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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.

Life Cycle Costing and Stainless Steel

Posted 31 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.

Alternative stainless steel grades - Part 1

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

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

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

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

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

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

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

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

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

AUSTENITIC 200 SERIES

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

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

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

Mechanical and Physical Properties

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

Some 200 series grades in comparison to 304

Attributes

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

Limitations

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

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

Applications

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

This article appeared in Australian Stainless Issue 40

Stainless revamp for Sunshine Coast beach

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

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

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

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

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

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

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

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

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

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

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

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

This article featured in Australian Stainless Issue 40.


Posted 1 July 2007

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

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

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

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

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

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

This article featured in Australian Stainless magazine - Issue 40.


Posted 1 July 2007

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

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

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

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

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

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

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

This article featured in Australian Stainless Issue 40

Stainless style and sunscreen

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

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

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

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

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

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

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

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

This article featured in Australian Stainless Issue 41.

What's cooking?

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

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

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

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

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

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

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

This article featured in Australian Stainless Issue 41.

Hygiene a priority for food production
Hygiene is a top priority at a facility which processes more than 40,000 tonnes of chicken a day, so it is not hard to imagine the scale of stainless steel fabrication needed to meet that expectation.

drainASSDA member and Accredited Fabricator Stainless Metal Craft has recently completed work on the design and fabrication of stainless steel equipment for Inghams Enterprises’ processing plant at Edinburgh Park, north of Adelaide, and hatchery at Monarto, south of Adelaide.

The projects incorporate numerous custom-designed installations, including a series of 300mm wide channelled drainage at the processing plant in runs of 60m that will withstand the weight of forklifts, and slot drains with integrated sumps (Figure 1) at the hatchery that will tolerate extremely harsh cleaning compounds.

Stainless Metal Craft General Manager Graeme Bunt said the slot drains, in particular, were a specialised project requiring innovative tool work, because of the size and depth required.

He said the slot drains were fabricated at their facility at Emu Plains, NSW, then shipped to Adelaide in 8m lengths where they were site welded to form continuous drains of 44m.

Mr Bunt said grades 304 and 316 were both used at the facilities, depending on the application.

“For most of the general usage areas, such as laundry chutes, bump rails, hand rails, hands-free wash stations, walk-through showers and chequer plate platforms and stairs, we were able to use 304,” Mr Bunt said.

“But in more specialised areas or where harsh chemicals may be used, such as slot drains, some clean points, freezer coving, boot washers and fire hose reel cabinets, we had to use 316 to ensure the material would withstand the harsh environment.”

Mr Bunt said freezer coving (a hygiene requirement to prevent food from being caught where the wall meets the floor) is usually made from epoxy-coated concrete, but there was concern this would wear down with ongoing snap freezing of the chickens. Instead, about 180m of 3mm grade 316 were used.

Strict regulations within the food industry also determined the need for grade 316 stainless steel fire hose reel cabinets.

Mr Bunt said most of the stainless steel was supplied by ASSDA members Atlas Specialty Metals and Midway Metals. The processing plant was handed over to Inghams at the end of September and the hatchery will also be handed over this year.

STAINLESS STEEL STATISTICS

Further Processing Plant
•    55 hands-free wash stations
•    80 clean points
•    180 metres of freezer coving
•    12 boot washers
•    18 fire hose reel cabinets
•    300mm wide channelled drainage in runs of 60 metres – strong enough to withstand weight of forklifts

Hatchery
•    495 metres of slot drains
•    10 hands-free wash stations
•    800 metres of Schedule 40 pipe bump rails
•    45 clean points
•    7.7 square metre egg shell hopper

This article featured in Australian Stainless Issue 41

Alternative stainless steel grades - Part 2

This article is the second 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 1.

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

Grade    

Carbon    (max)

Manganese  Chromium  Nickel  

Copper

201 16/4 0.15 5.5-7.5 16.0-18.0 3.5-5.5 -
202 17/4 0.15 7.5-10.0 17.0-19.0 4.0-6.0 -
J1 15/4 0.08 7.0-8.0 15.0-17.0 4.0-4.5 1.5-2.0
J4 15/1 0.10 8.5-10.0 15.0-17.0 0.8-12 1.5-2.0
304 18/8 0.07 17.5-19.5 17.5-19.5 8.0-10.5 -

 

 

 

 

 

 

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.

The growing demand from China and the rest of the developing world has driven up the price of the alloying elements in stainless steels.  The relative cost of different grade groups of stainless steels has also changed, depending on the content of the more expensive alloying elements, particularly nickel and molybdenum.

In the last issue we described the austenitic 200 series group, one of the alternative groups to the austenitic 300 series that traditionally dominate the market.  This article describes the other two alternative groups, ferritic and duplex grades.

FERRETIC 400 SERIES

These stainless steels have the ferritic structure also found in carbon steels.  They do not contain the nickel addition used to stabilise austenite in 300 series grades.  The quality of ferritic grades has advanced with modern steelmaking equipment and, after several generations of ferritic grades, a number of technical limitations have been overcome.

Toughness is the remaining limitation that has not been overcome.  All ferritic grades show the ductile to brittle fracture transition well known from carbon steels.  Unlike the carbon steels, there is no phase transformation when heated during welding, and hence the grain size of the HAZ can be high.  This limits the toughness of the ferritic stainless steels, and with a few exceptions they are used at up to about 3mm thickness, where the toughness transition temperature after welding is adequate.

There are ferritic grades with 10.5-30% chromium, and many also contain molybdenum.  The ferritic grades have the corrosion resistance their chromium and molybdenum contents give them, and in addition they are very resistant to stress corrosion cracking.  Later generations of ferritics are not susceptible to sensitisation and intergranular corrosion.

The ease of fabrication of ferritic grades, which behave in a similar way to carbon steel, has seen them used to replace competing materials and grow the market for stainless steels.  A recent publication of the International Stainless Steel Forum “The Ferritic Solution – The Essential Guide To Ferritic Stainless Steels” (available from ASSDA) has several examples.

Grade Cr Mo N Ni C Mn Other PRE*
AUSTENITIC 300 SERIES                
304 18.1     8.1 0.04     18
316 17.2 2.1   10.2 0.04     24
FERRITIC 400 SERIES                
409 11.5       0.02   0.18Ti 12
430 16.5       0.04     17
AWM 404GP™ 21.0       0.010   0.4Cu, 0.3Ti 21
444 17.7 1.8     0.02   0.45(Ti+Nb) 24
AWM 445M2™ 22.1 1.05     0.007   0.20Ti, 0.20Nb 26
DUPLEX                
LDX 2101® 21.5 0.3 0.22 1.5 0.03 5.0   29
SAF 2304® 23.0 0.3 0.10 4.8 0.02     27
2205 22.0 3.1 0.17 5.7 0.02   0.15N 37
SAF 2507® 25.0 4.0 0.27 7.0 0.02   0.3N 46

*Pitting Resistance Equivalent (PRE) = %Cr + 3.3x%Mo + 16x%N

Mechanical and Physical Properties

Yield strength is a little higher than that of the austenitic grades, and tensile strength a little lower.  Ductility is about half that of the austenitics, and is similar to carbon steel.

Ferritic grades cannot be strengthened by heat treatment, and since their work hardening is weak they are rarely strengthened by cold work.  Ferritic stainless steel work hardens in a similar way to carbon steel, which can be an advantage, particularly in fabrication where experience and settings gained with carbon steel can be applied to ferritic stainless steels with few modifications.

Ferritic grades are ferromagnetic, and have much lower thermal expansion and higher heat conductivity than austenitic grades.

Attributes

First generation ferritic stainless steels are usually used unwelded, as they have high carbon (~0.05%), which causes the formation of brittle films of low corrosion resistance on HAZ grain boundaries.  Grade 430 is the most widely used of this group: it has enough corrosion resistance for indoor applications such as food preparation and display equipment, but is rarely fusion welded.  Grade 430 is usually used with a bright annealed (BA) finish: finishes in ferritic grades are generally brighter than their austenitic equivalent.  Large amounts of first generation ferritic grades, with molybdenum added for extra corrosion resistance, are used for automotive trim.

Second generation ferritic stainless steels have lower levels of carbon and nitrogen, and have titanium and/or niobium added to combine with what’s left.  This makes the grades more weldable, and the first second generation ferritic grade developed, 409, is now widely used in automotive muffler systems.  The current production of 409 in USA rivals the tonnage of the most popular stainless steel, 304.  Welds in second generation grades are tough at room temperature up to about 2mm thickness, and do not suffer from sensitisation or stress corrosion cracking.  There are titanium treated versions of 430, widely used in whitegoods such as welded washing machine drums.

Third generation ferritic grades have even lower carbon, nitrogen, titanium and/or niobium additions, with higher contents of the corrosion-resisting elements chromium and molybdenum.  The most common grade of the group, 444, is used for challenging applications such as heat exchangers and hot water tanks.

Fourth, or new generation grades, are further refined using vacuum equipment to achieve better toughness and weldability, and better surface quality.  They are often used in applications where austenitic grades fail by chloride stress corrosion cracking or pitting corrosion, and they are increasingly being used in many applications to replace the common austenitic grades.

Limitations

The limited toughness of ferritic grades has been noted, and they are rarely used in structural applications.

A further limitation is the tendency of ferritic stainless grades to suffer 475°C embrittlement and phase formation more quickly than austenitic grades, which limits their use to about 350°C in the higher chromium grades.  However, large tonnages of the lower chromium grades are used in automotive muffler systems at higher temperatures without problems.

Applications

The largest tonnage of ferritic grades is used in automotive muffler systems, and there are also significant uses in automotive trim, commercial catering equipment and indoor decorative applications.  The higher alloyed later generation grades give outstanding performance in heat exchanger and piping systems for chloride-containing aqueous solutions and seawater, where stress corrosion cracking of austenitic grades can be a problem.  The ferritics are also ideally suited for roll forming to roofing, walling and rainwater goods.

DUPLEX GRADES

These grades consist of an intimate mixture of about equal amounts of austenite and ferrite.  About half of the amount of nickel needed to be fully austenitic at the chromium content is added in most of the grades.  A newer grade, LDX 2101, follows the approach of the 200 series austenitics by using manganese instead of most of the nickel.

There are grades within the duplex group with a range of different corrosion resistances, depending on the chromium and molybdenum contents.  The duplex grades tend to use more chromium and less molybdenum than an austenitic grade of similar corrosion resistance - a more economical balance.

As chromium is increased in the austenitic 300 grades to improve corrosion resistance, more nickel must be added, making high chromium austenitic grades expensive.  The more corrosion resistant duplex grades, containing less nickel and a better balance of chromium and molybdenum, have penetrated the market to a greater extent than the leaner alloys, and 2205 has become the most common alloy where the corrosion resistance of grade 316 is inadequate.

The duplex grades are much more resistant to stress corrosion cracking than the austenitic grades, and they are effectively immune in potable water.  They are also less prone to sensitisation than austenitic grades, although not immune.

Mechanical and Physical Properties

Duplex grades have about twice the tensile strength and 50% higher yield strength than austenitic grades.  The ductility is about half, but is still high enough to give good formability, with work hardening behaviour similar to that of carbon steels.  Unwelded, duplex grades are tough to low temperatures (-50 to -100°C), and they can often be welded to give transition temperatures well below 0°C.

Duplex grades cannot be strengthened by heat treatment, and since their work hardening is weak they are rarely strengthened by cold work.
Duplex grades are ferromagnetic, and have lower thermal expansion and higher heat conductivity than austenitic grades.

Attributes

Their much higher strength than austenitic grades often allows duplex grades to be down-gauged to thinner material, with good savings in costs.
The higher strength can be a handicap if the opportunity of down-gauging is not taken, as forming loads are high and may be beyond the capability of the equipment.  Many of the uses of duplex grades are at thicker gauges (greater than ~1.2 mm), where the savings of down-gauging can be achieved without getting to the lighter sheet metal gauges that fabricators can find difficult to weld.

Welding duplex grades requires more control of welding parameters, particularly heat input and interpass temperature, but pre-heat, post-heat and post-weld heat treatment are not required and weldability is considered good.

Limitations

The high alloy content of most duplex grades makes them susceptible to embrittlement from the formation of intermetallic phases after extended service at high temperatures.  Corrosion resistance is also reduced.  Service temperatures are generally limited to less than about 300°C.

Applications

The higher strength of the duplex grades makes them suitable for large tanks, and savings of 40% or more in material costs can be achieved.  They are also used for heat exchangers and chemical equipment, often where chloride stress corrosion cracking has limited the life of austenitic grades.

COMPARISON OF TYPICAL TENSILE AND ELONGATION PROPERTIES OF GRADE GROUPS OF STAINLESS STEELS

tableone

 

 

 

 

 

 

 

 

 

 

 

This article appeared in Australian Stainless Issue 41.

Stainless advance for water treatment plant

Never has there been a time in Australia when water preservation was so critical.  As populations rise and dam levels fall, the importance of treating and reusing water has become not a question of “if” but a question of “when”.

bundambaThe construction of Bundamba Advanced Water Treatment Plant (BAWTP) west of Brisbane is aimed at alleviating pressure on South East Queensland’s existing dams and waterways by providing an alternate water supply for end users in the region, initially Swanbank power station.  

The project has had great flow on benefits for the Australian stainless steel industry as infrastructure requirements point to the material for its strength, corrosion resistance and application performance.

The world-class BAWTP is a joint venture between Thiess Pty Ltd and Black & Veatch, who are responsible for the engineering, design, procurement and construction. Management of the project is in alliance with the Queensland Government. A number of ASSDA members were sub-contracted by Thiess Pty Ltd for various stages of the project, including ASSDA Accredited Fabricator D&R Stainless, Perfab Engineering and Stainless Pipe and Fittings Australia.

Following a tender process, D&R Stainless was engaged for off-site pipe spooling. The quantity of stainless steel used for the job, including around 3000 flanges, meant that D&R Stainless was issued with the materials by Thiess Pty Ltd as needed.  

Many of the piping materials for the first two stages of the project were supplied to Thiess Pty Ltd by Stainless Pipe and Fittings.  Materials were in excess of 350 tonnes and included pipe, pipe fittings and flanges in grade 316L with sizes ranging from 25-600nb.

 

bundamba2Once delivered, D&R Stainless cut and bevelled the pipe and then welded and passivated internally and externally before undergoing hydro testing.

D&R Stainless Director Karl Manders said that, not only did the pipes use grade 316, but they were also fabricated to Australian Standard 4041, class 1.

“Because the pipework adhered to such a high standard, 10% of all welds were x-rayed for quality,” he says. Passivation of the pipe welds involved applying pickling paste inside and out, and then scrubbing and flushing to avoid loose scale, important for the fine filtration of the water treatment plant.

Karl says quality was something Thiess Pty Ltd took very seriously, with a welding inspector and quality checker appointed at their premises.

“This was to ensure all welding and passivation was performed at the highest standard, and also to ensure that production off-site was consistent with installation schedules onsite”.

Perfab Engineering was also sub-contracted by Thiess Pty Ltd for the manufacture of the reverse osmosis (RO) skids at its workshops in Newcastle, working closely with the designers from suppliers Koch Membrane Systems in the United States.

The work carried out by Perfab included fabrication and surface treatment of the carbon steel skid frames, fabrication of the stainless steel pipework, full mechanical installation of the valves, instrumentation and RO pressure vessels, pneumatic fitout, electric fitout and testing.

The high pressure pipe spools were fabricated from Sch 40S pipe with 300# flanges and low pressure pipe spools from Sch 10S pipe with 150# flanges.

Perfab has three orbital Gas Tungsten Arc Welding (or TIG) machines that were operated around the clock to ensure the tight delivery times were achieved, however Perfab Engineering General Manager Damien Ryba says “the biggest contributor to the success of the job was having a well trained, highly skilled and productive workforce committed to the success of the project”.

At present, the BAWTP 1A is in full operation and delivering water to the Swanbank Power Station. Thiess Black and Veatch Director, Gus Atmeh, said that the BAWTP 1A project was delivered ahead of schedule and this was due to the support of the project by high quality stainless steel fabrication shops from across Australia and particularly from South East Queensland, who provided stainless steel components for state of the art process equipment and piping: “Without them we could not have made it on time.”

This article featured in Australian Stainless Issue 41

Stainless cleans up university grounds

The thought of public rubbish bins usually attracts images of black smelly wheelie bins with broken lids and flies.  However, if you walked through the University of Queensland in Brisbane’s St Lucia, you would be greeted, instead, with clean stainless steel and lovely bright colours.

wheeliebins

The installation of between 30-50 new double-bin enclosures has added splashes of colour and flair to the university grounds.  Designers Street and Garden Furniture Co enlisted the services of long time contractors and ASSDA Accredited Fabricators Rocklea Pressed Metal to manufacture the pieces.

Featuring laser cut patterns, bright colour spray painting (to distinguish general rubbish from recycling) and a unique shape, the bins were designed with the surrounding art deco buildings in mind.

Street and Garden Furniture Co Director David Shaw says he often uses stainless steel for outdoor use because of its robustness and he found it particularly useful for the bins.

He says students tended to decorate large surface areas with posters, so using stainless steel meant they could be easily cleaned.

“Much of the damage is often caused by people emptying the bins,” Mr Shaw also says. “So we tried to design them to make them easily accessible.  If the surface gets damaged, they can be simply re-surfaced.”

Manufacture of the bins involved 12.24 square metres of 1.6mm grade 304 sheet with a number 4 finish and 18 lineal metres of 25 x 1.6mm grade 304 square tube. A considerable amount of laser cutting was done to adopt the academic shield and to break the large surface area with an aesthetic pattern.  A floating top was also designed to minimise the dominance of the wheelie bin size and to provide a shield against weather.

The designs were done by Street and Garden Furniture Co and then sent to Rocklea Pressed Metal as a CAD file.
David Shaw says his longstanding relationship with Rocklea Pressed Metal has been built through a history of confidence and delivery.

“An awful lot of the things we do, those guys are involved in,” he says.  “I am totally confident they’ll provide me with what I’ve drawn.”

The University of Queensland project is a longstanding one, dating back to 1997.  The project also incorporates the installation of light poles, tree grates, signage and seats, much of which Rocklea Pressed Metal has contributed to.

This article featured in Australian Stainless Issue 42.

Testing for grade confirmation

Raw material price fluctuations and increasing demand for stainless steels have driven demand for lower cost alloys as alternatives to the traditional “300” series steels. This has been met through a range of existing and new, innovative steels with different properties, performance and availability broadening the range of alloys that might be found in the market. But as with the traditional stainless steels you can’t tell what they are by looking at them.

This article describes most of the range of test methods available for grade confirmation. The method used depends on the budget, size of job and the potential consequences of having the wrong alloy.

Why test?

Contract documents may require formal test certificates.  Usually these are issued by the mill and unless there is reason to doubt them this is sufficient.  However, sometimes a positive material identification (PMI) is required for safety critical items such as LPG valves. Legal cases also tend to be very demanding about precise documentation.  Some products may also be lacking in documentation and traceability.

Unexpected poor performance often prompts calls for material testing. Such testing removes one variable in things that might have gone wrong but the cause is more frequently inadequate surface finish or errors in design or fabrication.

Finally, reverse engineering of an existing product from a competitor or overseas supplier often requires detailed materials’ information.

What level of testing is required?

General or intermediate level guidance could cover differentiation between carbon and stainless steel or between 304 and 316 or between 300 series and 200 series or ferritic grades.

Full laboratory chemical analysis will be needed for some cases (such as determining low carbon grades) or when it has become a legal rather than a technical issue.

Full mechanical and metallurgical analyses may also be required if strength or hardness are essential design elements.  If the material has undergone subsequent surface modification then the required investigation could be extensive – and expensive.

Simple physical tests

Appearance is not a reliable indicator of the grade of stainless steel as the differences are determined more by surface treatments than alloy composition.  Even the differences between mirror polished surfaces are fairly subtle.  The table below shows slight differences in density of some stainless steel alloys but density determination is not a convenient method.

Alloy

Density (g/cc)

430, 3Cr12/5Cr12

7.7

2205

7.8

304, 310

7.9

316

7.98

A widely accepted test is a magnet.  Duplex, super duplex, martensitic and ferritic stainless steels are strongly attracted to a magnet while annealed austenitic stainless steels are not.  However, cold worked austenitic stainless steels are weakly attracted to a magnet so cold formed ends to a vessel, cold rolled bolts and bent corners will be affected by a magnet.  This applies to both the conventional chromium-nickel 300 grades and the chromium-manganese 200 series austenitic grades.

The strength of the effect that a magnet has on a material can be related to the relative permeability and the graph shows the different effect of the same level of cold work (bending) on various austenitic alloys. The grades with higher nickel or austenitising elements (310 or 316) show much lower magnetic properties. In comparison, mild steel has a relative permeability somewhere between a few hundred and 2000.  Relative permeability of duplex and ferritic alloys is in the hundreds.  Precipitation hardening alloys are magnetic but the degree depends on whether the alloy is martensitic or semi-austenitic.

graph

Chemical tests

The proprietary kits are designed to test for a specific element and have a limited shelf life.  If you have a project requiring multiple tests then they are very useful. However, if you only require a couple of tests a year, then it may be cheaper and more thorough to run a full laboratory test.

Molybdenum

The most common test uses a single drop of solution to distinguish between low and high molybdenum content. The “Moly Drop” test will distinguish between 304/304L and 316/316L but the test will also give a positive result with 317/317L, 904L, the 6% Mo grades, 444, 2205 and the super duplex grades.  The test requires a clean, dry, grease free surface and it sometimes helps to lightly abrade the surface.

The yellow drop (as shown) will darken after a few minutes but the reaction speed is slower if the surface is cold.  It is a comparative test and scrap additions during production may give enough molybdenum to give a slight colouration.

The test is therefore most reliable if a known 304 and 316 are tested with the unknown. If the sample is to be used in service, then the chemicals should be washed away immediately after the test.

There is another chemical test using ethyl xanthogenate to form a red or pink complex when molybdenum ions are dissolved in solution.  The molybdenum is dissolved from the surface either by using a hydrochloric or sulphuric acid.  The strength of the colour depends on the level on molybdenum in the alloy.

Manganese

The increasing use of high manganese stainless steels has led to several manganese test kits operating on the same principal as the electrochemical test for molybdenum. The semi-quantitative results of a kit test for manganese are shown in the photographs below.

Apart from the recent low nickel, high manganese stainless grades, there have been specialist 200 series grades used in generators, higher strength (pre duplex) marine alloys and for anti-galling applications.

colouringSulphur

A practical and rapid test for a high sulphur (free machining) stainless steel (303 and 430F are the most common) is to prepare sulphur prints using photographic paper soaked in 3% sulphuric acid for several minutes.  The treated paper is pressed onto a cleaned surface for about 5 seconds. High sulphur levels are shown by a brown colour.  Once again, this is a comparative test so low and high sulphur samples should be compared to the test piece.

Instrumental techniques

There are two basic techniques each with two variants. The automated instruments are expensive and would normally be used for large projects, or by scrap metal merchants, manufacturers or specialist NDT contractors.

Spark spectroscopy requires a flat surface preferably about 20mm in diameter. An electrical spark is generated and the colour of the spark is determined by the elements present.  The elemental concentration is controlled by the intensity of the specific colours. In automated instruments, the spectrum is compared to a library of data and percentage composition is calculated for each element.  Calibration is required against materials with similar composition.  A sparking mark is left on the surface and must be removed if appearance or fatigue resistance is important.  The instrument’s accuracy tends to be lower than a laboratory instrument and exposure to air excludes measuring nitrogen.

The older “Metascopes” were also spark spectroscopes but relied on visual comparisons of line brightness so their accuracy was very operator dependant. Grinding spark identification using a hard, high speed grinding wheel is even older technology. It will cause a grinding burr and is extremely dependent on the operator skill.  Spark bursts are related to the carbon content and characteristic sparks/carrier lines are related to the alloying metals. Chromium in steel produces a spark stream that is orange-red in colour. A yellow colouration caused by nickel persists all along the spark whereas the orange specks of chromium appear only near the origin of the spark stream, in close contact with the grinding wheel. Relatively narrow and short spark streams, white-yellow in colour, are produced in type 304 stainless steels.

The second broad method is X-ray fluorescence.  Older instruments used one or more radioactive sources although more recent miniaturisation of X-ray tubes means that some instruments generate X-rays directly.  Regardless of their source, the X-rays excite electrons from the inner shells of the elements and when outer electrons fall into the newly vacant shell, a characteristic spectrum of light – generally with a number of lines – is emitted.The instrument measures the intensity of counts in each line and compares it to an internal databank.  Provided that the surface is clean and smooth and the measurement is for long enough to give good statistics (typically between 20 and 60 seconds), then the alloy can be identified.  However, because of the physics of X-ray fluorescence, it cannot analyse for light elements, especially carbon or nitrogen.  The units are light and easy to use as seen in the picture. One advantage for reporting is that results can be directly downloaded into a computer records system

Laboratory measurements

Atomic Absorption (AA) or Inductively Coupled Plasma Spectroscopy (ICP) techniques use laboratory instruments after a sample has been digested in (usually) a mixture of acids. This is slow and may be more expensive than a spark test but it will give a more complete and reliable result.  Carbon requires a separate (LECO ignition) test and detecting silicon by either method requires aggressive chemicals to get the silicon into solution.


Which test?

  • Is it 430/2205 or 304/316?
    A magnet will be strongly attracted to 430 and 2205 but only weakly to deformed parts of 304 or 316.
  • Is it 430 or 2205?
    Both are strongly magnetic but only duplex 2205 will give a positive moly drop test result.
  • Is it 304 or 316?
    A moly drop test will give a positive result with 316.
  • Is it a low carbon grade?
    Only a spark spectrometer can distinguish between low and standard carbon grades.

In all these cases a full laboratory analysis will answer the question and provide a full composition for about $100.

This article appeared in Australian Stainless Issue 42.

The assistance of ASSDA colleagues is gratefully acknowledged - in particular, Peter Moore from Atlas Steels.

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.

Standing the test of time

The $10 million stainless steel revamp of Melbourne’s Bourke Street Mall has certainly lived up to its original purpose, providing a durable, clean and simple linear theme.

In 2006, inspired by success stories of nearby stainless street furniture, the City of Melbourne council conducted a life cycle costing analysis – with astounding results.

City of Melbourne Industrial Designer Marika Mulqueen said stainless steel ensured low maintenance costs and design flexibility.

“Using stainless steel over powder coated steel significantly reduces ongoing maintenance costs. A comparison found that while stainless steel can initially cost more, over a 20 year period maintenance costs can be up to 50 per cent less than powder coated steel. Maintenance involves a once a year pressure clean instead of the need for regular repainting to deal with scratching and paint peeling,” she said.

“Scratches do not show up as easily because the furniture is brushed stainless steel and is not prone to fading,” she said.

MME provided smooth mechanical finishing which minimises dirt retention for optimum corrosion resistance.

The project included new seating, drinking fountains, recycle bins, banner poles and a new fit-out for the tram zone.

Stainless steel was chosen as, when the correct surface finish is applied, it is virtually maintenance free.

John Bainbridge of ASSDA member MME Surface Finishing presented the department with information on the value of considering the life cycle cost advantage of stainless steel and the importance of specifying the correct surface finish.

ASSDA member TRJ Engineering fabricated the commemorative totem poles. The poles use grade 316 stainless steel in a No.4 scratch finish. Each consisted of two pressed cylinders at the base of the pole which had L.E.D. lights mounted on both sides behind a glass facia.

The cylinders were formed in a CNC brake press which worked very well to prevent any surface roughness.

The last part of the project was completed in-house before installation and electro-polishing.

The Melbourne Technical Design Department has since recommended that all future street furniture commissioned by the council be stainless steel specified.

 

This article featured in Australian Stainless magazine - Issue 44, Spring 2008.

Photography courtesy of Andrew Curtis.

Stainless to reduce greenhouse gas emissions

To overcome environmental concerns around landfill, Perth’s largest waste management authority, Mindarie Regional Council, is building a facility for the 70 per cent of household waste that is organic material and can be composted.

The $80m building is due for completion in 2009 and will save on landfill, reduce greenhouse gas emissions, and will produce a rich organic matter that may be added to Perth’s sandy soil.

The new composting facility, to be built using a prize-winning technology developed by Canadian firm, Conporec, comes at a time when the ongoing feasibility of landfill in crowded cities is questionable.

In September this year a new hazard came to light when residents of the outer-Melbourne suburb of Cranbourne were advised to leave after pockets of methane were found in their homes at a dangerous 60-65 per cent concentration. The methane had leached from a nearby landfill - concentrations of 5-15 per cent are considered an explosion risk.

The composting building’s odour removal system uses extraction ducts to capture and then transport air to a biofilter. Stainless steel was specified because of its corrosion resistance.

Organic waste is broken down as it would be in nature, but the composting process is much faster. The compost is produced in a sealed building at negative pressure, where moist air is forced through. The resulting atmosphere in the building is hot, humid and corrosive. Composting produces heat which quickens the corrosion process, particularly in Perth’s hot climate.

Turbo Air Technology Pty Ltd of Bayswater, Perth, fabricated the extraction ducts from AWM 404GP® stainless steel, supplied by ASSDA Major Sponsor Austral Wright Metals.
John Dubbelman, Managing Director of Turbo Air Technology Pty Ltd, says the best specification for the job wasn’t necessarily what had been used in the past.

“Experience with similar installations in Canada led the project managers Kerman Contracting Limited (KCL) to specify grade 304 stainless steel for the ducts,” John says.

“With the help of Austral Wright Metals, we were able to convince them of the fabrication and cost benefits of AWM 404GP®, a ferritic stainless steel with equivalent corrosion resistance to 304. We have used it for the lock-seamed spiral ducts, lobsterbacks, and plenums. We fabricated the new grade without dramas, and KCL is now installing it. It looks good.”

This article appeared in Australian Stainless Issue 44.

Keep Contamination Out and Quality In

Posted 31 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.


Posted 31st July 1993

A new product design company, KOZ Functional Art will shortly be launching a bath ware series called "Bath Art" made entirely from stainless steel

KOZ's mission is to design and manufacture distinctively Australian innovative domestic wares - "Functional Art". The name expresses our design commitment to quality and the integration of meaning, aesthetics and function. KOZ's research found that stainless steel is an ideal material for the Bath Art application because of its durability , low maintenance, design flexibility and ease of manufacture. The Bath Art range comprises four products - shower caddy, soap holder, toothbrush and tumbler stand and spare toilet roll holder.

Throughout development of the range KOZ has been determined to manufacture from stainless steel and do so in Australia in spite of much opinion from industry that this was not possible, on both counts.

A new firm with a long learning curve ahead, KOZ contacted the Australian Stainless Steel Development Association to find out how ASSDA could assist.

KOZ required manufacturers for its designs who could produce high quality wire and spinning fabrications from stainless steel in short runs in Brisbane. KOZ also required information on material supply for some illusive components.

ASSDA was able to draw on the experience and knowledge of members to provide lists of potential fabricators and an offer of introductions from which a fabricator has been found. ASSDA was also able to provide a list of materials and component suppliers both from within and without the Association where necessary. The advice was prompt and enabled KOZ to get on with the manufacturing business. Of great surprise was that the entire process could be achieved in Brisbane.

The free form design of Bath Art products requires a different aptitude than is usual for traditional wire work and the results of product development have been pleasing for KOZ and we believe for the fabricator as well. All the products have been fabricated from type 304 stainless steel wire in gauges ranging from 1mm to 6mm. Primarily joining has been achieved by resistance welding, through a small amount of TIG welding is also incorporated. Following fabrication the products are electropolished to a bright chrome-like finish.

KOZ has tested products for saleability in pilot arrangements with local retailers. This has resulted in orders beyond KOZ's current ability to produce, a situation rapidly being addressed.

For KOZ and Bath Art the future looks promising.

The Australian Stainless Steel Development Association has provided a short-cut along the learning curve for KOZ, enabling our designs to be rapidly placed in production with a minimum of expenditure and heart-ache. For many designers the gap between good design and an excellent product is wide. The service provided by ASSDA has been invaluable in helping KOZ bridge the gap.

Roger Simpson of the Design Institute of Australia stated earlier this year that only those Australian manufacturers with forward thinking that focus on the longer term, develop new strategies and high quality products who will effectively compete in the world market and succeed in the 1990's. I am happy to be working with some of them. I firmly believe that organisations like ASSDA are essential in fostering and facilitating the development of such companies within the stainless steel industry.

Written by Julia Lembryk, Designer, KOZ Functional Art.
This article featured in Australian Stainless Magazine - Issue 1, July 1993.

Stunning Little Creatures
ASSDA Accredited Member TFG Austline Pty Ltd was recently entrusted to install a new brewhouse and fermentation cellar for Little Creatures Brewery in Fremantle, Western Australia.

Over a five-month period, a team of Austline fabricators and specialised welders installed 25 vessels, five kilometres of stainless steel pipework, heat exchangers and over 3,000 fittings and valves into the
new brewhouse.

Austline Manager, Tom Moultrie, said the construction process was quite unique. “The whole project was carried out with the old brewery, bar and restaurant sandwiched between the new brewery and fermentation cellar,” he said.

Little Creatures Project Manager, Roger Bailey, said stainless steel was specified for its corrosion resistance and low maintenance requirements.

Stainless also provides micro-biological stability, ensuring a very high level of sanitation and minimal possibility for contamination, he said.

“Using stainless steel is an innovative way to achieve reusable water in the brewery,” Mr Bailey said.

Grades 304 and 316 were both specified in different applications, depending on the product being carried.

Not one hour of trading time was lost during installation. “Any cross over where we worked on the areas still being used were done at night,” Mr Moultrie said.

    

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