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Stainless delivers savings for Sydney Water

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

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

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

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

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

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

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

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

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

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

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

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

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


Posted 1 July 2005

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

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

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

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

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

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

Low nickel austenitic stainless steels

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

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

The Cost of Nickel and Its Addition to Stainless Steel

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The Rise of the "200 Series" Steels

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

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

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

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

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

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

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

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

Some New Contenders

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

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

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

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

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

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

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

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

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

Credits

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

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

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

Turning industrial systems into architectural features

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

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

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

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

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

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

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

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

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

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

 

Reducing risk with stainless flameproof technology

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

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

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

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

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

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

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

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

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

Stainless steel water cooled exhaust manifold

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

Stainless steel exhaust conditioner

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

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

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

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

Images:

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

Top right - A Combilift with stainless steel exhaust conditioner.

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

Right - Toyota forklift built to Zone 1 hazardous area.

Alloy C-276: A Super Alloy for Processing Plants

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

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

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

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

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

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

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

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

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

Preventing Coastal Corrosion (Tea Staining)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

CONDITIONS REDUCING THE RISK OF TEA STAINING

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

GUIDANCE IN FABRICATION

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

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

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

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

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

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

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

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

KEY DESIGN RECOMMENDATIONS

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

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

Further Reading

ASSDA's Australian Stainless Reference Manual Edition 7, 2012

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

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

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

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

Training your stainless steel specialists with ASSDA

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

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

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

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

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

Atlas Specialty Metals

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

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

Bridgeman Stainless Solutions

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

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

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

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

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

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

Rockpress (Rocklea Pressed Metal)

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

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

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

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

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

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

Manufacturing malt with stainless steel

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

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

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

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

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

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

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

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

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

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

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

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

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

No. 4: The workhorse finish

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.

Stainless steel 'Travellers' mark journey of migration
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.

Stainless rebar enhances technology performance

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.

Stainless spirit out of this world

The grand scale of Rings of Saturn at Melbourne’s Heide Museum of Modern Art takes on even more significance when you learn about the artist.

sculptureRenowned Australian sculptor Inge King AM was born in Germany in 1918, moving to Australia in 1951 and forging her career despite a culturally conservative landscape at the time.

The 89-year-old artist created the 400cm x 600cm x 500cm Rings of Saturn in 2005-2006 as part of her Celestial Series, using stainless steel to create the sense of floating, lightness and reflection that prevails in outerspace.

“Stainless steel is not suitable for every work, but these pieces were inspired by a story on space research I saw on TV and they needed a certain spirit,” Ms King said.

“By using stainless steel with a sanded finish, the piece is very durable and it breaks and reflects the light, so at any time of the day it looks different.”

Ms King makes scale models of her sculptures, but the physical demands of creating the final work requires her to contract out the fabrication.

Using Ms King’s 50cm model of Rings of Saturn, Melbourne fabricator Robert Hook co-ordinated the laser cutting of about 3 tonnes of 5mm grade 316 stainless steel, then welded the two full circles and two semi-circles.

He took the welds down with a 5 inch grinder, then used a polifan disc to smooth them out. He created the linished look with Poly-PTX flap wheels and used a 9 inch, 100 grit sanding disk on the larger surfaces.

Rings of Saturn was commissioned through the Heide Foundation, with support from Lindsay and Paula Fox, and sits in Heide’s Sir Rupert Hamer Garden.

Inge King will hold an exhibition of mostly stainless steel works at Australian Galleries, 35 Derby Street, Collingwood, Victoria in April-May 2008.  Visit their website for more information.

This article featured in Australian Stainless magazine - Issue 42.

Inge King, Rings of Saturn 2005-2006
Heide Museum of Modern Art Collection
Commissioned through the Heide Foundation with significant assistance from Lindsay and Paula Fox 2005
Photographer: John Gollings 2007, 2006
Copyright: Inge King & John Gollings

Chlorine and chloride: Same element, very different effect

Posted 1 July 2007

Choosing the correct grade of stainless steel for a tank, pipe or process vessel requires (at the very least) information about the temperature, pH and chemical composition of the contents.  One of the most important items of the chemical composition is how much chloride (salt) is present.  Analysis reports often give the concentration as milligrams per litre (mg/L) or sometimes as parts per million (ppm) of Cl.  However, Cl is also the symbol used for the element chlorine.

So what is the difference?

Chlorine is a poisonous, yellowish green gas which readily dissolves in water to give a strong disinfectant or bleach.  The strength of a bleach solution is sometimes measured by the “available chlorine”.  Swimming pools are usually treated with dilute hypochlorite solutions which produce a few parts per million (ppm) of chlorine.  This acts as a strong, oxidising biocide.  Drinking water is normally treated to give a residual of 0.2 to 0.5 mg/L of chlorine.  (There are also other disinfection methods such as chloramine or ozone.)

Chlorine is very aggressive to stainless steels.  The Nickel Institute guidelines for continuous exposure at ambient temperatures (~20˚C) and neutral pH (~ pH7), are that 304 can cope with 2ppm chlorine and 316 ~5ppm chlorine.  In alkaline solutions (pH>7) higher concentrations are possible but this does not help much in swimming pools or drinking water.  Chlorine frequently causes corrosion problems.  Chlorine attack can occur with bleach laden washdown water if pools form in drains which are usually empty.  Chlorine concentrations in droplets or water films immediately above a still pool or water tank can be higher than the chlorine level in the bulk water. When dosing concentrated chlorine into pipes or tanks, it must be well mixed otherwise concentrated streams will eat out downstream elbows or tank walls near the chlorine inlet.

Much higher concentrations can be used for short periods as the attack on the stainless steel must initiate and form a stable pit for failure to occur.  The American Water and Wastewater Association permits 25ppm for 24 hours in cases of emergency disinfection.  The food industry can use up to 100ppm in hot water for minutes followed by rinsing and/or passivation.  It is an effective biocide because the kill rate depends on (exposure time) * (concentration of biocide) but the stainless steel is resistant to the chlorine for the relatively short, high concentration exposure.

And what about chlorides?

Chloride occurs naturally in drinking water and ranges from less than 10mg/L in Melbourne to more than 200mg/L in Adelaide. Chloride is not oxidizing and is not a biocide.  The most common form is sodium chloride.  Seawater is about 3% sodium chloride although there are other compounds.  Nickel Institute guidelines for continuous exposure at neutral pH and ambient temperatures permit chloride levels of 200ppm for 304, 1000ppm for 316 and 3600 ppm for 2205 duplex.  The guidelines allow for the presence of crevices (such as bolt heads, flanges or deposits) but assume that the surface has been passivated. In alkaline environments (pH>7) higher chloride levels can be tolerated.  Higher temperatures reduce the permissible chloride level. Temperatures over 60˚C are not recommended for 304 or 316 as they are at risk of sudden failure from chloride stress corrosion cracking.

The message

Chlorine and chloride are different forms of the same element but with vastly different effects on stainless steel.  Chlorine is bleach and stainless steels can only tolerate exposure to a few ppm continuously.  Chloride is part of the salt in natural waters and even 304 can cope with a few hundred ppm at ambient temperatures and pH~7.

This article appeared in Australian Stainless Issue 40

Alternative stainless steel grades - Part 1

This article is the first of a two-part series outlining new and emerging stainless steel grades which may be considered as alternatives to the more traditional and widely known varieties. Read Part 2.

The growing demand from China and the rest of the developing world has driven up the price of alloying elements added to stainless steels.  Over the last five years nickel prices have risen to ten times what they were.

Chromium and molybdenum have also risen strongly, and the price of stainless steel scrap – which steelmakers use extensively – has soared.  Inevitably, stainless steels have also seen large price increases, with little relief in sight. Growing demand and the time required to develop new supply sources mean that nickel and other alloy prices are unlikely to drop to the levels seen a few years ago.

Higher prices are driving stainless steel users to seek more cost effective solutions:  the optimum choice of grade is a blend of engineering and economic factors, and the choice may be different in a new cost environment.  The most common stainless steel grade, 304, is used in about 60% of applications for stainless steel around the world.  Grade 304 contains about 8% of nickel, which is used to form the ductile austenite crystal structure.  Grade 316, with 10% of nickel and higher corrosion resistance given by an addition of 2% molybdenum, is also very common.  It is used in marine environments.  Users are seeking more cost effective alternatives to both these austenitic 300 series grades.

Austenitic 200 series, duplex stainless steels and ferritic grades can all be used instead of 304 and 316, if they are selected, designed, fabricated and used appropriately.  This article and the next in the series describe the alternatives to the more traditional grades, with their abilities and limitations.

The alloying elements in stainless steel contributing most to corrosion resistance are chromium and molybdenum.  Within each of the alternative groups there are grades with different corrosion resistance resulting from the chromium and molybdenum contents.

The well known austenitic 300 series grades contain the highest levels of nickel.  The austenitic 200 series grades contain less nickel, and manganese is added to make the austenite crystal structure form.  Because the 200 series grades have the austenitic crystal structure their mechanical and fabrication properties are similar to the familiar 300 series.

Ferritic grades have the same crystal structure as carbon steel, and have similar mechanical and fabrication properties and do not contain a nickel addition.

Duplex grades are not fully austenitic.  They are formulated to be a mixture of equal amounts of austenitic and ferritic grains in the microstructure, which generally means the nickel content is about half of that in an austenitic grade of the same chromium content.

AUSTENITIC 200 SERIES

These grades are austenitic despite their lower nickel because they have more manganese.  Manganese is about half as effective in forming austenite as nickel, so for every 1% of nickel left out, about 2% of manganese has to be added – at the same level of chromium, which suppresses the formation of austenite. Half the nickel in these grades has been replaced by manganese and the price of manganese is also rising strongly.

First developed in the 1930s, most of the common 200 series grades have corrosion resistance similar to the ferritic grade 430, lower than grade 304, because the chromium content is lower.  Newer Indian developments (grades J1 & J4 in the table) have centered on grades with significantly lower corrosion resistance. There are other proprietary 200 series grades with higher chromium contents used in marine and anti–galling applications.

The austenitic 200 series are the closest in behaviour to the 300 series of the alternative groups.  Hence they are the easiest to convert to.

Mechanical and Physical Properties

The tensile strength of common 200 grades exceeds 600MPa, i.e. about 20% higher than 304.  The 0.2% proof stress is more than 20% greater than that of 304 but the elongation at fracture is similar.  In contrast with carbon steel, all the austenitic stainless steel grades have tensile strengths at least double the 0.2% proof stress, a consequence of their high rate of work hardening.  Some newer grades include copper to reduce this.  Because of the austenitic microstructure of annealed 200 series grades they are ductile down to cryogenic temperatures and do not suffer brittle fracture. In comparison with the physical properties of 304, the 200 series have very similar density, elastic modulus, electrical and thermal properties.

Some 200 series grades in comparison to 304

Attributes

The ductility and formability are similar to the 300 grades although the lower nickel gives a greater risk of delayed cracking after heavy cold forming.  Welding is similar to the 300 series grades although the 200 grades may have higher carbon and may suffer sensitisation (loss of intergranular corrosion resistance) if welded in sections thicker than 5 mm.  Stress corrosion cracking resistance is similar to the 300 series.  Like 304 and 316, 200 series grades do not respond to a magnet when in the annealed condition, but become magnetic after cold work.

Limitations

The lower chromium levels mean that the 15% chromium grades have lower corrosion resistance than ferritic grade 430.  Even the 16 & 17% chromium grades are somewhat inferior to 304 in corrosion resistance, since it appears that a 200 series grade has slightly less corrosion resistance than a 300 series grade with the same chromium level.  This may be due to the high levels of sulphur present in 200 series grades from some sources.

Steelmakers do not want 200 series scrap mixed with 300 series scrap as the high manganese levels reduce the life of steelmaking refractories.  Batches of 300 series scrap suspected of being contaminated with 200 series are likely to attract only the much lower 200 series scrap price.  Hence strict segregation of off – cuts is required.
At present none of the 200 series grades are routinely stocked in Australia.

Applications

As with all grade groups, it is important to choose a grade with corrosion resistance adequate for the application.  The lower chromium 200 series greades detailed in the table are generally suitable for use with mild acids and alkalis including most foods (pH not less than 3).  They are satisfactory with 20˚C potable water and are suitable for indoor exposure – furniture, bins, etc.  They are used extensively for cookware and serving bowls – applications where the corrosion conditions are not severe since the utensils are washed and dried.  The formability and deep drawability of the 200 series are especially useful for these applications.

This article appeared in Australian Stainless Issue 40

Stainless revamp for Sunshine Coast beach

A revamp of Kings Beach in Caloundra, QLD, has had a gleaming response, with stainless steel a major contributor to the brand new look.

Kings BeachInitial stages included new seats, hand railing and some draining, but the most recent instalment  focussed on the beach-side swimming pool and recreational area with balustrades all around. Although 2 or 3 different builders have been used during the project to date,

ASSDA Accredited Fabricator Paige Stainless was involved with all stages. Kilometres of stainless steel tube was used to fence the 98 metre pool circumference with top and bottom rails and railings.

“There was also some peripheral work, such as seats and railings that lead into the pool area,” says Kevin Finn of Paige Stainless.

Kevin says that whilst the end result of stainless steel looks great, the builders had little choice but to use the material.

“They did look at aluminium for the pool fencing.  Stainless steel was certainly the most expensive but with the corrosive environment and longevity required, it was imperative that they use stainless steel.”

The project used only grade 316, supplied by ASSDA members Atlas Specialty Metals and Tube Sales at both 600 and 800 grit polishes to  help prevent tea staining.

The unique setting of the pool (located on the beach), meant fabrication was largely done onsite.

“Because of the different shapes of the pool and the way we had to configure the posts for the fencing, we couldn’t manufacture panels in the workshop,” says Kevin.  “It would have been too disjointed so, instead, we rolled the shapes to the outline, cut them to length and then physically made it on site to ensure the most accurate fit.”

Some work had to be scheduled around tide times as the pool sits 10 feet from sea level with the fence right on the edge.  To get around this, Kevin said every second post was welded from the inside with the remaining posts completed on the outside.

To further help protect the job from tea staining, the welds were hand passivated with a gel and then coated with three different coatings from the Cyndan Rapelle range.  These coatings were “Stainless Steel Cleaner”, “Cleans All” and “Stainless Steel Sentry”.

Following installation, the Council was provided with a maintenance schedule, including recommendations for the use of these products.

This article featured in Australian Stainless Issue 40.


Posted 1 July 2007

An exhibition showcasing the use of stainless steel in an artistic sense will, for the first time ever, coincide with ASSDA’s annual conference in October.

Warrick Timmins - HouseboatSponsored by ASSDA member ELG and presented in partnership with Cooks Hill Galleries, the exhibition entitled Stainless Evolution, will be on display in the main auditorium at the PacRim 2007 Conference in Newcastle this October.  The pieces created will use various types of stainless steel, for the exclusive viewing of PacRim delegates.

timminsartWarrick Timmins of Newcastle is one such artist who has used stainless steel in his pieces to depict his love of water.  Warrick says he enjoys designing forms that challenge his skills and pushes the dimensions of the materials he uses.

He says he uses stainless steel for its ‘strength, beauty and reflective qualities’.

Following on from the conference, the art exhibiition will be moved to Cooks Hill Gallleries in Newcastle, under the direction of Mr Mark Widdup.

Images are pieces by Warrick Timmins that were included in the exhibition.

This article featured in Australian Stainless magazine - Issue 40.


Posted 1 July 2007

The work of Anna Eggert is not new to ASSDA, or to those familiar with the 2005 Reference Manual where her pieces entitled “Belinda’s dress” featured on the cover.

anneeggertTwo years on, Anna’s love of stainless steel continues, as she begins work on a new project which has seen her nominated for the 2007 McClelland Award.

The work, which will be put forward for a chance at the $100,000 prize money, is similar to that shown, and again uses stainless steel mesh.

“Mesmerized” is an eight piece artwork  continuing an investigation into the female identity.  In particular, Anna explores the inherent nature of those outside the Muslim religion, who become ‘mesmerized’ by their own curiosity of a women dressed in hijab.

The production of the pieces begin with a roll of stainless steel mesh.  The material is rolled out and a pattern is penned before cutting with a nibble.

All pieces are made with grade 316. The base layer of the pieces use quite a coarse stainless steel with a 1.0mm aperture x 0.56mm wire diameter (known as 16/24). A softer layer is then used on top, with a mesh known as bolding cloth which has an aperture of 710 micron and wire diameter of 0.20mm.

Anna says all her stainless steel mesh is supplied by Metal Mesh in Sydney who have been very supportive of her work. Various pieces of Anna’s repertoire of work will be displayed in NSW, Canberra and Noosa in the coming months, with the winner of the McClelland Award to be announced in November.

This article featured in Australian Stainless Issue 40

Stainless style and sunscreen

Form and function have long been the essence of good design, which is why the transformation of this Canberra building is such a success.

canberrabuildingASSDA member and Accredited Fabricator Interspace Manufacturing Pty Ltd was commissioned to design and fabricate screens to update the building aesthetically, as well as provide the workers inside the building with protection from the sun.

Interspace Managing Director Jorgen Hansen said the unique design of the mesh transformed the facade of an ordinary building into an interesting piece of architecture.

“Not only is the design aesthetic, but the screen helps reflect a percentage of the sun’s rays from entering the office windows,” Mr Hansen said.

“Woven wire mesh is a versatile product and can be used in a number of different applications, such as security, sunscreening, cladding, partitions, balustrades, ceiling panels and facades, as seen in our Canberra project.”

The final project, which cost $95,000, incorporated 321 woven mesh panels in grade 304 stainless steel measuring approximately 540mm x 1900mm each. The mesh was supplied by ASSDA member Metal Mesh from Terrey Hills, NSW.

Mr Hansen said stainless steel was used for the project because of its longevity in external environments and the minimal maintenance required to keep it looking brand new.

“Stainless steel has a durability that will last the lifetime of the building and, with periodic washing, its appearance will be retained, often with no other maintenance necessary - an important and cost-effective factor.”

This article featured in Australian Stainless Issue 41.

What's cooking?

Bruce Harding is not the first person to be frustrated by rusty cast iron hotplates and grills on his barbecue – the difference is that he did something about it.

bbqDrawing on more than 25 years experience in the stainless steel industry, Mr Harding and his team at Equipment Tech Pty Ltd have developed a range of stainless steel hotplates, grills and baking dishes (sold under the name of Topnotch) that can be retro-fitted to almost any barbecue.

The company uses austenitic T304 and ferritic stainless steels, which are mostly supplied by ASSDA members Sandvik and Atlas Specialty Metals.

Mr Harding said these stainless steel grades played an important role in addressing the design challenges, including the ability to expand and contract under heat.

“The grades we have selected really work together with our design to prevent food sticking to the hotplates and grills,” Mr Harding said.

Laser cutting and a specially developed electropolishing procedure are used to fabricate the products.

Equipment Tech has produced over 100,000 Topnotch stainless steel cooking surfaces since launching the product commercially 5 years ago.

This article featured in Australian Stainless Issue 41.