. The upgraded sewage treatment plant is due for completion in mid 2005. The Illawarra Wastewater Strategy is part of WaterPlan 21, Sydney Water’s long-term strategy for sustainable water and wastewater management.

ASSDA provides technical advice and access to resources on the water and wastewater industries - for details phone 07 3220 0722.

ASSDA Major Sponsor, The Nickel Institute, can provide essential information on waste water. This information is available for download from www.stainlesswater.org.

Standards Australia distributes the Water Services Specification (WS-SPEC:2000) incorporating guidelines for stainless steel. Visit www.standards.com.au for purchase.

This article featured in Australian Stainless Issue 28, May 2004.

Grade 2205 for High Corrosion Resistance and High Strength

Combining many of the beneficial properties of both ferritic and austenitic steels, 2205 is the most widely used duplex stainless steel grade. Its high chromium and molybdenum content gives the stainless steel excellent corrosion resistance. The microstructure provides resistance to stress corrosion cracking and ensures high strength.

The grade is generally not suitable for use at temperatures above 300oC or below -50oC because of reduced toughness outside this range.

You are most likely to encounter 2205 stainless steel being used in industrial environments such as petrochemical, chemical, oil, gas and paper plants.

Alternative Grades
2205 has been available for several years - in general this complies with UNS grade designation S31803. More recently, product has become available complying with the higher corrosion resistant composition UNS S32205, as in table 1. Both these alternatives are known as 2205.

Composition
Grade 2205 has a micro structure of roughly equal amounts of ferrite and austenite, hence the 'duplex' description. The duplex structure of 2205 has the following properties:

  • High strength.
  • Lower thermal expansion coeffecient than austenitic steels but greater than carbon steels.
  • High resistance to corrosion, particularly stress corrosion cracking, corrosion fatigue and erosion.

The high content of chromium and molybdenum and the addition of nitrogen gives the steel further beneficial characteristics:

  • High general corrosion resistance.
  • High pitting and crevice corrosion resistance.
  • Good sulphide stress corrosion cracking resistance.

The addition of nitrogen gives a further increase in pitting and crevice corrosion resistance.

Table 1: Composition of 2205 and Alternative Grades (Single Values are Maximum)

Grade Common Name C% Mn% Si% P% S% Cr% Ni% Mo% N%
S31803 2205 0.030 2.00 1.00 0.030 0.020 21.0-23.0 4.5-6.5 2.5-3.5 0.08-0.20
S32205 2205 0.030 2.00 1.00 0.030 0.020 22.0-23.0 4.5-6.5 3.0-3.5 0.14-0.20

 

Corrosion Resistance
The grade has excellent corrosion resistance and is superior to grade 316, performing well in most environments where standard austenitic grades may fail. 2205's low carbon content gives the grade a high resistance to intergranular corrosion and has better resistance to uniform, pitting and crevice corrosion due to its high chromium and molybdenum content.

As 2205 is a duplex stainless steel, the grade is also less sensitive to stress corrosion cracking in warm chloride environments, unlike austenitic stainless steels. The grade also has good resistance to stress corrosion cracking when exposed to hydrogen sulphide in chloride solutions.

High mechanical strength combined with excellent corrosion resistance gives 2205 high corrosion fatigue resistance.

Heat Resistance
Although 2205 has good high temperature oxidation resistance, this grade, like other duplex stainless steels, suffers from embrittlement if held for even short times at temperatures above 300oC. If embrittled this can only be rectified by a full solution annealing treatment. 2205 is annealed at 1020-1100oC followed by rapid cooling. This treatment applies for both solution annealing and stress relieving.

Mechanical Properties
Mechanical properties for grade 2205 stainless steels are given in table 2.

Table 2: Mechanical Properties of 2205 (Annealed Condition)

 

Table 3: Physical Properties of Grade 2205 (Typical Values in Annealed Condition)

Tensile strength 620MPa min   Density 7,805kg/m3
Yield strength 450MPa mi   Elastic modulus 200GPa
Elongation 25% min  

Mean coefficient of thermal expansion

Brinell hardness 293 HB max   0-100oC 13.7µm/m/oC
Rockwell hardness 31 HR C max   0-315oC  

 

Physical Properties
Typical physical properties for grade 2205 stainless steels are given in table 3. There are surprisingly large variations in the values from different manufacturers for notionally identical materials.

2205 has a microstructure containing approximately 50% ferrite in the annealed condition, quenched from about 10500C. Higher annealing temperatures often result in an increase of ferrite content.

Fabricability
Due to the high yield strength of 2205, greater forces are required for the cold forming of this duplex steel, and will require larger capacity equipment than would be required for austenitic steels.

Processes such as stretch forming, deep-drawing and spinning are more difficult to perform.

Welding of 2205 is good by all standard methods, however, with the following restrictions:

  • Do not pre-heat or post-heat the material, heat input must be kept low.
  • Allow the material to cool between passes, preferably to below 150oC.
  • Use correct filler grade 2209. Autogenous welding should be avoided.

Forms Available
Grade 2205 is available in hot rolled plate and strip, cold rolled sheet, plate and coil, forgings/bar, tube and pipe and in threaded fittings and flanges.

Applications
Grade 2205 is typically used in the construction of heat exchangers, pressure vessels, tanks, tubes and pipes for the following industry areas:

  • Chemical processing, transport and storage.
  • Oil and gas exploration and processing equipment.
  • Marine and other high chloride environments.
  • Pulp and paper digesters, liquor tanks and paper machines.

Specifications
For many products grade 2205 is covered by the same specifications that include the common austenitics - ASTM A240M for flat rolled and ASTM A276 for bar. Duplex grades of tube have their own specification - ASTM A789M and A790M covers duplex grades of pipe.

Credits
ASSDA would like to thank Peter Moore of Atlas Specialty Metals and Graham Sussex of ASSDA in the development of this article.

Main image: 2205 hot water tank for beef abbatoir. Photo courtesy of ASSDA Accredited Fabricator, G&B Stainless Pty Ltd.

This article featured in Australian Stainless magazine - Issue 30, January 2005.

Specifying Stainless Steel Pressure Piping for High Rise Buildings

Brisbane's tallest residential tower, The Aurora will stand 69 levels and will set an important precedent in the use of stainless steel pressure piping in high rise buildings when the Bovis Lend Lease project is completed in January 2006

 

Situated on the corner of Queen, Eagle and Wharf Streets in the Brisbane CBD, The Aurora utilises stainless steel pressure piping instead of conventional copper piping to ensure adequate water pressure for each of the 478 two and three bedroom apartments in the $250 million development.

ASSDA member, Blucher Australia, supplied approximately 250m x 108mm OD x 2mm Mapress tube and fittings, 90 degree and 45 degree bends, sockets, flange adaptors and tees in grade 316 stainless steel.

The Aurora project is different to conventional installations due to a single metered water supply being provided to a common pump set for both potable and fire fighting services.

The potable supply is then directly pumped to a reservoir at the top of the building, thus eliminating large costs of having to set aside floors for transfer tanks, pumps etc.

The fire service is branched off the potable supply immediately after the pump set and separated with a non-return valve allowing potable supply to continue the 70 storey rise to the top floor gravity feed tank. The potable water supply is to be an approved system and also able to withstand both the head pressure created by the vertical rise and pressure of emergency back up pumps in the event of a fire, which in this case is 2490 kPa.

The Mapress 316 Stainless Steel Press-Fit System was recommended by Mark Tapley of Plumbing Contractor Tapworth and Booth and specified by Hydramellenia, the subsidiary of Brisbane Hydraulic consultants Steve Paul & Partners. The system is able to withstand a high working pressure of up to 2600 kPa or 26 Bar. The system can be pressure tested up to 4000 kPa or 40 Bar.

Blucher Australia is presently proceeding with Standards Australia to obtain MP 52 certification for potable water supply and once obtained, the Mapress System will be the only stainless steel system, complete with tubes and fittings to achieve this certification.

The Mapress Stainless Steel Press-Fit System carries European pressure certification suitable for this particular application and the pressure rating for the system. No other stainless steel 'system' holds an MP 52 certification so the major change was acceptance by Brisbane City Council.

The Mapress Stainless Steel Press-Fit System was chosen for a combination of reasons including longevity, ease of installation and the system's ability to handle high pressure.

As a part of Blucher Australia's guarantee and OH&S requirements, Blucher Australia Technical Manager, Ian Johnson trained Project Manager Mark Tapley, Site Foreman Steve Woods and four other employees involved in The Aurora project in the use of the specialised Hydraulic Press-Fit tool and installation procedures.

Blucher Australia hold stock of all the stainless steel components required to do the installation. Delivery, in conjunction with the good organisation skills of Steve Wood of Tapworth and Booth, was straight forward.

Hydramellenia, the subsidiary of Steve Paul and Partners, is convinced of the benefits and is currently specifying the Mapress system for other projects. Blucher Australia has already supplied to the smaller Metropole Apartments Project, also in Brisbane, and has received inquiries from other consultants who have heard of this project.

This article featured in Australian Stainless magazine - Issue 30, January 2005.


Posted 1 July 2005

These extraordinary sculptures shine with life when fashioned from stainless steel, demonstrating the diversity and beauty of the material.

Stainless Steel Lacewing - Brisbane, Australia Stainless Steel Brolga - Sydney, Australia

Main image:
Stainless Steel Snake 'Soho" - Artist: Damien Elderfield
Fabricated by Damien Elderfield, Melbourne

Left:
Stainless Steel Lacewing - Artist: John Coleman
Queensland Cultural Centre Busway, Brisbane

Right:
Stainless Steel Brolga - Artist: Allen Minogue
Fabricated by Townsend Group, Sydney

These images were featured in Australian Stainless Issue 32, Winter 2005.

Strata: A Majestic Streetscape in Stainless Steel

When South Australian developer, John Culshaw of Pentroth Pty Ltd proposed the design for the Majestic Roof Garden Hotel in Adelaide, the original proposal was for plain vertical bars for the car park grille of the Bent Street facade

Instead of surrendering to drab, pre-fab vertical bar grille designs, the developer actively sought a stylish alternative to the car park status quo. He commissioned artists Sue Rodwell and Trevor Rodwell to create ‘Strata’, a stainless steel grille design that aesthetically showcases the hotel building and provides a ‘majestic streetscape’ experience for Bent Street pedestrians.

The artists’ intention was to excise the barrier that would be created by the vertical security bars, which were uninviting at street level. Taking this as their starting point, they researched the replacement of verticals with horizontals to create a calm but dynamic form.

Strata lines of sandstone (used on the Frome Street facade of the hotel), contour lines, isobars from weather charts and the winged roof line of the hotel all helped to drive the inspiration for the unique design. From these lines, the artists devised a series of twenty-two panels, in sets of one, two and three. Each set is a unique design so that the complexity of the concept was acknowledged.

The grille runs the length of the hotel on Bent Street, integrates with the building and the electrically operated entrance doors to the car park and storage areas of the hotel. The nature of these horizontal waving lines creates a dynamic effect because it seems that they swing in and out because of an optical illusion when viewed from an oblique angle. By day the sky and daylight are reflected from the satin surface of the steel and at night the street and hotel lighting is reflected.

The artists chose stainless steel for their artwork for several reasons. The material used had to be strong to fulfill the structural requirements of a security grille. The artists also required it to be aesthetically complementary to the contemporary and stylish design of the hotel.

The artists went through an intense design development stage to arrive at a formula for the curving lines that worked visually. Using this formula each panel was then drawn on a computer as vector lines, which were then converted to DXF files for driving the laser cutting equipment.

The panels were fabricated by Donato Steel Fabrications from 4mm thick 304 grade stainless steel sheet supplied by ASSDA major sponsor, Sandvik Australia Pty Ltd. The artists’ designs were laser cut by Molnar Laser Cutting Services and then plate linished both sides to a number four satin finish. The sheets were then welded on the inside into the frames constructed of 38mm square stainless steel tube supplied by ASSDA major sponsor, Atlas Specialty Metals.

The intention with these panels was to create a frame within a frame, the second frame being the walls and pillars of the hotel into which they were bolted. Therefore, the construction of the panels became part of the artwork.

The artists are very pleased with the result of the installation of ‘Strata’. Pentroth Pty Ltd and the Adelaide City Council are pleased that it adds to the ambience of Bent Street and creates a lively streetscape for pedestrians. Opposite the Hotel (and currently under construction) are Bent Street Apartments which will have retail facilities at ground floor level – ‘Strata’ provides a pleasant environment on the street which is also overlooked by the apartments above.

The stainless steel fabrication meets all the requirements of a car park security grille while providing a lively streetscape in the city. The artists believe this is a good example of creating something meaningful out of a necessity. That is, a car park grille that had to be created but it did not need to be ugly and aggressive for pedestrians at street level or for those living in the adjacent apartments.

Images courtesy of Sue Rodwell and Trevor Rodwell.

This article featured in Australian Stainless magazine - Issue 30, January 2005.

Low nickel austenitic stainless steels

The most common grades of stainless steel are 304 and 316, which are particularly popular because their austenitic microstructure results in an excellent combination of corrosion resistance, mechanical and physical properties and ease of fabrication.

The austenitic structure is the result of the addition of approximately 8-10% nickel. Nickel is not alone in being an austenite former; other elements that are used in this way are manganese, nitrogen, carbon and copper.

The Cost of Nickel and Its Addition to Stainless Steel

The cost of the common stainless steels is substantially determined by the cost of ingredients. The cost of the chromium that is the essential "stainless ingredient" is not high, but additions of elements that improve the corrosion resistance (especially molybdenum) or that modify the fabrication properties (especially nickel) add very much to the cost.

Costs for nickel have fluctuated from US$5,000 or US$6,000 in 2001 to US$15,000 per tonne in 2004.

Similarly, molybdenum has dramatically increased from approximately US$8,000 per tonne in 2001 to around US$50,000 per tonne in 2004.

These costs impact directly on the two most common grades: 304 (18%Cr, 8%Ni) and 316 (17%Cr, 10%Ni, 2%Mo). The impact is most keenly felt in grade 316, which has suffered an increase to its cost premium above 304.

Other grades such as the duplex 2205 (22%Cr, 5%Ni, 3%Mo) and all more highly alloyed stainless steels are also affected.

Relative costs of the ingredients are shown in Figure 1, but these do vary widely and sometimes rapidly over time. These costs were correct in late 2004.

Relative Costs for Alloy Ingredients (Late 2004) Alloying Additions - Manganese Replacing Nickel

The point of the alloying elements is that they achieve certain changes to the corrosion resistance or to the microstructure (which in turn influences the mechanical and fabrication properties).

Chromium is used to achieve corrosion resistance, and molybdenum adds to this.

A common evaluation of corrosion resistance of stainless steel grades is the Pitting Resistance Equivalent (PRE), where this is usually evaluated as PRE = %Cr + 3.3 x %Mo + 16 x %N. A neat equation, but unfortunately only a guide.

The PRE gives a guide to ranking of grades, but is not a predictor of resistance to any particular corrosive environment. What is apparent is that pitting corrosion resistance can be increased by molybdenum, but also by chromium or by nitrogen additions. These are much cheaper than molybdenum. Despite its high PRE factor, nitrogen has limited effect on corrosion resistance because of low solubility, ie. <0.2%.

The microstructure of the steel is largely determined by the balance between austenite former elements and ferrite former elements.

On the austenite former side carbon, manganese, nitrogen and copper are all possible alternatives to nickel. All these elements are lower cost than nickel.

As is the case for the PRE, the Ni-equivalence formulas are a guide but do not tell the full story; each element acts in slightly different ways, and it is not possible to fully remove nickel and replace it with, for example, copper or nitrogen.

Manganese acts as an austenite former but is not as effective as nickel, and Cr-Mn steels have higher work hardening rates than do apparently equivalent Cr-Ni steels.

Carbon is a very powerful austenite former, but has only limited solubility in austenite, so is of limited value in a steel intended to be fully austenitic.

Although not recognised by the PRE formula, nickel has positive effects on resistance to some corrosive environments that manganese does not duplicate.

There can also be synergy between the elements. Addition of nitrogen has the double effect of forming austenite and of increasing the pitting corrosion resistance. And manganese is a strong austenite former in its own right, but also has the effect of increasing the solubility of nitrogen.

The Rise of the "200 Series" Steels

Manganese is therefore a viable alternative to nickel, ranging from a minor addition to an almost complete replacement.

The development of high manganese austenitic grades first occurred about fifty years ago, during one of the (several) previous periods of high nickel cost.

At that time some Cr-Mn-Ni grades were sufficiently developed to be allocated AISI grade numbers Ü 201 (17%Cr, 4%Ni, 6%Mn) and 202 (18%Cr, 4%Ni, 8%Mn) are high Mn alternatives to the straight chromium-nickel grades 301 and 302, and are still included in ASTM specifications as standard grades.

Their consumption over the following decades has been low relative to their Cr-Ni equivalents. The reasons for the poor take-up of these lower cost grades have been:

  • Very high work hardening rate (this can be an advantage in some applications).
  • Slightly inferior surface appearance Ü considered unacceptable for certain applications.
  • Additional production costs Ü higher refractory wear in melting in particular.
  • Corrosion resistance is lower in some environments, compared to Cr-Ni grades.

An additional issue is that Cr-Ni and Cr-Mn-Ni austenitic scrap is all non-magnetic, irrespective of nickel content, but scrap merchants evaluate scrap on the basis of assumed nickel content.

This has the potential to destabilise scrap markets. The upshot is that the cost reduction (due to lower ingredient cost) has been generally insufficient to move applications from the traditional Cr-Ni grades.

Take-up has often been because of technical advantages of 200-series in niche applications, not cost-driven.

Some New Contenders

The last decade has seen the rise of some new contenders in the Cr-Mn-Ni austenitic group. The main development work has been in India and the principal application has been kitchen ware Ü cooking utensils in particular.

The very high work hardening rate of the low nickel / high manganese grades has been acceptable to a point in this application, but additions of copper have also been made to reduce this problem.

India has been a fertile development and production venue for these grades because of local economic factors.

Other Asian countries have also become strong markets and more recently also producers. The Chinese market is particularly strong, and there is substantial demand in China for the Cr-Mn-Ni grades, often referred to generically as ?200-seriesî stainless steels.

Other centres of production are Taiwan, Brazil and Japan. Alloy development has resulted in a range of austenitic grades with nickel contents ranging from 1% to 4% and up to over 9% manganese. None of these grades are included in ASTM or other internationally recognised standards as yet.

The growth rate in production of these low-nickel austenitic grades has been very rapid. The most recent data published by the International Stainless Steel Forum (ISSF) shows that in 2003 as much as 1.5 million tonnes (7.5% of the worlds stainless steel) was of this type. In China the proportion has been estimated to be 25% in 2004.

Problems still exist however, and large-scale conversion of Cr-Ni applications to Cr-Mn-Ni-(Cu) grades is not likely.

The principal issue is lack of control ‹ unscrupulous suppliers misrepresenting low-nickel product as grade 304 with some resultant service corrosion failures, and degradation of scrap due to contamination by low-nickel material.

As at the start of 2005 the future is unclear. Although it seems logical that there should be a place for the low nickel austenitic grades, the practical issues may mean that grade selectors will instead choose to either continue to use the higher cost Cr-Ni grades, or to seek lower cost alternatives amongst the ferritic or duplex grades.

Credits

ASSDA would like to thank Mr Peter Moore, Technical Services Manager of Atlas Specialty Metals, for the contribution of this article.

This technical article was featured in Australian Stainless magazine # 32 - Winter 2005 and is an extract from the Grade Selection section of the Australian Stainless 2005 Reference Manual.

To order a copy of this essential technical resource for the stainless steel industry, download an order form from the ASSDA website - www.assda.asn.au or phone the ASSDA office on 07 3220 0722.

Turning industrial systems into architectural features

A Queensland stainless steel fabrication company has successfully turned a product usually found in industrial environments into an architectural design feature that is gaining popularity on Australia’s east coast.

Stainless steel screens and grates have traditionally been used for filtering and cleaning in the mining, petrochemical, food processing and water treatment industries — applications where water transfer is required.

ASSDA member, Paige Stainless Fabrications has taken the grating concept further, beyond a simple drainage system, by using the product in architectural applications such as stair treads,  walkways and entry mats.

Paige Stainless Fabrications designs and manufactures ‘heel proof’ stainless steel products using close bar longitudinal / transverse grating.

One example of the product in action can be found at the Andrew ‘Boy’ Charlton Pool, Sydney, a popular swimming icon suspended over spectacular Woolloomooloo Bay.

Architects, Lippmann Associates, won a RAIA Architecture award in 2003 for public building design. As part of the project design, Lippmann Associates specified stainless steel stair treads and entry mats.

ASSDA Major Sponsor, Atlas Specialty Metals, supplied grade 316 L stainless steel to the project because of it’s high corrosion resistance. The stainless steel product delivered the desired functional, environmental and aesthetic values that find appeal to architectural environments rather than traditional forms of drainage.

In further applications, the grade 304 stainless steel grating product has been used extensively for entry mats to the following buildings:

  • Ambros Building (corner Bent and Phillip Streets, Sydney).
  • AMP Building - Sydney
  • Customs House, Sydney
  • IBM Building, Sydney
  • National Australia Bank Administration, Melbourne Docklands

This article featured in Australian Stainless magazine - Issue 32, Winter 2005.

 

Reducing risk with stainless flameproof technology

Where flammable or combustible materials are stored or handled, there can be a severe risk of an explosion or fire if handling equipment such as forklift trucks are not flameproofed.

A Combilift with stainless steel exhaust conditioner from Chess FlameproofFlameproofing of material handling equipment is the science of reducing the risk of an explosion or fire by means of specialised principles and technologies.

Three components are needed in order to generate an explosion or fire.

  1. A flammable or combustible material eg. liquid, gas or dust.
  2. Oxygen eg. air.
  3. Ignition source eg. electrical sparks,  mechanical sparks, hot surface and static discharges.

Sources of ignition include flames and sparks from exhaust systems, arc and sparks from electrical equipment, hot surfaces and static build up.

Chess Flameproof, a division of ASSDA member Chess Engineering Pty Ltd, specialises in the conversion of materials handling equipment for use in hazardous areas.

Materials handling equipment such as forklift trucks, tow tractors, sweepers, scissor lifts and boom lifts ranging from 1 ton to 32 tonnes have all been designed and manufactured to remove or reduce the risk of the equipment becoming the source of ignition. Both diesel and battery electric powered forklifts can be flameproofed. Note spark ignition engines ie. LPG and petrol are not permitted in any hazardous areas.

Left to right: A stainless steel flame arrestor, a corrugated stainless steel exhaust flex, a stainless steel final flame trap element and a stainless steel flame arrestor. In addition to flameproofing, Chess Engineering manufactures custom forklift attachments, engine protection systems, speed sensors/controllers and cabins as well as custom modifications and general forklift engineering.

To overcome the possible sources of ignition, a number of protection techniques are used:

Stainless steel water cooled exhaust manifold

Extreme temperatures of the gases leaving the cylinder head of the engine can easily cause the exhaust manifold to climb in temperature to a level where it may possibly ignite surrounding hazardous area atmosphere. To overcome this problem a stainless steel water cooled exhaust manifold is fitted.

Stainless steel exhaust conditioner

An exhaust conditioner is a water tank that channels the hot exhaust gases and particles through a labyrinth thus cooling and filtering.

Depending upon the area classification, a final flame trap element may be fitted as a secondary measure. Inside the exhaust conditioner is a very corrosive environment because of the exhaust gases, water and elevated temperatures.

Toyota forklift built to Zone 1 hazardous areas For standard conditions, grade 316 stainless steel has proved to be more than adequate for this application and withstands the harsh environment providing welding and post welding procedures are correctly followed. Alternatively for extremely corrosive conditions, a duplex stainless steel has been used.

This article featured in Australian Stainless Issue 32, Winter 2005.

Images:

Main image - Stainless steel flame arrestor or flame trap used on the engine inlet to cool and quench flames that may arise from combustion malfunction.

Top right - A Combilift with stainless steel exhaust conditioner.

Above - A stainless steel final flame trap element (centre) and (left) a corrugated stainless steel exhaust flex with braided sleeve used to absorb engine movement and vibration.

Right - Toyota forklift built to Zone 1 hazardous area.

Stainless Steel Bulk Solvent Storage Facility Completed

When coatings manufacturer, PPG Industries’ original bulk solvent storage facility had come to the end of its economic life, the company elected to install a new $8m facility that is both efficient and fully compliant with numerous safety, environmental and good design principles on its Clayton, Victoria site

 

Established in the 1950s, the bulk solvent storage facility receives a diverse range of bulk solvents and monomers, sourced from petrochemical producers in particular and delivered to the site by bulk road tanker.

PPG Industries Project Manager, Tom Van Loon, said he went in search of a stainless steel fabrication contractor with both the experience and capacity to undertake the major components on a qualitative and timely basis.

“Projects of this nature are normally awarded to a contractor on a turn key basis, but we elected to engage a competent team of designers and supervisors, outsource most services and work in close cooperation with our appointed fabricator Furphy Engineering and the suppliers of the process equipment” Mr Van Loon said.

On site at Clayton, the tanks are fully enclosed within a three-compartment concrete ‘vault’. The 400mm thick vault has dimensions of about 28 metres by 22 metres with a depth of 5.5 metres.

The tanks have been backfilled with washed silica sand to maintain low ambient product temperature and provide additional fire protection. As an additional safety protection each solvent tank is nitrogen blanketed.

Furphy Engineering purchased the majority of the stainless steel for the project from ASSDA member, Midway Metals.

“The tanks for the UST project required a total of 70 tonnes of 6mm thick, grade 304 stainless steel which were fabricated at the Furphy Engineering workshops in Shepparton, Victoria.

“The welding of each tank was subject to non-destructive testing by radiography during fabrication, followed by hydrostatic testing of each tank prior to delivery” said Darren Leeder, Furphy Engineering’s Sales and Marketing Manager.

Located above the underground storage is the process control system, extensive delivery pumping and pipework and three tanker unloading bays.

Furphy’s also fabricated all the stainless steel pipe spool work, comprising over 1,500 individual spool pieces amounting to more than 4,500 metres of stainless steel pipe work to deliver the solvent raw materials to the manufacturing centres on the site.

All fabrication was undertaken to various standards including AS 1692-1989: Tanks for flammable and combustible liquids and other best practice standards for the environment, plant safety and related quality aspects.

As Project Manager for PPG Industries, Tom Van Loon says that the project was completed on time and to budget.

“The project outcome has been particularly pleasing as the storage facility has scope to handle PPG’s anticipated growth in the future.”

This article featured in Australian Stainless magazine - Issue 33, Spring 2005.

New 9kg Stainless Steel Gas Bottles


Posted 31 October 2005

Strong demand from prestige boating and yachting manufacturers has prompted the production and release of new stainless steel nine kilogram LPG gas bottles.

Melbourne-based fabricator and ASSDA member, Stainless Tanks and Pressure Vessels (STPV) produce grade 316L stainless steel gas bottles that offer significant resistance to corrosion, making the product ideal for cooking in marine and boating applications.

The new gas bottles will also complement the increased production of barbecues now manufactured in stainless steel and are supplied with standard gas fittings.

The refillable gas bottles have a ten year inspection life in line with industry codes and comply with gas liquids code under AS 2470.

STPV principal Chris Miller said he commenced manufacturing the gas bottles after enquiries from a number of prestige boating and yachting manufacturers in search of a superior, corrosion resistant supply tank, which can readily be refilled.

“We have since commenced supplying several barbecue manufacturers who produce a range of superior products in stainless.”

The stainless steel bottles are available from Southern Stainless, Gold Coast and Marine Barbecues, Newcastle. Alternatively, contact Stainless Tanks and Pressure Vessels for outlets.

Stainless Tanks and Pressure Vessels manufactures a wide range of standard and to order stainless steel tankage equipment for the fire protection, process industries and numerous industrial applications.

This article featured in Australian Stainless magazine - Issue 33, Spring 2005.

Recycling of Stainless Steel Scrap

Today, environmental factors are at the forefront of material selection for specifiers. Stainless steel’s long service life, 100 percent recyclability and its valuable raw materials make it an excellent environmental performer.

 

 Stainless steel objects rarely become waste at the end of their useful life. Recycled stainless objects are systematically separated and recovered to go back into the production process through recycling.

As well as iron, stainless steel contains valuable raw materials like chromium and nickel which makes recycling stainless steel economically viable.

Stainless steel is actively recycled on a large scale around the world by recyclers who collect and process scrap (recycled stainless steel) for re-melting all around the world.

Scrap collection
The use of stainless steel scrap is fundamental to the steelmaking process. There are two types of scrap - reclaimed scrap (old scrap) and industrial scrap (new scrap).

Reclaimed scrap includes industrial equipment, tanks, washing machines and refrigerators that have reached the end of their service life.

Industrial scrap includes industrial returns or production offcuts from manufacturing by industrial engineering and fabrication sources.

Today, stainless steel is made up of approximately 60% recycled content including:

  • 25% reclaimed scrap
  • 35% industrial scrap
  • 40% new raw materials

The useful service life of stainless steel products is long so the availability of scrap is dependent on levels of production from decades ago.

With an average content of 25% of old scrap, stainless steel is close to the theoretical maximum content of material from end-of-life products.

Recycling the scrap
Specialised expertise and sophisticated technology is needed in recycling to separate and prepare each type of alloy for remelting.

A recycling processor feeds the scrap into a large shredder to break it into smaller pieces.

It is then chemically analysed and stored by type.

This process may include ‘blending’ the scrap into chrome steels, nickel alloys and other types of stainless steels.

After blending into piles for specific customer requirements the scrap is then loaded into containers for export to overseas mills.

The global market for scrap
Virtually, all Australian stainless steel scrap goes overseas. There’s a small market for stainless steel scrap in Australia for use in the foundries business. Foundries often use profile offcut or plate material scrap products.

At least 30,000 tonnes of stainless steel scrap in Australia will be exported a year to stainless steel mills in countries including China, South Korea, Taiwan, India and Japan.

China, for example, is using approximately 800,000 tonnes of industrial scrap. Reclaimed scrap is also on the increase in China and is expected to reach 2.5 million tonnes in 2005.

For mills, scrap is important because recycled stainless steel contains valuable raw elements including chromium, nickel and molybdenum that are gathered, processed and reused in the production process. The more scrap used in furnaces by mills, the less raw materials are required in the production process.

Stainless steel mills

Scrap along with other raw materials, ferrochromium (chrome/iron), ferro moly (molybdenum/iron) and nickel are blended into an electric furnace.

After melting, impurities are removed, the molten metal is refined and the chemistry analysed to determine what final adjustments are necessary for the specific type of stainless steel being produced.

The molten stainless steel is then cast into slabs or billets before production of plate, sheet, coil, wire and other forms in preparation for use by industrial manufacturers.

The stainless returns to you
Industrial manufacturers produce stainless steel items that you use everyday including cutlery, pots and pans, kitchen sinks and many architectural, industrial and other components.

At each stage of the production and use process, stainless steel retains its basic properties and utility value. Unlike many industrial and engineering materials, stainless steel may be returned to its original quality in the supply chain without any degradation.

You can be assured that even after its long service life, your environmentally-efficient stainless steel will always return to you bright, shining and new!

For more information about stainless steel, contact the Australian Stainless Steel Development Association on 07 3220 0722 or visit www.assda.asn.au

ASSDA acknowledges the assistance and contribution of Ignatius Brun of ELG Recycling Processors, the International Stainless Steel Forum (ISSF), the Nickel Institute and Peter Moore of Atlas Specialty Metals in the production of this article.

Consumption of stainless steel scrap - 2004

  • China — 2.8 million tonnes of production using 900,000 tonnes of scrap.
  • Japan — 2.4 million tonnes of production capacity using 900,000 tonnes of scrap.
  • South Korea — 2.3 million tonnes of production using  800,000 tonnes of scrap.
    Product mix 80% austenitic, 20% ferritic.
  • Taiwan — 2.6 million tonnes of production using 600,000 tonnes of scrap.
  • India  — 1.4 million tonnes of production using 300,000 tonnes of scrap.

Note: Australia sends a proportion of stainless steel scrap to all of the above countries.

This article featured in Australian Stainless magazine - Issue 33, Spring 2005.

Specifying Stainless Steel for Luxury Beachside Homes

Stainless steel enjoys a strong and enduring reputation for visual appeal and structural integrity in a wide range of applications. This broad appeal has made stainless steel an ideal choice for value-adding luxury homes on Sydney’s northshore.

 

Spiral Staircase - Collaroy
One particular luxury home overlooking the beach at Collaroy was owned by former rugby league test captain Brad Fittler at the time. The home featured an external steel spiral staircase. However, its close proximity to the surf had caused the painted staircase to corrode in less than 12 months of installation.

Salt deposits had accumulated on the structure, causing the staircase to rapidly corrode in the harsh coastal environment.

Builder, Binet Homes commissioned ASSDA member, DJQ Industries to fabricate and install a stainless steel spiral staircase that could cope with the sustained salt exposure inherent with coastal applications.

DJQ Industries fabricated the new staircase out of grade 316 stainless steel supplied by ASSDA Major Sponsor, Fagersta Steels. The staircase was welded into sub-assemblies and electropolished by Regents Park Electroplating on completion of fabrication prior to installation on site.

The corrosion resistance of stainless steel in this environment and exposure to natural rain washing will mean this installation will have a long service life with minimal maintenance.

Pool with a View - Palm Beach
Substitute your morning coffee for a dip in this luxury home pool with a spectacular eye-opening view of northern Sydney’s beautiful Palm Beach.

ASSDA member DJQ Industries was contracted by Bellevarde Constructions to supply and install stainless steel balustrades, pool edging, fence and other household fittings.

ASSDA Major Sponsor Fagersta Steels supplied grade 316 stainless to DJQ Industries for the $200,000 project. The project was fabricated to meet all building and structural codes with finishes suitable for a marine environment.

The unique pool edge detail provides a less obtrusive mounting for the glass and stainless steel was used extensively in the construction of framework for the pool platform steps. Stainless steel items for the house included a chimney cowl, chimney cap, downpipes, trench type floor drains to bathrooms and sliding door tracks to all north facing walls on two levels.

The extensive use of stainless steel in this luxury home highlights the importance of specifying stainless steel for maximum corrosion resistance and enduring visual appeal.

This article featured in Australian Stainless magazine - Issue 33, Spring 2005.

Stainless Metal Craft

Artisans of Fabrication

Traditionally artisans of yesteryears searched for the right stone or timber and personally hand carved their works of art. However, modern artists and sculptors now work collaboratively to create sculptures using a wider range of materials including stainless steel

Installation artist, Marion Borgelt is a modern artist who in early 2005 completed the most significant work in her 25 year career. However, this is no public installation.

Located high on the 32nd floor of the JP Morgan Chase building overlooking Circular Quay, 'Time and Tide (wait for no man)' features 16 stainless steel spheres resting on an ascending spiral of 16 sandstone pliths. The 4000 kilogram sculpture represents the different phases of the moon and demonstrates how people in corporate life are governed by the global clock.

ASSDA Accredited Fabricator, Stainless Metal Craft took up a challenge that some of the metal workers never faced before. Mimicking artisans of years gone by, man and machine merged through the use of skilled computer experts and metal workers.

Many hours were spent in the complex machining operation and many more in the mirror polishing, to complete the 16 hollow spheres. The team of modern fabricators at Stainless Metal Craft worked tirelessly to bring Borgelt's design to fruition.

Based in Emu Plains, Stainless Metal Craft uses the latest processes and technology to manufacture architectural and commercial building products for industries such as health, aged care, councils, government and schools.

This article featured in Australian Stainless magazine - Issue 35, Autumn 2006.

Alloy C-276: A Super Alloy for Processing Plants

OMG Cawse Pty Ltd is the owner and operator of a nickel and cobalt mining operation and processing plant that is located 55 kilometres north east of Kalgoorlie.

Extracting nickel involves acid leaching using sulfuric acid in a high temperature and pressure autoclave to dissolve the nickel and cobalt from the oxide ore.

The wastes from this process are very acidic and require a highly corrosion resistant material for the lining of the sump tank.

When various concrete coatings for the sump tank were trialed and failed, OMG Cawse opted to install Alloy C-276 to engineer out the continuous maintenance of the concrete coatings.

Alloy C-276 is a super nickel alloy (not a stainless steel), a material that remains resistant in the most corrosive environments such as in chemical processing, waste treatment, pollution control and pulp and paper production.

ASSDA member, Specialised Engineering Services (WA) fabricated a 3mm thick liner for a sump tank from Alloy C-276 plate supplied by ASSDA Major Sponsor, Atlas Steels.

Measuring 9m long x 2.5m wide x 1m to 1.3m deep, the tank is filled with water and receives up to 98% sulphuric acid.

Alloy C-276 is also one of the few materials that can withstand the corrosive effects of chlorine dioxide, wet chlorine gas and hypochlorite.

This article featured in Australian Stainless Issue 34 - Summer 2005.

Preventing Coastal Corrosion (Tea Staining)

When used properly, stainless steel enjoys a strong and enduring reputation for visual appeal and structural integrity in a wide range of applications and environments.

But, like all materials, stainless steel may become stained or discoloured over time, impairing the overall look. This brown discolouration - tea staining - has been identified in coastal applications in Australia and overseas.

Factors affecting tea staining have been researched by ASSDA and the information gathered has been supported by experiences from around the world.

This article provides information on tea staining and what fabricators, specifiers and end users should do to help avoid it and enjoy the long life and clean appearance of stainless steel.

WHAT IS TEA STAINING?
Tea staining is discolouration of the surface of stainless steel by corrosion. It is a cosmetic issue that does not affect the structural integrity or the lifetime of the material. Tea staining occurs most commonly within about five kilometres of the surf and becomes progressively worse closer to the marine source.

However, wind exposure, pollution levels, local sheltering and higher temperatures can create environments where tea staining might occur 20 kilometres or more from the surf. The effect is much less severe around sheltered bays. These same factors also increase corrosion rates of alternative materials.

Other causes of staining that are not tea staining include carbon steel contamination, uncleaned welds and chemical fumes such as hydrochloric acid or bleach. The ASSDA Reference Manual has more details on this.

WHY DOES TEA STAINING OCCUR?
The relationships between the contributing factors are complex, but generally become increasingly critical closer to salty water. Tea staining occurs when local conditions (such as temperature, relative humidity and presence of corrosive substances on the surface) are too aggressive for that stainless steel grade in its installed condition.

There are important factors that promote the occurrence of tea staining that should be considered, as shown in the box and explained below.

1.    Presence of corrosive substances
The presence of sea salt on the surface of the stainless steel is one of the major factors that causes tea staining. Sea salt has the characteristic of staying wet until a very low relative humidity (RH). The result of this is that the surface stays wet (and is corroding) longer with sea salt compared with sodium chloride. However, presence of industrial pollutants could also make the conditions more aggressive.

2.    Atmospheric conditions
A combination of atmospheric conditions with high humidity (eg tropical climates) and a high temperature creates worse conditions for the occurrence of tea staining. The high humidity generates a film of moisture that dissolves the salt deposits and creates a corrosive solution on the surface. The low humidity and absence of corrosive deposits means that tea staining is rarely a problem indoors.

3.    Surface orientation and design
Poor drainage promotes corrosion whether it is because the surface is near horizontal or has a texture that traps contaminants. Conditions are very aggressive in rain sheltered areas such as the underside of sloping roofs, downpipes under eaves or in a building rain shadow. These can cause significant tea staining. Designs with corners or crevices (such as intermittent welds) can trap water and lead to more serious corrosion than tea staining.

4.    Surface roughness
Deep grooves or metal folds on a surface are more susceptible to corrosion because they can trap salts (chlorides). When the surface dries the salts become concentrated, making the conditions more aggressive. A deep groove will have more trapped water (and salts) so the bottom of the groove will be exposed to salt concentration above its resistance for longer - which will initiate corrosion. There is a critical surface roughness of approximately 0.5 μm Ra for cut or abraded surfaces. Abraded surfaces smoother than approximately 0.5µm Ra are much less susceptible to corrosion.

5.    Surface characteristics
To achieve the best corrosion performance of a stainless steel, the surface should be clean, free of contamination such as carbon steel swarf or manganese sulphide inclusions, and have a continuous passive layer. Acid pickling, acid passivation or electropolishing for sufficient time will remove these contaminants from the surface as well as restore the passive layer, leaving the stainless steel with a clean and corrosion resistant surface. If a stainless steel is welded, the heat input will locally destroy the passive layer (a dark non-protective oxide is formed around the weld). To achieve best corrosion performance and restore passivity of the weld, the heat tint and underlying chromium depleted layer must be removed. How this is done is described later.

6.    Appropriate grade
There are several hundred grades of stainless steel with different chemical composition but only about 10 in common use. All owe their corrosion resistance to the thin chromium oxide film on the surface, although other additions such as molybdenum and nitrogen can improve the corrosion resistance, especially in chloride-containing environments. A formula based on the content of these three elements is useful to rank the corrosion resistance of different grades. This Pitting Resistance Equivalent [PRE] number is calculated by %Chromium + 3.3 %Molybdenum + 16 %Nitrogen. The PRE ranges from 10.5 for the grades with the lowest corrosion resistance to more than 40. For acceptable corrosion resistance, typically a PRE of approximately 18 is adequate away from marine influences, PRE of approximately 24 is required for marine atmospheres while severe marine atmospheres may require PRE of approximately 34. The higher the PRE, the greater the corrosion resistance.

7.    Maintenance
Stainless steel is a low maintenance material but it is not generally maintenance free. A light and regular wash is best and natural rain washing may be sufficient. If not, then consider washing the stainless steel when you wash an adjacent window. Lower grades will require more regular maintenance and if the environment causes sticky deposits, a solvent and detergent mix may be required. Application of oils or waxes will temporarily restrict chloride access to the stainless steel but they need regular renewal. These temporary protectives also tend to attract debris and dull the surface.

CONDITIONS REDUCING THE RISK OF TEA STAINING

1.    Absence of corrosives - especially salt.
2.    Atmospheric conditions - lower temperatures and low relative humidity (RH) are better.
3.    Surface orientation and design - free drainage and avoidance of traps which can concentrate corrosives. This includes open exposure to allow   rain washing.
4.    Surface roughness - smoother is better.
5.    Chemical cleanliness or passivation of the surface improves the corrosion resistance.
6.    Appropriate grade for exposure conditions - increasing PRE increases corrosion resistance.
7.    Maintenance - or corrosives will accumulate.

GUIDANCE IN FABRICATION

Design, fabrication and handling
Poor design and fabrication can lead to tea staining or more serious corrosion of stainless steels. Surfaces should be free draining, boldly exposed to rain washing and avoid channelling of run-off. Horizontal surfaces or curves which cause ponding are specific problems. Abraded surfaces should not be rougher than 0.5µm Ra and the grain should be vertical to avoid ponding and collection of contaminants. For abraded surfaces, the best corrosion resistance will be achieved if a nitric acid passivation treatment is carried out as a final step.

Competent stainless steel fabricators will avoid carbon steel contamination (which can cause other corrosion problems), so choose designers and fabricators that are experienced with stainless steel to achieve the best outcome.

Appropriate grade selection
Each stainless steel has a limit to the concentration of salts that it can comfortably resist: the higher the alloying content (Cr, Mo and N), the higher the resistance to corrosion. Exposure of a particular grade of stainless steel to a more aggressive environment than it can resist will cause tea staining.

Grade 316, or a grade with equivalent corrosion resistance, should be selected as a minimum within five kilometres of the surf. For critical applications (eg splash zones, unwashed areas or rough surfaces), higher grades of stainless steel such as duplex or ‘super’ grades may be required.

The lower alloyed and less expensive grades (such as 304 or 430) will probably become tea stained or even suffer more severe corrosion in a marine environment.

Treatment of welds
Pickling after welding is one method of promoting good performance of stainless steel near the coast. This chemical treatment normally uses a mixture of nitric and hydrofluoric acid in a gel, paste or bath. It removes the welding oxide and chromium depleted layer underneath and rapidly restores the passive layer, which gives stainless steel its corrosion resistance. A darker heat tint means a thicker oxide and a longer exposure to pickling acids is required. Pickling removes material from the surface in a controlled way and may etch and dull the stainless steel surface. Excellent gas shielding, so there is no more than a pale straw colour, may avoid pickling provided the environment is mild. An alternative is to mechanically remove the scale and underlying chromium depleted layer, followed by a chemical passivation treatment using nitric acid. Any mechanical removal must not unduly roughen the surface.

Installation and inspection
After installation, the completed structure should be visually inspected for surface damage or contaminants. If contamination is suspected, several cycles of a misting and drying test with tap water is relatively simple. The sensitive ferroxyl test (described In ASTM A380) may also be used in critical applications. If discovered, imperfections should be removed and the corrosion resistance chemically restored by pickling or passivating treatments or by electropolishing.

Do not use hydrochloric acid
Hydrochloric acid, sometimes used to clean cement or mortar residues, must not be used on stainless steel — it will stain the surface and usually start more serious corrosion.  

KEY DESIGN RECOMMENDATIONS

Plan to get the desired result
Marine environments are the most aggressive for all building materials.
Stainless steel’s corrosion resistance in marine environments means that installations are likely to remain structurally sound for decades (see image on right).

It must be recognised, however, that keeping a pristine surface finish requires understanding and, usually, additional cost. Determine your expectation of the structure and plan ahead to achieve and maintain the intended result. This normally includes a maintenance program.

Environment
Tea staining is most likely to occur up to five kilometres from a surf beach and one kilometre from still marine waters. There is no hard and fast rule: wind and weather conditions play a big part and the severity of the conditions increases sharply as you approach the surf. AS 2312 suggests that in some special circumstances, 20 kilometres from the coast can still constitute a marine environment. The closer to the source of salt, the more critical it is to follow the recommendations in this Bulletin.
Areas that are sheltered or not rain washed are particularly susceptible. Tropical and high humidity areas are also more at risk of tea staining.

Specify and insist on a smooth and clean surface finish
To minimise the risk for tea staining the smoother the surface the better. A surface roughness of less than 0.5µm Ra  is strongly recomended. Surfaces smoother than 0.5µm Ra will have even better corrosion resistance. The most corrosion resistant, mechanically finished surface is a mirror polish (ASTM A480 No.8 or EN10088.2 class 2P). It is very smooth, resistant to salt accumulation and easy to clean. The surface roughness of a mirror polished surface is so low that it is not reliably measurable by mechanical (stylus) instruments.
A No.4 finish just means an abraded (linished) finish. Specifying a No.4 finish is inadequate without indicating the required roughness.  
The Euronorm standard EN10088.2 (finish 2K) recognises this and requires Ra<0.5µm but also that the abraded profile is a clean cut.

Components used near the sea can be made more resistant to tea staining if they are passivated to remove surface contaminants such as steel smears, weld spatter or sulphide inclusions. Mild levels of contamination may be removed by nitric acid passivation which should not change the surface appearance although it may slightly cloud a mirror polish. More severe contamination by particles of steel or grinding debris may require pickling which etches and usually dulls the surface. Either process may use pastes or gels (which can be applied on site) or liquids in baths in a factory. These chemical processes take longer if it is cold.

Electropolishing has been found to be extremely effective in removing surface contamination and passivating the surface. It also brightens and slightly smoothes the surface as well as rounding sharp edges and removing the peaks left from polishing operations. Electropolished surfaces have a characteristic lustre but may not be mirror smooth. A mechanically mirror polished surface will normally lose its mirror reflectance if electropolished.

Smoother mill finishes such as 2B and Bright Annealed (BA) are widely available in flat products. Provided they are not damaged during fabrication, they offer good resistance to collection of salt deposits and hence to tea staining.
Rolled embossed finishes may be suitable for some applications. These have very smooth surfaces but with a pattern that lowers reflectivity. Think carefully about the pattern and how it will be oriented — avoid pools of water sitting on the surface.

Specify and insist on the right grade
In marine environments, use grade 316 or one with equivalent corrosion resistance unless the job is aesthetically critical and regular maintenance is unlikely.

Where there are high aesthetic expectations a number of more corrosion resistant stainless steel grades can be considered. The first step up from 316 is 2205 and then the super duplex grades, although the high molybdenum austenitics and high molybdenum ferritics may also be useful. Smooth surface finish and maintenance are still important with these grades.

Treatment of welds
For general architectural applications welds should comply with AS/NZS 1554.6 Level 2, Class B. (Details of other weld finish classifications are given in the ASSDA Reference Manual). However, this specification does not guarantee the absence of structurally minor surface defects which can act as traps and corrosion initiating sites. The protruding weld can be ground flush, and good resistance to tea staining achieved (a Grade I finish) when polished to 320 grit or finer finish. The smoother the surface, the better the tea staining resistance. Passivation will occur in chloride free, moist air within a day. Chemical passivation treatment with nitric acid may be applied to:

  • Substantially reduce the time required for passivation
  • Provide a more corrosion resistant passive film
  • Remove possible iron contamination
  • Dissolve exposed manganese sulphide


Chemical passivation must be applied after abrasion if the environment is particularly aggressive.
An alternative cleaning treatment is a Grade II blast cleaned finish. This will require a post blasting passivation treatment. The blasting should remove heat tint and the chromium depleted layer but not make the surface roughness worse than 0.5 µm Ra, must not leave folds or crevices and should not embed corrodents. The Grade II stainless steel wire brushing treatment is not adequate to control tea staining.

Where a polished (or linished or ground) finish is desired, abrasives should be used with lubrication if possible. In selecting abrasives, consideration should be given to matching the surrounding finish.

A Grade II pickled finish will provide good tea staining resistance without grinding the weld flush, provided there are no significant surface crevices/defects. Where linishing or blasting is not performed, pickling of site welds (using mixed hydrofluoric plus nitric acids) should take place as a final step in the weld procedure.

Pickling will remove any fabrication contaminants and restore the passive chromium oxide layer, resulting in a corrosion resistant surface. Electrocleaning has been used instead of pickling to remove weld scale and heat tint, especially when hydrofluoric acid use is restricted. While passivation treatments do not normally affect appearance, pickling treatments are likely to dull bright surface finishes. Electropolishing is also a very effective method of passivation. ASSDA's Australian Stainless Reference Manual describes these treatments in more detail.

Specify and insist on regular maintenance
Washing removes deposits (such as salt) that can cause corrosion. It is necessary to avoid tea staining. Rain washing the surface is helpful in reducing tea staining, so design the job to take advantage of the rain, but ensure good and even drainage.

Stipulate that the stainless steel also be washed when cleaning of the surrounding area takes place. As a guide, stainless steel should be washed if a window requires washing. For best results, wash with soap or mild detergent and warm water followed by rinsing with clean cold water. The appearance of the surface can be improved further if the washed surface is wiped dry.

If routine cleaning of the surrounding area does not take place, washing frequency for the stainless steel is recommended as in Table 1 below.

It is essential that abrasive cleaners or those containing chlorides or bleach are NOT used to clean stainless steels as they will damage the surface. If some tea staining does occur, then an assessment of the 7 points is required to determine why the problem occurred. Simple mechanical polishing is unlikely to both remove current and prevent future teastaining. Reasonably simple chemical cleaning and passivation is usually the most effective treatment. ASSDA's Australian Stainless Reference Manual has more details.

Download ASSDA Technical FAQ6: Preventing Coastal Corrosion (Tea Staining) (Edition 3, Feb 2010)

Further Reading

ASSDA's Australian Stainless Reference Manual Edition 7, 2012

Australian Standard AS/NZS 1554.6 Welding Stainless Steel for Structural Purposes

ASTM Standard A380 Standard Practice for Cleaning, Descaling and Passivation of Stainless Steel Parts, Equipment and Systems

Nickel Institute, Japan Stainless Steel Association Successful Use of Stainless Steel Building Materials publication No 12 013

Nickel Institute Guidelines for the Welded Fabrication of Nickel-containing Stainless Steels for Corrosion Resistant Services publication No 11 007.

Common Traps to Avoid


Posted 1 April 2006

Errors in stainless steel fabrication can be expensive and difficult to resolve. So a 'Get it right the first time' approach to stainless fabrication is necessary to gain the best result. Check the ASSDA website regularly for a local Stainless Steel Specialist.

ASSDA Accredited Fabricators - Ensuring the Best Result
ASSDA Accredited Fabricators
are companies and individuals that have a common understanding of successful technical practices for fabricating stainless steel.

To ensure the highest standard in quality, Accredited Fabricators belong to the ASSDA Accreditation Scheme, an ASSDA initiative that is intended to achieve self regulation of the industry, for the benefit of both industry members and end users.

The Accreditation Scheme criteria requires all fabricators to conform to stringent standards of competence, training and education, personal and professional conduct, adhering to a Code of Ethics and a Code of Practice, and committing themselves to continuing competency development.

The Scheme gives owners and specifiers of stainless steel greater certainty that fabrications using stainless steel will be performed by technically competent industry specialists.

COMMON TRAPS TO AVOID

Surface damage, defects and contamination arising during fabrication are all potentially harmful to the oxide film that protects stainless steel in service. Once damaged, corrosion may initiate. Common causes of surface damage and defects during fabrication include:

Scratches and Mechanical Damage

Scratches and gouges form crevices on the steels surface, allowing entrapment of process reactants or contaminants, providing ideal locations for corrosion. Scratches may also contain carbon steel or other contaminants embedded by the object that caused the scratch.

Scratches will also raise customer concerns in situations where appearance is important. Mechanical cleaning is the most effective way to remove them. Prevention would be better.

SURFACE CONTAMINANTS

Common contaminants likely to attack stainless steel include carbon steel and common salt. Dust and grime arising during fabrication may contain these contaminants and should be prevented from settling on stainless steels.

Oil, grease, fingerprints, crayon, paint and chalk marks may also contain products that can provide crevices for localised corrosion and also act as shields to chemical and electrochemical cleaning. They should be removed.

Residual adhesives from tape and protective plastic sometimes remain on surfaces when they are stripped. Organic solvents should remove soft adhesive particles. If left to harden, adhesives form sites for crevice corrosion and are difficult to remove.

The most frequently encountered fabrication problem is embedded iron and loose iron particles, which rapidly rust and initiate corrosion. Other common sources of contamination are abrasives previously used on carbon steel, carbon steel wire brushes, grinding dust and weld spatter from carbon steel operations, introducing iron filings by walking on stainless steel and iron embedded or smeared on surfaces during layout and handling. All should be avoided.

WELDING

The high temperature characteristics of welding can introduce surface and other defects which must be addressed.

Undercut, spatter, slag and stray arc strikes must be minimised as they are potential sites of crevice corrosion. General cleanliness and removal of potential carbon contaminants such as crayon marks, oil or grease is important in obtaining good weld quality. It is also important to remove any zinc that might be present.

Scale on a welding site. Note the crevice corrosion and corrosion from the weld heat tint at this seaside site.HEAT TINT AND SCALE

Heat tint and scale occur when stainless steel surfaces are heated to moderately high temperatures in air (3500C+) during welding.

Deleterious oxides of chromium may develop on each side and on the under surface of welds and ground areas. These oxides lower the corrosion resistance of the steel and during their formation the stainless steel is depleted of chromium. The oxidation and the portion of the underlying metal surface with reduced chromium should all be removed by mechanical, chemical or electrochemical means to achieve the best corrosion resistance.

DISTORTION

Stainless steel has a relatively high coefficient of thermal expansion coupled with low thermal conductivity, at least compared with carbon steel. So, stainless steel expands rapidly with the input of heat that occurs during welding and the heat remains close to the heating source. Distortion can result. Distortion can be minimised through using lowest amperage consistent with good weld quality, controlling interpass temperatures and using controlled tack welding, clamping jigs with copper or aluminium backing bars as heat sinks on the welds.1

Defects DiagramREMOVAL OF SURFACE CONTAMINATION

There are three methods of repairing the surface of stainless steel.

MECHANICAL CLEANING

Wire brushing should only be done with stainless steel bristles that have not been used on any other surface but stainless steel. Clean abrasive disks and clean flapper wheels are commonly used to remove heat tint and other minor surface imperfections. Also effective is blasting with stainless steel shot, cut wire or new, iron-free sand (garnet is a common choice).

This image was taken a month after installation. Corrosion resulting from rough finishing technique is evident. Note also the crevices that are likely corrosion sites.CHEMICAL AND ELECTROCHEMICAL CLEANING

Embedded iron, heat tint and some other contaminants can be removed by acid pickling, usually with a nitric-hydrofluoric acid mixture or by electropolishing. These processes remove, in a controlled manner, from the affected areas, the dark oxide film and a thin layer of metal under it, leaving a clean, defect-free surface. The protective film reforms after exposure to air.

Passivation

Passivation involves treating stainless steel surfaces with, usually, dilute nitric acid solutions or pastes. This process removes contaminants and allows for a passive film to be formed on a fresh surface, following grinding, machining etc.

Care must be taken. Nitric acid treatments will remove free iron, but not iron oxide contaminants. Passivating, unlike pickling, will not cause a marked change in the appearance of the steel surface.

Fabricated pipe showing carbon steel pickup. INSTALLATION

Stainless steel is best installed last to avoid damage during construction. Also, careful storage and handling including protective coating films are required prior to and during installation to minimise risk of damage to the stainless steel structure.

A primary goal of the stainless steel industry is to have finished products put into service in a 'passive' condition (free of corrosive reactions). Stainless steel is a robust and relatively forgiving material, but adherence to informed, good practice will ensure satisfaction for customers and suppliers alike.

Understanding stainless steel is important to its successful application. Ask your stainless steel representatives whether they have successfully completed ASSDA's Stainless Steel Specialist Course. Their commitment to product knowledge will be your key to success.

REFERENCES

1. NI & Euro Inox (1994) Design Manual for Structural Stainless Steel NiDI Ref. No. 11 013

RESOURCES

  • AS 1554.6 'Welding Stainless Steel for Structural Purposes'
  • Australian Stainless 2005 Reference Manual, ASSDA
  • Stainless Fabrication Group, New Zealand, 'Code of Practice for the Fabrication of Stainless Steel Plant and Equipment'
  • Nickel Institute (NI) 'Cleaning Stainless Steel Surfaces Prior to Sanitary Service'
  • ASSDA - www.assda.asn.au
  • BSSA - www.bssa.org.uk
  • Nickel Institute - www.nickelinstitute.org

ASSDA acknowledges the assistance and contribution of Mr Peter Moore, Technical Services Manager of Atlas Specialty Metals in the production of this article. Photographs courtesy of Peritech and Outokumpu.

This technical article featured in Australian Stainless magazine - Issue 35, Autumn 2006.

Training your stainless steel specialists with ASSDA

Transforming apprentices into stainless steel specialists can be a challenging but rewarding experience for employers seeking to improve quality, retain staff and increase profitability.

Underpinning theory and practical training in stainless steel represents only a small part of TAFE fabrication education in Australia. Understanding of standard industry terms such as pickling and passivation, crevice corrosion and knowledge of all the stainless steel grades by students even after completion is minimal.

In response to this problem, ASSDA developed the Stainless Steel Specialist Course, a 16 module training course that provides the industry with the underpinning knowledge required to meet the quality demands of architects, asset owners and end users.

Since the course was released in April 1999, it has provided more than 1000 Australian students with specialist knowledge of stainless steel, its properties, performance and uses.

In 2006, ASSDA upgraded the specialist course into an interactive e-learning flash presentation with images, animations and video for faster, more rewarding training for fabricators, sales representatives, estimators and engineers - anyone working with stainless steel.

Atlas Specialty Metals

ASSDA Major Sponsor, Atlas Specialty Metals recently enrolled more than 70 students in the new e-learning course. Mr Tony Hodges, an internal salesperson for the Melbourne branch, became the first stainless steel specialist to complete the new intermediate course.

However, two rapidly expanding Queensland ASSDA Accredited Fabricators are using the Stainless Steel Specialist Course in different ways to ensure their staff are trained and retained as quality stainless steel specialists.

Bridgeman Stainless Solutions

Mr Len Webb, Managing Director of Bridgeman Stainless Solutions uses the course as an incentive to encourage employees to advance their knowledge of stainless steel and as a 'shortlist' for promoting motivated staff.

As a growing company, Bridgeman Stainless Solutions faces worsening skills shortages in an increasingly competitive labour market.

Mr Webb said that ”the next person that walks up to me and says I want more money or I will go and work for Billy down the road, I needed a strategy enabling me to offer more money to these employees, while retaining committed employees.”

The company offered to enrol current employees in the Intermediate Course and several took up this opportunity. Those who completed and passed the course are recognised for their efforts in the form of a bonus.

So far four of the seven tradesmen have now completed and passed the course, and as such have improved their overall knowledge of stainless steel and increased their understanding of the requirements for welding and fabrication. In turn they have all received their bonuses in recognition of their participation.

“Recognising these tradesmen were interested in doing the Specialist Course allowed me to develop a stronger more committed workforce and to give them the chance to move forward with the company. We will continue to support our tradesmen in further learning at every opportunity,” Mr Webb said.

Rockpress (Rocklea Pressed Metal)

Mr Dave Osborne, General Manager of Rockpress (Rocklea Pressed Metal) is impressed by the effect the increase in knowledge has had on the workshop floor.

At Rockpress, the course is compulsory for the majority of employees from second year apprentices to estimators and managers. In 2005, Mr Osborne enrolled 22 employees in the Full Certificate course. Two employees have already passed the course and nine people currently qualify for an Intermediate Certificate.

“Customers always put a great demand on you and it is changing everyday and we have to compete globally like everyone else does.

“This course gives them the underpinning theory on what makes stainless steel, what it is,  what to watch for when they weld it, what to look for when fabricating with stainless steel.”

Many of the staff study the modules at the same time, resulting in many discussions about course topics at lunchtime. Improved knowledge of the various grades of stainless steel and correct welding practices has also meant that staff now understand enough to ask questions and can individually identify where potential failures can be prevented.

This article featured in Australian Stainless Issue 36, Winter 2006.

Australian Stainless Products

Built on Reputation

Alistair Patterson has a flair for the food and beverage industry that borders on obsession. As the sole proprietor for ASSDA Accredited Fabricator, Australian Stainless Products, Patterson's reputation within the industry means when projects are on, he is onto it!

Australian Stainless Products are custom manufacturers of quality stainless steel food, beverage and pharmaceutical process products and equipment.

Established more than 20 years ago, Australian Stainless Products started out building basic dairy machinery, primarily small repairs and maintenance of equipment for a few of the local food processing equipment plants.

“Back then the business was basically building milking machinery. We did small repairs and maintenance and equipment for a few of the local food processing plants in the area.”

Now, the Melbourne-based company manufactures original equipment from large tanks, vessels and hoppers including process equipment up to 50,000 litre capacity.

Working with a small but loyal client base, Patterson has worked with some engineering consultants such as dairy equipment supplier DeLeval for more than a decade.

“It's quite a small industry. We operate by word of mouth and references of jobs. It takes a long time to build, grow and develop a business within this industry,” said Patterson.

This article featured in Australian Stainless magazine - Issue 35, Autumn 2006.

Safe Disposal with Simcraft Stainless Steel Products

As a general rule, the waste management method adopted for disposing of radioactive substances is critical. The main method of disposal is the dilution and dispersion of radioactive wastes using stainless steel equipment such as isotope flushing sinks

 

Last year, the University of Western Australia's School of Biomedical, Biomolecular and Chemical Sciences moved into the new $65M Molecular and Chemical Sciences building with state-of-the-art laboratories and equipment.

Generally, the materials used in biological sciences research work contain low radiotoxicity substances, however, full precautions are taken to ensure safe handling.

As part of the School of Biomedical, Biomolecular and Chemical Sciences upgrade, many of the laboratories were fitted with a number of isotope sinks and flushing isotope sinks fabricated by ASSDA Accredited Fabricator, Simcraft Products.

Isotope flushing sinks are designed to prevent splashing and to allow for the gradual flow of waste liquid into a stream of waters as it runs to waste.

Simcraft Products fabricates the sinks in 1.2mm grade 316 stainless steel with satin finish to the Australian Standard, AS2243.4.

Isotope flushing sinks feature an absolutely splash free flush action with a non-turbulent continuous curtain of water for a total surface wash and can also be custom built for hospitals, medical centres and laboratories.

This article featured in Australian Stainless magazine - Issue 35, Autumn 2006.

Manufacturing malt with stainless steel

Australians really enjoy a good beer - at home barbeques, parties, music concerts, sporting events - in fact, everywhere!

World beer consumption is increasing by more than two per cent a year, a trend that is set to continue. There is an important relationship with beer consumption and demand for its main and critical ingredient - malt.

Malting is the partial germination and kilning of a grain, usually barley. Malt gives varying colour, flavour and body to beer depending on the style of malt being used.

Australia is a key player in the world market representing about 32 per cent of world trade in malting barley and 12% of the world malt trade.

Joe White Maltings, an ABB Grain Ltd company, is Australia's largest malt producer with eight malting plants Australia-wide with a capacity to produce 500,000 tonnes annually.

An expansion at the company's Perth plant in May 2006 saw production capacity more than double from 90,000 tonnes to 200,000 tonnes.

ASSDA member, Stirlings Australia sourced more than 155 tonnes of grade 304 stainless steel 2B finish from ASSDA Major Sponsor, Outokumpu Stainless for the expansion. As the largest malting facility in the southern hemisphere, the Perth plant features stainless steel vessels throughout with cylindrico-conical steep vessels, circular germination vessels, a separate circular kiln, full automation and in-place cleaning.

ASSDA member, Stirlings Australia sourced more than 155 tonnes of grade 304 stainless steel with 2B finish from ASSDA Major Sponsor, Outokumpu Stainless for the expansion. Stirlings Australia also used its hi-definition plasma cutting service for processing of material ranging from 2mm to 20mm thick sheets by 1200,1500 and 2000mm wide plates.

The Perth-based global metals distributor also supplied more than $150,000 worth of stainless steel to Built Environs subcontractors for the fabrication of the project.

Press Construction Services were supplied with various grade 304 stainless steel pipe, plate, angle and flats including processing of all plate material for the fabrication of six steep vessels.

ASSDA member, Austline Fabrication of the Foodline Group of Companies was supplied various grade 304 stainless steel sheet, plate and angle for the fabrication of fan ducts and kiln hoods.

From this expansion, Joe White Maltings are able to meet increased demand from producers of most Australian beers and for the major brewers throughout Asia.

This article featured in Australian Stainless Issue 36, Winter 2006.