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Savings for Stainless


Posted 30 November 2003

Researchers from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Cooperative Research Centre for Welded Structures (CRC-WS) have developed a welding process for stainless steels and other corrosion-resistant metals that is significantly faster, cheaper and easier than current practices.

The patented process is an elaboration of standard gas-tungsten arc welding (GTAW), and uses a specially designed torch that establishes and maintains a ‘keyhole’ at the joint.

The weld then proceeds, zipper-like, with the melted sides of the keyhole fusing at the back as the torch melts new material in front of it.

Keyhole GTAW is most effective for materials of low thermal conductivity, such as titanium and stainless steel, but does not work with good thermal conductors such as aluminium.

‘In comparison to conventional GTAW, machining of the edges to be joined is greatly reduced, it uses about one-twentieth the filler material, and reduces the welding time by about tenfold’ says Dr Ted Summerville, a commercial manager at CSIRO Manufacturing & Infrastructure Technology in Adelaide.

Applications of the technology include tube making, welding of rotatable products such as pipes and the joining of large sheets. The technology is particularly advantageous for welding thicker materials.

In keyhole welding, the arc melts the metal right through on both sides of the joint. Via surface tension, this establishes a stable structure which joins the front and rear surfaces through the width of the material. The weld pool is thus anchored, preventing the ejection of molten material.

The result is a process which is not only relatively inexpensive to acquire, but is also cheap to operate. The torch melts right through the joint where the two metal pieces to be welded abut, and molten metal extends through the depth of the material – up to 12mm thick for steels and 16mm for titanium alloys.

Very little filler material is needed to make the joint – about 50g/m for welding 12mm thick stainless steel, compared with about 1kg/m using conventional GTAW. And the joint is made in one pass, compared with up to seven for the thickest steels and titanium alloys.

Reduction to a single pass means that the metal at the site of the weld is only at risk of contamination once, whereas if it is welded seven times, there are seven opportunities for contamination.

The lack of multiple passes also vastly increases welding productivity. Typical examples of keyhole performance include single-pass welding of 12mm thick austenitic stainless steel at speeds of 300mm/min, 8mm carbon–manganese steel at 500mm/min, and 3mm ferritic stainless steel at 1000mm/min.

In one comparison, the welding time of 35min/m for 12mm stainless steel plate using conventional GTAW was reduced to <3.5min/m using the keyhole method.

And the quality of the welds is generally excellent. ‘We have qualified the process against a range of American standards’, says Dr Summerville, ‘and it has always passed’.

In addition, it is clean welding process. Fume generation using conventional GTAW is very low, and the same is true for keyhole GTAW.

The drawback to keyhole GTAW is that the torch can only be used in the conventional downhand position – the joint must be made between horizontal sheets with the torch vertical.

Recent work, however, has demonstrated that it is possible to operate the technology ‘out-of-position’, and this could lead to many new applications in the future.

‘If keyhole welding could be done in any position – for instance, if you could rotate the torch around pipe – it would increase the market for the technology by about ten times’, says Dr Summerville.

The technology is currently being licensed by the joint owners of the technology – CSIRO and the CRC-WS – and licencees are already successfully applying the technology in USA and Finland.

A number of licensees in these markets have reported significant productivity improvements.

Licenses for the keyhole welding technology are being offered in Australia, Europe and USA for use in the manufacture of products ranging from spiral-welded pipe to railway rolling stock.

This article featured in Australian Stainless magazine - Issue 26, November 2003.

Stainless Bathing Box of Shattered Dreams

Tamarama Beach or as local Sydneysiders call it 'Glamarama Beach', is well known as the place for beautiful people to be seen and for the rest of us to dream.

 

Artist, Graham Chalcroft set out to distort self-image in the name of fun by capitalising on the beach's former fairground history to design and fabricate a sculpture - 'Bathing Box: the impossible change room of shattered dreams'.

The stainless steel sculpture was a crowd favourite at the 'Sculpture by the Sea' exhibition held in November 2003 from Bondi Beach to Tamarama Beach in Sydney NSW.

The sculpture's design aesthetic was inspired by archival images of traditional late 19th century bathing boxes and how they have evolved.

Each sculpture profile is based on the curves of the human form - one male and one female. On approaching the convex/concave doors, the mirror distorts the body with startling effects.

ASSDA member, Stainless Sections, kindly donated six sheets of 304 with a No. 8 mirror finish for profiles fitted inside the doorframes.

For accuracy and efficiency, Chalcroft use T & M Engineering Group in Smithfield to computer design and laser cut the sheets to be clamped on the structural wood faces and strips.

"The stainless steel performed extremely well. It handled well in fabrication and the thick protective coating saved the steel from potential scratching," said Graham Chalcroft.

"The mirrored steel coped with the heat, wind, salt spray and suffered no scratching from the many thousands of hands touching the artwork," he said.

'Sculpture by the Sea' is in its seventh year and is the largest free outdoors sculpture exhibition in the worlds with over 200,000 visitors.

Photos by Graham Chalcroft.

This article featured in Australian Stainless magazine - Issue 27, February 2004.

Restoring Stainless

Brewed for Efficiency

When Carlton & United Breweries (CUB) announced plans last year to expand production capacity at the Yatala site in Queensland, the company considered both purchase of new stainless tankage as well as transfer of tanks from its Sydney brewery and re-use of second hand tanks in its inventory.

 Six such vessels had been stored by CUB on leased land in the City of Redcliffe, unsealed and exposed to the weather.

Constructed in 321 stainless, the 3 x 12 metre tanks were out of service for the last ten years and placed in the yard for future use.

The six beer storage tanks are part of a series of 16 tanks built in 1966, that have proven the test of time and reinforced the material's durability and returned back to service 'as good as new'.

ASSDA member, D & R Stainless was approached to upgrade the six 1,000 hectalitre (hl) vessels to the new fittings with design verification and tested to meet AS 1220 Standard.

The Brisbane-based fabricator modified, checked and tested the beer storage tanks so as to meet CUB's exacting standards for beer production which would include popular CUB brands such as VB, Fosters Lager, Carlton Midstrength and Crown Lager, allowing them to be used as part of the ongoing expansion.

Work on the six tanks involved cleaning down and refurbishing with new stainless steel tubes and fittings supplied by Matrix Process Solutions.

The six tanks were taken to D & R Stainless and pumped with 4,000 litres of water constantly through the system and back through the CIP spray balls so that all of the tank area was wet to see if there was any carbon steel pick up.

All tanks were checked thoroughly for any rust spots and repolished where required. New nozzles were also installed and internally polished.

D & R Stainless Manager, Ray Powell was initially concerned that the carbon steel supporting rings around the vessel would bleed through onto the stainless as there were no compensating plates.

"We only had one tank [the first tank] that had a problem and that was laminating in the heat effected zones. And that was only on one tank on the bottom of the seams, so we came back in and dye checked, found the problems, ground back and repaired," Mr Powell said.

"The quality of the tank is in good condition. The beauty of stainless is that if it's looked after it will last forever and proof's in the pudding, they're coming up nearly 40 years old - they've certainly proved the test of time," he said.

The expansion of CUB's Yatala facility follows an announcement in April last year of the closure of the Kent Brewery in NSW by February 2005.

This operational review will see the relocation of over 50 beer fermentation and storage tanks from Sydney, a brand new twin stream brewhouse and new filtration equipment to the Queensland facility, which is CUB's most efficient brewery. Total project cost is around $170 million.

As a result of the review, the Yatala facility will double its capacity from 230 million litres of beer a year to over 500 million litres.

Despite being out of service for more than a decade, the excellent condition of the tanks ensures that stainless steel has significantly contributed to product quality and cost efficiency for Carlton & United Breweries long into the future.

This article featured in Australian Stainless magazine - Issue 27, February 2004.

Threaded Fittings to ISO 4144 Standard

For many years there has not been a Standard to cover the low pressure stainless steel cast pipe fittings commonly used in Australia and other countries around the world.

These are commonly termed “150lb” or “BSP” pipe fittings. In most cases the fittings that have been supplied were a mismatch of various Standards.

The fittings were dimensionally in accordance with a number of American Standards, whilst British Standard threads were used. This led to the fittings having threads that in some cases were non-compliant - basically there was insufficient length to accommodate the thread.

ASSDA, through its Technical Committee, identified this problem in the early 90s and through the publication of ASSDA’s Technical Bulletin No 1, highlighted the problems to the Australian market. ASSDA also looked for a mechanism to have these problems rectified.

ISO 4144 "Pipework - Stainless Steel Fittings Threaded in Accordance with ISO 7-1"
After investigating the alternatives it was decided that International Standard ISO 4144 could be the conduit to rectifying the problems. ISO 4144 in its 1979 form covered most of the committee’s concerns, but it did not allow for cast fittings - only wrought stainless steel.

After correspondence with the Australian and International Standard bodies, it was ascertained that ISO 4144 was due for revision, which presented a golden opportunity to have the standard rewritten to cover all of the Technical Committee’s concerns.

ASSDA was invited to represent Australia on the committee established to review the Standard and actively took part in the full process of its revision. Not all of the Committee’s recommendations were accepted. Finally, in early 2003 the new Standard was published.

What has been achieved?
The major improvements that have been adopted in the new Standard are:

a.    The use of castings as well as wrought materials.
b.    All cast fittings are to be properly heat-treated by solution annealing.
c.    The reduction in dimension, a more economical fitting.
d.    The thread standards allowed have been clearly defined.
e.    An introduction of pressure-temperature ratings for application of the fittings.
f.    The inclusion of eight new types of fittings into the Standard.
g.    The inclusion of DN 100 (4”) fittings.

Now that ISO 4144:2003 allows for the use of castings, Australia finally has a Standard that covers the products that have been in common use for many years.

The requirement that all castings are to be fully heat-treated will alleviate some of the corrosion problems that have been encountered in the past.

The dimensions of the fittings have been revised dramatically, thus giving a lighter and more economical fitting.

The wall thickness is the major dimension that has been reduced and it can be reduced by a further 20% if the fitting is made from wrought material.

ISO 7-1 sealing pipe threads are to be used on all fittings. The external and internal threads are to be tapered, but the internal threads may be parallel. The only exception to this is the threads on the Unions and their mating nut, which are allowed to have a variety of parallel threads.

Pressure temperature ratings for application of fittings have been specified (refer to Table 1).

Table 1 - Pressure-Temperature Rating

ome fitting types supplied into Australia were not covered in the old ISO 4144 Standard.

Eight new types have been included in the new Standard: these are 90° Reducing Female Elbows, Reducing Female Tees, 45° Equal Female Elbows, 90° Male x Female Elbows, Crosses, Reducing Nipples, Male x Female Unions and Male x Male Unions.

With the inclusion of the DN 100 (4”) fittings, the Standard now has a comprehensive range of products.

Some Disappointments with the New Standard
In the new Standard, apart from some minor editorial errors, there are two points of concern to the ASSDA Technical Committee.

Firstly, the new wall thicknesses that are stated as minimum could lead to a product being supplied that may not meet the expectations of the customer.

Even though the Standard allows for thin wall product, such thin walled fittings could be subject to distortion during the threading process or during installation. Care must be taken that this does not occur.

The second concern within the Standard is the length of the minimum external thread that has been adopted. The title of ISO 7-1 is “pipe threads where pressure tight joints are made on the threads”.

The minimum length specified can accommodate a thread that seals if it is manufactured to close tolerance. Care is required in manufacture to achieve this outcome.

Although it was recommended to the International Committee that it accept external thread lengths that could accommodate a thread at both ends of the tolerance range, the Committee did not adopt these recommendations.

Table 2 highlights the external thread lengths that were adopted compared to the external thread lengths that were recommended by Australia.

Table 2 - External Thread Length Comparisons

Conclusion
ASSDA believes minimum thread length is a concern to all suppliers and users of these fittings and care should be taken in their selection.

If mating fittings do not seal on the threads and interfere with the washout they may leak.

It is recommended that fittings should only be sourced from reputable and experienced manufacturers and supplied to ISO 4144:2003.

Overall, the Standard is a considerable improvement on what was available, and with care in the selection, the end user will be in a more certain and much safer environment than in the past.

Credits
This article was written by Kim Burton, Group Supply Manager of Prochem Pipeline Products Pty Ltd and an ASSDA Technical Committee member. ASSDA also acknowledges the contribution of Technical Committee member Peter Moore, Technical Services Manager of Atlas Specialty Metals, in the development of this article.

Download Technical Bulletin (April 1997 - pdf 920k)

This technical article featured in Australian Stainless magazine - Issue 27, February 2004.

Cleaning and Protecting Stainless Sculptures

"Windhover" is a dramatic stainless steel sculpture created by the late Lenton Parr, located on the eastern foreshore of Port Phillip Bay in Sandringham, Melbourne.

Unveiled in December 2001, the sculpture's vertical lines and arcs are evocative of the yachts often seen sailing out on the Bay.

However, two and a half years of zero maintenance and exposure to salt spray from the bay have taken their toll, turning the surface of the stainless steel a blotchy brown.

Called tea staining, it's caused by deposition of salt on the surface which is then trapped in the crevices of the brushed finish.

Regular reactivation by rain has perpetuated a corrosion cycle leading to quite rapid and severe surface staining.

The problem was how to clean the sculpture and then to ensure that it would remain protected from tea staining in the future.

Conventional weld pickling products containing hydrofluoric acid are very aggressive and risk damage to or discolouration of the surface.

Strong acids may also create an environmental and safety hazard when used in such a public place.

Many cleaning formulations are available based on phosphoric, sulphamic, oxalic or nitric acids. They have various degrees of handling and disposal restrictions.

The formulations may also contain mid abrasives and wetting agents/detergents to aid the cleaning process.

In July 2004, ASSDA Member, Revolution Advanced Metals and Materials, used a cleaning paste based on a moderate concentration of phosphoric acid which is relatively safe to handle.

Inadvertent skin contact by this product does not cause the burning and possible ulceration associated with strong concentrations of nitric and hydrofluoric acid preparations.

The cleaning product was brushed on and left to react for 3-4 hours. The brown tea staining gradually disappeared.

In some particularly bad sections a second application was necessary to completely remove all traces of the staining, but it left a completely blemish-free surface.

In this case, residue from the cleaning product was simply washed away with water. In other cases, however, check with local authorities for correct disposal procedures.

One of the problems when washing stainless steel with water is the streaking caused by uneven drying.

This was very noticeable on the sculpture.

Also, because it is unlikely that ongoing regular cleaning will occur, it is also important to limit the access of chlorides to the surface. Otherwise the staining problem will recur.

To overcome both these problems, a water-based protective product with oils and non-ionic surfactants but no phosphates was sprayed on and wiped over.

After polishing with a dry cloth all streaking vanished. It left an invisible film that stopped further streaking and fingermarks.

Best of all, it brought up the lustre of the brushed finish, and left Windhover looking as good as the day it was made.

Regular re-application should maintain the finish and help prevent tea staining in future.

Correct design, fabrication and on-going maintenance will all assist in keeping stainless steel sculptures and other structures erected adjacent to the coast in good condition.

Words and images courtesy of Jim Picot, Revolution Advanced Metals & Materials.

This article featured in Australian Stainless magazine - Issue 29, September 2004.

Crevices and Corrosion

A crevice is a narrow gap between a piece of metal and another piece of metal or tightly adhering material like plastic or a film of bacterial growth.

Many metals and alloys are susceptible to crevice corrosion, but in stainless steel, crevices are the first and most common place for corrosive attack to begin. With a little understanding, crevice corrosion can either be avoided or minimised.

Crevices can be:
• The space under a washer or bolt head.
• The gap between plates bolted together.
• The gap between components intermittently welded.
• The space under a sticky label.
• The space between a gasket and the metal in a flange (especially if the gasket is absorbent).
• Any other tight gap.

Crevices can be designed into the structure, they can be created during fabrication or can occur during service.

Prevention measures should therefore also aim at design, fabrication and service.

Why crevices can corrode
To work at its best, stainless needs free access to oxygen. Crevices are wide enough to permit entry of moisture, but narrow enough to prevent free circulation.

The result is that the oxygen in the moisture is used up. In addition, if chlorides are present they will concentrate in the stagnant conditions and, by a combination of reactions, the moisture can become acidic.

These are all conditions that can lead to the breakdown of the passive film on the stainless. Attack can then progress rapidly.

Crevices can create conditions much more aggressive than on adjacent surfaces. Having crevices builds in weak spots where attack can begin and begin in much less severe conditions than anticipated for the remainder of the structure.

Table one shows laboratory measurements of critical temperatures needed to cause pitting on an open surface (CPT) and crevice (CCT) attack of a metal plate beneath a PTFE washer in a 10% ferric chloride solution.

The CCT is at least 20˚C lower than the temperature to cause pitting corrosion in this aggressive liquid. (Ferric chloride solution is an aggressive corrodent and is used because it is similar to the liquid in a pit when it is actively corroding.)

Factors influencing crevices:

Crevice Shape
The geometry of the crevice will influence its susceptibility to attack and the speed of progress. The narrower and deeper (relative to its width) a crevice is the worse attack will be.

Metal to flexible plastic crevices tend to be narrower than rigid metal to metal gaps so metal to plastic joints provide more aggressive crevices.

Environment
The more aggressive the liquid outside the crevice, the more likely it is that the crevice will be attacked.

This is why crevice attack can be a problem in a salty swimming pool but not in a fresh water tank.

In the atmosphere, crevices beside the sea give more problems than in rural environments. If the liquid outside the crevice is very oxidising, eg with bleach, hydrogen peroxide or ozone, then crevice attack will tend to be more severe.

Temperature
Once the CCT is exceeded, then as with pitting corrosion, higher temperatures mean corrosion is more rapid. The rule of thumb is that a 10˚C rise in temperature will double the corrosion rate.

This means that when comparing Far North Queensland to Tasmania, not only are crevices more likely to start corroding but also that once they do, they will corrode faster because the temperature is consistently higher.

Alloy resistance
Using a more corrosion resistant alloy gives less crevice attack. For example, in seawater at ambient temperature, crevices will form on 304 if there is a 0.9mm gap, on 316 if there is a 0.4mm gap and on 904L (similar corrosion resistance to 2205) if there is a 0.15mm gap.

Minimising the risk of crevice corrosion

Good design, fabrication and operating practices will anticipate and hence minimise crevice corrosion.

Design
Design to minimise the occurrence of crevices.  If a crevice is a necessary part of a component’s design – can it be made wider?

Full penetration butt welds are best for joints.  Seal lap joints and avoid gaps between pipes and fittings.

Minimise use of bolted connections and other fasteners. Where crevices can’t be avoided use a steel grade resistant to crevice corrosion in the operating environment. It is also possible to seal the crevices to keep out corrosive liquids, but care must be taken that the seal is permanent.

Be careful that the sealant “wets” the surface. If it doesn’t it may form its own crevice. Sealants that dry and shrink can form their own crevices.

Gaskets between flanges will probably form a slight crevice, but if the gasket does not absorb the liquid and is compressed between the surfaces (and not bulging around the flange), then the crevice is usually shallow enough so that crevice corrosion is not a problem.

Fabrication
Ensure full root penetration of welded joints with smooth weld bead. Avoid under cut and cracks in welding. Use of sticky labels or markers of various kinds (such as crayons) should be avoided, as should smears of grease or oil.

“Smooth and clean” at all times. ASSDA Accredited Fabricators are assessed on their knowledge of crevice corrosion.

Operation
Sediment and scale can both result in crevices.

If the problem can’t be designed out, routine maintenance will minimise risk. Crevice corrosion under bacteria film can occur. Maintaining circulation reduces the risk that debris will collect and form crevices in dead legs or low flow areas.

Further Reading
The Nickel Institute’s free publication #11021 “High Performance Stainless Steels” contains much of the information used in this article.

This publication and a mathematical model useful for assessing crevice corrosion risk can be downloaded from the Nickel Institute website - www.nickelinstitute.org

If more detailed corrosion mechanism information is required, then “Corrosion of Stainless Steels” by A. John Sedriks is a good intermediate point.


Reinforcing pad, staggered welds - adequate strength.


Reinforced pad, seal weld - best corrosion resistance.


Staggered fillets - severe crevice


Continuous fillets both sides - crevice sealed


Figure 1: Typical crack defects around a weld (WTIA)

Credits
The Australian Stainless Steel Development Association (ASSDA) would like to acknowledge the contribution of the following Technical Committee members for their contribution to the production of this article.
•  Richard Matheson - Executive Director, ASSDA
•  Graham Sussex - Technical Specialist, ASSDA
•  Peter Moore - Technical Services Manager, Atlas Specialty Metals

This article featured in Australian Stainless magazine - Issue 29, January 2004.

Versatile Style with Stainless Decorative Tiles

A revolution is about to take place in the tiling industry with the introduction of stainless steel decorative tiles with a versatile design that will add style to any kitchen, bathroom, restaurant, bar and even as a feature wall.

There are many benefits to using stainless steel tiles. The tiles cannot burn or crack, graffiti can be easily removed, will not rust and is a stylish upgrade to the standard one piece splashbacks.

Available from Futura Tiles (Border Sheetmetal), the tiles are available in a wide variety of sizes, patterns, finishes and grades. Size ranges include: 65 x 290mm freeze, 290 x 290mm tile, 390 x 390mm tile.

Runaway Bay Designer Builder, Kerri Phillips, was so happy with the product that he installed the stainless tiles in his own kitchen and found cutting the tiles no problem at all.

"They provide you with special blades. It's a delicate operation, as long as you're careful it's fine," says Phillips.

ASSDA major sponsor, Fagersta Steels, supplies grade 304 stainless and patterned sheet from ASSDA member, Rimex Metals to Futura Tiles (Border Sheetmetal) to produce the tiles.

The tiles are also available in various Rimex patterns and finishes including the standard brush finish, 5WL and 6WL surface finishes.

Manufactured from grade 304 stainless as standard, the tiles are also available in grade 316 stainless for applications with a close proximity to marine environments.

Installing stainless steel tiles
Stainless steel tiles are basically the same as laying most floor and wall tiles. Cut tiles using similar ceramic grinding methods by using blades with 1mm steel cutting wheels.

Grouting
When grouting, apply grout to tiles leaving the protective film covering on the face of the tile. Use only fine, sanitised water resistant grouts and do not apply sanded or abrasive grouts. Remove excess grout with a clean sponge leaving a smooth grout line.

Removing film covering
Peel the protective film covering from the tiles, then with a clean sponge, remove any grout left behind from the edges of the covering. Leave approximately 30 minutes and dust off with a clean lint free cloth.

Protecting
After all dust film from the grouting has been removed apply a small amount of polishing oil to a clean rag and wipe with the grain of the tile to remove any excess oil. This will resist finger printing and water spotting and will enhance and protect the stainless steel surface.

Images courtesy of Karl Johnson, Futura Tiles (Border Sheetmetal).

This article featured in Australian Stainless magazine - Issue 29, September 2004.

Stainless Steel Enhances Hayman Island Views

North Queensland's Hayman Island Resort welcomes thousands of guests every year to the Great Barrier Reef island destination. Also attracted by the beauty of the resort, cockatoos have eaten away at the timber balcony railings and balustrades

 

To combat the work of the troublesome cockatoos, the resort management called for stainless steel to replace the timber railings and balustrades on the fifteen year old building.

ASSDA major sponsor, Atlas Specialty Metals, supplied approximately 1,000 linear metres of grade 316 stainless steel including 76 x 42mm oval tube and 38mm diameter round tube in high polish to Mackay-based fabricator, Jeff Eales Sheetmetal for the project.

Stainless steel was used extensively for the balcony top rail and posts on all three levels of the pool wing accommodation block. Because many of the balconies are at the edge of the pool, oval profile tube was specified to prevent glasses or bottles being placed on the rail and then being bumped into the pool.

Also, to ensure guests receive uninterrupted ocean views, stainless steel wire rope was installed on each of the balustrades. This helped to eliminate the restricted views given by the previous timber material.

ASSDA member, Arcus Australia Pty Ltd supplied stainless steel wire for the balcony balustrades and ASSDA member Bridco supplied the wire fittings, turnbuckles and swages for the resort balustrading redevelopment.

Guests have commented on how the use of stainless steel complements the surroundings, improves the views and suits the building style.

Hayman Island Resort management are also impressed with the new stainless steel railing as it stops the bird problem, requires low maintenance and is easy to clean. All these qualities make the tropical ocean views much better.

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


Posted 31 January 2005

Sydney's New Year's Eve has always been celebrated in spectacular style and this year's event shined with the inclusion of a giant glitter ball featuring stainless steel.

Hanging from the Sydney Harbour Bridge was 'Fanfare', a five storey-high spherical structure covered in 354 stainless steel pinwheels that spin as the ball rotates.

The sculpture, designed by New Zealand artist Neil Dawson, is Sydney's first three-dimensional bridge effect in the event's history.

ASSDA major sponsor, Sandvik Australia Pty Ltd and ASSDA member, Stainless Sections supplied 90 sheets of 10' x 4' x 1mm or approximately 2.7 tonnes of stainless steel in number 8 finish to ASSDA member, DME Engineering Services for the fabrication of the pinwheels surrounding the structure.

During the day the pinwheels of  'Fanfare' spin in the winds of Sydney Harbour reflecting the many colours of the sky. At night the sculpture becomes a part of the light show, acting as a canvas for projections and reflections.

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

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.

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.

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.

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.

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.