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St ainless Steel for High Per formance Enclosures Stainless steel is the ultimate materials solution for electrical enclosures in safeguarding the network and communications technology invested in underground mining sites.
Olympic Dam is a large polymetallic underground mine located in South Australia, approximately 550km northwest of Adelaide.
enclosure specific to BHP’s requirements. The customised solution was supplied through Auslec Electrical and Data located in Wingfield.
Home to a major source of oxide copper gold deposit, Olympic Dam produces combined quantities of copper, gold, uranium and silver through an underground mining system integrated with a metallurgical processing plant. The large deposit was discovered in 1975 and in 1988, the mine was opened by WMC Resources. Today, Olympic Dam is owned and operated by BHP, following its acquisition of WMC Resources in 2005.
The outcome was a double door stainless steel field cabinet, 1000mm deep and capable of housing electrical and monitoring equipment. Due to the remote location of the project and the type of equipment installed, stainless steel sunshades and lockable handles were included to reduce heat within the enclosure and prevent vandalism.
ASSDA Member and Accredited Fabricator B&R Enclosures was contracted by MPS Building & Electrical to assist with finding a solution to a fibre enclosure hub capable of linking four mining shafts to the surface. B&R’s design and engineering team worked closely with MPS Building & Electrical to design and fabricate an
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Grade 316 stainless steel with a No. 4 surface finish was specified for the custom-designed enclosures, with material supplied by ASSDA Member Outokumpu in 1.5mm thick sheet. Underground communication networks are a critical link between operations below ground and at the surface to ensure efficiencies in production and personnel safety. Protecting the equipment that delivers these communication
networks is vital and stainless steel offers the durability and longevity required to deliver a robust structure to ensure preservation of the internal hardware. In addition, grade 316 stainless steel offers excellent corrosion resistance, particularly to pitting corrosion which can occur in inland Australia due to high salinity in the ground water. B&R have worked alongside BHP and MPS Building & Electrical on past projects, installing enclosure solutions into a variety of different applications. B&R’s ability to design custom solutions along with their reliable service meant MPS Building & Electrical could confidently deliver this project and supply an enclosure suitable for harsh mining environments and extreme weather conditions. As a result of good collaboration and local technical expertise, the project’s stainless steel enclosure design is now a standard specification for future installations across Olympic Dam.
ASSDA MEMBER CONTACTS: B&R ENCLOSURES Ben Bridges, Group Sales & Marketing Manager +61 7 3714 1111 | sales@brenclosures.com.au www.brenclosures.com.au OUTOKUMPU Mark Armitage, Sales Manager/Service Centre +61 3 9369 3344 | mark.armitage@outokumpu.com www.outokumpu.com
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Pickling and Pas sivation of St ainless Steel One of the most common misunderstandings in specifications for stainless steel fabrication relates to the post-fabrication treatments to restore or enhance the corrosion resistance. The surface treatment processes invoked vary between pickle and passivate, passivate, or sometimes simply pickle. Needless to say, whilst pickling and passivation are two distinct processes, a lack of clarity can cause some confusion between the owner and the builder/fabricator about what is expected and required. This article briefly outlines the factors that affect the corrosion resistance of stainless steels, what surface treatments can be used and how they affect the steel’s surface to improve corrosion resistance. Corrosion Resistance and its Controls
Pickling
Stainless steel is resistant to aggressive environments because of a very thin, self-repairing, chromium-rich complex, oxide film present on the surface of the steel. It is not completely impervious, but it dissolves many orders of magnitude more slowly than it reforms. The passive layer is more resistant for alloys with more chromium, molybdenum and nitrogen. This is the reason for the empirical, composition based Pitting Resistant Equivalent (PRE(N)) index which is often used as a ranking tool in selecting which stainless steel will be used in new applications. However, the alloy composition is not the only control of the passive film’s strength, and hence its corrosion resistance. There must also be an adequate supply of oxygen and moisture to maintain the integrity of the passive film. This requires either good design or a maintenance program – and preferably both.
Pickling uses a mixture of nitric and hydrofluoric (HF) acids. The wide range of concentrations and exposure times are described in ASTM A380 Standard Practice for Cleaning, Descaling and Passivation of Stainless Steel Parts, Equipment and Systems. Typically the nitric concentration is up to 10 times the HF concentration, but pickling is slow unless the HF is more than about 3%. Longer pickling times are required at lower temperatures or if a high alloy is being used, i.e. super duplex takes longer than duplex which requires longer than 304. If a paste is used, the contact area acid gets exhausted unless it is stirred, e.g. with the application brush. Thorough washing is needed to remove all residue even from crevices and, to avoid stains, it is important not to allow acid or rinse water to dry on the surfaces.
For a specific alloy, i.e. a specific PRE(N), the passive film (and hence the corrosion resistance) can be improved by chemically oxidising the steel’s surface. Air and water are good and the ASTM standard dealing with passivation (A967 Standard Practice for Chemical Passivation Treatments for Stainless Steel Parts) advises that for many environments, no further treatment is required for satisfactory service. However, oxidising or chelating chemical treatments will provide better corrosion resistance.
Roughness Corrosion resistance is indirectly improved if the surface is smooth and clean (free of contaminants) to facilitate the self-renewal of the passive film. For abraded surfaces there is also a critical surface roughness of 0.5μm Ra that should not be exceeded. This is recognised in surface finish 2K in EN 10088.2. It seems that for steels, the size of abrasives causing this roughness is too large to cut the surface cleanly and leaves rough edges and metal debris which can accumulate dirt and corrosives – hence more rapid corrosion with coarser polishing.
Contamination The bête noir of stainless steel: carbon steel contamination. If it is not removed, the stainless steel will rust. In marine environments, it will collect chlorides and cause large rust stains and small pits in the stainless steel. If it is mechanically removed, it is likely that the smeared steel will leave a larger rust stain, although it may be less intense. Acid treatments can remove carbon steel deposits and have the added advantage that they can also remove surface breaking manganese sulphide (MnS) inclusions. These MnS inclusions do not have a passive film and act as initiating points for corrosion.
Welding If you have welded your fabrication and there are rainbow coloured bands along the welds, they are zones where the passive film has been destroyed. Under the darker colours, there will be a wedgeshaped layer with a lower chromium content than the bulk stainless steel. Corrosion will initiate in these coloured bands. The weld tint colours can be mechanically removed provided the grinding is not too rough. Chemical removal by pickling is often a better option.
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OHS and environmental considerations mean that using a pickling contractor is easier, safer and ensures the appropriate disposal of acid and pickled heavy metals. Contractors will often use a temperaturecontrolled, stirred tank or, sometimes, a spray pickling solution in an acid-proof and bunded bay. Unless an additional level of passivation is required for a very aggressive environment, the outcome is a pickled item that is passive.
Chemical Passivation The traditional and very effective acid is nitric, typically between 15% and 25% for about two hours, although it is not uncommon to drop machined parts into a bucket of nitric acid for half a shift. The passive film is significantly strengthened and the ratio of chromium to iron in the surface layers can exceed 1 – compared to <0.4 in the bulk. Nitric acid will also remove rust stains and sulphide inclusions plus, more slowly, carbon steel smears. Phosphoric acid will remove rust and sulphide inclusions, but it is not oxidising and will not strengthen the passive film. Another method of strengthening the passive film of a chemically-clean surface is to use a hydrogen peroxide solution – lots of free oxygen and only water residue. There are other acids that will strengthen the passive film and dissolve carbon steel and inclusions, but by a different method. Citric and oxalic acids and EDTA all have a carboxylic acid [O-C-OH] atomic structure, and once the acid dissolves the unwanted metal, the positive ion is trapped by the negative oxygen atoms in a process called chelating or sequestering. This process is used in wastewater treatment to remove metals. In passivation, it is important to rinse thoroughly. Chelating treatments are widely used in the food industry as formulations which include biocides, so the citric acid does not contribute as a food source. There are a number of special cases detailed in ASTM A380 which require care when pickling: • Sensitised or hardened (nitrided or carburised) areas may suffer intergranular attack. • Free machining stainless steels requires an inhibitor or it will pit. • Martensitic stainless steels can suffer hydrogen embrittlement. All of the above methods are chemical treatments which are quite traditional and generally well applied. Further information is provided in ASTM A380, which also details test and inspection methods to confirm surface cleanliness.
Three Definitions
CLEANING Removal of contaminants such as soil, grease, oil, etc. using low-chloride detergents and/or solvents to allow free access for water and oxygen to grow the passive film. The bulk material is not affected and the surface looks brighter. Chlorinated solvents may be a risk as residues can degrade if heated and may cause pitting. In vessels or pipework, it is important to drain and dry the surfaces.
PICKLING The removal of any high temperature scale and any adjacent low chromium layer of metal from the surface of stainless steel by chemical means.
It also removes embedded or smeared carbon steel, inclusions and loose flakes of stainless steel left from abrasives. It will leave a matt finish, which may be paler if the pickling is extended. It provides a passive surface immediately on rinsing â&#x20AC;&#x201C; hence you pickle and get a passive surface.
PASSIVATION The treatment of the surface of stainless steel, often with acid solutions (or gels), to remove contaminants and promote the formation of the passive film on a surface that was freshly created, e.g. through grinding, machining or mechanical damage. It will remove acid soluble inclusions such as MnS. Clean humid air will form a passive film on clean stainless steel and the appearance will not change. Chemical passivation strengthens the passive film and typically takes an hour or so at ambient temperatures. Air passivation is adequate unless the environment is very aggressive for the grade.
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1. Rusting steel contamination from shearing stainless sheet. Photo courtesy of Graham Sussex. 2. Rainbow oxide from poor gas shielding during welding. Photo courtesy of HERA. 3. Before (left) and after (right) pickling of welded fitting. Photo courtesy of Graham Sussex. 4. Welded components after pickling to remove heat tint and possible steel contamination. Photo courtesy of Australian Pickling & Passivation Service.
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St ainless Shines in Darling Harbour Mirror finished stainless steel sign blades can be found scattered along the central boulevard of Sydney’s revitalised Darling Harbour. Through a recent $3.4 billion transformation, Darling Harbour has become Australia’s largest entertainment and events precinct boasting world class facilities, including over 40,000 square metres of exhibition space. This urban rejuvenation builds on the success of Darling Harbour and in turn, will generate $200 million annually in economic benefit for the NSW economy.
ASSDA Member and Accredited Fabricator Stoddart were engaged by Lend Lease to manufacture and install 19 stainless steel wayfinding sign blades for Darling Harbour’s ‘once in a generation’ re-development. The sign blades are featured in groups of two and three, each standing seven metres tall and two metres wide.
The Harbour is ringed by attractions, entertainment and extraordinary waterfront restaurants. The Boulevard creates an active north-south pedestrian connection between Central Station and Cockle Bay. Its prime location is within walking distance of most points in the Sydney CBD therefore wayfinding signage is pivotal in navigating people through and around the precinct.
258 panels of grade 316 stainless steel were used for the sign blades in order to provide housing for LED display screens throughout the precinct. The structural stainless steel frame also mounts speakers and power outlets. All stainless steel used in this project was supplied by ASSDA Member, Fagersta Steels. Featuring a mirror profile finish, the stainless steel signs create a stunning visual effect through the reflection of the countless city lights and surrounds of the bustling tourist and entertainment mecca. Stainless steel was specified by landscape architects, Hassell, for its aesthetic appeal and high-quality attributes. The Harbour’s salt water environment and location was also a consideration in the materials specification, being adjacent to the city centre. It is only fitting for quality material such as stainless steel to be showcased in one of the world’s most desirable entertainment and event destinations.
ASSDA MEMBER CONTACTS: FAGERSTA STEELS Chris Glenn chrisglenn@fagersta.com.au | +61 3 9091 5100 www.fagersta.com.au STODDART Donna Sardelich, Business Development Manager NSW dsardelich@stoddart.com.au | +61 2 8832 4318 www.stoddart.com.au
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ASSDA INDUSTRY NEWS AND EVENTS
AUSTRALIAN INDUSTRY STAINLESS STEEL SUPPLIER AND FABRICATOR AWARDS Celebrating innovation and excellence in Australian stainless steel supply, design and fabrication. Launched at PacRim Stainless 2017, the ASSDA Awards Program presents three individual prestigious awards voted on by the industry. The Flat Product Supplier and Long Product Supplier of the Year Awards recognises excellence in supply performance. The Fabricator Project of the Year Award recognises excellence in Australian stainless steel design and fabrication.
Above: Tom Moultrie (TFG Group) and Stephen Lawrence (Furphy Engineering), ASSDA Fabricator Project of the Year 2018.
FLAT PRODUCT SUPPLIER OF THE YEAR
LONG PRODUCT SUPPLIER OF THE YEAR
FABRICATOR PROJECT OF THE YEAR
2017 YC Inox Co., Ltd.
2017 YC Inox Co., Ltd.
2017 Stoddart, Wynyard Walk
2018 Daming International Holdings Ltd.
2018 YC Inox Co., Ltd.
2018 Furphy Engineering and TFG Group, Fuchs Lubricants Plant Expansion
The Peter Matheson Industry Service Award was also introduced in 2017 to recognise the commitment and service of industry veterans to the Australian stainless steel industry. In 2017, we applauded Ken Hayes for over 43 years of service and Sam Adel for over 50 years of service. At the 2018 event, Peter Moore was recognised for over 30 years of service, Ian Ward for over 31 years of service and Alex Gouch for over 30 years of service.
For more information about the ASSDA Awards Program, please visit www.assda.asn.au.
MARK YOUR DIARIES 9-10 October 2019 Sofitel Gold Coast WAVES OF CHANGE, OCEANS OF OPPORTUNITY
Join us on the Gold Coast for Australia’s ONLY premier conference event bringing together the local stainless steel industry and colleagues from abroad in an exclusive networking environment. Brief program overview: • Two half-day conference sessions with an exceptional line-up of speakers from around the globe • Gala Dinner: Australian Industry Stainless Steel Supplier and Fabricator Awards • Social networking activity at the Gold Coast’s latest attracttion, Top Golf For further information including sponsorship opportunities, visit www.assda.asn.au.
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AUSTRALIAN STAINLESS REFERENCE MANUAL 2019 ASSDA is excited to share that it will release the eighth edition of its Australian Stainless Reference Manual in 2019. Often referred to as the ‘stainless steel bible’, the Australian Stainless Reference Manual is an industry guide and comprehensive resource to stainless steel. First published in 1996, the Reference Manual is a 200-page plus publication designed to stand as an informative reference tool and essential guide for anyone connected with the building, manufacturing and design industries. It contains a wealth of technical information from properties and performance to grade selection, design and fabrication, plus guidance on relevant national and international standards, an extensive glossary on stainless steel terminology and a full listing of ASSDA Members, Accredited Fabricators, and their capabilities.
ADVERTISING OPPORTUNITIES Prominent position tenders close 5.00pm (AEST) 28 February 2019
Pictured: 2012 Reference Manual
ASSDA invites all interested parties to tender for the prominent positioning pages, including the inside front cover, inside back cover, centre page spread and back cover. Minimum bids apply and you must be an ASSDA Member to be eligible to bid for a prominent position.
Standard advertising bookings close 5.00pm (AEST) 7 March 2019 Don’t miss the opportunity to advertise in the 2019 Australian Stainless Reference Manual, which will remain in circulation for at least the next four years. Halfpage and full-page advertising space is available starting from AU$2,500.
For more information including the full Media Kit, visit www.assda.asn.au.
ASSDA PLATINUM MEMBERS
ASSDA GOLD MEMBERS Fagersta Steels, Midway Metals, Stanch Stainless Steel Co., Ltd., Stoddart, Viraj Profiles Ltd, YC Inox Co., Ltd.
ASSDA SILVER MEMBERS Amity Pacific, Arucs Wire Group, Austral Wright Metals, Australian Stainless Distributors, Callidus Welding Solutions, ChingHann Industries Co., Ltd, Dalsteel Metals, Daming International Import & Export Co., Ltd., Froch Enterprise Co., Ltd., Metal Centre Australia, Mideast Metals FZCO, Prochem Pipeline Products, Sanwa, Yue-Seng Industrial Co., Ltd.
MORE INFORMATION Enquiries for further information on any material presented in this publication should be directed to ASSDA: Level 9, 307 Queen Street T +61 7 3220 0722 Brisbane QLD 4000 AUSTRALIA E assda@assda.asn.au www.assda.asn.au EDITORIAL Contributions of story ideas specialising in stainless steel and its applications are welcome from members of ASSDA. ADVERTISING Advertise in the only publication that reaches a targeted group of 5000+ in the Australian stainless steel industry. Rates available at www.assda.asn.au CONTACT Lissel Pilcher, Editor: lissel@assda.asn.au DISCLAIMER ASSDA sources articles and advertisements from a variety of contributors and accordingly does not accept responsibility for the accuracy of the contents of this publication nor the suitability of specific applications referred to herein for any particular use. Competent advice should be sought before acting on any matter contained in this publication.
AUSTRALIAN STAINLESS STEEL DEVELOPMENT ASSOCIATION
Growing the market for stainless steel.