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Posted 31 October 2005

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.

 


 

Posted 31 October 2005

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.


Posted 31 October 2005

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.

Artisans of Fabrication


Posted 1 April 2006

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.


Posted 1 January 2006

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.


Posted 1 January 2006 (revised and updated February 2010)

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.


Posted 1 July 2006

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.

Built on Reputation


Posted 1 April 2006

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.


Posted 1 April 2006

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.


Posted 1 July 2006

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.


Posted 1 April 2006

When the Gold Coast City Council was seeking a stable and visually stunning medium for use on their Kirra Point board walk project in 1999, they looked no further than stainless steel and after six years in service, it still looks great.

Council engineers chose stainless steel for the upright posts and moveable handrail system for safety, corrosion resistance and aesthetic reasons.

When designing the project, the board walk had to take into account a steep vertical drop to the beach below - an important safety issue met by using stainless steel handrailing.

The board walk project was undertaken in two stages, the first of which involved constructing a concrete walkway and handrails along the Kirra Point foreshore. The second stage saw the construction of a timber board walk out over the foreshore onto the beach.

ASSDA Accredited Fabricator, Stoddart (Tom Stoddart Pty Ltd) supplied 186 custom made upright posts and supplied and installed 326 metres of stainless steel tubular handrails. Both were made from 316 grade stainless steel with a number 4 finish.

The upright posts were passivated in nitric acid after manufacture to ensure a clean surface and promote corrosion resistance.

The knowledge that ASSDA requires for its Accreditation Scheme was used in the execution of the structure, ensuring the ongoing satisfaction of the Council with minimal maintenance.

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


Posted 31 October 2006

Hygiene and the 'cleanability' of equipment used in the production of food are paramount. The widespread use of stainless steel equipment in the food industry goes some way towards ensuring these criteria are met - but the assurances provided by stainless steel are only as good as the fabrication quality of the equipment.

Following a presentation at ASSDA’s annual conference in 2003 on the quality of food fabrications, particularly in the dairy industry, it became apparent that fabrication specifications, if they existed, were often inadequate and inconsistent.

As a result, ASSDA launched a co-operative venture, working closely with many fabricators involved in the food industry, to create the recently released "ASSDA Food Specification: Fabrication and Installation of Stainless Steel Process Plant and Equipment in the Food and Beverage Industries".

The title may be complex, but the intention is simple: used in conjunction with ASSDA's Accredited Fabricator Scheme, it will standardise fabrication practices in Australia and improve efficiency and reliability by raising the standard of quality delivered.

ASSDA's Food Spec is not intended to replace accepted national and international standards. Instead, it reflects their requirements in the design and fabrication process specifically for food and beverage plant. The specification is intended as a step forward from the more generic advice offered by the well-known "Blue Book", published ASSDA's sister organisation NZSSDA.

The Food Spec supplements the purchaser's specification and contract, with the purchaser's performance criteria and the supplier's design being the default conditions. There are prescriptive sections, such as those relating to spacing for access or acceptable levels of heat tint. However, best practice is flagged with the expectation that a contrary decision must be well supported. The consistent theme throughout is the delivery of cleanable surfaces in a hygienic environment.

The specification can be broken into four sections:

  1. Scope, definitions, interpretation, document hierarchy and suppliers systems required.
  2. Design requirements with both general rules and specific items for process equipment, process piping and other piping;
  3. Fabrication requirements for:
    • overall necessities of grade, materials care, welding and finishing procedures;
    • process vessel fabrication, whether by the supplier or others;
    • the handling, welding and finishing of process tubing at ambient or elevated pressure; and
    • the fabrication of non-product contact pipework at low or high pressures.
  4. Practicalities such as transport, installation, commissioning and insurance.

The specification includes two appendices that list relevant standards and a discussion on the pros and cons of autogenous and filler metal sue in welding of tubing.

There is no doubt that ASSDA's Food Specification fills a void in the food industry. It is now up to operators in the industry to use it to improve practices in both their own businesses and the industry as a whole.

Copies of the specification are available from the ASSDA office on (07) 3220 0722. Details of the complementary Accredited Fabricator Scheme are available from www.assda.asn.au

This articles was written bu ASSDA's technical advisor, Graham Sussex.

The ASSDA Food Specification has drawn on the work of many operators in the industry and their assistance in time and documents is gratefully acknowledged.

This article featured in Australian Stainless magazine - Issue 37, Spring 2006.


Posted 1 July 2006

No 4 finish stainless steel is the workhorse of the light fabrication industry. The easiest of the finishes to maintain, No 4 finish is used for work surfaces, handrails and where appearance is important.

A 'No 4' surface is produced by cutting the surface with abrasive belts to remove a very small amount of metal without affecting its thickness.

For architects and designers, No 4 finish gives low gloss and best apparent flatness of panels.  For fabricators, the No 4 finish is directional, allowing easy matching of surfaces and refinishing of welds. For end users, the surface can be repaired to remove any service damage.

No 4 finish is duller than the other common finishes, 2B and BA and is generally used where lower reflectivity or gloss is required and where welds and other fabrication marks are to be refinished to match the original surface. This is not possible with 2B and difficult with BA.

Abrasive belts have very fine grains of refractory material such as silica, alumina and zirconia embedded in an adhesive layer on a flexible cloth or paper backing. The belts are wider than the stainless steel, which is usually worked on as coil, or sometimes in individual sheets. The steel is run slowly under rolls, on which the abrasive belts run.

The polishing machines at stainless steel mills lubricate the cutting action by flooding the strip with oil. This helps to keep it cool, and gives a finer, more uniform surface.

The variability of the process means not every No 4 finish looks the same, even from the same source. Different manufacturers use belts with different combinations of grit sizes, and the finish can vary through the life of a set of belts.

Where it is important that the appearance of material matches on a job, it should all be taken from the same pack of sheets, used sequentially and in the same orientation. A reasonable match in appearance can be achieved more readily with No 4 finish than with 2B or BA mill finishes.

No-4-finish.jpg The Owner of this resource has not specified a description BA-finish.jpg
No 4 Finish 2B Finish BA Finish

Standards

Until recently, standards defined No 4 finish in terms of the coarseness of the abrasives used to produce a general purpose finish widely used for restaurant equipment, kitchen equipment, shopfronts and food processing. New editions of the American and European standards define limits of surface roughness achieved.

Finishes produced by use of abrasives may be called ground or polished or abraded or linished. These words describe a process and do not specify the end result.

ASTM A480 defines No 4 finish simply as, “General purpose polished finish, one or both sides”. It also states, “No. 4 - A linearly textured finish that may be produced by either mechanical polishing or rolling. Average surface roughness (Ra) may generally be up to 25 micro-inches (0.64 micrometres). A skilled operator can generally blend this finish.”

The practice in Australia is only to use 'No 4' as a description of a polished finish and it is not a rolled finish. The European standard, EN10088-2, defines two finishes, '2J' and '2K'. There is no prescription of the appearance or roughness of the '2J' finish, but '2K' is defined as surface Ra below 0.5 micrometres. The notes state, ”Additional specific requirements to a 'J'-type finish, to achieve adequate corrosion resistance for marine and external architectural applications.”

Figure 1: No-4-finish-graph.jpg Figure 2: 2B-finish-graph.jpg
Figure 1: Surface trace of a typical No 4 finish
(Ra = 0.41 micrometres)
Figure 2: Surface trace of a typical 2B finish
(Ra = 0.20 micrometres)

The surface traces of Figure 1 and Figure 2 show comparisons between typical No 4 and 2B finishes. Unlike a 2B finish which is generally rougher on thicker coil, the roughness of No 4 does not vary with the steel thickness.

While Ra can be specified to give better control of the corrosion properties of the surface, it correlates only moderately with appearance and is also difficult to measure reproducibly.

Gloss is the amount of light reflected whether specular (mirror like) or diffuse. It is moderately correlated with appearance and with surface roughness, but can also have problems when used for specification.

Neither Ra nor gloss are suitable for specification for critical jobs in architecture. Two finishes with the same Ra can look substantially different, as can finishes with the same gloss level.

For critical jobs appearance is best specified using reference samples viewed under agreed conditions. These should be large enough that they can be viewed from a variety of angles and distances - appearance can vary with viewing angle.

Corrosion Resistance

The corrosion resistance of a No 4 finish is usually lower than that of a mill finish (BA or 2B) on the same grade.

The surface scratches or grooves produced by abrasion expose sulphide inclusions, which are always present in all steels, and can act as a catalyst for corrosion.

The passive surface layer is more likely to be disrupted somewhere on the vastly increased surface area with all its sharp peaks and deep valleys. It is difficult to keep the surface clean when there are intersecting valleys, torn metal flaps or peaks that have been folded over.

Corrosion resistance may be reduced depending on the stainless steel grade used. By using grade 316 with a No 4 finish in aggressive environments, the corrosion resistance is negated and may be less than on 304 with a 2B or BA finish.

Figure 3: The accceleration of the corrosion of the surface at Ra above 0.5 micrometres is apparent.
Figure 3: The acceleration of the corrosion of the surface at Ra above 0.5 micrometres is apparent.

Figure 3 shows the results of electrochemical tests for corrosion of a polished surface. Corrosion resistance of a smooth surface can be better than the corrosion resistance of an abraded surface of a more highly alloyed grade.

The orientation of the No 4 finish is also important. When the lines on the surface are vertical, drainage is easier and corrosion resistance is better than when the lines are horizontal.

The reduced corrosion resistance of the No 4 finish is not likely to be of concern in mild applications such as food preparation and display. However, in more aggressive conditions such as marine and industrial atmospheres it is important to be aware of the reduced corrosion resistance of No 4 finish and to take steps to improve the resistance.

Corrosion resistance of No 4 finish can be improved by pickling the surface in a mixture of hydrofluoric and nitric acids, or passivating in a nitric acid solution.

The passivation treatment dissolves the sulphide inclusions in the surface, but doesn't change the appearance of the surface. The pickling treatment is more aggressive and removes both the sulphide inclusions and some of the rougher parts of the surface, dulling the appearance.

Unfortunately it is almost impossible to achieve a uniform finish, and it is rarely practical to pickle for better corrosion resistance. Passivation is often used. ASTM A967 “Chemical Passivation Treatments for Stainless Steel Parts” specifies a number of treatments with various acid strengths, temperature and contact time.

Electropolishing the surface can also improve the corrosion resistance and brighten the surface. The peaks on the surface are smoothed, reducing the Ra value and increasing the reflectivity or gloss. The sulphide inclusions may also be removed or reduced.

Protection of the Surface

No 4 finish is usually supplied with a protective plastic film of white polyethylene, which often has printed lines on the plastic in the same direction as the No 4 polish.

It is best to keep the film on the surface of the steel during fabrication, to prevent handling and transport damage. The film has limited resistance to sunlight, and should not be left on the steel in the sun for more than a week or two - an hour or two if the film isn't black underneath. The film may bake onto the surface and either become brittle or tear into strips on removal, or leave the glue on the steel surface.

Glue on the steel will trap dirt, and may cause rapid surface discolouration or tea staining.  If it is suspected there is residual glue on the steel, swab the surface with a solvent such as Methyl ethyl ketone (or MEK - a solvent) available from panel beaters suppliers. You may need to test other solvents, depending on how the glue has polymerised.

The water break test tells you the surface is clean - clean water dries as a film, doesn't stand in bubbles on the surface. A final wipe with a glass or window cleaner will ensure a streak free finish.

Cleaning

No 4 finish can usually be kept clean by wiping down with a damp soft clean cloth. For grease, moisten the soft cloth with ammonia solution, or with one of the household liquid grease removers. Very hot water is also quite effective.

Wiping should always be in the direction of the polishing lines. Some No 4 finishes can pull threads and fluff from the cloth which are very hard to get off the steel.

Abrasive cleaners and materials such as Scotchbrite™ should never be used as these will change the appearance of the surface. If you want to change it, try an inconspicuous area, then treat the whole surface - but it's difficult to get it uniform.

There are also white powder stainless steel cleaners (Clark and Esteele), made of sulphamic acid, which can be wiped over the surface on a damp rag to brighten it - test an inconspicuous area first. Fingerprints can be made less obvious by applying a light oil to the surface. There are many proprietary products available, usually labelled 'stainless steel cleaner'. Choose an oily one, although it will tend to trap dust.

This ASSDA technical article was written by Dr Alex Gouch, Development and Technical Manager of Austral Wright Metals. ASSDA acknowledges the assistance and contribution of Mr Peter Moore, Technical Services Manager of Atlas Steels and Dr Graham Sussex, ASSDA Technical Specialist in the production of this article.

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


Posted 1 July 2006

Telling the tale of migration to Victoria is 'The Travellers', a series of giant stainless steel sculptures sliding quietly across the Sandridge Rail Bridge on Melbourne's Yarra River.

Stainless Steel 'Travellers' Mark Journey of MigrationUnveiled just three days from the start of the Melbourne 2006 Commonwealth Games, the 10 sculptures are a tribute to multiculturalism.

Each of 'The Travellers' figures represents a period from our Indigenous and immigrant histories (as defined by historian Dr James Jupp) and were designed by Lebanese Artist, Nadim Karam of Atelier Hapsitus.

'Gayip - The Aboriginal Period', the first sculpture, is stationed permanently on the river bank to depict the Indigenous owners of the area who were here already.

Nine of the 10 sculptures cross the river three times a day on a fixed bogie system to represent stages of migration in Australia's history from the convict and gold rush periods through to European and refugee settlement.

More than 3.7 km of stainless steel (in 4455 pieces) was used to create the sculptures.

ASSDA member, Silverstone Engineering fabricated the majority of the 10 sculptures from grade 316 stainless steel supplied by ASSDA Major Sponsors, Sandvik Australia Pty Ltd, Atlas Steels and ASSDA Member, Midway Metals Pty Ltd.

Each of 'The Travellers' figures represents a period fro ou Indigenous and immigrant histories.The remaining stainless steel sculptures were fabricated by Danfab, JW Metal and Able Engineering.

Stainless steel rectangular hollow sections were used on the outer frames. The inner rails were made of pipe and bar. Some of these rectangular hollow sections were inductarolled (rolled after heating by using an induction furnace) by Melbourne company, Inductabend, with a discoloured zone or heat band running around the material.

The sculptures required much tighter radii than had previously been delivered, and Inductabend's equipment was pushed to its limits when bending the steel sections.

Following fabrication, the sculptures were then polished to 0.4 Ra, cleaned and then passivated to ensure high corrosion resistance.

Originally built in 1888 by David Munro, the Sandridge Bridge is considered one of the earliest examples of steel girder bridge construction in Australia.

The $3 million 'Travellers' sculptures project was part of an $18.5 million Sandridge Bridge Precinct development funded by the City of Melbourne and the State Government that includes a new pedestrian bridge, a plaza and a youth precinct on the north bank.

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


Posted 31 October 2006

Fabrication quality within the food industry is firmly in the spotlight with the release of ASSDA's Food Specification. This issue we feature an ASSDA Accredited Fabricator's quality work in the food industry.

Loss in production due to installation of new equipment is always undesirable, which is why an upgrade on the scale of Australia Meat Holdings’ recent boning room expansion at Aubigny (west of Toowoomba, Qld) was even more remarkable.

The project, managed by Wiley & Co, more than doubled the size of AMH’s existing boning room, improved work place ergonomics and provided for future growth – all without interruption to production.

The expansion incorporated more than $4 million worth or 100 tonnes of stainless steel, around half of which was fabricated by ASSDA Accredited Fabricator G & B Stainless from Crestmead, Qld.

G & B Stainless director John van Koeverden said their company’s work on the project involved 20 to 30 people in their workshop and eight people on site for around 5 months.

The company fabricated and installed the majority of conveyor equipment, including the product conveyors, empty carton conveyors and packed carton conveyors.

Mr van Koeverden said mainly 304 and some 316 stainless was used for the double and triple tier conveyors.

“One of the unique features of the job was the two 60 metre long boning conveyors and integral slicing tables, which we designed specifically for this application,” he said.

“The tables incorporate over 100 stations and feature pneumatic lifts to raise the tables up to 90 degrees for ease of cleaning.”

G & B Stainless used a glass bead blast finish over most of the stainless steel, primarily to remove weld stain and further enhance the hygiene features of stainless steel.

Wiley & Co project engineer Scott Hebbard said the fact that G & B Stainless was ASSDA Accredited played a role in their selection to fabricate the majority of the stainless steel equipment in the new boning room.

Four other fabricators shared the remainder of the work, including the fully enclosed walkways and the conveyors up to and taking away from the vacuum packing equipment.

This article featured in Australian Stainless magazine - Issue 37, Spring 2006.


Posted 1 July 2006

Stainless steel's non-magnetic properties were an important factor in the design, building and construction of the University of New South Wales' (UNSW) new Analytical Centre.

The facility has been designed to enhance the performance of high-tech analytical equipment such as the UNSW's nuclear magnetic resonance instruments (NMRs).

The centre is one of six components in the North Mall Development Zone (NMDZ) project, located within the Kensington Campus of the University of New South Wales (UNSW).

According to Mr Ed Smith of McLachlan Lister, the Project Directors of the NMDZ, building will accommodate both staff and equipment from the University's existing Electron Microscopy Unit (EMU), Nuclear Magnetic Resonance (NMR) and centre and eight other technical scientific instrument centres.

“The five NMRs within the Analytical Centre will emit very strong electromagnetic fields. A standard ferrous concrete reinforcement would adversely effect these fields and consequently the performance of these machines”.

ASSDA member, Ancon Building Products supplied 150 tonnes of 304 and 316 grade stainless steel ribbed reinforcement bar for the concrete slabs, beams, piles and columns.

Both 304 and 316 stainless steel are non-magnetic and strong enough to replace carbon steel reinforcement bar in the design.

Some stainless steel pile cages were passivated after welding. Ancon Building Products cut and bent all bars to schedule, longer bars were created using stainless mechanical couplers, which were custom fabricated.

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


Posted 31 October 2006

This article is the first in a series showcasing the uses of 445M2 stainless steel. Read Part 2. Read Part 3.

Australians' love of the water has always provided challenges to the construction industry, particularly when it comes to choosing materials that can be used in aggressive environments such as near the coast or swimming pools.

Stainless steel grades 316 and 304 have long been the obvious solution in these applications, but the key factors of formability, cost and corrosion resistance are now shining the spotlight on an alternative grade.

445M2 stainless steel has been used in Australia for a number of years for roofing and walling applications, and its characteristics are now proving useful for a broader range of applications.

The material, supplied by ASSDA member Austral Wright Metals, is being used by Dunning Engineering Services Pty Ltd for a range of stainless steel pergola brackets.

Dunnings - a South Australian based manufacturer of builders and plumbers hardware, who also operate a sheet metal pressing and fabrication facility - developed the range in response to the growing demand for better corrosion-resistant products that can be used in aggressive environments.

The company experimented with punching and bending various grades of stainless steel, including 316, but it was 445M2's formability that provided the crisp, clean angles they were seeking, with the advantage of reduced tool wear.æ Dunnings was also able to fabricate with existing tooling and machinery, avoiding the prohibitive cost of new dies and tooling.

More importantly, 445M2 is a marine grade stainless steel with the corrosion resistance of 316 or better and a cost that falls between 304 and 316.

Dunning spokesperson John Gill said 445M2 resisted the salt from the surf, and gave safe performance over a long life - even when painted.

"Due to the formability of 445M2, the savings to our business have been enormous and we are now looking at other areas where 445M2 could be applied."

This article featured in Australian Stainless magazine - Issue 37, Spring 2006.


Posted 31 October 2006

New technology to assist with accurate design is always welcome, but it is important that users proceed with caution when using international design tools.

There is no doubt that designing with stainless steel offers endless opportunities for architects and engineers to be both creative and functional. At the same time, it is critical that the design is right for the application.

Thanks to the internationally-recognised research of an Australian expert, as well as some design software now available free online, getting the design right for stainless steel structures has never been easier. However, as outlined below, it is more important than ever for design engineers to use caution when using international technology.

History of Design in Australia
The Australian Standard for design of stainless steel structures, AS/NZS 4673:2001 “Cold-formed stainless steel structures” was first published in 2001 and provides methods for design calculations. Applicable to cold-formed structures, including construction with tubular hollow sections, it provides a means of designing light and innovative structural solutions.

Traditionally, design engineers have reached for ‘load tables’ – or, strictly, Member Capacity Tables. Most design offices have tables with the results of calculations for various steel sections and loading regimes, generally published by suppliers of carbon steel.

But carbon steel has different properties from stainless steel, so these tables are not right for stainless steel – they may be too conservative or not conservative enough.

Another problem is that some engineers have assumed because they can find a section in carbon steel load tables, they can source it in stainless steel – only to discover they can’t, after doing an expensive design.

Designing with Software
Load tables for stainless steel are available from the Steel Construction Institute in the UK. The SCI is an independent, technical, member-based organisation with over 850 corporate members in 40 countries around the world.

Now the SCI has made available free software for design calculations for stainless steel members, using the methods of the European Design Manual, published by Euro-Inox.

Available over the web at http://www.steel-stainless.org/software/, the software speeds structural design calculations for a range of sections and stainless steel grades.

However, a word of warning: the software uses methods in compliance with parts of Eurocode 3 “Design of steel structures”. The Australian code for design of stainless steel structures, AS/NZS 4673:2001, follows the methods of the USA code, not the Eurocode. This is logical, as the Australian codes for the design of cold-formed carbon steel structures are also aligned with the USA codes and the trend in the Australian construction industry is to employ cold-formed steel to achieve lightness, material efficiency and enhanced strength.

So the SCI software must be used with some caution – it is the best available, but not ideal. The software should not be used in conjunction with the Australian code AS/NZS 4673:2001, as mixing clauses of different specifications is not an acceptable practice. This caution applies particularly to the design of welded structural members, which is catered for by the SCI software but not within the scope of the Australian Standard.

Future Improvements
In January 2005, Professor Kim Rasmussen of Sydney University was appointed chairman of the American Society of Civil Engineers (ASCE) Standards Committee responsible for the American “Specification for the design of cold-formed stainless steel structural members”. This is the Standard that formed the basis of AS/NZS 4673:2001.

The ASCE Standards Committee will be updating the American Standard and Professor Rasmussen will present the new rules implemented in AZ/NZS4673 to the American committee, together with design recommendations derived from recent and ongoing research at Sydney University.

The ASCE Committee is expected to adopt the new rules and recommendations. Subsequently, there is likely to be an update to AZ/NZS 4673 – so there is an ongoing cycle of improvement, helped along by the world-class research in stainless steel structures undertaken by Professor Rasmussen and his students at the University of Sydney.

What Does it all Mean?
In short, international design tools such as the free software available from the SCI can provide some assistance in getting the design right for stainless steel structures, but they don’t provide all the answers and can even complicate matters. Sometimes good design means getting back to basics.

This ASSDA technical article was written by Dr Alex Gouch, Development and Technical Manager of Austral Wright Metals.

ASSDA acknowledges the assistance and contribution of Professor Kim Rasmussen from the School of Civil and Mining Engineering, University of Sydney.

This article featured in Australian Stainless magazine - Issue 37, Spring 2006.