Logo


Posted 15 December 2006

This article is the second in a series on common finishes. The first (Winter edition 2006) dealt with the abraded 'No. 4' (2K, 2J) finish. This article looks at 2D, 2B and BA: smooth and corrosion resistant surfaces produced at the steel mill. Subsequent articles in this series will cover mirror polished (No. 8 or 2P) and profiled and hot rolled (No. 1) finishes.

What are Cold Rolled Finishes?
Cold rolled finishes apply to flat products such as sheet or coil, with thickness less than about 5mm and usually less than 3mm.  They are firstly hot rolled into a strip (or cast into a slab which is hot rolled into a strip) and then cold rolled. Cold rolling reduces the thickness by at least 50%.  This smooths the surface, refines the grain structure and causes differences in the mechanical properties along and across the rolling direction.  In the case of austenitic and duplex alloys, the process hardens and strengthens the stainless steel.  Finally, the steel is softened by annealing in a furnace.  Each surface finish may undergo additional processes to improve the surface further.  The smoother the surface finish is, the higher resistance to corrosion it will be.

These mill produced finishes must be handled carefully as surface damage such as scratches, grinding marks or spatter cannot be matched by polishing with abrasives or etching with chemicals.  Of the 3 finishes, BA is most nearly able to be matched by a mirror polish.

Standards
The most common definitions of these surface finishes are provided by ASTM A480 and EN 10088. In both cases it is the cold rolled manufacturing method that is specified rather than specific, measurable characteristics about the surface. We have used ASTM A480 as an example:

ASTM A480:
No. 2D – A smooth, non-reflective cold-rolled annealed and pickled or descaled finish. This non-directional finish is favourable for the retention of lubricants in deep drawing applications.

No. 2B – A smooth, moderately reflective cold-rolled annealed and pickled or descaled finish typically produced by imparting a final light cold-rolled pass using [large diameter] polished rolls. This general-purpose finish is more readily polished than No 1 or 2D finishes. Product with 2B finish is normally supplied in the annealed plus lightly cold-rolled condition unless a tensile-rolled [harder and stronger] product is specified.

Bright Annealed [BA] Finish – A smooth, bright, reflective finish typically produced by cold rolling followed by annealing in a protective atmosphere so as to prevent oxidation and scaling during annealing.

2B
2B is the most widely used stainless steel surface finish. It is especially common in industrial, chemical and food processing applications such as process vessels and tanks. It is also used in some architectural applications that will not be closely examined for uniformity of finish such as downpipes and gutters.

When specifying this finish think about these attributes:

- 2B is the most economical finish
- it is highly corrosion resistant because it has been chemically pickled and is smooth
- over broad areas and between batches, etc it is not uniform and may not match in appearance
- it has been produced in the mill and can’t be   matched after fabrication- it is often protected by plastic films until final cleanup and commissioning

2D
2D is used around the world in applications where its low reflectivity is important. The largest application is in roofing materials. The surface is rougher than 2B and retains lubricants better making it appealing for deep drawering. 2D surfaces are not designed for appearance so the limitations on matching of weld and other surface damage is not as critical.  Railcars are a typical example where thicker sheet and ongoing abrasive damage make the rougher 2D a suitable finish.

When specifying this finish think about these attributes:

- 2D is not commonly available in Australia
- it is highly corrosion resistant because it has been chemically pickled and is relatively smooth
- over broad areas and between batches, etc it is not uniform and may not match
- it has been produced in the mill and can’t be matched after fabrication

Bright Annealed (BA)
The classic use of a BA finish is domestic: the interior of a dishwasher or clothes washing machine. In the clothes washer, it also provides a smooth, non-abrasive surface for the clothes to slide around.  The mirror like surface is also used in road mirrors where a precise image is not required.

When specifying this finish think about these attributes:

- BA is common in some grades and thicknesses, but not all
- it is highly corrosion resistant because it is very smooth
- different batches may not match
- it has been produced in the mill and can’t be exactly matched after fabrication although a mechanical mirror polish can be close.

Post Production Processing to Improve Corrosion Resistance
All the cold rolled processes include a pickling stage. Pickling is the removal of high temperature scale and the adjacent low chromium layer of metal from the surface of stainless steel by chemical means. Pickling will also remove manganese sulphide inclusions and any other contamination on the surface. Pickling results in a very clean, highly corrosion resistant surface, but will slightly roughen the surface.

Pickling any of these finishes will cause a matt or etched rougher area, most apparent on the BA surface and least on the 2D.

Differences Between Alloys
Most articles on finishes assume that standard grade austenitic stainless steel is used.  Typically a highly corrosion resistant grade has a duller appearance than the same thickness material with a lower corrosion resistance.  This illustrates the more aggressive measures required to remove oxide scale from a high alloy austenitic or duplex than a standard grade 304 or 316.

There is little data on finishes of ferritic grades but general observation shows that for comparable thickness and finishing processes, cold rolled 430 is brighter than 304. It is not known if this difference extends to comparisons between more highly alloyed grades.

This article featured in Australian Stainless magazine - Issue 38, Summer 2006.


Posted 15 December 2006

Internationally renowned, Yackandandah based sculptor Benjamin Gilbert was commissioned to create a series of sculptures for Melbourne’s Commonwealth Games.  Extending six metres in the air, the exhibits laid testament to three different stages of a pole–volter whilst displaying the versatility and artistic merit of stainless steel.

Benjamin used grade 304 stainless steel, supplied by ASSDA major sponsor Atlas Specialty Metals in Wadanga.  He has worked with stainless steel for 10 years and believes it is cost effective and cheaper to use than other materials. Also, the added ability of using off cuts in his work suited Benjamin’s ‘green’ focus.

“As a practising environmentalist, there are some good arguments for using stainless steel,” Benjamin says.

Indeed, stainless steel is one of the most recycled metals in the world and, according to the International Stainless Steel Forum, any given stainless steel object has an average recycled content of about 60%.  Benjamin also says the fact that stainless steel doesn’t need to be finished (ie painted) makes it an attractive material.

“For what you pay extra in materials, you don’t need to spend on additives.”

Using a sculpting technique taught to him during his time in Estonia, Benjamin has successfully adapted it for use with stainless steel.

The sculptures used up to 100kg of stainless steel – 1mm sheet, 5mm rod and a 25mm square tube substructure underwater.  With the ability to flex in the wind, the 35mm poles are re-enforced with inner tube to build up spring, similar to a leaf spring on a trailer suspension.

Benjamin enjoys ‘non-trade’ related thinking with his designs and, although he admits to having difficulty sourcing tools in Australia, he says the lighter, thinner materials are easy to use when spot welding and give greater flexibility when using metal shears.

During his work, Benjamin used a thin disk on a 5” grinder and a stainless steel wire wheel to ‘texturise’ the surface.  He believes there is “a lot more that can be done with finishes”, particularly by hand.

Other projects Benjamin has worked on, incorporating the use of stainless steel,  include a life size work of the Ned Kelly Gang (at Beechworth) and a bigger public artwork for the Camden Museum and Library redevelopment in South Sydney.  Once completed, in late January, a 16 metre grapevine in stainless steel will be exhibited, in recognition of the first grapevine in Australia.

Photograph by Rob Lacey Photography, Wodanga.

This article featured in Australian Stainless magazine - Issue 38, Summer 2006.


Posted 15 December 2006

For those who love to indulge in a life of sun, surf and sand the idea of placing a barbeque in such rust-promising environments is not often an option as their longevity is compromised.

But Gold Coast company Southern Stainless has bridged the gap between a nautical lifestyle and the great Aussie tradition by manufacturing barbeques in stainless steel.

ASSDA member Southern Stainless typically specialises in the manufacture of stainless steel products including wine storage and fermentation tanks and marine fitouts, but supplying stainless steel barbeques, boat mounting systems and accessories to the general public, wholesalers, retailers and building industry has proven to be one of their fastest growth areas.

The barbeques are made from 316  grade stainless steel, with a  2205 duplex grade stainless steel plate, which is more corrosion resistant and easier to clean.

The barbeques are fully welded to enhance strength and use an electropolished finish to aid in corrosion resistance and provide a durable surface.

Southern Stainless Managing Director Phillip Brown says the barbeques can be designed to suit customer requirements and are 100% Australian owned and made.

“Chinese manufacturers retail theirs slighty under our price,” Phillip says.  “A certain percentage of the market will always go for the cheaper alternative, but when consumers are looking for quality, they tend to stick with locally-made products.”

This article featured in Australian Stainless magazine - Issue 38, Summer 2006.


Posted 1 April 2007

This article is the third is a series showcasing the uses of 445M2 Stainless Steel. Read Part 1. Read Part 2.

The Applied Science Building at the University of NSW is a landmark in the Eastern suburbs of Sydney. This world-class multi-storey complex of research laboratories and lecture theatres has recently been extended and upgraded, including the air-conditioning and fume extraction systems.

The new air conditioning and ventilation systems were placed on the roof. Management at the University were concerned that the upgrade would be a major disruption and not one they wished to endure more than once in a generation. They needed materials to be long-lasting and require minimal maintenance.

As contractors on the project, Croydon industries chose a new generation marine grade stainless steel. 445M2 was selected for the ducts of the roof, which were exposed to a marine atmosphere created by surf at Maroubra Beach just a few kilometres away.

Brian Clark at Croydon Industries says, "This was the first time we used 445M2, and we were a bit apprehensive - but it gave us no problems. It formed very easily, producing clean lines and well shaped panels with no flaws.

"The stream diffuser sheet of perforated metal was a dream to make.

"The punching ran cool, they sheet came out flat, with very little burr and at a lower cost than the familiar 316. We're glad we opted to use 445M2, it's been a win-win for all."

This article featured in Australian Stainless magazine - Issue 39, Autumn 2007.


Posted 1 April 2007

This article is the final in a series on common finishes. Previous articles in this series dealt with the workhorse No. 4 (2J/2K) (AS36, Winter 2006) and the mill finishes 2R (BA), 2B and 2D (AS38, Summer 2006). This article looks at mirror, profiled and coloured surfaces.

Mirror polished surfaces, as the name implies, have a bright reflective surface which give a mirror like image.  They are the most labour intensive mechanically finished surface with an obvious impact on cost and time of production.  As fl at product, mirror finishes are produced by post mill abrasive polishing of either hot rolled or cold rolled sheet or strip.

Although mirror finishes are only defined in standards for flat products, it is also possible to generate a mirror polish on surfaces where there is sufficient access for the grinders and polishing mops.  The exception to this is materials with large or variable microstructures such as some castings or heavily cold worked items or welds.  In these cases, it may not be possible to obtain a mirror surface with a clear image or a uniform lustre.

Mirror polished surfaces are produced by grinding with successively finer abrasives where the next grit size is not selected until all the scratches produced in the previous stage have been removed.  The surface is then buffed with “mops” (which may be soft or hard) and sticks compounded with binders and rouge of whose particle size depends on the required finish.  The buffing stage does not remove much material and, if there are scratches from earlier grinding stages, they will show up as rounded furrows.  Contamination with a larger grit particle will give isolated, but very unsightly scratches.

A mirror finish is the only one that will produce a clear image of its surroundings.  Finishes such as the cold rolled BA or an electropolished 2B or even a No 4 finish with a very low Ra that is then electropolished, will be brilliant and reflective but they will not form a sharp reflected image.

 

Specifications
Both ASTM A480 and EN10088-2 include mirror finish specifications called No 8 and 2P respectively.  Mirror finish is described as a non-directional finish which is reflective and has good image clarity.  The surface will be essentially free from grit lines due to the initial grinding stages but there will be visual differences between surfaces produced by different suppliers to these specifications.

For mirror finishes, requiring that the surface has a specific surface roughness (Ra) is not very useful.  Gloss measurements are a useful technique on fl at surfaces especially if both diffuse and specular reflection are measured.  Not surprisingly, diffuse reflectance is always higher. If a higher level of confidence is required for critical applications, then agreement on comparison with a finished sample in agreed conditions is recommended. It is the most reliable method of detecting random scratches.

Applications and Limitations
Mirror finish is most widely used for plates in presses, on the interior surface of moulds and also for small mirrors, reflectors and architectural panels.

The two primary limitations are:

• the most commonly used grades (304 and 316) are quite soft so that any cleaning process must avoid scratching the surface with residual dust or applied cleaning compounds, and

• large fl at areas of mirror polish throw scratches, grease or dirt markings into sharp contrast.

The first limitation is overcome by careful cleaning protocols using adequate water rinsing.  The effect of random marks and scratches is reduced if the surface is corrugated at the macro level described below when using surfaces that are texturised (single sided deformation) or embossed/rigidised (through thickness deformation).  However, while mirror sheet may be profi led, it is more common to apply profi ling treatments to cold rolled sheet.

Profiled or Patterned Surfaces
EN10088-2 uses categories 1M and 2M for sheet material that has been patterned on one side only.  The 1M group applies to hot rolled base materials while the much more common 2M applies to cold rolled base materials, usually with a 2B, 2D or 2R (BA) finish.  In corrosive environments it is essential to orient the pattern to allow free drainage.

Through Thickness Deformation
EN10088-2 lists 2W for cold rolled sheet that has been cold rolled into a through thickness corrugated  pattern. The cold work strengthens the sheet and may permit the use of thinner sheet.  The rigidity also helps control oil-canning, i.e. local buckling caused by thermal expansion during fixing or temperature changes during the year or day.  The surfaces are often described as embossed or rigidised.

Coloured Stainless Steel
Stainless steel can be painted provided that the surface is scrupulously clean and has sufficient profile to mechanically anchor the paint.  Using a stainless steel base metal offers the advantage that, even if the coating is damaged, any rusting is superficial and will not lead to long term structural failure as has occurred when protective coatings fail on steel or aluminium structures.

However, painted organic coatings are a clumsy means of colouring stainless steel.  If it is simply to be blackened, then the molten sodium dichromate process or a hot sulphuric acid treatment or even an electrodeposited and baked organic coating could offer greater durability.

Other colours are offered by an electrochemical deposition process that deposits and hardens an enhanced oxide film on the stainless steel although usually only on 304.  The colour depends on the thickness of the oxide and progresses from blue to gold to mauve and green with time of exposure.

The colour is similar to the interference colours in an oil slick or soap bubble with interference between the light refl ected from the top of the oxide and base metal.  In theory the colouring could be reproduced on any simple shape but in practice, it is only available on sheets.  The coated sheets may be deep drawn, formed, bent and fixed mechanically but welding destroys the coloured film.  While the oxide film is harder and more resistant to scratching than the basic 304 substrate, it is still susceptible to mechanical damage and so is not suitable in areas subject to heavy traffic.  Corrosion tests on blue coatings on 304 showed slightly improved resistance to atmospheric and acidic chloride exposure over the resistance of 304.

This article featured in Australian Stainless magazine - Issue 30, Autumn 2007.


Posted 1 April 2007



Northern Stainless Director and Operations Manager Darren Colbert said a stairway to heaven for a Fannie Bay home in Northern Territory meant minimal upkeep in a potentially corrosive environment.

“We wanted low maintenance because he (the home owner) is only 1km from the ocean,” Darren said. “He is well shielded from the sea but we still electropolished - to avoid tea staining.”

Stairway to Stainless HeavenThe staircase used 560 kilograms of grade 316 stainless steel supplied by Atlas Specialty Metals in Berrimah. Standing 4.5metres high and stretching out 3.5metres, the structure was built to complement the handrails around the pool area as well as the balustrades around the upper level of the dwelling.

A great deal of individual attention was given to the stair treads, using 3 millimetres of stainless steel which was laser cut and punched. Further laser cutting was used to provide aesthetic features under each step. The two main stringers used 6-inch stainless steel pipes, which were electropolished to achieve their final look.

The end result was a spiraling stairwell from the pool area to the upper level of the home, which requires only minimal maintenance and looks simply gold!

This article featured in Australian Stainless magazine - Issue 39, Autumn 2007.


Posted 1 April 2007

When ASSDA Accredited Fabricator Nepean Engineering was awarded the tender for the manufacture of the stirring mechanisms for 10 thickeners for the Goro Nickel Mine in New Caledonia, they had no idea of the enormity of the venture. But having now completed the two-year undertaking they reflect on what has been their biggest stainless steel project to date.

 

 

Although the nickel mine was a massive development, Nepean Group Owner and Managing Director David Fuller admits the initial stages of commencement were a little “stop-start”.

“We won the tender 2 years before from GLV Australia Pty Ltd (Dorr-Oliver Elmco) but the project was cancelled,” he says. “We then had to re-tender and were lucky enough to win it again.”

Manufacturing finally commenced in August 2005 and was completed in March 2007.

Nickel Mine uses 400 tonnes of stainless steelDavid says the project resulted in 410 tonne of stainless steel product, including an additional 370 tonne of carbon steel. The contract export value was $10 million. Varying grades were used including 338 tonnes of 316L, 65tonne of 904L and 7 tonne of AL6XN. The thicknesses ranged from 1.6mm up to 80mm.

Six of the thickeners were 70 metres in diameter and required the manufacture of 33 metre long raking arms. Because a highly corrosion resistant material was needed where the nickel extraction occurred, Nepean Engineering used 904L for its high nickel and chromium content. The thick sections required meant that 316L and 904L were used to avoid sensitisation and the subsequent risk of intergranular attack.

Super-austenitic grade AL6XN with 6% molybdenum and high nitrogen, offered better corrosion resistance and was used in one of the smaller thickeners, which extracts cobalt. This material was imported from America.

When manufacturing commenced Nepean Engineering experienced quite a few challenges as a large amount of material was non-standard size.

“316L angle was unavailable so all angles were pressed from flat plate,” David says.

Pressing was performed across the grain. This required joining 2 x 8 metre sheets using sub arc welding so that the longer angles could run across the sheet. The sheets were then cut to fit the plasma cutter, which could handle 6 x 17 metres. Some of the angles were formed in Nepean's 1000 tonne press and others were subcontracted for specialist pressing.Nickel Mine uses 400 tonnes of stainless steel

Special dies were made for Nepean's press to allow larger angle radius. Furthermore, pipe unavailability due to wall thickness requirements meant up to 2 semi-circular half sections of pipe had to be pressed then sub arc welded together to achieve a die of the required length and diameter. For quality purposes, all welding required procedures. Nepean Engineering created a procedures manual for approval by the client.

Contamination from processing and handling was an issue that required focus. Nepean Engineering built a new factory dedicated to stainless steel with inserts at work stations, on forklift tines and on cranes plus separation sheets on presses and rolls to avoid cross contamination. All welds were pickled after fabrication. However, it became evident that not all contamination had been removed with further contamination also occurring due to airborne grinding particles. In order to provide a clean surface with a uniform overall appearance, flap disc grinding and garnet blasting was performed which removed any contamination, excess flux, heat tint and oxides.

With such a large quantity of stainless steel on site and with varying grades and material thicknesses, clear identification was imperative. Traceability was adopted on all parts and processes of the project with the introduction of a colour coding system to identify the different grades of stainless steel.

Material heat numbers were stamped on all components. Maps and naming schedules were used so that each component had a part number and could be identified on a drawing. A spreadsheet was produced to advise the client of the heat number of the plate from which each part was cut. This then could be traced to a material certificate to provide the chemical and mechanical properties of that particular plate or item.

Weld traceability was also adopted on all parts of the project. Again maps and naming schedules were used so that all welds could be identified. Each welder was assigned an identification number, which was then traced against the weld number and placed on a spreadsheet similar to the material traceability spreadsheet.

Other parameters traced were the type of wire used, wire batch numbers, flux type and batch and welding procedures.

Non-destructive testing (NDT) was employed with dye penetrant and ultra sonic tests on the non-magnetic, austenitic stainless steel components and magnetic particle and ultrasonic on the carbon steel components.

David Fuller said “the job was a major challenge but one that Nepean Engineering rose to”. “The experience we have acquired, along with the additional infrastructure built puts us in good stead for future projects of this magnitude.”

This article featured in Australian Stainless magazine - Issue 39, Autumn 2007.


Posted 1 December 2009

Specifying for industrial-size cooking kettles requires close attention to heating processes, product carried and operating temperature.

ASSDA Accredited Inox Fabrications Australia design and manufacture steam jacketed cooking kettles from 250L to 2000L capacity.

The kettles’ heat-up time is effective through design of the lower hemispherical shell which is constructed from SAF2205 providing increased longevity for use with steam and is designed in accordance with the Pressure Vessel Code AS1210.

All food contact surfaces are grade 316 and are smooth and crevice free to avoid corrosion. Non-product contact surfaces are grade 304.

A grade 316 horizontal scraped surface agitator ensures even distribution of heat throughout the product and reduces ’burn-on’.

The horizontal agitator also provides good mixing, particularly with products containing particulates. The scraper blades are made from food grade engineered plastic which is capable of withstanding high temperatures.

When selecting correct material usage, careful consideration must be given to the environment in which the equipment is to be used: the type of product and if it contains corrosive elements, the operating temperature and the heating process to ensure success of the final product. Stainless steel meets these requirements.

This article featured in Australian Stainless magazine - Issue 45, Summer 2009.


Posted 1 December 2009

Longevity won’t be an issue with the latest version of this sculpture. Cherry Blossom first appeared as an ice sculpture - complete with spinning cogs - in the 2008 Russian Ice Cup.

After winning the Mayor’s prize its creator, Melbourne-based artist Benjamin Gilbert, constructed a stainless steel version for Bondi’s “Sculpture by the Sea” exhibition.

ASSDA member Atlas Specialty Metals sponsored the project, providing 316 stainless to suit the coastal environment.

Mr Gilbert specified stainless steel for its neutral colour, polishing the surface with stainless wire brushes to allow salts to build up.

“I don’t really like shiny stainless finishes. A patina is more realistic and neutralises visual effects from its surroundings,” he said.

The panels were both TIG and MIG welded, pickled and polished to achieve a buffed silver leaf effect.

“The work is a combination of Harold Holt mystery and my work with Greenpeace and the Wilderness Society,” Mr Gilbert said.

“It is the first large work I’ve made purely for my own satisfaction in years.”

Cherry Blossom is showing at Canberra’s Corinbank Arts Festival in late February and will then travel to Europe for Denmark’s version of “Sculpture by the Sea” in May.

This article featured in Australian Stainless magazine - Issue 45, Summer 2009.


Posted 1 December 2008

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

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

Safe, Hygienic and of Little Concern to People with Nickel Sensitivity


Posted 31st July 1993

Over the past few years stainless steel cookware has undergone scrutiny to determine its safety as a product for use by people with nickel contact dermatitis and it has been shown to have no ill effect.

Early in 1993 Mr G. Norman Flint visited Australia and described current thinking in Europe concerning the use of stainless steel cookware by nickel sensitised people. Mr Flint is a consultant to the Nickel Development Institute based in the United Kingdom and is responsible for presenting nickel's case in regulatory developments of the European Community.

Mr Flint held meetings attended by manufacturers and health workers and presented conclusions of recent research indicating that pick-up of nickel from stainless steel utensils in domestic cooking operations was of no significance in relation to the naturally occurring level of nickel in the uncooked food. This effectively deems the cookware safe for use by sensitised people.

About 10-15% of women and 1 -2% of men are sensitised to nickel and, on close and prolonged skin contact with nickel, some nickel alloys and solutions of nickel salts, suffer from nickel contact dermatitis. Sensitisation requires a significant initial exposure to nickel such as can occur following the insertion of nickel plated earrings after ear piercing when corrosion of the nickel plating may expose the damaged skin to soluble nickel compounds during healing (which explains the higher rate for women).

The incidence of sensitisation has led to a ban on the use of nickel plated "keepers" in Sweden and a proposal for regulations in the European Community to ban nickel containing studs and earrings from the piercing procedure. The proposal also seeks to restrict the release of nickel from alloys used in articles in close and prolonged contact with the skin such as necklaces, bracelets, watch straps etc. to ~0.5J.lg Ni/cm2/week and in coated products to the same amount for a period of three years.

Mr Flint explained that some food stuffs are considerably higher in nickel than others and that avoiding these foods can greatly reduce the intake of nickel for sensitised people. In the light of some reports that dermatologists were concerned that food cooked in stainless steel vessels could exacerbate dermatitis in some cases of nickel sensitisation, research has been undertaken at Bonn University and the BNF/ Fulmer Research Laboratory over the past two years. The research used natural foodstuffs (particularly those high in oxalic acid and salt and likely to create an environment where nickel corrosion from the steel might occur during preparation) and concluded that pick-up of nickel from stainless steel utensils in domestic cooking operations was of no significance in relation to the naturally occurring level of nickel in the uncooked food.

Mr Flint concluded that although in some cases nickel contact dermatitis may be exacerbated by a high nickel diet, many dermatologists in Europe believe that the nickel consumed must exceed about five times that of the average daily diet before any significant effect is observed. Cooking in stainless steel cook-ware will not produce a significant increase in the amount of nickel consumed over that which exists in the food already.

  • The average daily intake of nickel is around 200 micrograms (from 2kg of food) per day in the United Kingdom.
  • Cocoa, cashew nuts, soya beans and oat flakes have nickel contents well above average (cashew nuts have 50 times the average).
  • Nickel Development Institute sponsored tests revealed:
    a) nickel pick-up, even in the most extreme case (rhubarb in a new utensil) is not significant.
    b) pick-up diminishes rapidly below detectable levels with repeated use of any utensil.

This article feature in Australian Stainless magazine - Issue 1, July 1993.


Posted 31st July 1993

Stainless steel plates are the core component of a revolutionary brazed plate heat exchanger manufactured by Melbourne firm Multistack International Limited.

The heat exchangers are designed to replace conventional gasketted-plate and shell-and-tube designs. After pioneering work was conducted in Europe in the late 1970's Multistack have achieved higher efficiencies and longer operational life after an Australian development program of several years and "many millions of dollars".

Type 316 stainless steel plates stacked on top of each other form the basis of the heat exchanger's design. Each plate is embossed with a channel formed under high pressure, to very fine tolerances and then enrobed with a thin sheet of copper. Plates are paired to form a complex lattice of channels and alternating sets of channels carry refrigerant and coolant. Multistack claims that in its heat exchangers turbulent flow at high pressure allows more efficient heat transfer than any other design.

Paired sets of plates are assembled on top of each other, tested and brazed at high temperature under vacuum conditions. Through capillary action the copper brazing medium forges the paired lattice system together forming a strong pressure vessel.

"Stainless steel has been specified for its ability to be cut, formed and heat treated reliably to form a pressure vessel which is durable and able to resist attack from aggressive refrigerants and coolants", according to Multistack Managing Director Roger Richmond-Smith.

Multistack heat exchangers have achieved exceptional reliability in service and are constructed to conform with the American Society of Mechanical Engineers pressure vessel code. Meticulous testing of stainless steel mate-rials is conducted before any pressing takes place.

The heat exchangers can be used for many fluid to fluid (including gas) heat transfers where it is not necessary to clean the heat exchanger's surfaces, but the largest proportion of Multistack's production is for use in the company's patented modular water chillers, for large central plant air conditioning systems.

The advantages of the compact heat exchangers are exploited in the chillers to create modules that can be transported in standard lifts (greatly reducing the costs of refitting existing buildings), use HCFC22 refrigerant (which is favoured under the Montreal Protocol for protection of the ozone layer) and optimises efficiency by operating only enough modules to meet required cooling load during the course of each day.

With these advantages it is not surprising that large numbers of Multistack chillers are in service globally in a wide variety of configurations. The company reports that its second largest installation (39 modules) is the World Trade Center, New York and its largest (42 modules) is Zhian Jin Shopping Centre, Henan Province in China.

The potential use for Multistack modular chillers is not restricted by the health of the building industry. Adherence to the Montreal Protocol will see the replacement or adaptation of about 4,000 existing water chillers in Australia well before the end of the century. The numbers in Europe and the United States are a staggering 45,000 and 80,000 chillers respectively, according to recent industry estimates.

To service international customers the bulk of Australian chiller production is exported and licensed chiller production plants are operating in the United States, China, Spain and South Africa.

This article featured in Australian Stainless magazine - Issue 1, July 1993.


Posted 31st July 1993

Life Cycle Costing (LCC) has long been used in planning for reliability and maintenance for complex engineering systems in defence, airline, railway, offshore platform, power station, and other applications.

A basic attribute of stainless steel is the ability to provide long-term perfor-mance with a minimum of downtime and cost associated with maintenance. As a result LCC is of particular importance to the stainless industry.

Whilst the mathematics of LCC can be quite complex the International Chromium Development Association (ICDA) has developed an IBM or compati-ble PC program on floppy disk which can be easily applied to most examples.

The Australian Stainless Steel Development Association can make this program available to any interested party on request.

LCC analysis provides a more secure basis for comparing and selecting material options than the traditional method of judgements based on comparing acquisition costs alone. This particularly applies to situations where the initial cost is high and downtime for unplanned maintenance is costly.

In circumstances where stainless is being considered or introduced into new fields of applications, comparisons are often made with materials of a lower initial cost such as coated carbon steel or plastics.

Here the reasoning should progress well beyond the simple initial cost com-parison and take account of the long term cost assessments associated with mainte-nance replacement and operating stop-pages.

LCC is the tool to make this assessment and the ICDA program makes it easy.

Calculating LCC
In the LCC calculation, consideration is given only to relevant costs which are directly or indirectly affected by the material options being considered. Besides the cost of material, these include costs of installation, operation, maintenance, stop-pages, replacements and possibly the residual value at the end of the service life. The time intervals at which the various costs arise during the selected life cycle period must also be taken into account.

Before the various cost items can be put together, those that arise every year and those that occur at certain time intervals during the service life must be converted into present values.

Again the complexities of the mathematics are catered for by the PC program.

Examples are the best way of demonstrating LCC principles and application and two are offered to illustrate the point.

The first is from Swedish practice and features roofing.

The building industry is one of the most rapidly expanding markets for stainless steel and roofing is a major growth application. A method based on seam welding 0.4mrn strips of cold rolled stainless steel was invented in Sweden in the 60's and has since found favour in Europe and Japan. An LCC calculation was carried out based on these material options:

• galvanised and plastic coated carbon steel, double folded edges
• 0.4mm stainless stee I strip, seam-welded and single folded edges (type 316 for coastal areas or polluted atmospheres, otherwise type 304).

In this example the LCC period is 50 years and a real interest rate of 3% is used (comparative figures are given per sq metre):

Material Material Cost Installed Cost LCC
Carbon steel
1.1
2.1
2.1
Stainless Steel type 316
2.0
2.8
1.4
Stainless Steel type 304
1.6
2.6
1.3

 

 

 

 

The LCC result shows that stain-less steels are less costly than galvanised and plastic coated steel. Galvanised carbon steel requires replacement after about 20 years. The calculation does, however, not take into account the risk of damage to building substructures each time the covering is replaced. The stainless steel alternative is the only one which is virtually maintenance free.

The second example is a mixing tank for a water treatment plant.

The dimensions of the tank are 3 metres long, 1.5 metres wide and 1.5 metres high. The entire tank is raised off the floor by four steel channels beneath the tank; these ensure that spills do not accumulate beneath the tank.

The design brief requested evalua-ion of three materials. (i) mild steel with applied fibre-glass lining, (ii) stainless steel alternatives of Type 304 and duplex grade 2205 (UNS S31803).

As the 2205 was not readily avail-able in angle and channel products, these were substituted by type 304 for the 2205 design as these components were not to be in regular contact with the corrosive environment.

The evaluation was carried out using the LCC PC program from the International Chromium Development Association available in Australia through ASSDA.

Experience suggested that both the 304 and 2205 would probably survive without replacement for the full twenty years, whereas the mild steel was expected to last for only about eight years before replacement. In addition both the stainless steels were expected to require only minimal inspection and cleaning as regular maintenance in comparison with fairly extensive patching of the mild steel and its lining.

The "Summary of Present Value Costs" table of Figure I shows the resulting LCC analysis -the Type 304 stainless steel is lowest cost, closely followed by the 2205 and with mild steel substantially more expensive due to its higher maintenance and replacement costs.

The "Value of Lost Production" in the summary table is shown as zero -this implies all maintenance and replacement is carried out in scheduled shut downs for other plant maintenance. Shut downs causing lost production could substantially add to the Total Operating Cost of the option requiring this unscheduled maintenance.

The ICDA LCC software also gives a more detailed breakdown of the contributions to the initial costs and operating costs, and a "sensitivity analysis" on all the inputs which is shown in Figure 2. The latter gives the effect on the total LCC for each material option of an independent change (eg of 20%) in each of the inputs. This information is vital in determining which of the input items must be accurately known and which are of lesser importance. In this case the sensitivity analysis indicates that the most critical data is the time before replacement becomes necessary. The assumption was that the 304 and 2205 would both survive for the full twenty years; from the sensitivity analysis it is apparent that if the 304 fails before this time (possibly due to its lower pitting corrosion resistance compared to the 2205), the 2205 duplex stainless steel becomes by far the cheaper option. Clearly a good knowledge of the actual operating conditions to be encountered is crucial to the correct selection.

Acknowledgments:

1. This article has drawn on material contained in a publication Life Cycle Costing - Evaluation of a Method of Use For Stainless Steel Applications by Sten Von Matern of Avesta AB, Sweden.

This has been made available to ASSDA through A vesta Sheffield Pty Ltd. This contribution is gratefully acknowledged.

2. The computer diskette "Life Cycle Costing" was developed by and supplied to ASSDA by the International Chromium Development Association.

This article featured in Australian Stainless Magazine - Issue 1, July 1993.


Posted 1 July 2007

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


Posted 1 July 2007

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


Posted 1 October 2007

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.


Posted 1 October 2007

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.