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Running Water

Water authorities tackle water shortages with stainless steel.

Water is a fundamental human need. It is central to our lives, from what we drink, to what we use in washing ourselves, our clothes and a multitude of other uses. Safe, clean and palatable water comes at a price though, and when leaks occur in distribution systems, additional costs are incurred as even more water must be found and treated. Security of water supply is a prerequisite for sustainable growth and dealing with leakage is a universal challenge. To combat the scourge of leaks, a number of water distribution authorities across the world have implemented affordable solutions utilising stainless steel, which not only saves money, but water, a precious resource.

Tokyo, Japan

Prior to the 1980’s, water shortages in Tokyo were chronic and rationing was occasionally required. When the city’s water provider, the Tokyo Metropolitan Government Waterworks Bureau (TMGWB), analysed leakage repairs, they determined that 97% were on the distribution pipes of 50mm diameter or less. In Tokyo, there are more than two million such connections that take the water from the mains to internal systems in buildings. Historically, lead pipe was the preferred material for distribution lines because it is soft, malleable and easy to work with, especially for the last few metres from the mains to buildings. Once lead pipe is in the ground, however, various forces can act on it. Vibrations from traffic and construction work as well as subsidence and earthquakes can cause the soft lead pipes to deform, become detached or even break.

In 1980, TMGWB started to actively replace all service connections with grade 316 (UNS S31600) stainless steel pipe. In 1998 corrugated grade 316 (S31600) stainless steel pipe was introduced for distribution lines that take water from the mains to final destinations in homes, offices and industrial plants. The pipe is corrugated at regular intervals to allow for it to be bent during installation, to accommodate changes in direction and the avoidance of obstacles without additional joints. It also allows for movement of the pipe during earth movement and seismic events. By supplying a single length of corrugated stainless steel pipe, the number of pipe joints was greatly reduced. In switching to stainless steel pipe, the reliability of the water supply has increased and the leakage rate has been reduced by 86% from 15.4% (1980) to 2.2% (2013). To put this into context, since 1994 Tokyo has reduced annual water leakage by nearly 142 million cubic metres - the equivalent of 155 Olympic-size swimming pools per day, with savings in excess of US$200 million per year. Also, annual leak repairs have decreased from 60,000 (1983) to 10,000 (2013). Due to the corrosion resistance of stainless steel, TMGWB expects service life in excess of 100 years.

Graph below: Correlation between repair cases, leakage rates and installation of stainless steel pipes in Tokyo.
Courtesy of the Bureau of Water Works, Tokyo Metropolitan Government.

 

Taipei, Taiwan

In 2002, a severe drought brought intermittent water supplies to the Taiwanese capital over a 49-day period. Of the 450 metering areas in the city, 40% were losing half of their water or more before it reached consumers.

Analysis of repair cases showed that while polybutylene pipe made up only 3% of the length of the system, it accounted for 28% of all leaks. Approximately 90% of all problems occurred in plastic pipes, with the vast majority (83%) caused by cracking.

In 2003, the Taipei Water Department began a similar program to Tokyo, replacing distribution lines with corrugated grade 316L (S31603) stainless steel pipe. Although the ongoing program has so far only replaced 35% of the lines, the result has been a reduction in water loss from 27% (2003) to 17% (2014). This adds up to an annual saving of 146 million cubic metres of water, the equivalent of 160 Olympic-size swimming pools per day.

In 2014, a drought occurred with even less rainfall than the 2002 event which precipitated the pipe replacement program. However this time, the improvement in leakage rates achieved since 2003 meant there was no interruption to the water supply.

The 2002 drought in Taipei caused severe water shortages.
Image courtesy of the Taipei Water Department.

 

Western Cape, South Africa

South Africa is by nature a semi-arid country; its annual rainfall is only half the global average. It has a population of 55 million and is facing freshwater scarcity. It is estimated that at least 37% of its clean drinkable water is lost due to leakage from old and unreliable infrastructure.

The Groot Drakenstein Valley is the cradle of the South African deciduous fruit and wine industries. Water is supplied to over 800 farms including 50 vineyards. Here, there are numerous examples of carbon steel and cast iron pipes that have failed in many areas after just one year due to the very aggressive acidic soils and high water table. “We started a project in 1992 in the Drakenstein Municipality to replace existing piping with stainless steel,” explains André Kowalewski, Senior Engineer - Water Services, Drakenstein Municipality. “We have reduced water loss to around 13% in comparison to the 37% national average. Ten years back only the Drakenstein Municipality used stainless steel. Now 80% of the Western Cape municipalities do.”

André and his team plan for a life expectancy in excess of 50 years. Stainless steel used in Drakenstein is primarily grade 316 and in some cases grade 304 (S30400) in visible locations. Projects are currently focussed around pumping, purification, storage, pipelines and sewage. One such project is a 500 mega-litre/day delivery system completely in grade 316 stainless steel.

Stainless steel pipe in the Western Cape resists aggressive acidic soil conditions.
Images courtesy of Johan Van Zyl.

   

 

Investing in the future

The experience of Tokyo, Taipei and the Western Cape gives water authorities the confidence to specify stainless steel for piping systems. While the initial cost compared to competing materials may be higher, stainless steel has been shown to be a good investment over its long life, paying back each year in reduced maintenance and cost per litre processed.

This article was originally printed in Nickel Magazine (August 2016, Vol. 31, No.2), published by ASSDA Sponsor Nickel Institute.

This article is featured in Australian Stainless Issue 57 (Spring 2016).

Banner image: Corrugated pipe installation. Image courtesy of Tokyo Suido Services/Showarasekan.

Stainless Steel in Western Australia Subsea Applications

Stainless steel is the material of choice for subsea hydraulic and control line applications because of its excellent corrosion resistance, material strength benefits and weldability.

 Subsea production in the oil and gas industry involves offshore, in situ equipment to facilitate the exploration, development, production and transportation of energy reserves from underwater fields. It is a viable form of oil and gas production, providing economic, productivity and environmental benefits.

Perth-based ASSDA Member and Accredited Fabricator Diverse Welding Services (DWS) recently completed detailed design and fabrication works on two major subsea projects operated by multinational oil and gas exploration and production companies.

Apache Corporation’s Coniston and Novara Redevelopment Project, completed in February 2014, is a subsea oil field located 65km north of Exmouth. The project involved an upgrade to the Ningaloo Vision floating production, storage and offloading (FPSO) unit and development of the neighbouring Coniston and Novara oil fields, which links these fields into the existing Van Gogh manifolds via dual production flow lines. The equipment operates in water 340 to 400m deep.

DWS was contracted to detail the design, fabrication, installation and NDT testing of the small-bore hydraulic control and chemical injection lines for five subsea production manifolds.

2,380m of 316L stainless steel wall tube in various sizes ranging from 0.375” OD x 0.083” up to 1.000” OD x 0.156” was used, plus 30m of Inconel 625 0.750” OD x 0.134” wall tube.

Chevron Australia’s Wheatstone Project, located 12km west of Onslow on the Pilbara coast of Western Australia, is one of Australia’s most significant LNG projects. Currently in progress and at almost 60% complete, it will become the country’s first third party natural gas hub. DWS was contracted to fabricate, install and test small-bore tubing and free issue components to Multiple Quick Connect (MQC) plates. The main free issue components consisted of logic caps, cobra heads, single line couplers and acid injection items requiring small-bore interconnecting tubing on four MQC plates serving the subsea isolation valves (SSIV) for the 44” trunkline, 24” and 14” flowlines, and the 18” APACHE/KUFPEC line.

SAF2507 super duplex stainless steel was used for the MQC plates including over 80m of 0.625” OD x 0.083” wall tube, 20m of 316L 0.375” OD x 0.083” wall tube and 130 Swagelok 90° elbow butt-weld fittings. The MQC plates were fabricated by PT Profab Indonesia, then shipped to DWS in Perth for detailed fit-out using autogenous orbital welding processes. After testing, the completed MQC plates were shipped back to PT Profab Indonesia for installation into the SSIV manifolds.

All welding by DWS for both projects was completed using an autogenous orbital welding process, specified by the clients for the small-bore hydraulic tubing welding due to its excellent control of welding variables, repeatability of application and maximisation of corrosion resistance of exotic materials. DWS produced high quality welds that when tested under the G48 Method A – Pitting Resistance Testing, proved resulting weight loss to be less than 0.36g/m2.

Orbital welding is an automatic method of Tungsten Inert Gas (TIG) welding of thin tubes, usually without filler wire. Its advantages are a uniform weld profile and excellent gas shielding giving minimal heat tint. The ends of the tube are prepared and clamped in an enclosed head, which is flushed with external shielding and internal purging gas – usually argon, although gas mixtures can be used. The cycle starts by striking the arc and proceeds as the head slowly rotates around the tube. A specific weld head can deal with several diameter tubes. The weld is usually in the centre of the head, although heads are available for offset joins used with joints to elbows or valves.

DWS completed 1200 welds for the Coniston and Novara Redevelopment Project and 204 welds for the Wheatstone Project, which passed 100% radiographic/liquid penetrant testing in accordance with ASME B31.3 NFS. The excellent gas and heat input control of the orbital welding produced internal surfaces that did not require post-weld cleaning. The external surfaces around the welds were abrasively treated as required for aesthetics reasons.

The DWS facility includes five autogenous welding machines complimented with seven welding heads of assorted ranges allowing DWS to complete weldments from 0.25” OD to 6” OD tube/pipe schedules as required for these project works. This coupled with their extensive range of other qualified weld procedures for this process allows DWS to meet clients’ stringent fabrication, application and quality specifications.

         

This article is featured in Australian Stainless Issue 55 (Winter 2015).

Cutting a Carbon Footprint

Coca-Cola Amatil is reducing the carbon footprint of its 600ml PET bottles by 22% with the help of stainless steel.

Innovation in process technology and the successful application of stainless steel has led to efficiency gains and sustainable outcomes for one of the world's most recognised brands in the food and beverage industry.

In 2011, Coca-Cola Amatil (CCA) announced a $450 million investment in PET bottle self-manufacture, or ‘blowfill’ technology at its production facilities across Australia, New Zealand, Indonesia, Papua New Guinea and Fiji.

Blow-fill technology is a manufacturing technique that allows companies to produce their own PET (polyethylene terephthalate) bottles within their own facility. It allows manufacturers to form, fill and seal bottles in one continuous process at the one location without human intervention. Blow-fill has enabled CCA to make its PET bottles using significantly less PET resin, resulting in production of the lightest-weight bottles in the global Coca-Cola system.

Previously, CCA would buy blow-moulded bottles from a third party supplier, transporting them to its own facility to sterilise and fill with product. CCA’s integration of these three steps into one operation has automated its production lines, creating economies of scale and
optimising efficiencies of operation.

CCA’s Kewdale facility in Perth is one packaging line that recently completed its installation of blow-fill equipment, procured from Krones AG, a German-based process manufacturer.

CCA engaged ASSDA member and Accredited Fabricator TFG Pty Ltd for the installation and fabrication of the stainless steel interconnecting pipework for the facility’s new blow-fill equipment.

Sydney-based ME Engineering detailed the scope of works, and coordinated the process engineering and installation of the new equipment.

Over 6km of 304L and 316L AS1528 standard grade stainless steel tube was supplied by ASSDA sponsor Prochem Pipeline Products, ranging in size from 25mm-200mm diameter.

The TFG team purge TIG welded all stainless steel components on site and internally passivated the stainless steel using citric acid.

ME Engineering’s Project Manager Andrew Meagher said grade 316L was specified for CCA’s Kewdale facility because of the high chloride content of the water supply in Perth.

With spring water one of CCA’s main products, sanitation is key to avoiding microbiologically-influenced corrosion.

Tom Moultrie, General Manager of TFG, said that whilst there are other materials that can be specified for equipment using compressed air, stainless steel provides aesthetic appeal, trusted hygiene and longer life span.

The use of stainess steel has been successful in the output of this project, with CCA’s State Projects Engineer Simon Wall stating that ‘as a beverage manufacturer, food safety aspects of our processes and equipment are critical to ensuring the integrity and quality of our products – an area that stainless steel ensures.’

Kewdale’s new blow-fill line commenced operation in June 2012. It features 14 blowing stations, 108 filling nozzles and 18 capping stations, and has the capacity to produce 26,000 bottles per hour.

Mr Wall said the investment in PET bottle self-manufacture will continue to deliver savings in raw materials - bottles are made using less PET resin and less water is used in the bottling process - and meet future consumer growth and demand.

CCA’s ongoing commitment to innovation and sustainability has maximised production capabilities whilst minimising the use of resources.

By the end of 2012, 10 blow-fill lines will have been deployed across CCA’s production facilities in Australia, bringing self-sufficiency to over 70%. Once all 26 production lines are implemented, CCA estimates a saving of 7000 tonnes of PET resin per year, a 15% reduction in bottle weight and 50,000 truck movements eliminated per year. Overall, this is reducing the carbon footprint of every 600ml bottle by an average of 22%.

Images courtesy of TFG Pty Ltd.

This article is featured in Australian Stainless magazine, issue 52.

Helical Coil Gets a U-Neek Bend

Fabricating equipment for the chemical sector requires solid high quality materials and superior workmanship. In April 2011, ASSDA member and Accredited Fabricator U-Neek Bending Co Pty Ltd put the finishing touches on a radiant helical coil at their factory in Dandenong, Victoria.

The coil, designed as a heater for Titanium Tetrachloride (TiCl4) production, is 11.4 metres long with a diameter of 3.05 metres and required more than 7 tonnes of high grade Inconel Alloy.

U-Neek’s Business Development Manager, John Lovell, said the client chose to have this material shipped from America.
“At around US$1000 a metre, Inconel Alloy is a very expensive option but it has great heat transfer properties and is completely non-corrosive,” Mr Lovell said.

The Western Australian client, who declined to be named, were looking for a fabricator that, in addition to having a proven record in metal bending, could work to their particular requirements for this critical process componet.

“U-Neek weren’t just competitive in pricing,” said Greg, a project engineer with the client. “They succeeded with all the trial projects we sent them.”

“To ensure total quality control, we provided a comprehensive report that detailed every step of the process, including the names of every person who worked on the individual stages,” Mr Lovell said.

U-Neek Engineer Dale Theobold said the coil was manufactured to exacting tolerances using a range of Inconel Alloy materials.
“We used 150NB Schedule 40 seamless 600 for the pipes and flanges, 366-04 WPNCI-S for the elbows, B168-08 for the plate and 253MA for the high temperature pieces,” he said.

Once completed, the coil then had to undergo a rigorous series of tests. The butt welds were verified with full radiography, the attachment welds were submitted to liquid penetrant inspection (LPI), and a full hydro exam was done on the coil itself.

“The coil was filled with distilled water to test its heating capabilities. Then the coil was pressurised with nitrogen, to a dew point of -12°, to remove all traces of water and moisture prior to transporting,” Mr Lovell said.

The transport frame and mounting jigs were manufactured from mild steel. To ensure no cross contamination, Inconel strips were fitted to the mounting points. The coil was lifted onto the back of a semi-trailer for final transportation to Perth, using U-Neek’s 16 tonne travelling overhead cranes.

Images courtesy of U-Neek Bending Co Pty Ltd.

This article features in Australian Stainless magazine - Issue 50, Summer 2011/12.

Brewery to Excel with Local Fabrication

A worrying trend among Australia's major resource companies is the increasing amount of engineering, detailing and fabrication work being sent offshore - a move that has had significant impact on local fabrication. But there are some positive signs in the food and beverage sector that local fabricators are more than capable of meeting design and fabrication expectations.

When ASSDA member and Accredited Fabricator, A&G Engineering, put in a bid to build 10 x 100 hectolitre beer fermenters for Casella Estate - a company best known for their Yellowtail wine label - they had to compete against companies as far away as Europe for the coveted project.

But A&G had a few advantages over the offshore companies: they had worked with Casella before, fabricating 88 x 1.1 million litre wine tanks for the company’s tank farm in Yenda, NSW; they have supplied stainless steel tanks to Australia’s leading breweries, wineries and beverage companies; and they are one of the largest users of stainless steel in Australia.

A&G’s win is an important victory for the Australian industry as a whole and another milestone for A&G Engineering, which was founded in 1963.

The five-month Casella Brewery project, completed in August 2011, saw 25 of A&G’s 200 staff use 65 tonnes of 304 grade stainless steel (including 2-4mm coil and 8mm plate) to build the 10 vessels.

A&G’s Design Manager Heath Woodland said the tanks were designed to AS1210-2010 pressure vessel standards, in order to withstand a pressure rating of 115kPa.

The stainless was welded with A&G’s semi-automated welding process and the internal welds were polished to achieve a 0.6Ra surface finish, to meet beverage industry standards of a food grade finish.

A&G built the vessels at their Griffith and Irymple plants, before transporting them to Yenda. With the beer fermenters now in place, it is hoped the Casella Brewery will be operational by the end of 2011.

Images courtesy of A&G Engineering.

This article is featured in Australian Stainless magazine - Issue 50, Summer 2011/12.

Stainless Steel and Plumbing Standards

After three years of development, the first stage of a Standard covering the grade and dimensions of stainless steel pipes and tubes suitable for water supply and drainage systems has been completed. This interim Standard will be converted to a full Australian Standard in 2009.

The Standards Committee included ASSDA representative Neil McPherson of OneSteel, supported by the Technical Committee.

To avoid possible confusion and protect against corrosion problems in aggressive water supply areas, grades 316 and 316L are specified for the plumbing installation Code of Practice. All materials that satisfy the requirement for water supply and drainage systems must be included in the installation Standard AS/NZS 3500 Parts 1 & 2, which covers the material, grade and approved jointing method for piping systems.

If a material is included in Part 1 Water Supply (for drinking water), it will need to be certified against a product standard to Level 1, while Part 2 Drainage & Sanitary Plumbing requires Level 2 certification. The main difference is that Level 1 products require testing under AS4020 Material in Contact with Drinking Water to confirm lack of water contamination. Stainless steel product readily passes this testing.

All fittings, including the mechanical jointed pressfit and roll grooved types used for the plumbing services, are also tested and certified. AS3688 Metallic End Connectors defines the criteria against which these fittings are certified, including the additional pressure and fatigue testing to demonstrate strength of joint assembly.

Stainless steel using mechanical jointing systems

Mild steel, copper tube and plastic pipes have dominated building water systems for many years. However, high rise developments over recent decades have changed the building industry requirements for water supply and fire protection systems. These systems now require materials with a much higher pressure rating and corrosion resistance.

Stainless steel is recognised as a material most suited to meet these requirements. However, older on-site methods for jointing and fabrication has limited the use of stainless steel.

The approval of mechanical pressfit and roll grooved systems for all water systems has provided a major market for stainless. Stainless steel pipes and fittings have been installed as a solution to specific technical issues including a corrosive environment, high pressure requirements of the hydraulic services system, high operating temperature, or where the project owners are looking for a whole-of-life sustainable product solution.

The following projects illustrate some design and installation specifications around Australia.

Casey Aged Care Facility, Heidelberg, Victoria

108mm and 76mm tube in 316L was supplied by Blucher for a low pressure system feeding rainwater from storage tanks to pumps. Stainless steel was chosen due to concern of longevity and water contamination from other materials due to water levels in storage tanks being low or empty for long periods during dry spells. The Mapress stainless steel pressfitting system was familiar to the plumbing contractor who felt it was labour saving and easy to install. Plastic pipes were used from the roof to the plastic rainwater storage tanks.

Western Corridor Recycled Water Project, SE Queensland

The Mapress 316 pressure system was chosen for rapid, simple installation. There was a lack of pipe fitters available so socket welding was not possible and other trades made the installation. Sizes ranged from 15 to 54mm with butyl rubber sealing rings containing pressures up to 1,000kPa. The stainless steel was used for potable, treated and fire water as well as compressed air. The Mapress system supplied by Blucher has been used in all three waste water treatment plants in the Western Corridor as well as in the Gold Coast Desalination Plant.

Centre Court Business Park, North Ryde, NSW

Heating and chilled/condenser water installations used 316L schedule 5 pipe in both 50 and 100mm diameter in this 30,000m2 low rise complex. Stainless steel offered reliable protection from corrosion and the Victaulic roll grooved system offered ease of assembly.

Suncorp building, Sydney CBD

Refurbishment of the combined fire and drinking water system in a 1972 building used OneSteel Building Services supplied 316L schedule 10 pipe and fittings in 3m, pre grooved lengths for assembly in restricted duct spaces. The 43 floors plus 3 basements ensured high pressure requiring strong stainless steel which also met the drinking water AS4020 requirements.

Centrepoint Tower, Sydney CBD

Stainless steel pipe and fittings were supplied by OneSteel Building Services to replace corroded carbon steel in the 305m tall tower. Systems changed were the fire and potable water and the gas lines. 300m of 316L was supplied in 2.7m lengths which were roll grooved and assembled using Victaulic couplings in a very constricted service duct. Sizes used were 100mm and 50mm in schedule 10 except for gas lines in schedule 40.

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

Stainless Refinery First of its Kind
Australia’s first grain-to-ethanol refinery has begun production in Queensland, with an expected output of more than 80 million litres a year.

Seven pressure vessels and five columns were fabricated by ASSDA Accredited D&R Stainless from 30 tonnes of grade 304 stainless
steel supplied by ASSDA member Sandvik.

The column sizes range from an acid reduction column 750mm in diameter and 14.2 metres long to a beer column 1900mm in diameter and 24 metres long. 

The columns were fabricated to tight tolerances set by process design engineers Detla T Technology, in the United States.

Chief Executive Officer of Dalby Bio-Refinery Limited, Kevin Endres, has worked with Delta T technnology in the US.

Mr Endres said stainless was the obvious choice for its durability. A project of this size requires a low maintenance and reliable material.

All design and manufacturing was carried out by D&R Stainless to ASME VIII complying with AS1210.

D&R also fabricated 6000 metres of grade 304 piping in sizes from 20NB to 500NB requiring over 6100 elbows, flanges and fittings from ASSDA member Stainless Pipe & Fittings Australia.

All piping was x-ray quality and met ASME B31.3.

Mr Endres said the refinery will eventually expand to output over 200 million litres of ethanol per year.

This article appeared in Australian Stainless Magazine -  Issue 45, Summer 2009.

 

Grade 431

A versatile, high strength martensitic stainless steel

Martensitic stainless steels are a less well-known branch of the stainless family. Their special features – high strength and hardness – point to their main application area as shafts and fasteners for motors, pumps and valves in the food and process industries.

The name “martensitic” means that these steels can be thermally hardened. They have a ferritic microstructure if cooled very slowly, but a quenching heat treatment converts the structure to very hard martensite, the same as it would for a low alloy steel such as 4140. Neither the familiar austenitic grades (304, 316 etc) nor the duplex grades (2205 etc) can be hardened in this way.

Grade 431 (UNS 43100) is the most common and versatile of these martensitic stainless steels. It combines good strength and toughness with very useful corrosion resistance and in its usual supply condition can be readily machined.

Chemical Composition

The composition of 431 specified in ASTM A276 is given in Table 1 below.
Grade 431_Table 1

 

 

 

The inclusion of a small amount of nickel in grade 431 is different from most other martensitic grades. This small but important addition makes the steel microstructure austenitic at heat treatment temperatures, even with such a high (for a martensitic grade) chromium content. This high temperature austenite enables formation of hard martensite by quenching.

Corrosion Resistance

The relatively high chromium content gives grade 431 pitting, crevice and general corrosion resistance approaching that of grade 304, which is very useful in a wide range of environments including fresh water and many foods.

Grade 431 has the highest corrosion resistance of any of the martensitic grades. Corrosion resistance is best with a smooth surface finish in the hardened and tempered condition.

Grade 431 is sometimes used for boat shafting and works well in fresh water but is usually not adequate for sea water.

Heat Resistance

Grade 431 has good scaling resistance to about 700°C but, as martensitic steels are hardened by thermal treatment, any exposure at a temperature above their tempering temperature will permanently soften them. 600°C is a common limit.

Mechanical Properties

The application of grade 431 is all about strength and hardness. Table 2 below lists mechanical properties of the grade annealed and in hardened and tempered “Condition T”.

Grade 431_Table 2

 

 

 

 

 

 

 

 

 

 

 

Heat Treatment

A feature of grade 431 is that it can, like other martensitic steels, be hardened and then tempered at various temperatures to generate properties within a wide spectrum, depending on whether the requirement is for highest possible hardness, or best ductility, or some balance between these. Hardening is by air or oil quenching, usually from 950-1000°C.

The tempering diagram in Figure 1 shows properties typically achieved when the hardened steel is tempered at the indicated temperature. A tempering temperature within the range 580 – 680°C is usual. Tempering between 370 and 570°C should be avoided because of resulting low impact toughness.

Tempering should follow quenching as quickly as possible to avoid cracking. Softening is usually by sub-critical annealing, by heating to 620 – 660°C and then air cooling.

Grade 431_Figure 1

Physical Properties

Density

7700kg/m3

Elastic Modulus

200GPa

Thermal Expansion (0-100°C)

10.2µm/m/°

Fabrication

Machining is readily carried out in the annealed condition, and also in the common Condition T. Modern machining equipment enables high speed machining at this hardness of about 30HRC.

Welding of 431 is rarely carried out — its high hardenability means that cracking is likely unless very careful pre-heat and post-weld heat treatments are carried out. If welding must be done this can be with 410 fillers to achieve high strength but austenitic 308L, 309L or 310 fillers give softer and more ductile welds.

Cold bending and forming of hardened 431 is very difficult because of the high strength and relatively low ductility.

Forms Available

Grade 431 is available in a wide range of bar sizes — virtually exclusively round but some hexagonal. Most other martensitic grades are only available in round bar, although the higher carbon 12% chromium “420” series of grades may also be available as hollow bar and as blocks and plates intended for tooling applications.

Alternatives

Another approach to high strength stainless steel bar is a precipitation hardening grade, such as 17-4PH. These grades have similar corrosion resistance and offer some advantages in producing long, straight, higher strength shafts.

Shafts to be used in more corrosive environments are likely to be a duplex or super duplex or nitrogen-strengthened austenitic grade. These, however, have lower achievable strengths than martensitic or precipitation hardening grades.

Specifications

Grade 431 is usually specified by ASTM A276, with composition as in Table 1. In the Australian market, however, there are usually two deviations from A276:

  1. It is most common to find this grade supplied in the hardened and tempered “Condition T” to AS 1444 or BS 970, with specified tensile strength of 850-1000MPa. Yield and elongation are typically in conformance with the limits listed above. ASTM A276 only lists a Condition A version of grade 431 — this is the annealed condition that would normally require hardening heat treatment after machining.

  2. The second deviation is that it is usual for cold finished stainless steel bars stocked in Australia to be with the all-minus ISO h9 or h10 diameter tolerances. Hot finished “black” bars with all-plus ISO k tolerances may also be available.

 

This article was prepared by ASSDA Technical Committee member Peter Moore from Atlas Steels. Further technical advice can be obtained via ASSDA’s technical inquiry line on +617 3220 0722.

This article featured in Australian Stainless magazine - Issue 48, Autumn 2011.

stainless integral to design

Posted 17th December 2009

LWA44 101 650x250 for web

A dam upgrade project in South Australia has achieved a world-first zero carbon footprint for water infrastructure and has used stainless steel as part of the unique design. The Little Para Dam upgrade incorporates a Hydroplus Fusegate System, with stainless steel fabrication carried out by ASSDA Accredited Fabricator LWA Engineering.

The Fusegates are similar to those built at Jindabyne for the Snowy Hydro in 2007, featuring a cast in-situ concrete design with stainless steel inlet wells and seal fixings in order to provide a 100 year design life and virtually no maintenance. However, for the Little Para dam upgrade, SA Water accepted the lean duplex stainless steel (LDX 2101) proposed by CivilTEC for the superstructure of the units for the following reasons:

  • it would provide similar corrosion resistance to 316 grade stainless steel, but with a higher tensile strength (450N/mm²) and at a much lower price;
  • an off-site fabrication system would reduce the amount of time required on site at Little Para from eight months to just six weeks, thereby reducing site administration overheads and running costs for all parties involved; and
  • the extremely efficient design (by WSP Group) used far less construction materials than would normally be required for a project of this nature and LDX 2101 is manufactured using approximately 65 per cent recycled material.

LWA Engineering Managing Director Larry Watson said LWA Engineering had been working with ASSDA Major Sponsor Sandvik on the stainless steel components of the project.

“With a Carbon Pollution Reduction Scheme on the agenda, a zero carbon footprint has never been more important,” Mr Watson said.

“One of the main reasons SA Water wanted to use this design with this material came down to the reduction in carbon footprint which minimised the offset required to achieve zero emissions. This is the first zero carbon infrastructure project in the country.”

The walls of the Fusegate bucket are formed from a composite steel shell comprising two 4mm thick stainless steel ‘skin’ plates spaced 150mm apart. A lattice work of ribbing is then welded onto the plates.

Around 70 tonnes of LDX 2101 were supplied by Sandvik for the walls and internal ribbing of the five Fusegates. The material was imported in 4mm thick coil form, which was then cut to length at Sandvik’s Sydney premises, with ribs being cut in Melbourne (RCR Laser) and Adelaide. The wall panels were cut on Sandvik’s 2m-4m laser bed to within ±0.2mm of accuracy.

LWA Engineering marked out the 2m high inner and outer ‘skins’ to form the composite wall panels and spot welded the vertical and horizontal 40mm-4mm thick LDX ribs in position before pre-setting and stitch welding. When the two ‘skins’ were brought together they were fixed in position using a 12mm diameter stainless steel rod which is pushed through 13mm holes in the overlapping lugs and welded at the top and bottom rib location.

Each Fusegate wall was fixed to a pre-cast concrete base chamber using a continuously welded stainless steel base plate cast into the concrete during pre-casting. Prefabricated inlet wells comprising 8mm thick LDX plate continuously welded along splice points were bolted into place on site.

The composite wall design saved about 40 per cent of the stainless steel required when compared with a traditional single-plate design.

The Little Para Dam spillway upgrade will be completed in early 2010.

CONTACTS

LWA Engineering
www.lwaengineering.com.au

Sandvik Australia
www.sandvik.com

LWA-IMG_0180 600dpi for web

Hydrostatic Testing of Stainless Steels

Guidelines to Ensure Long Service Life

Design engineers frequently specify stainless steel in industrial piping systems and tanks for its excellent corrosion resistance. While stainless steel’s unique characteristics make it a standout leader in the durability stakes of alloys, it is not completely immune to corrosion.

Premature failures of the stainless steel can occur due to Microbiologically Influenced Corrosion (MIC). This corrosion phenomenon usually occurs when raw water used for hydrostatic pressure tests is not fully removed from the pipework and there is an extended period before commissioning of the equipment. The result is localised pitting corrosion attack from microbacterial deposits that, in severe cases, can cause failure within a few weeks. MIC is easily prevented using proper hydrostatic testing techniques.

MIC

MIC failures occur by pitting corrosion, often at welds, where colonies of bacteria may form. A number of different bacterial species are known to cause the problem, but the detailed mechanism is not known.

Iron utilising bacteria appear to be the dominating microbial species involved with MIC occurring in stainless steel. Anaerobic sulphate-reducing bacteria pose a greater risk of instigating or accelerating corrosion often under a layer of aerobic slime or microbial deposits. However others, such as manganese utilising bacteria (generally from underground waters), have also been discovered.

MIC is extremely aggressive and difficult to eliminate once established, so it is surprising and disappointing that there is limited knowledge of MIC within the engineering community. Fortunately, MIC is easily avoided by using good practices during the initial hydrostatic testing. Education and promotion of proven hydrostatic testing practices which prevent MIC are vital to minimising its potential impact on the stainless steel industry.

                    

Hydrostatic testing practices to eliminate MIC

In order to eliminate MIC, it is recommended that the following practices are used.

1. Fabrication practices

Crevices should be eliminated or at least minimised during the fabrication process, as they are the preferred sites for attachment and growth of microbial colonies. They also provide traps for chemicals which could concentrate and cause pits.

The likelihood of MIC will also be reduced by:

  • Using full penetration welds; and
  • Purge welding to prevent the formation of heat tint; or
  • Removing heat tint by grinding or pickling.

Arc strikes and weld splatter should also be ground off and pickled.

2. Use clean water

The cleanest water available should be used in a hydrostatic test, such as demineralised, steam condensate or treated potable water. Untreated or raw water from dams or bores should be avoided when conducting a hydrostatic test but, where this is not possible, the water should be sterilised (e.g. by chlorination) before use. If sterilisation is not practical, the requirements for short residence time and subsequent drying of the system are extremely important. The cleaner the water, the less ‘food’ there is for MIC bacteria to live off and multiply.

It is important to ensure that there is no trace of sediment in the stainless steel system during testing to avoid silting, as the water is normally not circulated during a hydrostatic test. This may require the test water to be filtered to ensure it is free of all undissolved solids. Sediments can provide the conditions for crevice attack.

3. Draining and drying

Thoroughly draining and drying the stainless steel system immediately following a hydrostatic test (preferably within 24 hours, certainly within 5 days) will almost certainly prevent the occurrence of MIC.

Horizontal pipelines should be installed in a sloping direction to make them self-draining.

Drying can be achieved by pigging (cleaning with foam or rubber scrapers), followed by blowing dry air through the system. Beware of blowing higher temperature moist air through cold pipework unless the air is dried before being introduced to the system. If warm air is used, it should not be from a gas burner as condensation may occur.

Draining and drying of systems following a hydrostatic test should only be disregarded when the system is placed into service immediately following the test. Partial draining is potentially very serious as subsequent slow evaporation of even clean residual water can produce very concentrated and aggressive solutions.

4. Chloride content and temperature

During hydrostatic testing of stainless steel equipment, the chloride content of the test water must be within the range to which the stainless steel grade is resistant. Figure 1 shows the maximum temperatures and chloride contents to which stainless steels are resistant in water with residual chlorine of about 1 ppm.

The limits shown in Figure 1 may be exceeded provided the contact time of the water is brief, i.e. 24-48 hours.

If the chloride content of the test water is uncertain, the water should be analysed.

5. Standards

NACE and API standards for a number of products and installations provide guidelines for hydrostatic testing, including limits for water quality and contact times. These standards should be consulted for specific details for the fabrication in hand.

Conclusion

The benefits of stainless steel’s corrosion resistance are well proven in many industrial applications involving piping systems, but failures can occur during hydrostatic testing if care is not taken. Attention to a few simple details will prevent surprises a few months down the track, allowing the long service life available from stainless steel to be fully realised.

This article featured in Australian Stainless Issue 47 - Spring 2010.