AUSTRALIAN STAINLESS Specialising in stainless steel and its applications
Photo credit: Barwon Valley Stainless
ISSUE 70 2020
FEATURE
Screening Melbourne’s drinking water Stainless steel is playing a vital role in delivering effective bulk water intake screens for Melbourne’s water supply. Designed and manufactured in Brisbane, ASSDA Member Aqseptence Group Australia has recently delivered one of the largest passive intake screens in the Southern Hemisphere. Having produced more than 4,000 screens for the last 50 years, this latest milestone achieved a nomination in the hotly contested Process Industries category of the 2019 ASSDA Fabricator Project of the Year Award. In mid-August 2019, Aqseptence Group was engaged by a joint venture of John Holland and KBR to provide design and construct services for a significant capital works project, covering multiple Melbourne Water assets. The screen is used as a bulk water transfer screen for the O’Shannassy Dam, located east of Melbourne. Distributing clean drinking water to most parts of Melbourne, it is a critical asset storing 3.1 gigalitres of water among a series of reservoirs on
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the city’s periphery. The mammoth screen took approximately two months to design and manufacture. The Johnson Screens T96E passive intake measures an impressive 8.6 metres wide and stands 3.6 metres high. It is constructed entirely in grade 316L with a mill finished plate and No. 4 finish wedge-wire and bar. K-Tig welding was used to join 10mm plates to achieve overall plate size to roll into tubes. The entire fabrication was then pickled and passivated. Grade 316L, a standard material of construction at Aqseptence Group, was specified for the grade’s ability to resist general and localised forms of corrosion, a risk even with relatively low chloride inland water sources. Additionally, being easy to source and fabricate, its versatility in taking many forms and profiles is clearly on display.
The intake screen is used to provide an uninterrupted water withdrawal source while protecting assets from foreign matter and most importantly, protecting wildlife by guaranteeing uniform and low through-flow velocities. This fish-friendly screen is also a passive design as it has no moving parts, therefore simplifying maintenance and reliability. Aqseptence Group’s Vee-Wire slot system was used to ensure uniform flow through the screen at a controlled velocity, to protect surrounding marine life. Additionally, using the strength properties of 316L, the screen has sufficient mechanical rigidity to support its own weight along with hydrostatic pressures. Stainless steel was specified due to its low impact on the environment, on both the reservoir and the clean drinking water it supplies, paired with its durability, corrosion resistance and material strength attributes.
Aqseptence Group is now focused on working with the broader network of water infrastructure authorities to help upgrade their water supply assets and continue to service the City of Melbourne for future generations with the use of stainless steel.
ASSDA MEMBER CONTACT Aqseptence Group \ Chris Susanto, Business Unit Manager ANZ – Water Processing Solutions 07 3867 5555 \ asiapacific.water@aqseptence.com \ aqseptence.com 3 – Australian Stainless Issue 70
TECHNICAL
SEVEN WAYS TO PREVENT TEA STAINING
of stainless steel
Handrail abraded to 0.5µm Ra and then electropolished for excellent corrosion resistance.
When used properly, stainless steel enjoys a strong and enduring reputation for visual appeal and structural integrity in a wide range of applications and environments. But, like all materials, stainless steel may become stained or discoloured over time, impairing the overall look. This brown discolouration - tea staining - has been identified in coastal applications in Australia and overseas. In the late 1990s, the newly formed ASSDA Technical Committee researched the reasons for the brown discolouration. ASSDA’s work, in collaboration with the International Molybdenum Association, led to guidelines published in 2001 explaining the causes and remedial techniques. The work was later refined to ASSDA’s FAQ 6. This clarified some of the misunderstandings that have circulated about atmospheric exposure and possible corrosion of stainless steels. It does not deal with immersed exposures. Corrosive chemicals in the atmosphere
Atmospheric conditions
In a clean atmosphere, the relative humidity is sufficient to maintain the thin self-repairing passive film which protects stainless steel. Given that chlorides are known to cause corrosion, locations within line of sight of the sea will tend to corrode, especially with onshore prevailing winds.
Stainless steel will not corrode unless there is a sufficient concentration of aggressive ions (generally chlorides) and there is free water but not a sufficient flow to wash away contaminants. Water will condense on clean metal if the temperature falls below the dewpoint but if there are chloride salts, then there is a lower critical relative humidity (RHcrit) which will form an aggressive salt solution by absorbing moisture from the air. This means that deposited sea salt can cause corrosion although the temperature is still below the dewpoint for a clean surface.
Extensive research using corrosion coupons has classified corrosivity using carbon steel and zinc while measuring corrosives such as chloride and sulphur dioxide – as an indicator of industrial activity. AS 4312 presents maps with bands of corrosion rates (from extreme to low) and corrosion rates with distance from the sea or a bay. For sheltered waters, corrosion rates drop to medium or lower within a few hundred metres, while for exposed areas like Cape Leeuwin in WA, Newcastle in NSW, or Cape Jervis in SA the rates can remain extreme to high for kilometres inland. The AS 2699 series of standards for ties used for brick fixing in walls uses deposited chloride measurements to arrive at similar bands of corrosivity. Those values define zones where increasing thickness of galvanizing or, 304 or 316 must be used successively depending on distance from the sea to achieve the design life in buildings. In rural or urban environments, corrosion of stainless steel is unusual although cosmetic staining can occur from vegetation, chemical spills or blown dust.
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A secondary atmospheric factor is that corrosion rates roughly double for every 10oC rise in temperature; all else being equal. For instance, corrosion staining will be worse in Darwin than in Hobart. Design, cleanability and drainage
Open, bold exposures allow natural rainfall to wash away grime and potentially corrosive deposits. However, drying retained runoff on horizontal surfaces, surface tension at sharp edges, in crevices, or in horizontal abrasion lines on vertical surfaces, all cause increasing corrosivity and do not meet the “bright and shiny” expectations for stainless steel.
Surface roughness and standards
The widely publicised surface roughness of “no more than 0.5µm Ra” for a tea staining resistant surface is codified as 2K in EN 10088.2 which includes a requirement for a clean cut profile, i.e. no flaps or sharp edges. ASTM A240/A480 suggests that a good fabricator can achieve about 0.6µm Ra for a No. 4 finish. ASSDA conservatively recommended finishing with 320 grit for 0.5µm. Ra is readily measured mechanically or by laser reflectance but, because multiple surface profiles can give the same Ra value, samples are frequently used for acceptance tests. Rough surfaces show significant tea staining. Unfortunately, the 0.5µm Ra requirement is sometimes specified for HRAP plate with a typical finish of Ra ~6µm. This causes unneeded expense in removing metal. Both thick HRAP plate and thin 2B (or BA) sheet or coil were pickled as their last processing step. Even with Ra greater than 0.5µm these finishes have good resistance to tea staining. However, a rougher surface is still less cleanable and is generally not as bright. Smooth 2B or BA finished sheet has good resistance to tea staining. There is ample evidence that smoother surfaces resist corrosion better and a mirror polish is the best possible mechanical finish. ASTM A240 and EN 10088.2 have descriptive definitions (for No. 8 or 2P respectively) which centre around high reflectivity and image clarity but do not specify Ra. Electropolishing electrochemically cleans the surface, removes sharp edges and smooths microroughness. It provides a deep lustre but not necessarily a clear reflection. However, it only slightly reduces Ra, e.g. 0.7 to 0.5 µm for a linished strip. Electropolished surfaces have excellent resistance to tea staining. Chemical cleanliness of the exposed surfaces
Stainless, carbon or galvanised steels may be fabricated in adjacent areas and carbon steel can contaminate the stainless steel either as floating grit or if tooling is used on stainless steel after processing carbon steel. Contamination during transport or handling is also possible. Any moisture will immediately corrode the carbon steel and cause a large brown stain compared to the contaminating particle - this is not tea staining. The illustration shows a rooster tail of carbon
Rough finish on support post causes significant tea staining.
steel contamination on a stainless steel surface from cutting Colorbond® nearby. The contamination can be removed by pickling or, more slowly, by a passivating nitric acid application. The widespread pale spots are light tea staining. In addition, an oxidising passivation treatment after the final metal removal substantially improves corrosion resistance, partly because the final passive film is thicker and has a higher chromium to iron ratio. However, for freshly abraded surfaces, the sulphide inclusions inherent in all steels are initiation sites for corrosion unless they are removed by a passivating acid. Bar product has more inclusions with at least 10 times the sulphur content of sheet or plate to aid machining. Nitric passivation does not change the appearance of even a mirror polished surface but does significantly increase its corrosion resistance. Further details of pickling and passivation are given in ASTM A380. What alloy should be selected
An ASSDA/IMOA selection tool is available by searching for ‘stainless-steel-selection-system’ on www.imoa.info. It asks about environment, finish, orientation and maintenance before providing a recommended material from 304 for urban or rural exposures up to 2205 for severe marine. It does not include ferritics mainly because they are not as widely used in welded fabrications. Alloys with similar or higher corrosion resistance (as assessed by PRE) could be substituted. Super alloys are not usual for atmospheric exposures. Maintenance – natural and/or applied
Stainless steel is low maintenance but not no maintenance. A rule of thumb is that if an adjacent window (or glass screen) needs washing, wash the stainless steel. FAQ 6 has recommendations including consideration of retained deposits and rain washing. One sub-tropical beachside council has implemented a 3 to 4-month cycle of a high pressure wash with low chloride water and detergent (and possibly a zero chloride solvent) before a fresh water rinse. Domestic cleaners, even non-abrasive ones, are not recommended as some have chloride activators and, because of their hygiene image, may have some bleach - which are both potentially detrimental.
2B finish on tank wall with minor tea staining and a rooster tail of rusting carbon steel.
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INDUSTRY
STAINLESS STEEL – THE RIGHT CHOICE FOR
an environmentally sustainable upgrade Stainless steel provides a cutting edge and environmentally friendly solution for industrial applications. Dow Chemicals, a global chemicals manufacturer, recently completed a major upgrade of the wastewater treatment system at their Victorian Point Henry coatings plant. The plant manufactures acrylic emulsions which find use in numerous applications including house paints. ASSDA Members Stirlings Performance Steels and Barwon Valley Stainless provided supply and fabrication services for this impressive wastewater treatment facility upgrade.
treatment plant upgrade due to their knowledge and expertise of wastewater treatments, both local and interstate. Their quality workmanship was reflected in this project as they provided civil and structural works, tank and pipe spooling fabrication, site installation and pump station commissioning. With over 25 years’ experience and competence in stainless fabrication, they were able to work successfully within Dow’s project time and location constraints.
Wastewater produced in the production facility is pumped into flocculation tanks for settling and the clear supernatant is sent for further biological treatment. This treated water is recycled back to production but is also used for irrigation on site to minimise freshwater consumption.
Stirlings Performance Steels supplied the entire portfolio of materials to Barwon Valley Stainless. This included cut-to-length large bore pipe, structural rectangular hollow section and various pipe fittings as well as laser/plasma profiled plate which were all in grade 316/L.
Geelong based Barwon Valley Stainless is a preferred Dow contractor and was selected to provide the complete scope of services for the wastewater
Reducing environmental footprint in industrial applications is important and material selection is a critical step in both maximising the lifetime of plant
and equipment, while minimising the need for maintenance and servicing. This upgrade successfully satisfied both these requirements with the use of stainless steel. Grade 316 is a popular material of construction where water is processed with relatively low chlorides at ambient temperature. It provides an optimal cost benefit compared with other steel-based alternatives which require coating or lining. Additionally, the close proximity of the site to Victoria’s Corio Bay requires resistance to corrosion from airborne seawater. According to Ben Arlidge, Project Manager at Dow, “Stainless steel has provided the perfect mix of performance, workability and cost for our new wastewater treatment facility.” The plant upgrade is a major step in providing long term certainty to the local Moolap economy, as well as in strengthening the Australian supply chain of domestic market paint products.
Photo credit: Barwon Valley Stainless
ASSDA MEMBER CONTACTS Barwon Valley Stainless \ Shaun Johnstone, Director \ 03 5248 5086 \ shaun@barwonvalleystainless.com.au \ barwonvalleystainless.com.au Stirlings Performance Steels \ Mark Hammill, Sales Manager \ 0447 792 516 \ salesvic@stirlingsps.com \ stirlingsps.com 6 – Australian Stainless Issue 70
ART & DESIGN
Stainless at first sight Located in the foothills of Perth, Aegis Amherst opened in July 2019 providing residential aged care in Canningvale, Western Australia. Set at the core focal point of the aged care facility presents a grand stainless steel balustrading ramp façade. ASSDA Member and Accredited Fabricator Balustrading WA were engaged by Absecon to fabricate and install a modern, safe, purposebuilt ramp that would encompass strength and aesthetic attributes.
Strength and beauty
The custom-designed ramp features an impressive 170 metres of grade 316 stainless steel tube. The handrails were manufactured from 50mm diameter stainless steel round tube. All stainless steel components were specified with a No. 7 high polish finish, supplied by several local suppliers including ASSDA Member, Stirlings Performance Steels. Mild steel flat bar was also used as the infill panels. Grade 316 stainless steel was specified primarily for its longevity, aesthetic appeal, and material strength. In addition, it is a durable and long-lasting alternative to competing materials. Balustrading WA were heavily involved in the design brief and process, due to the extensive curvature inherent in the site. A range of advanced surveying techniques had to be used to ensure the balustrading was fabricated and installed correctly. This included using 3D image scans set into GPS grid location co-ordinates, rather than manual site measuring or templating as with more straightforward designs. As an example, the stainless steel support posts were scanned and fabricated individually to size to ensure correct fitment. In total, the project took just over 12 months to complete. The stainless steel ramp reflects the aged care’s cornerstone of their philosophy, by providing their residents with an environment that is comfortable and safe while delivering an aged care that helps them lead active, mobile and healthy lives. This striking ramp facade continues to be the “hero” image for the facility, as stainless steel has once again delivered in compliance and material strength while fulfilling design and aesthetic needs. Photo credit: Balustrading WA
ASSDA MEMBER CONTACTS Balustrading WA \ Cliff Churchill, General Manager \ 08 9208 2900 \ cliff.churchill@balustradingwa.com.au \ balustradingwa.com.au Stirlings Performance Steels \ Matt Smith, Sales Manager \ 08 9366 6700 \ matts@stirlingsps.com \ stirlingsps.com 7 – Australian Stainless Issue 70
ASSDA’s Associate Membership Program
aims to formally engage and collaborate with specifiers and end-users to provide the support and resources required to make confident decisions on designing, specifying and using stainless steel materials. Membership benefits: • Free (limited) independent technical support and assistance in engaging with the local value chain • Discounted rates to educational webinars & online training • Free and/or discounted rates to ASSDA publications, including the 2020 Australian Stainless Reference Manual • Access to free lunch-and-learn stainless steel presentations
Work with ASSDA to support local industry and stainless steel manufacturing
Associate Membership is FREE to end-users and specifiers, with no joining or annual fees. For more information and to become an Associate Member, please contact ASSDA: +61 7 3220 0722 / assda@assda.asn.au assda.asn.au
PLATINUM MEMBERS:
GOLD MEMBERS:
SILVER MEMBERS:
Stanch Stainless Steel Co., Ltd.
Acerinox \ Amity Pacific \ Aqseptence Group \ Arcus Wire Group \ AusPress Systems \ Austral Wright Metals \ Australian Stainless Distributors \ Callidus Welding Solutions \ Ching-Hann Industries Co., Ltd. \ Chromeni Steels Pvt. Ltd. \ Dalsteel Metals \ Fagersta Steels \ Laxcon Steels Limited \ Metal Centre Australia \ Prochem Pipeline Products \ Sanwa \ Stainless Steel Wire & Mesh \ Vulcan Stainless \ Yue-Seng Industrial Co., Ltd.
Stoddart YC Inox Co., Ltd.
AUSTRALIAN STAINLESS MAGAZINE MORE INFO: Enquiries or further information on any material presented in this publication should be directed to ASSDA: Level 9, 307 Queen St, Brisbane, Qld, Australia 4000 \ +61 7 3220 0722 \ assda@assda.asn.au \ 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 are targeted group of 5000+ in the Australian stainless steel industry. Rates available at www.assda.asn.au. CONTACT: Tina Belesis, Editor: tina@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.