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Terrigal Boardwalk - Stainless sets the scene

The seaside town of Terrigal on the New South Wales’ Central Coast has welcomed a new addition to its foreshore with a scenic walkway using stainless steel.

The long-awaited Terrigal Boardwalk connects the existing pedestrian networks of the Terrigal Beach promenade and The Haven, providing a safe and accessible route around the headland. The new attraction provides social, health and economic benefits for the local community, allowing visitors and tourists to enjoy the public space and ocean front area.

The project was jointly funded by the Central Coast Council ($2.9M) and the NSW Government’s Restart NSW Regional Growth Environment and Tourism Fund ($2.98M). The Terrigal Boardwalk’s construction included a restoration of the adjacent rockpool, a new disability-access ramp and pathway to link the rockpool and boardwalk.

Engineered and designed by Arup, the boardwalk structure has a 50-year design life, demanding a robust design to ensure durability and longevity. The elevated boardwalk is 277m long and 3m wide, and complements the surrounding natural environment with its blackbutt timber decking and stainless steel balustrading.

The construction comprises of a reinforced concrete suspended deck structure, a suspended structural steel viewing platform with fibre-reinforced plastic open mesh, sandstone block revetment and a retaining wall ramp structure. For the bridge deck, 7.5m is the typical span of the precast deck planks between concrete headstocks on steel tubular piles. Solid concrete deck planks were chosen to protect the timber boardwalk above from wave damage and minimise overtopping for users. The boardwalk sits approximately 4.5m above sea level to be just clear of wave crests during strong weather events.

Materials selection was critical to meet the specified design life, with consideration given to the foreshore’s high level weather events and salt exposure. Grade 316L stainless steel was specified for the balustrading on both sides of the boardwalk, ramp handrailing and the rock platform staircase.

While aluminium was considered during the design phase, stainless steel was chosen due to the material’s proven performance, corrosion resistance and durability in a marine environment, and aesthetic benefits in conjunction with the timber decking and handrail specified. In addition, a costing exercise conducted by Arup presented the long-term benefits of using stainless steel outweighing its additional upfront cost over aluminium.

Constructed by Land and Marine Group, the project involved a high level of collaboration between multiple local suppliers and service providers to meet the exacting demands of the specification. 

ASSDA Member Synergy Engineering was engaged to fabricate and install the stainless steel handrails, balustrades and stairs, spotted gum timber railing and the structural steel viewing platform. The project involved the stainless steel fabrication of 247 balustrade panels, 119m of handrail balustrade and an 8-step 1200mm wide staircase with fibre-reinforced treads. TIG welding techniques were used throughout the fabrication and installation process to ensure precision and a clean aesthetic.

ASSDA Member Atlas Steels supplied over 15t of 316L stainless steel, including 3402m of 30x8mm flat bar and 1656m of 70x10mm flat bar. The project was undertaken in the midst of the COVID pandemic, presenting a number of challenges with the supply of imported stainless steel material and shipping lead delays. As a result, Atlas Steels took the initiative to laser cut stainless steel plate to size and engaged ASSDA Member Decoware Australia to polish the material to specification. Starting with a coarse 80 grit through to a 400 grit finish, a surface finish of Ra <0.5 µm was achieved. The resourcefulness of local service and skill assisted in meeting the project program, delivering a resolution for the unprecedented challenges.

A small proportion of material was sourced from ASSDA Member Viraj Profiles, and ASSDA Member Vulcan Stainless supplied an additional 11t of laser cut 5mm, 10mm, 16mm and 20mm 316L stainless steel plate for the project.

Following fabrication, all stainless steel balustrade panels and handrails were electropolished by ASSDA Member Australian Pickling & Passivation Service and delivered directly to site for installation by the Synergy Engineering team.

The beautiful coastal boardwalk features a viewing platform, integrated seating, LED lighting and access to the rock platform. Offering uninterrupted views of the Pacific Ocean and beyond, the Terrigal Boardwalk is certain to meet the performance requirements of its design with its quality construction and use of stainless steel. 

The Terrigal Boardwalk officially opened on 14 April 2021, with its first steps taken by local crowds alongside the New South Wales Premier Gladys Berejiklian, Parliamentary Secretary for the Central Coast, Adam Crouch, Central Coast Council Administrator, Dick Persson, and the Council’s new CEO, David Farmer.
 
    

This article is featured in Australian Stainless Magazine issue 72, 2021.

Structural design of stainless steel

Stainless steel is used for a wide range of structural applications including:

  • Beams, columns, platforms and supports in processing plant for the water treatment, pulp and paper, nuclear, biomass, chemical, pharmaceutical, and food and beverage industries;

  • Primary beams and columns, pins, barriers, railings, cable sheathing and expansion joints in bridges;

  • Entrance structures, canopies, cladding and support systems for masonry;

  • Security barriers, blast walls, hand railing and coastal structures. 

Case studies of a range of structural applications are available at the case studies section of  www.teamstainless.org/resources/information-center-for-stainless-steel-in-construction.

This introduction to structural design in stainless steel aims to highlight differences between the material properties and structural behaviour of stainless steel and conventional carbon steel normally used for structural purposes, e.g. grade 350 to AS 3678 and AS 3679.

It should be noted that stainless steel structures should not be simply designed using design standards for carbon steel, such as AS 4100 and AS 4600, because of the significant differences between the mechanical properties of carbon and stainless steels.

Selection of an appropriate alloy of stainless steel is the first step in any design process.

Austenitic stainless steels are most widely used for structural applications, though the use of duplex stainless steels is increasing, where it is possible to exploit the benefit of high strength (around 460 MPa, compared to a strength of around 220 MPa for austenitic stainless steels). This can be particularly valuable in weight-sensitive structures like bridges or on offshore topsides. Duplex stainless steels are more likely to be used in heavier gauges. Ferritic stainless steels are also suitable for structural applications, offering a corrosion resistant alternative to many light gauge galvanised steel applications. They are generally used in gauges of 4 mm and below although the 12% chromium utility alloys are used in thicker sections (vehicle chassis or high temperature ducting) when minor rust staining can be allowed.

Material properties

From a structural viewpoint, the main property that distinguishes stainless steel from carbon steel is the stress-strain response. In contrast to carbon steel, for which the stress-strain curve may be modelled as bi-linear for most compression and flexural member design purposes, the stress-strain curve of stainless steel is generally highly non-linear and without a distinct yield point. Figure 1 compares the stress-strain characteristics of various stainless steels with carbon steel for strains up to 0.75% and Figure 2 shows typical stress-strain curves to failure. (The figures show stress-strain curves which are representative of the range of material likely to be supplied and must not be used in design.) The distinctive mechanical properties - considerable strain-hardening and ductility - make austenitic and duplex stainless steel particularly well suited for structures required to withstand accidental loading due to their high energy absorption characteristics.

In the absence of a clear yield stress, it is common practice to define an equivalent yield stress for stainless steel by using a proof stress, usually the 0.2% proof stress. (By definition, the plastic - or permanent - strain at 0.2% proof stress is 0.2%.) The proportional (or linear) limit of stainless steels’ deflection ranges from 40 to 70% of the 0.2% proof stress.

As a result of the non-linearity, stainless steel loses stiffness at low stress levels. This affects the design rules for members that rely on stiffness to transfer loads, notably compression members and unbraced flexural members.As well as nonlinearity, the stress-strain characteristics of stainless steel also display non-symmetry between tensile and compressive behavior and anisotropy, i.e. differences in behaviour of coupons aligned parallel and transverse to the rolling direction. In general, anisotropy and non-symmetry increase with cold work and so are more significant in the design of lighter gauge heavily worked sections, rather than thicker walled structural sections.

It is possible to enhance the strength of austenitic stainless steel by cold-working to a much greater extent than for carbon steel.

The initial modulus of elasticity (Eo) of stainless steel alloys is slightly lower than that of carbon steel.

The behaviour of stainless steel at elevated temperatures differs to that of carbon steel because of the metallurgical differences caused by the composition. Stainless steel retains a greater proportion of its strength at temperatures above about 550 °C and shows better stiffness retention at all temperatures, which is important in design against fire for components such as blast and fire walls.

The coefficients of expansion (CTE) of austenitic stainless steel alloys are larger than those of carbon steel. At the same time, the thermal conductivity is lower. While the CTE is important in determining thermally  induced stresses and deformations, the combination of larger coefficient of expansion and lower thermal conductivity has the effect of substantially increasing the risk and possible extent of welding distortions than those experienced in fabricating carbon steel structural member. The duplex grades have similar thermal conductivity to the austenitics but with 20% lower CTE so the risk of welding distortion is slightly lower than with austenitics. 

Specifications and reference documents for design of  stainless steel structures

American Society of Civil Engineers (ASCE) has revised ASCE 8 Specification for the design of cold-formed stainless steel, applicable to lighter gauge austenitic and ferritic material in the annealed and temper-rolled condition (Reference 1). The 2002 version has been substantially updated because of extensive research work and will be issued late in 2021. This includes alternative treatments of compressive loading, i.e. effective width and direct strength. The structure of AISC 8 will be familiar to those using AS/NZS 4673:2001 although 4673 has now been withdrawn as an aged standard.

Also in 2021, the American Institute of Steel Construction (AISC) will release a new standard (reference 2) AISC 370 Specification for Structural Stainless Steel Buildings to reflect the substantial increase in the use of heavy structural stainless steel sections. It includes hollow sections as well as welded, hot rolled and bar products. It will be accompanied by AISC 313 Code of Standard Practice for Structural Stainless Steel Buildings (Reference 3) and an updated 2nd Edition of the 2013 AISC Design Guide 27: Structural Stainless Steel.

The Eurocode for stainless steel design, EN 1993-1-4, covers welded, hot rolled and cold formed products made from austenitic, duplex and ferritic alloys, at room temperature and in fire (Reference 4). The Design Manual for Structural Stainless Steel (4th Edition) was published in 2017 and gives essential information needed by designers concerning alloy selection, durability, material properties, design rules and fabrication, in accordance with EN 1993-1-4 and other European standards (Reference 5). A Commentary explains how the design expressions in the Recommendations were derived and gives background information and references. Design Examples demonstrate the use of the Recommendations. Section property and member capacity software is also available, all aligned to EN 1993-1-4.

This Design Manual and these supporting design tools are freely downloadable from www.steel-stainless.org/designmanual.

This article has been extracted from the 2020 Australian Stainless Reference Manual, available for purchase at assda.asn.au

REFERENCES: 1. ASCE 8-02 Specification for the Design of Cold-Formed Stainless Steel Structural Members, SEI-ASCE 8-02.  \   2. AISC 370-2021  \   3. AISC 313-2021  \  4. EN 1993-1-4:2006+A1:2015 Eurocode 3. Design of steel structures. General rules. Supplementary rules for stainless steels.  \   5.  Design Manual for Structural Stainless Steel, SCI Pubilcation P413, The Steel Construction Institute, 2017 (available from www.steel-stainless.org/designmanual).



This article is featured in Australian Stainless Magazine issue 72, 2021.

Lighting up Chinatown

Stainless steel lanterns now adorn the streets of Melbourne’s Chinatown, celebrating the cultural character of the longest continuous Chinese settlement in the western world.

Chinese lanterns are a symbol of Chinese culture worldwide, initially used to provide light and later adopted for religious worship, decoration and celebration. Traditionally made from silk or paper, the City of Melbourne recently evolved the Chinese hanging lanterns featured on Little Bourke Street from cloth to stainless steel.

In extensive consultation with the Chinatown Precinct Association, the City of Melbourne and GHD (Structural Engineers) reimagined the classic lantern with a detailed design that preserved the traditional aesthetic while examining a number of considerations. 

Durability and product life cycle were strong factors to reduce maintenance and regular replacement of the lanterns. Strength-to-weight ratio and resilience to local weather conditions was also important, with the completed design required to stay below 7kg to be viable for use on the existing catenary lighting system.

ASSDA Member Draffin Street Furniture worked closely with the City of Melbourne to bring the design to life, assisting with the materials selection and manufacturability of the lanterns. Two prototype lanterns were installed at the corner of Heffernan Lane and Little Bourke Street to test the design and seek feedback from local traders and the Chinatown Precinct Association.

Powder coated aluminium was initially selected as the design material however, stainless steel superseded the specification primarily for its strength and the ability for a thinner section of material to be used (0.6mm stainless steel sheet vs. 1.22mm aluminium sheet). In addition, stainless steel offered a more sustainable solution with a 25-year design life and little-to-no maintenance.

The final design resulted in a 700mm wide by 500mm high spherical lantern made from 316 grade stainless steel, powder coated with a luminous, metallic red colour. In Chinese culture, the colour red symbolises good fortune and joy. 

The lanterns were formed using laser cut 0.6mm sheet, with each panel formed into shape and fixed to a central aluminium frame. The custom-designed lanterns were manufactured by Draffin Street Furniture, and stainless steel material for the project was supplied by ASSDA Member Steel Color Australia.

80 new permanent lanterns were installed on the existing catenary lighting system, which was originally manufactured and supplied with the assistance of ASSDA Member Ronstan Tensile Architecture in 2009. The linear grid catenary suspended from the street’s buildings uses 316 grade stainless steel rectangular frames spaced equidistantly to hold the grid form, while permitting the suspension cables to connect to buildings at different heights depending on the availability of structural connection points. Designed to enhance the character of the precinct with Chinese lanterns and other iconography, the decorative and functional stainless steel catenary lighting system continues to perform structurally 12 years on since its installation.

Installation of the new hanging lanterns was completed at the end of July 2020. Brought to life using local design expertise and stainless steel, the lanterns maintain its symbolic heritage and will continue to provide a festive welcome to visitors for at least the next 25 years.
       

Image: @rayofmelbourne for @cityofmelbourne

This article is featured in Australian Stainless Magazine issue 72, 2021.

Stainless steel ignites  luxury, style and warmth

ASSDA Member and Accredited Fabricator Southern Stainless have taken outdoor entertaining to a new level with their custom-designed and Australian made stainless steel gas fire pit.

Alfresco living is a strong part of Australian culture, and Gold Coast based Southern Stainless saw an opportunity to bring warmth and elegance to the outdoor space with the use of stainless steel. Starting the design process in 2015 and with over 18 months of research and development, a stainless steel gas fire pit was born, meeting both Australian Standards and gas regulations. 

Elegant and simplistic in its design, Australia’s harsh coastal conditions inspired the firepit’s construction. Grade 316 stainless steel sheet with a 2B finish is used to construct the sleek body, door and burner tray, and 1.5mm 316 stainless steel tube is used to assemble the burner and legs. The fire pit has a stainless steel burner mounted into an enclosure to accommodate toughened glass pebbles surrounded by safety glass. Gas filters through the pebbles and ignites fire, giving the appearance of a floating flame.

Southern Stainless’ fire pits are available in square and round models, and measure 1m x 1m or 1m diameter. Both are fitted with two flame failure devices that automatically shuts off the gas if the primary pilot blows out. The flame failure devices provide additional safety while also making the fire pit extremely effective in windy conditions.

The fire pits have an LPG bottle compartment or can be designed to be plumbed into gas. In both instances, the fire pit comes with the gas controls and burner fully assembled. Only the glass safety sides need to be installed along with the toughened glass pebbles. If configured to be plumbed into natural or LPG gas, the appliance can easily be connected by any qualified gas plumber, or if ordered with an LPG bottle compartment, no installation is required.

Stainless steel is the clear material of choice when considering the great Australian outdoors. Grade 316 stainless steel has excellent corrosion resistance properties with an increased ability to resist pitting and crevice corrosion in warm chloride environments when compared with grade 304. It resists rusting in virtually all architectural applications, and is a durable, heat resistant and aesthetically appealing material option.

Stainless steel fire pits are built-to-last and combine physical warmth with visual luxury, offering year-round ambience to cater for the way of Australian outdoor living.


 

This article is featured in Australian Stainless Magazine issue 72, 2021.

 

A new twist on stainless design

With a striking and innovative design evoking visions of the Singapore based Helix Bridge, stainless steel has formed an integral part in creating one of Sydney’s most exciting new structures.

Commissioned by Landcom as part of the Lachlan Line Precinct development project in North West Sydney’s Macquarie Park, the yet to be officially named cyclist bridge provides visual flair, safe accessibility, and excitement to the area. In an area with typically heavy traffic congestion, the project’s promotion of reduced car dependency creates a significant positive impact to the surrounding environment.

The design is the first of its kind in Australia, utilising a double helix arrangement with a varying diameter along its curving 178m length. While the design elements certainly lend themselves well to aesthetics, structural requirements dictated much of the overall shape. A steel truss arrangement is used, required for the long sections spanning the multiple roads below its footprint. The diameter of the spiral increases at the bridge supports and tapers along its span.  At its narrowest, it is 5.5m in diameter, and 7.8m at its widest.

Approximately 170t of 2205 grade duplex stainless steel was used, along with around 220t of structural mild steel. Due to the large quantity of material required, multiple distributors supplied material mostly on an indent basis, with some delivered ex-stock. ASSDA Members Midway Metals, Stirlings Performance Steels and Vulcan Stainless all supplied material, with the majority of plate (up to 80mm in thickness) produced by ASSDA Member Outokumpu, managed through their Melbourne office. 

A minimum 100-year service life with minimal maintenance (becoming increasingly common in the design of bridges) was a key criterion, particularly important for the hard to access structural components. From the beginning, 2205 duplex grade presented as an ideal material, thanks to its hybridised microstructural properties granting it superior mechanical properties to many forms of mild and stainless steel. 

Put simply, being stronger allows for thinner sections to be used or, alternatively, more scope for efficient design such as larger spanning or increased resistance to bending moments. Mild steel was retained  for the helical outer structure, and painted blue, which was a central design requirement. 

Arup proposed duplex stainless steel for the deck structure and wearing surface within the helix due its increased strength to weight  properties whilst maintaining high durability performance.   

Outokumpu played an instrumental role in advocating the use of the material properties of duplex grade at the early design and concept stages. Backed up by global materials experts and with a wealth of expertise in supplying stainless materials for bridges all over the world, Outokumpu aimed to provide a technical solution through the use of duplex stainless, rather than simply tender for the supply of material. “The use of duplex stainless steels in bridges around the world is becoming more and more the material of choice, so it was great to see Arup in Australia embrace it in its design”, said Con Logos, Vice President APAC at Outokumpu. “A special thanks to George Miech from my team for his tireless effort in the early stages, working closely with both Arup and RMS to have duplex stainless specified”. 

Outokumpu also assisted the fabricator and the end client, Transport for NSW, with expertise, advice, and preliminary procedures in welding the material, particularly vital with the thicker sections which require great care to ensure optimal material properties are realised in the weld and adjacent areas.

The bridge was fabricated in Sydney in four modules, which were trial assembled prior to being delivered to site, where the four segments were positioned and secured over the course of four weekends. Specially designed lifting assemblies were necessary to ensure the segments were not overstressed. 

As bridge design increasingly demands greater durability, aesthetic and creative licence and structural performance, stainless steel, of the duplex family in particular, presents a wonderful option now and into the future.

Photo credit: Landcom

This article is featured in Australian Stainless Magazine issue 71, 2021.

 

Comparisons of hot and cold formed stainless steel

When comparing hot and cold formed stainless steel, the first question you would ask yourself is: are there any chemical differences between the two? ASSDA has previously published articles on the various surface finishes including the few hot and multiple cold finished processes, however this article concentrates on the differences. 

Since the 1970s, most stainless steel is produced by melting in an Electric Arc Furnace (EAF) and then the molten stainless steel is transferred to an Argon Oxygen Decarburisation (AOD) vessel or, less commonly, a Vacuum Oxygen Decarburisation (VOD) vessel. These processes control impurities such as carbon, sulphur, nitrogen, hydrogen and other impurities which could form oxide precipitates. For critical applications such as aerospace or precipitation hardening alloys, further refining is possible, but this is a smaller market. Critically, in AOD, using the injection of inert argon as the stirring agent into the melt allows control of nitrogen additions, e.g., for duplex or high austenitic stainless steels.  

Chemistry

The basic chemistry of a specific grade of stainless steel is the same regardless of how it is subsequently shaped, i.e., as hot or cold rolled, hot forged, cold drawn/shaped or simply cast –  with the proviso that cast stainless steels typically have more chromium and (often) more silicon than their wrought counterparts. In addition, even if cast products have been stress relieved, their microstructure is dendritic so that there can be significant composition differences (localised differences in corrosion susceptibility) between the early solidifying dendrites and the final bulk solidification.

Hot formed

Producing hot formed stainless steel is deceptively simple as shown in the graphic. Currently, for about 95% of production, the molten metal is decanted from the AOD into a cooled continuous caster and emerges horizontally as a slab. The microstructure in the slab is columnar from the outsides (because of the cooling by the caster walls) with a relatively uniform equaxial microstructure in the centre. It is also covered with heavy black oxide scale with a chromium deficient layer underneath – as with weld tints. Typically, the slab is then surface ground to remove solidification features and the scale which would both otherwise be incorporated into the surface during subsequent rolling. The slab is then charged into a reheating furnace and hot rolled to homogenise the microstructure and provide either plate or coil as the product form. The grains will now be more oriented along the rolling direction. The microstructure is then further refined (and internal stresses reduced) by annealing above 1000oC.

Unless the steel is to be used where appearance and maximum corrosion resistance is not critical, e.g., in a furnace, then after hot rolling it would be shot blasted to break up the scale and then pickled. The pickling causes the dimpled appearance of a Hot Rolled Annealed and Pickled (HRAP) plate surface because the pickling acid attacks the base metal at the defects in the black oxide scale. It also gives a typical surface roughness of 5 or 6 µm Ra. There is a potentially cosmetic corrosion issue if the (typically) fast pickle does not completely remove any shallow intergranular oxide penetrations, however this is unusual. For long product such as angles or channels, another visual distinction is that the edges meet at 90o compared to the radius of curvature determined by the thickness and ductility of a cold rolled product.

Cold formed

Cold rolled flat product is quite different because it usually starts at room temperature with a dimpled surface and finishes with thinner material – and watching the increase in speed of the sheet as it gets thinner is quite startling. There is a significantly more elongated microstructure along the rolling direction, and this enhances the anisotropy in transverse to longitudinal strength compared to the relatively slight effect for hot rolled material. Long product is not cold rolled but more correctly it is cold  shaped or formed.

The increase in strength with cold work can be substantial, especially in thin materials as the cold work increase can enhance the strength of the full depth. As an example, the table from ASTM A666 data shows the substantial change in mechanical properties for 304 from annealed to half hard, i.e. half the absolute maximum possible strength – which would have negligible ductility.

Effect of cold work on strength and ductility of 304

One effect of the increase in strength with cold work is that the limit of proportionality will increase with cold work, i.e., the linear deflection occurs up to a higher stress. The reduction in break elongation is simply reflecting the proof stress closing on the tensile stress from 40% to 73% as shown below.

Variation of thickness tolerances for cold and hot rolled materials

There are also differences in the tolerance between cold and hot formed material as shown by comparisons in A480 (flat product – sheet vs. plate) and A484 (sections). However, it is not as simple as “hot formed is less precise than cold formed” as seen below. 

Surface finish

Often it is important to consider appearance and corrosion resistance to the “bright and shiny” benchmark. Hot rolled material is always going to be dimpled, even when it is electropolished and exhibiting a brilliant lustre. It will be marginally more difficult to clean than a smoother cold rolled surface but abrading the surface to give a roughness of less than 0.5 µm Ra is counterproductive. You lose the passive stainless steel and an abraded surface potentially has sulphide inclusions exposed compared to the original pickled, sulphide free HRAP surface.

The inherent roughness of a cold rolled sheet decreases steadily as the plate is rolled thinner as shown in graph. It shows the decrease of Ra from the crushing of the peaks left from the hot rolling as the sheet gets thinner. The graph is for cold rolled annealed and pickled (2B) material and is useful when someone asks for a 2B finish for a thickness not in the band. However, thickness of pickled materials is not relevant to the corrosion resistance whereas the Ra is critical to an abraded surface both for reasons of cleanability and possible crevices from torn surface flaps plus, if not passivated, exposing sulphide inclusions.

 

This article is featured in Australian Stainless Magazine issue 71, 2021.

 

Award-winning stainless food plant

World-class processing systems demand high quality products, innovative features, and long-term yield increase, all of which have been delivered through superior workmanship, engineering, and the use of stainless steel.

ASSDA Member, INOX Australia, was engaged by a Melbourne based stock and soup manufacturer to design the integral process, fabricate, install, and commission a beef, chicken, seafood, and vegetable stock processing system. The processing system is entirely fabricated in stainless steel as it has been essential to the project design and fabrication, being the material of choice in demanding hygienic environments that involve high heat. 

Exceeding their client’s expectations, INOX supplied a processing system that provided multiple innovative features, winning the 2019 Food & Beverage Industry ‘Innovative Technology of the Year’ Award, and being nominated for ASSDA’s 2019 Fabricator Project of the Year Award. This extraordinary processing system features a single user operational interface, safe and ergonomic handling of the product during the process from start to finish and hygienic design of the process including zero wastage at end of production. It also improved the yield of raw materials by pressure processing instead of traditional atmospheric process.

The system works by depositing 1000kg of raw materials into a stainless steel basket which is lifted by an electric hoist into the automatically opened pressure vessel. The touchscreen operational interface is used to set and supply the water volume. The process is fully automatic to the set parameters and then alarms when the process is completed. Following the cooking procedure, the CIP (Clean In Place) water is circulated through the heating jacket of the vessel which serves two purposes. The first is to cool the cooking vessel to a temperature that allows the product to be discharged, and the second, to use the heat recovered from the cooking vessel to heat up the cleaning water. This reusable use of heating allows for no external heating of the cleaning water.

The liquid stock produced is then pumped through a specially designed filtration system, to a holding tank which is then ready for the product to be received by the external filling line. The stainless steel basket is then removed from the vessel and the waste product is dumped into a hopper underneath the basket, ready to be removed to a disposable waste bin. The basket is then cleaned within the vessel during the CIP process and does not exit the food processing room at any point, ensuring the equipment is cleaned and cannot be contaminated externally. 

An impressive 5000kg of 304 and 316L grade stainless steel was used to complete the project. All stainless steel material was supplied by ASSDA Members, Midway Metals, Vulcan Stainless and Tubesales Stainless. This included stainless steel tube, pipe, plate and sheet with 3mm to 12mm thickness. Several components (with thicknesses up to 75mm) required a large amount of specialised machining. The material was mechanically polished where required to achieve a better than 0.8 µm Ra surface finish. This superior material of choice meets the project’s sanitary requirements, offers structural integrity and excellent corrosion resistance in high temperature applications. 

 

This article is featured in Australian Stainless Magazine issue 71, 2021.

 

Stainless steel – a mainstay in water assets

A mainstay in the processing of sewage water in water recycling applications, stainless steel once again plays a critical part in working towards a sustainable future.

Western Water Treatment Plant (WWTP), south of Werribee in Melbourne’s Western District, is a critical asset responsible for processing around half of the city’s total sewage. The process requires a massive footprint, where a series of large lagoons use anaerobic (without oxygen) and aerobic (with oxygen) bacteria to sequentially break down and clean the feed water of solids and gases. The resultant recycled water is used for multiple non-drinking purposes, including irrigation and firefighting. 

WWTP is also largely energy self-sufficient. This energy is captured during the sewage treatment process by combusting biogas, which is captured under the covers. Biogas is used to meet much of the Plant’s electricity needs – preventing hundreds of thousands of tonnes of carbon dioxide entering the atmosphere each year. 

The site carries significant environmental importance to both the immediate and wider areas. Biogas production from the process is used to meet all the Plant’s energy needs through on-site power generation. The Plant is an enormous site – almost the same size as Phillip Island and a world-renowned wetland, declared a Ramsar site in 1983. It is home to many species of flora and fauna and a haven for birdwatchers – in summer it can host more than 100,000 birds in a month.

With current capacity concerns in the existing plant network, stretching back 120 years, and a forecasted increase in processing demands due to a growing city, the need for an additional nutrient removal plant (to complement the existing two) was established. More efficient in design and with more advanced monitoring and controls to provide class A recycled water, the new plant provides an additional 140ML of treated water per day. The plant was designed by Jacobs and built by UGL and CBP Contractors, with commissioning in 2019.

Grade 316L stainless steel was selected as a default material for the pipework, in 2B finish. Offering strong corrosion resistance even against contaminated effluent water, its ease of fabrication and ability to be installed without the need for coating and subsequent maintenance was also important.

ASSDA Member and Accredited Fabricator Roladuct Spiral Tubing was selected to manufacture and supply approximately 50t of spiral welded large diameter pipe, ranging from 300 to 1422mm in diameter. Feed material was supplied  by ASSDA Member, Midway Metals to Roladuct’s  Melbourne manufacturing site. 

Roladuct was nominated in 2019 for the ASSDA Fabricator Project of the Year Award, with judges impressed by the quantity of stainless steel used, as well as the significant environmental benefits realised by the plant upgrade.

As water assets continue to be upgraded and optimised for a growing country, stainless steel will continue to play a vital role in providing material performance and plant reliability for years to come.

 

 Photo credit: Roladuct Spiral Tubing

This article is featured in Australian Stainless Magazine issue 71, 2021.

 

Posted 25th September 2009

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Australian Stainless is a leading industry magazine devoted to showcasing the unique diversity and durability of stainless steel. Since its inception in 1993, Australian Stainless has assisted and encouraged specifiers and end users of stainless steel, with a focus on local fabrication.

For 17 years, Australian Stainless has been enjoyed by more than 8,000 readers across the country. In October 2009, Australian Stainless Online was launched to provide a readily available live news feed to a wider audience around the world. Australian Stainless is published by the Australian Stainless Steel Development Association (ASSDA), a non-profit industry group that aims to increase the consumption of stainless steel in Australia, through publication, education, accreditation and more.

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