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Design Software Vs Back to Basics

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

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

 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

Big Fish Swimming in a Small Pond

Northern Territorians know their barramundi, which is why ASSDA Accredited Fabricator Northern Stainless had to get it absolutely right when they reeled in the contract to design and fabricate this 1030mm specimen.

The silver fish has a mythical reputation in the NT, not least because of its shimmering, silver appearance.

Northern Stainless operations manager Darren Colbert said they had no hesitation in saying they could get the job done to their client's satisfaction, because of their ability to create the barra's mesmerising shimmer in stainless steel.

We knew stainless was the right material for the job because we needed the water feature to last in Darwin's tropical environment, as well as best represent the barra's colour, Mr Colbert said.

We promised the client that we would create something that everyone would want to steal and I reckon we delivered.

The fish, which was commissioned for Osborne Family Holdings Hastings over Mindil apartment complex in Fannie Bay, Darwin, was fabricated from around 15kg of 316 stainless steel with a No. 4 finish. It was then regrained and the scales were polished into it. A 6mm tube sits inside, enabling the water to spray the gill plate.

Mr Colbert said one of the challenges of the project was converting a graphic design program to create a laser file.

The barra was cut out flat with a laser, then rolled and hand curved to create the three dimensional sculpture.

When it is installed in situ (expected to be late October 2006), there will be a fishing rod mounted on the wall of the water feature, with an optic fibre fishing line threaded with a stainless steel fly hook. The entire sculpture will rock slightly, creating turbulence in the water and giving the impression that the barra is working hard against being reeled in.

This barra may not enjoy the freedom of the NT's waters, but it will certainly garner the same admiration as the real thing.

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

Mrs Crocket's Stainless Kitchen

Twelve months after the design and installation of a unique cabbage processing system in Melbourne, the importance of quality stainless steel fabrication has never been clearer.

 

ASSDA Accredited fabricator Bridgeman Stainless Solutions (Brendale, Queensland) was commissioned to design the unique facility at Mrs Crocket's Kitchens, which was completed in October 2005.

The $500,000 project incorporated various plate, sheet, pipe and RHS stainless in grades 304 and 316, and was specified to reduce the risk of contamination in the handling processes for all coleslaws, pastas and food products.

Bridgeman's Managing Director Len Webb said there was previously no system available to perform the process that Crocket's required.

"We engineered and designed the equipment with input from the Crocket's engineer. Always at the forefront of our minds was that the prevention of food contamination is paramount in commercial food preparation areas."

The design of the cabbage line was significant and a huge improvement to the current system set up at the head office site in Queensland. The new design incorporated all processes: tipping, coring, washing, dicing, hopper and outfeed, all in a compact line that now has significantly less labour attributed to it.

The stainless itself was rolled, formed, bent, welded, sanded and polished to meet food grade requirements. Mrs Crocket's Kitchens Maintenance Manager Mark McGauley says stainless was specified because it is easy to clean and maintain.

"We know that the contact area and machinery is clean so this ensures any piece of food that comes into contact with these areas is safe."

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

445M2: A New Generation Stainless Steel (Part 2)

This article is the second in a series showcasing the uses of 445M2 stainless steel. Read Part 1. Read Part 3.

The use of stainless steel plant and equipment in the food industry continues to prove its worth as an increasing number of processors adopt its use in line with the dedication and obligation to food quality and safety.

Whilst stainless steel grades 316 and 304 offer an environment of easy maintenance and cleaning, 445M2 stainless steel goes one step further.

445M2 panels have been supplied to Bertocchi Smallgoods by ASSDA Major Sponsor Austral Wright Metals, following a four-month trial of all three grades of stainless steel.

Bertocchi, a Melbourne-based company producing hams, bacon, salamis and other specialised continental smallgoods, sought an alternative to their existing painted steel linings after they discovered the life of the linings was too short for their high cleaning standards.

The walls and ceiling of the factory are regularly cleaned in line with a guarantee of the highest quality health and safety standards, together with absolute traceability of every unit of product.

This is where stainless steel stepped in.  The hardness and smoothness of stainless steel enables it to resist the adhesion of soils and bio-films, and the excellent corrosion resistance allows it to be easily cleaned and sanitised. Indeed, laboratory tests prove stainless steel is significantly more hygienic than other materials, even when used for food contact surfaces. Moreover, the taste and colour of food products are not affected by stainless steels.

After four months of trialing panels of stainless steel grades 304, 316 and 445M2, Bertocchi Smallgoods chose the new generation ferritic grade 445M2 to line the factory – ceilings and walls. With superior corrosion resistance to grade 316, 445M2 resists the powerful cleaning agents used to keep the factory clean, as well as the hot, humid and salty atmosphere around the brine lines.

So far, Bertocchi has installed 10 tonnes of 445M2 0.7 x 1219 mm sheet with a 2B finish.  The result?  A clean, bright factory that’s easy to keep that way.  And Bertocchi intends to keep going until the entire factory is lined with 445M2.

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

Smooth and Corrosion Resistant Surfaces from the Mill

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.

Stainless Steel Launches its Artistic Merit

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.

A Great Aussie Tradition Makes its Way

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.

445M2: A New Generation Stainless Steel (Part 3)

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.

Smooth and Corrosion Resistant Surfaces from the Mill

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.

Stairway to Stainless Heaven

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.

Nickel Mine Uses 400 Tonnes of Stainless Steel

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.

Specifying Quality

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.

Whale of a Time

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 Steels 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 30th November 1994

 

In late 1989 my partner Eric Kuhne was asked by Stuart Homery of Lend Lease to come out to Australia to work on the ground plane and lobby of a 28 storey office building about to start construction in Sydney. This building is the first of three towers and some foreshore development on the edge of the city centre at Darling Harbour. Our involvement in phase one led to the replanning of ground plane, lobbies, forecourt area, and addition of a large garden between the three towers, and a complete rework of the fore-shore development. The master plan continues to change most recently with a complete rework of the foreshore plans.

 

 

The changes and additions to the first phase of construction were driven by three ideas:

• restoring the ground plane as a place of human habitation rather than just a passage ideas.
• restoring the storytelling quality of architecture through the ornamentation and embellishment.
• treating the office building lobby as a series of spaces for communication and social contacts similar to those found in hotel lobbies rather than modern Sydney office building lobbies.

As a designer of buildings I am interested in ideas about how we use buildings, how to create place to enhance human life and in materials used in construction of these buildings.

In the design of buildings there are many points of view, tricks of the trade, theories and strategies. Designers tend to, fairly early in the game, separate their thinking about metal on or in buildings into two groups - yellow metals or white metals. We think of these metals as generally an either/or turning point fairly early on in the design process. Bronze and its variations and "silver" metals, like stainless, are rarely mixed by design architects.

Building precedents are powerful design influences and some precedents or models for the way I think about using stainless steel are:

• the glint from the St Louis Gateway Arch
• the British Art Centre at Yale with its stainless steel cladding
• the Louvre Pyramid - the structure and the rail finish on the circular stair within the pyramid

At Darling Park a "silver" metal finish was chosen and for most metal work stainless steel was selected. There are many variables in this decision, but amongst stainless steel's particular attributes were:

• stregnth; the round sizes we were using were only possible in stainless steel
• image as a quality material
• weatherability and durability, requiring little maintenance
• many rich and versatile finishes, achievable on a range of fabricated products
• because we were designing the ground plane, tactile attributes were an issue.

Many metal applications at Darling Park are within reach (handles, door furniture or other fixtures at ground level). Stainless provided a solid, quality sensation to touch. We think touching is good.

Finishes from mirror polish and finished stainless to a matt glass bead blasted texture were used for a combination of functional and aesthetic purposes. Major fixtures constructed from stainless steel include:

• canopies at main entrance, forecourt entrance and cafe
• the Broglas & grilles
• globe and gull atop flagpoles
• the entry doors, door pulls & mat
• handrails & balustrades
• the glazing system supports
• lift cars, interior & exterior panels & fixtures
• skylight glazing supports
• exhaust vents
• interior and exterior clocks
• safety strips in the steps
• lighting fixtures
• numerous trim & furniture details.

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.

Subwharfyen Steels Your Imagination

A childhood spent yacht racing was Newcastle artist Braddon Snape’s inspiration for his intriguing new piece entitled The SubWharfyen at Darling Harbour.

“I was always surrounded by beautifully machined or crafted stainless steel rigging and equipment,” he said. So when Sydney Wharf commissioned Mr Snape to create a large-scale work depicting the relationship between people and the sea, stainless steel seemed like a natural choice.

Mr Snape’s experience in working with hardy materials and a highly evolved visual language proved a winning combination. The finished product is a great success as a premium contemporary development for the area.

Sydney Wharf recognised the potential for stainless steel to meet the requirements of the project for both aesthetics and durability.

“The use of stainless steel relates to its surroundings on both a conceptual and material level,” Sydney Wharf’s Shaun Farren said. “It has a connection with the maritime context and is durable in a marine environment.”

ASSDA Accredited Fabricator Marko Stainless provided their fabrication services for the project, using 450 kilograms of laser cut 3mm sheet in grade 316 stainless steel to produce The SubWharfyen from a one-in-twenty wooden model. Three panels comprise the body, which were rolled to form the curved sides. The panels were TIG welded, and blades MIG welded after initial polishing. All welds were pickled, and the entire sculpture passivated after completion.

On Mr Snape’s specification, a minimum 320 grit finish was used for its satin-like quality. “The finish allows the sculpture to respond to the light and colour of its surrounding environment without being consumed by busy reflections,” Mr Snape said.

Mr Snape describes the sculpture as “a synthesis of my aesthetic, poetic, intellectual and practical response to the particular site and the surrounding locale”.

This articled featured in Australian Stainless Issue 44.

Changing costs of alloying elements

Sustained economic growth in China and the rest of the developing world has seen the demand for all the metals grow faster than the minerals industry can develop new mines and smelters.  The result is soaring prices for metals, and for coal and oil.

For a country like Australia - a big supplier of metals - it’s good news, and we have all enjoyed the benefits of the minerals boom. But those of us in the stainless steel industry have seen prices increase markedly, and it has been hard to cope with.  We live in interesting times.

In broad terms there are two main factors influencing the price development of stainless steel: the cost of raw material inputs and the level of demand measured against the capacity to make the steel (the capacity utilisation).

Much of the increase in stainless steel prices has come from the increase in the price of raw material inputs, and particularly nickel, which went through a peak over US$50,000/ton in May 2007.  

It’s back to around $20,000/ton now, but that’s still four times as high as it was in October 2001 – under $5,000/ton.

But it’s not just nickel.  As we saw nickel start to get over its spike, the press filled with stories of the increases our big miners were seeking for their iron ore.  And quietly, the price of chromium has soared from under $600/ton to over $6,000/ton.

Molybdenum, the element added to improve corrosion resistance above what you can get with chromium, has outdone all the rest, from $6,200/ton to a peak over $95,000/ton!  It’s lucky a mere 2 per cent of molybdenum is so effective in improving corrosion resistance.

In response, stainless steel makers and users have sought to get the best value from the alloying elements they use, by shifting between grade families and grades.

We have seen the rise of the 200 series austenitics, which use manganese instead of some or all of the nickel to get the ductile austenite structure.  They peaked at about 10 per cent of world production – but of course the increase in demand for manganese then pushed up its price, making the 200 series less attractive economically.

Duplex grades also offer a potentially cheaper alternative, most using only half the nickel of an austenitic grade with similar corrosion resistance.  A new development, LDX 2101 from Outokumpu, combines the approaches by substituting nearly all of the nickel with manganese.

Ferritic grades have a completely different crystal structure to austenitic grades because they have no nickel added.  That can make their alloying costs much lower, but the steelmaking needed to make good quality steels is more exacting, so the overall cost savings are not as dramatic.

Nevertheless, they can offer useful cost savings.  In recent years they have grown from about 20 per cent of world stainless steel production to 25 per cent or more, and the major steelmakers are predicting they will continue to grow. A recent publication by the International Stainless Steel Forum (ISSF) details the possibilities with this family of grades.

All the talk of metals price increases makes it hard to know what relative contribution each of the elements makes to the overall cost of stainless steel. Believe it or not, many people are not even aware that all stainless steels are mostly iron, so the news about iron ore prices tends to be lost on them. What does doubling the cost of iron ore do to the cost of stainless steel? And how does that compare with the other alloying elements?  Come to that, what effect does the oil price have? It’s not so long since respected economists were predicting $200 per barrel for oil.

These graphs show the ingredient contributions for the two most common grades of stainless steel, 304 and 316.  The bars show the main alloying elements in the grades, each bar representing the average for the year, except the last bar, which is the average for the first half of 2008.

The costs are an estimate of what the steelmaker has to pay to assemble the raw materials to make stainless steel. They don’t take into account the yield achieved, or possible premiums or contract prices paid.  Nevertheless, the graphs illustrate what has happened with alloy costs.  Of course, the steelmaker then has to turn these ingredients into stainless steel, so his overall costs are much higher.  We might expect higher conversion costs for ferritics, duplex steels and the manganese austenitics over traditional stainless steels such as 304 and 316.  

It is important to recognise that raw materials costs are not the only factor in steel pricing and that many factors will influence the day to day prices offered by suppliers.  We are only looking at the costs of the main alloying elements here which is fundamental but not the whole story.

In 304 the biggest culprit for cost rises has been nickel, but in 2008 nickel cost has fallen back to the 2006 level – and chromium and iron have taken over.  Notice that the iron in stainless steel now costs more than all the alloying elements in stainless steel together did in the early 2000’s – and chromium is now costing more than nickel used to.

Astute observers will know that the price of stainless steel has actually been falling in 2008, despite the alloying costs being higher than in 2007.  The lull in the demand for stainless steel has forced the mills to reduce their prices to stimulate sales, and these are tough times for the mills.

The effect of the oil and coal price increases?  Studies suggest it takes about 12 barrels of oil to make a ton of grade 304, so the $100 rise in the price of a barrel since 2002 adds about $1,200 to the cost of a ton of 304.  To put that in perspective, the base price of stainless steel in 2002 bottomed at about that level!

So what has caused all these surges in prices, and where do we go from here – higher, stable, or a return to the earlier levels?  The cause is clear; it is economic growth in the developing world, outside the mature, stable economies that used to dominate the world economy.

This is particularly true for the BRIC group: Brazil, Russia, India and China.  These have all been growing strongly and sustainedly for a number of years, China being pre-eminent.
While their economies were still small, the net increase in demand for metals was not much affected, but their overall demand has now grown to the extent that even when their economies slow, world net demand keeps growing strongly.

The IMF continues to forecast growth rates over 10 per cent for China out to 2013.  After all, over a billion people have lived in poverty for a long time, and their government is committed to developing the country to help them out of it.  Analysts reckon that only about 15 per cent of the demand for metals in China is fuelled by demand outside China, the rest is for domestic consumption.

Stainless steel has not been singled out by these shifts in the world economy.  All the metals, except aluminium and zinc, are currently at about five times the price they were when the boom started.  So much for materials substitution as a way of getting over the price increases!  China has grown so strongly that over the current decade it will consume over half of the copper, aluminium, nickel and zinc used in the world.  Even if China does falter, the other developing countries are not far behind.

The rate of growth in demand is a real challenge for the minerals industry to keep up with it.  It’s not quite the same situation as we see in oil, but it’s not markedly different.  Does anybody think we will ever return to $30 a barrel for oil?  Unlikely, and it’s unlikely we’ll see a return to historical levels for metal prices either.

This article featured in Australian Stainless Issue 44.


Posted 31st July 1993

Quality is the buzz word of the last part of the 20th Century and manufacturers ignore quality control at their peril. With proper attention to detail, stainless steel will provide satisfactory service for many years. The Chrysler building in New York has a stainless steel finish that is in excellent condition after 60 years.

Stainless steel is a quality material and for products made from it to meet the demanding quality standards required, there are some special features that those used to fabricating other materials must watch if their product is to meet their customer's expectations.

Surface contamination is one of the danger areas.

Contamination with carbon steel - embedded iron.

If stainless steel is fabricated with tools previously used for forming mild steel there is almost certain to be carbon steel pick up from these tools onto the stainless steel surface. Grinding wheels used for both carbon steel and stainless products or machining stainless steel with conventional steel cutting tools are particular dangers.

These iron particles will form a galvanic couple with the stainless steel and quickly rust. At this early stage they could be cleaned away with a mild abrasive with little or no damage to the stainless steel surface. If they are left, it could be another story!

When the carbon steel particle rusts, as it is sure to do, it will form iron oxide that will eventually turn into ferric chloride, Figure 1. There are always chloride ions available particularly in marine atmospheres. The resultant ferric chloride will rapidly attack the stainless steel and pitting corrosion will result, generally visible as rust in a pattern related to the source of contamination.

In the fabrication area mark up tables, and the platens of cutting and bending equipment should be covered with cardboard or plastic that is frequently cleaned down or replaced. Crane hooks and forklifts should be similarly protected. A protective plastic film on the surface can limit the amount of pick up that can occur during handling.

Embedded iron will not only arise from fabricating equipment. Hot rolled sheet or bar will not be treated for surface contamination when delivered. Ground finished products are safer. During the manufacture of large vessels carbon steel particles or swarf from other areas of the shop can also be transferred into the tank on workers' boots and clothing and care must be taken to avoid this.

Small particles of embedded iron can be removed by nitric acid applied either as a paste or immersion. Heavier contamination may require a nitric/hydrofluoric acid treatment. These processes are know passivation or pickling.


Other Contamination

There are other dangers during fabricating that can generate crevice corrosion conditions. Adhesive tape is the classic case. The area under the tape is low in oxygen and if moisture can seep under the tape - and it most probably can - a crevice is created where corrosion can occur.

The same sort of crevice can be formed under grease, crayon markings or residual adhesive left after the protective film is removed. Also, some films, if left exposed to the sun's UV radiation for more than a few hours harden and both the film and underlying adhesive are very difficult to remove.

In most industrial areas deposits can build up on the surface. This problem can be eliminated by washing the surface down - a good rule of thumb for architectural applications is to wash exterior stainless steel at about the same frequency as the building windows require washing. Maintenance manuals supplied with stainless steel fixtures or components should specify this cleaning requirement.

Welding also requires attention. Weld spotter and potential crevice corrosion points at the initiation and run out points of a weld run can be a problem as can contamination with grease, crayon marks or carbon steel in the weld area, including an edges, is essential.

Another area of concern is the oxide film formed during welding and the concurrent decrease in alloy content of the material under the weld. In all cases it is good practice to passivate the steel after the welding.

Written by Noel F. Herbst, Director, Nickel Development Institute of Australasia
This article featured in Australian Stainless Magazine - Issue 1, July 1993.