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Issue 179 July/August 2012
TWI Events
September 2012
SeminarJoint TWI/EWI Aerospace eventThu 13 - Fri 14Munich, Germany
Technical Group MeetingMaterialsTue 18Great Abington
October 2012
SeminarBSI LaunchBS 7910Wed 24 London
Technical Group MeetingWelding ProcessesThu 25 Yorkshire
SeminarAutomotiveTue 30Great Abington
November 2012
Technical Group Meeting and BSI Standards Meeting
Offshore oil and gas
Mon 19 – Tue 20
Aberdeen
Workshops and seminars are recognised
Continuous Professional Development events
T h e m a g a z i n e o f T W I
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Mobile electron beam welding provides the solution for fabricating large structures
In conjunction with the ManOS (Cost-effective Manufacture of Offshore Wind Turbine Foundations) project, and specifically to showcase its reduced pressure EB gun and the capabilities
of mobile local vacuum sliding seal technology, TWI hosted a recent seminar and technical demonstration at its Low Carbon Energy Manufacturing Technology Centre in Middlesbrough, UK. The event on 19 April 2012 was attended by partners of the ManOS project (see below) and delegates from UK industry and academia with interests in large scale steel fabrication and offshore wind power engineering.
Chris Punshon of TWI began by presenting the progress made by the ManOS project, which aims to enable faster, more efficient and cheaper
Continuous developments in out-of-vacuum-chamber electron beam (EB) technology are pushing at techno-economic barriers previously preventing the uptake of single pass, thick-section, low distortion EB welding of large pressure vessels and structural fabrications. The ability to use EB technology outside a vacuum chamber, coupled with the introduction of new sliding seal vacuum technology means that the welding process is given greater mobility enabling an increasing number of technical applications and commercial opportunities across a range of industries.
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July/August 2012
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production of offshore marine foundations. The project, funded by the UK Technology Strategy Board, has successfully developed and demonstrated EB wedding in thick section steels with offshore application relevance and validated the resulting metallurgical and mechanical properties.
The ManOS partnership comprises TWI, Nippon Steel Corporation and Aquasium Technology Ltd, with KBR acting in a consultative role.
Chris introduced the focus of the event – the demonstration of a full penetration, 60mm wall thickness, 1300mm longitudinal seam weld in a 2350mm diameter S355 steel tubular (representative of an offshore wind turbine tower foundation structure), which took less than six minutes to complete.
Professor T Ishikawa, Nippon Steel Corporation, Japan, concluded by presenting delegates with details of a proprietary grade of S355 steel, which has recently been granted Germanischer Lloyd’s approval for EB welding due to its excellent as-welded and postweld heat treated properties, including exemplary sub-zero impact toughness.
All attendees were impressed by the demonstration, the technology supporting the EB welding capability and the opportunities that this mobile variant brings for application of EB welding to large structures where conventional EB has been prohibited due to the need to operate within a vacuum chamber.
Please contact [email protected] for further details or if you wish to explore this technology further for your applications.
Alstom WindSpainPower industry
Class NKJapanShip classification society
Connect Plus ServicesUKProject management of M25 motorway
Dyson LtdUKDomestic appliances
Eltek Semiconductors Ltd,UKComponent obsolescence management
Ensitech Pty LtdAustraliaTIG Brush® and the Ensitech surface finishing system
Fontaine Trailer CompanyUSAManufacture of lightweight trailers
John Mayes Engineers Ltd UKSupplier of petrochemical, process, energy and allied industries
Martin-Baker Aircraft Co LtdUKEjection and helicopter seats. Al/Ti composites
Mediplus LtdUKPressure/pH sensitive catheters and plastics
Murata Manufacturing Co LtdJapanCeramics for electronic applications
NMB Minebea UK LtdUKBearing design and manufacture; aerospace and commercial
Oceanic Marine Contractors (OMC)United Arab EmiratesOffshore construction Raytheon Systems LtdUKElectronics, defence, fire protection and automotive
ScrewFast Foundations LtdUKCivil engineering
New Members of TWITWI is pleased to welcome the following as Industrial Members
We are always open to applications from Materials Scientists, Metallurgists and Welding Engineers, in particular experts in corrosion and ferritic steels with knowledge of the oil and gas sector.
For current vacancies, please see our careers page www.twi.co.uk/careers or to apply speculatively email your CV and cover letter to [email protected]
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July/August 2012
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The work involves a novel method for producing mixed metal multi-coloured layered materials using FSW and compares the results with the ancient Far Eastern art of Mokume Gane.
Mokume Gane is a unique process involving sheets of different coloured metal alloys bonded together into a laminated billet before being carved or milled to expose interior layers. The material is then hammered or rolled into a flat sheet which is used to form jewellery or hollow-ware.
Using these multi-coloured layers in the process has given TWI a unique insight into how the material flows around the friction stir tool and has thereby enhanced TWI’s tool design capability.
Work has shown that it would be feasible to use FSW to produce Mokume Gane materials from a number of different metals including gold, silver, platinum, palladium, copper and brass.
FSW can produce well-bonded materials in laminate form in which the materials have been both bonded and mixed, forming an attractive and repeating pattern that can be reproduced. The fact that mixing occurs at the same time as the bonding provides a reduction in the amount of subsequent work required to form the patterns that give Mokume Gane its appeal.
The method does not require high-temperature furnaces or the need to avoid oxidation of the metals and very little cleaning or sample preparation is required. It is also a relatively low-energy process since the whole sample does not require heating.
The patterns formed are unique to FSW and have the potential to be widely varied by changing the lay-up of the materials to be bonded and the friction stir conditions. After reaching steady-state conditions the patterns formed are stable and repeat in a regular manner but with a small natural and random variation, making each piece unique.
The bonds formed in the friction stir zone are a
combination of the intimate physical contact between the metals resulting in metal-to-metal bonds plus thermally enhanced mechanical alloying, producing microstructures not possible by conventional processing.
The nature of FSW means that large ingots of bonded material can be produced relatively easily using multiple passes of the friction stir tool through laminate layers. Other material lay-ups are possible, giving many possible variations in pattern, for example, bars of materials side by side or materials with regions inset with a second material.
On the smaller machines, such as the TTI, the maximum ingot size is ~300 x 150mm, with thickness determined by the number and thickness of the layers to be bonded but in the region of 10-30mm. Such large sizes are impossible using any other Mokume Gane production technique. In theory the larger PowerStir machine could make much larger sheets measured in metres.
With the constant development of FSW and the increasing availability of machines and tooling capable of carrying out the process, there is a great potential for both large companies and smaller individual makers to begin to experiment and develop new Mokume Gane materials.
In time this approach could also lead to the production of visually stunning architectural panels
For further information, contact [email protected]
Ancient and modern technologies overlapJapanese jewellery creation, and the more modern practice of friction stir welding (FSW) came together recently in a project involving the art and design sector of Sheffield Hallam university and TWI.
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Technology Transfer
Job Knowledge
119 Complying with NACE Hardness Requirements
Carbon steels in service in the offshore and oil refinery industries are susceptible to a cracking mechanism known as sulphide (SSC) or hydrogen (HSC) stress cracking when in sour service, ie when hydrogen sulphide (H2S) is present in the process fluid. Although the cracking is described as stress cracking, the main problem is the hardness of the parent metals, the weld and its heat affected zones (HAZs).
NACE (formerly the National Association of Corrosion Engineers) has published two specifications that provide guidance on reducing the risk of in-service cracking, one of these also being an ISO standard. The difference between these two primary specifications is the definition of environmental and service conditions for sour service. The first standard, ANSI/NACE MR0175/ISO 15156, Petroleum and natural gas industries - Materials for use in H2S-containing environments in oil and gas production, is intended for offshore applications and NACE MR0103, Materials resistant to sulphide stress cracking in corrosive petroleum refining environments, for onshore process plant. The latter specification refers to a recommended practice document for controlling welding activities to ensure a low and acceptable weldment hardness; NACE SP0472 Methods and controls to prevent in-service environmental cracking of carbon steel weldments in corrosive petroleum refining environments.
Whilst both MR0175 and MR0103 cover a wide range of materials (carbon, duplex and stainless steels, nickel and aluminium alloys) SP0472 and this article are concerned with carbon steels only, classified as P1 in ASME IX, ie hot finished carbon steels with a specified ultimate tensile strength less than 480MPa (70,000psi) and how weldment hardness in these steels can be controlled. Note that the BS EN 10028 steels are now assigned P numbers in ASME IX.
Both MR0175 and MR0103 have virtually identical requirements for specifying parent metal properties of carbon steels for sour service; the principal additional requirement being a maximum hardness. All steels that have been cold worked must be stress relief heat treated to ensure the hardness is less than 22HRC (Rockwell hardness, equivalent to 248HV or 235HB). Carbon steels other than P1 can be used provided that their hardness is also less than 22HRC.
Parent metals may be weld repaired as part of the plate production regime. These base metal repairs must also comply with the NACE requirements with respect to weld metal and HAZ hardness. In addition, although SP0472 is concerned with the results of welding any thermal cutting process will produce HAZ which, if not removed or welded over may result in HSC. 3mm of material should be removed to ensure that there are no areas of unacceptably high hardness.
SP0472 requires that the HAZs of all pressure boundary welds and internal attachment welds in pressure containing equipment comply with a maximum hardness of 248HV10, as do repair welds and some external attachment welds. Welding processes covered by SP0472 are the more common processes; manual metallic arc (MMA), MAG, FCAW,TIG and submerged arc welding.
To minimise the risk of producing unacceptably hard HAZs steels with a carbon equivalent (CE) less than 0.43 based on CE = C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15 should be used. This is less of a problem with many of the BS EN steels as these are specified to have low carbon contents or a maximum CE less than 0.42. ASME steels are permitted far higher carbon contents with no requirement to specify all of the elements required by the CE formula so care needs to be taken when ordering pressure containing materials against the ASME codes; ASME A 516 Gd70, for instance, can have a CE as high as 0.52. It will also be necessary to specify limits on micro-alloying elements such as niobium (Nb), titanium (Ti) and boron (B).
The hardness of production weld metal is limited to 200HB (211HV) although E60XX and E70XX electrodes and TIG and MAG deposits made with ER70S2, -S3 and -S4 and –S6 (with less than 0.1% carbon and less than 1.6% manganese) are exempt from this production
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Technology Transfer
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This article was written by Gene Mathers.
testing requirement. This implies that additional filler metal certification and batch control on the shopfloor is necessary to demonstrate compliance. It is difficult to achieve this maximum hardness figure when there is a large amount of dilution from the parent metal, for example when depositing root passes or from single pass fillet welds where very close control of the welding parameters is required. HAZ hardness may also be controlled by four separate methods; close control of the cooling rate, temper beading, postweld heat treatment (PWHT) and procedure qualification testing.
Control of the cooling rate requires the time to cool from 800-500OC (t8/5) to be controlled so that hard microstructures are avoided. This cooling rate must be specified for production welding, formulae for the calculation of t8/5 taking into account the relevant variables. Thickness, process heat input, joint configuration, preheat etc are given in Appendix C of SP 0472. The method is qualified by carrying out a pre-production weld test on representative parent material using the fastest cooling rate at which the HAZ hardness is acceptable; Several tests may be required. A successful test qualifies all other production welds made with cooling rates slower than that of the test piece, calculated from the formulae in Appendix C. This may require the welders to be specifically trained to deposit weld metal within very tight limits on travel speed, weaving etc and will require close supervision during production welding.
Temper beading is a method of reducing the hardness of HAZs by using the heat input from subsequent weld runs to refine and temper the HAZ of underlying weld passes. Clause QW290 of ASME IX specifies the requirements for temper bead welding, essential variables and weld procedure qualification. Hardness testing is mandatory and the positions of the hardness impressions are given in SP0472; the maximum hardness being required by the NACE specification.
The technique is useful when there is a need to carry out a local weld repair but requires very precise placing of weld runs and skill on the part of the welder to ensure a correct and consistent bead overlap and travel speed and that the temper bead layer does not overlap onto the base metal HAZ. Lengthy training is likely to be required before the welder can pass the qualification test and apply the technique in production. PWHT will reduce both the hardness of a weld and the residual stresses and both will reduce the risk of cracking. Depending on the construction code there may, in any case, be a requirement to PWHT - ASME VIII, Unfired pressure vessels, requires PWHT over some 32mm thickness, ASME B31.3, process piping, when thickness exceeds 19mm. As high a PWHT temperature as possible should be used to achieve the maximum amount
of tempering. BS EN 13445 Part 4 – the pressure vessel code - permits PWHT temperatures as low as 550OC and there is also an option in BS PD 5500 to use a similar low temperature which may not give the required reduction in hardness.
Welding procedure qualification is the most common method of complying with the hardness requirements. It is carried out in accordance with ASME IX requirements using production material or a steel of the same grade but with the maximum carbon equivalent of material to be used. The welding variables are recorded during welding of the test piece and hardness testing is mandatory, the hardness of the test weld HAZ to be less than 248HV, that of the weld metal less than an average of 210HV.
In addition to the ASME IX requirements, SP0472 requires butt and fillet welds to be qualified separately; although not mandatory, it would also be advisable to qualify separately single and multi-pass fillet welds. The hardness in a single pass fillet weld can easily exceed 300Hv, particularly when welding on thick steel, say over 25mm thick.
Test piece thickness (and hence the cooling rate) may be an issue since ASME IX allows production components to be twice the thickness of the qualification test piece. Where PWHT is not carried out on the thicker components, thought needs to be given to whether the procedure qualification test is carried out using the thinnest test piece allowed by the code or a test piece matching the maximum production thickness.
The welding procedure specifications (WPS) to be used in production must contain parameters matching those of the qualification test piece. Production welds must not differ more than -10 and +25% of the test piece and heat input, preheat and interpass temperatures must be the same as or greater than those of the test piece. Production welding is restricted to the same specification and grade of steel with matching or lower carbon equivalents.
Quality control must be based on best practice with well trained and qualified welders supervised by competent welding foremen and inspectors. Post weld inspection and NDE will be as required by the construction code. SP0472 does not make hardness testing of production welds mandatory but since an acceptably low hardness is crucial to satisfactory in-service performance and is sensitive to so many variables, it is advisable to perform some checking of weld and HAZ hardness on completion. This requires the use of portable hardness testing equipment and Job Knowledge articles numbers 74 and 75 discuss some of the methods available.
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July/August 2012
TWI Certification Ltd is pleased to announce the award to William Hare UAE LLC of Execution Class 2 Certification for certified Factory Production Control (FPC), in line with European CE marking.
The successful audit process at the company’s Abu Dhabi base in the United Arab Emirates was completed under the TWI UKAS accredited BS EN 1090-1 scheme for structural steelwork. William Hare UAE is the first to receive certification under the new TWI FPC system accredited scheme.
TWI Certification Ltd’s Ian Hogarth said: ‘We are delighted to announce the recent success of William Hare UAE. This was the first audit carried out by TWI Certification under the new scheme, and an indicator of worldwide industry focus on compliance with stringent technical standards to ensure competent production systems for safety critical components.’
During the recent audit, William Hare also achieved certification to ISO 3834-2, demonstrating compliance with EN ISO 3834 Quality Requirements for Fusion Welding of Metallic Materials. This scheme also satisfies EWF/IIW criteria for EN ISO 3834 certification.
William Hare UAE receives the first TWI certification for Factory Production Control
With a LinkedIn following of over 5000 and a fast-growing Twitter audience, TWI is pleased to be showcasing a selection of videos, photography and technical news on its newly launched Facebook site. Liking the TWI Facebook page will allow you to keep up to date with hot topics of news and events from the company, enjoy photography and video footage of a wide range of welding, joining and inspection processes, and to catch up with exciting developments in materials engineering and joining technologies.
TWI Chief Executive Christoph Wiesner comments: ‘I am delighted to announce the launch of TWI on Facebook. Our presence here is a further boost to the success of our online business and social networking channels, with membership of the TWI Technology Engineering group on LinkedIn fast approaching 6000 and our Twitter feed a great source of news and engineering information. Our online presence brings us closer to our customers and our customers closer to us.’
TWI showcases technical news and videos on Facebook
Q
Aregister now www.twi.co.uk
Are there any methods of improving the fatigue strengths of welded joints?
How difficult is it to braze titanium to steel?
In electronics reliability, what are ‘HALT’ and ‘HAST’?
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July/August 2012
News in briefGlobal success starts in Nigeria for TWI’s plastics welder training and certification.
An increase in demand for plastics welder training and certification is being driven by global changes in legislation that require certification to guarantee the skill and knowledge of welders when installing plastic fabrications. TWI can respond to this demand by delivering quality training in plastics welding processes and supporting this with recognised CSWIP certification.
MainLine action - well on track
A unique £4m rail project tailored to the needs of railway asset managers is about to complete its first quarter, already with considerable success.MainLine is an FP7 project and is
aimed at maintenance, renewal and improvement of rail transport infrastructure to reduce economic and environmental impact.
During its three year duration, the project will develop methods and tools that will contribute to a more cost efficient and effective improvement of European railway infrastructure, including earthworks, bridges, tunnels and track, based on whole life considerations.
TWI Certification Ltd achieves independent body status for certification of structural steelwork
The United Kingdom Accreditation Service (UKAS) has recently awarded TWI Certification Ltd authority to carry out conformity assessment for steelwork manufacturing companies
under the Construction Products Directive. With the new scope, TWI Certification is able to offer accreditation to ISO 3834 (Quality Requirements for Fusion Welding) and Factory Production Control (FPC), helping companies to gain the CE mark for their products.
For further information on TWI visit the website at www.twi.co.uk
For over two decades TWI has delivered training and examinations in India across many technologies As oil and gas contracts arise around the world (and increasingly in renewable energy) and as health and safety requirements become tighter, these certified individuals are best placed to fulfil the growing need for properly trained and competent workers.
In September 2011, Jim Kerins was appointed to establish a TWI office in Chennai, to focus largely on NDT and inspection techniques and deliver training and technical support. In January 2012 the office was opened and is now proud to be employing local manpower and resources.
To compete on a global scale, companies in India recognise the need to continually invest in engineering quality and embrace new processes and technologies. This opens the door wide for TWI’s new and novel NDT techniques, not just in terms of research and development, but training and technical support as well.
India proves a strong market for NDT; training, research and development
The first Japanese highly sensitive chemiluminescence analyser in Europe is now being demonstrated in TWI’s advanced materials laboratories at Great Abington, Cambridge, following a collaboration agreement with equipment developers Tohoku Electronic Industrial Company Ltd (TEI).
The agreement presents TWI with exciting opportunities for materials analysis and allows TEI to demonstrate the capabilities of the equipment to interested organisations in the UK and further afield for a range of applications – the chemiluminescence analyser is the most sensitive photon counting device and spectrometer in the world, detecting down to 50 photons/cm²/sec (about 1/10000 of a firefly) or 10-15W.
Chemiluminescence, or the discharge of ultra weak light invisible to the human eye, is generated in all materials as a result of atmospheric oxidisation. Use of the TEI chemiluminescence analyser will impact, for example, on studies in the advancement of high performance polymer materials in the aerospace or automotive industries, on quality control in the food industry and on biochemical degradation studies. Potential applications include: Measurement of peroxide content of soybean oil;
oxidation of beer or milk powder; chemiluminescence spectrum of food oil; analysis of human skin surface lipid peroxides; tumour cell detection; oxidation of tablets; oxidation of materials including polymers, elastomers and rubbers.
Dr Rie Yamada, President of TEI commented: ‘The agreement with TWI is an exciting move for our company in scoping future global opportunities for the use of the chemiluminescence analyser. We are delighted to showcase the equipment in TWI’s advanced materials laboratories.’
There are 500 cheminluminescence analyzers in operation in Japan; the unit at TWI is the first from TEI to be introduced in Europe.
Contact [email protected] for further information
Exciting opportunities for chemiluminescence measurement as TWI demonstrates Europe’s most sensitive analyser
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Connect is the bi-monthly magazine of TWIEditor Candy SmelliePhotography Simon Condie Production Candy Smellie © Copyright TWI Ltd 2012
Articles may be reprinted with permission from TWI. Storage in electronic media is not permitted.
Articles in this publication are for information only. TWI does not accept responsibility for the consequences of actions taken by others after reading this information.
This publication is also available in alternative formats. Please contact [email protected] to request a copy.
Published by TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK Tel: +44 (0)1223 899000 E-mail: [email protected] www.twi.co.uk
TWI Technology Centre (North East) Tel: +44 (0)1642 216 320 Fax: +44 (0)1642 252 218
TWI Technology Centre (Yorkshire) Tel: +44 (0)114 269 9046 Fax: +44 (0)114 269 9781
TWI NDT Validation Centre (Wales) Tel: +44 (0)1639 873100 Fax: +44 (0)1639 864679
TWI AberdeenTel: + 44(0)1224 691222
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Issue 179 July/August 2012
