Issue 158 January/February 2009

A new partnership has been announced to accelerate the introduction of affordable silsesquioxane resins that enhance the performance of coatings, adhesives and bulk polymers.

Thomas Swan & Co. Ltd. has partnered with TWI to

commercialise their patented Vitolane® technology – a novel, affordable manufacturing route for silsesquioxanes which allows a high level of functional versatility.

Silsesquioxanes have a ceramic (silicon-oxygen) backbone with organic groups attached and aim to combine the benefits of polymers and ceramics in their performance and flexibility.

These organic-inorganic resins can be tailored to offer a range of functions to coatings, adhesives and bulk polymers such as improved abrasion resistance, increased resistance to heat and solvents and better barrier properties.

The technology is being actively investigated for a range of industrial applications such as durable coatings for

white goods and consumer electronics, hard optically-clear coatings for DVDs and CDs, flexible packaging and novel low-viscosity adhesives.

‘TWI has break-through technology to make the key performance benefits of silsesquioxanes much more accessible to industry’ says Russell Clarke of Thomas Swan. ‘Our partnership with TWI will create a secure manufacturing base to produce and supply these materials and so accelerate their adoption across a wide range of applications.’

For more information, please contact enquiries@vitolane.com

Diary events

February 2009

Offshore Oil and Gas Technical Group Meeting Reeled and flexible pipelines Wed 11 Aberdeen

March 2009

Industry Panel Meeting Aerospace Thu 19 Great Abington

Technology Event NDT Open Day Wed 25 Great Abington

April 2009

Seminar TAGSI Tue 7 Great Abington

TWI/NMI Seminar Astride the packing roadmap Wed 22 Great Abington

Institute of Rail Welding - 15th Technical Seminar Rail welding goes underground Thu 30 tba

Joint Welding Processes and Polymers Technical Group Meeting Technologies for cost reduction of wind tower fabrication Thu 30 Middlesbrough

May 2009

Annual Conference Welding & Joining Society Wed 13 – Thu 14 Great Abington

June 2009

Technology Group Meeting Materials Tue 2 Great Abington

For further details of events, contact TWI’s Meetings Section meetings@twi.co.uk

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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Thomas Swan to launch TWI’s advanced abrasion resistant additives

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January/February 2009

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Aker Subsea Ltd – Subsea Field

Development

UK Oil and gas development

Ahresty Corporation

Japan Aluminium die casting

Bredero Shaw (Singapore) Pte

Singapore Pipe coating

Contitech Beattie Ltd (including

Dunlop Oil & Marine)

UK Hose and coupling assemblies, fluid handling equipment

CTCI Arabia Ltd

Saudi Arabia Petroleum refining and transportation

Delphi Diesel Systems - Advanced Engineering UK New product development for diesel injectors

Exheat Ltd UK Petrochemical electrical heating and control systems

Geemac Sales & Marketing Ltd UK UK sales agent for sports and leisure equipment

HallRail Ltd UK Manufacture of railway switches and crossings, together with fabrications

Jimah Energy Venture (JEV) Malaysia Independent power plant

Klaus Raiser GmbH Germany Welding and friction welding

Mech-Tool Engineering Ltd UK Design, engineering, manufacture of metal structures for the oil, gas, petrochemical and energy industries

Microalloying Institute USA Metallurgical consulting, welding procedures and materials selection

Norsk Titanium AS Norway Production of titanium

PetroRabigh Saudi Arabia Petrochemical manufacture

Raytheon Systems Gls-Hlw Ltd UK Electronics for defence, fire protection and the automotive industry

SAIC Motor Technical Centre

China Automotive manufacture

Termate Ltd

UK Design and manufacture of electrical busbar systems with associated consultancy and testing

The Japan Steel Works Ltd

Japan Clad steel pipe

Thomas Swan & Co Ltd

UK Performance and speciality chemical manufacturing

Vanitec

UK Promotion of vanadium

A long-established North West company with an excellent track

record has become more effective at tendering for nuclear contracts, thanks to assistance from the North West Supply Chain project.The company operates at the Sellafield site and its specialist services include maintenance and demolition of large structures and nuclear decommissioning and waste conditioning. Management’s aim: to win more business in the UK civil nuclear market. Its strategy is to further improve the company’s ability to tender successfully. Assistance was provided by TWI’s nuclear decommissioning consultant Evan Wright, who has over 35 years’ direct experience of working in the nuclear industry. Evan said: ‘Working with the company, some previously submitted tenders were reviewed

from the perspective of the client’s assessor.‘Although the company clearly demonstrated considerable ability, recommendations were made regarding future tender responses; for example, ensuring that these are formatted to align with the structure of the Invitation To Tender questions, and that relevant photos with captions are included to help communicate the company’s track record.‘Specific advice from a key customer’s assessor was also provided in a one-to-one meeting with the company,’ said Evan.The advent of the Nuclear Decommissioning Authority and consequent restructuring of supply chains, along with the introduction of more open competition, have created a new business environment in UK civil nuclear decommissioning.

Through expert advice and in-depth assistance, the North West Supply Chain project is helping companies meet the challenges presented by this new scenario.To organise NWSC assistance, or if you need more information, please contact: nwdsc@twi.co.uk or visit www.nwdsc.com

Tendering strategy meets challenge of new business environment

New Members of TWITWI is pleased to welcome the following as Industrial Members.

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January/February 2009

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Most manufacturing processes result in residual stresses which

can be at a level high enough to affect the structural integrity of the component.

Without knowledge of the residual stress field, assessments are often overly conservative. There are many

measurement techniques available but there are disadvantages to many of those in current use.

Mechanical methods, such as centre-hole drilling, have been used extensively but they require material removal and are therefore destructive. X-ray and neutron

diffraction methods are non-destructive but expensive.

TWI has recently investigated a new technique based on laser generated ultrasound. It is advantageous in that it is non-contact, non-destructive and can be used in most materials. Variations in the velocity of the ultrasonic waves can be related to the residual stress state. Finite element modelling has been used to determine the capability

and sensitivity of the technique for residual stress measurement by looking at both uniform tensile residual stress fields of different magnitudes and tensile residual stress fields that vary in magnitude through the thickness of a steel plate.

The modelling results show a clear correlation between the magnitude of the residual stress and the surface acoustic wave behaviour.

Laser generated ultrasound is believed to be a viable technique for residual stress measurement with the advantages of being non-destructive, applicable to most materials and relatively inexpensive to apply. The technique has the potential to be more readily used and therefore removes the need for over-conservative assumptions for residual stress in fitness for service and engineering critical assessments.

For more information on this technique, contact nmo@twi.co.uk

Residual stress measurement – an alternative solution

Predicted sound energy field after (a) 600 nanoseconds and (b) 4200 nanoseconds. Pulse is excited via a laser pulse (top left) then the ultrasonic pulse generated travels along the surface.

The Handbook of Plastics Joining, published by William Andrew Inc. in

1996, has been completely revised by staff from TWI’s Polymer Group.

The new edition has now been published and is a unique reference publication that provides detailed descriptions of all of the plastics joining processes, from conventional ultrasonic welding, adhesive bonding and mechanical fastening through to newer techniques such as laser and friction stir welding.

The second part of the book contains

data on the joining of specific plastics materials, divided into 25 generic polymer families. The book also contains an international suppliers directory and an extensive glossary of key terms used in plastics joining.

The Handbook of Plastics Joining, Second Edition, edited by TWI’s Mike Troughton, is available to industrial and professional members of TWI at a reduced price of £140. http://www.twi.co.uk/content/professional_handbook.html

TWI leads revision of unique publication

(a)

(b)

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Technology Transfer

The development and use of high strength low alloy (HSLA) steels has been driven by the need to reduce costs, the higher strength compared with a conventional carbon-manganese steel enabling thinner and lighter structures to be erected. The majority of these steels are to be found in structural applications; offshore structures, yellow goods, buildings, shipbuilding etc. Tensile strengths of up to 690MPa are achievable whilst still maintaining good weldability and high notch toughness, often better than 50J at -60°C.

There are two methods by which both high tensile strength and toughness is achieved – by micro-alloying, adding small amounts of strong carbide and nitride formers and by very careful control of the rolling temperature - controlled rolling or thermo-mechanically controlled processing’ (TMCP steels).

The highest strengths are achieved by a combination of the two methods. The aim of both methods is to produce as small a grain size as possible, fine grain giving the best notch toughness and each halving of the grain diameter producing a 50% increase in tensile strength.

Improved weldability is an additional objective and this is achieved by reducing the hardenability of the steel, the carbon content of some steels being lower than 0.05% C, and reducing undesirable elements such as sulphur and phosphorous to as low a level as possible.

To compensate for the loss of carbon and to increase tensile strength small

additions of alloying elements such as niobium (<0.10%), titanium (<0.030%) and vanadium (<0.15%) are made, perhaps also with small amounts of molybdenum, chromium, copper and nitrogen. These elements are strong carbide and nitride formers, producing a fine dispersion of stable precipitates that inhibit grain growth during hot rolling and assist in nucleating fine grained ferrite during cooling.

These elements also provide some increase in strength by precipitation hardening. Controlled rolling by the TMCP hot rolling method may also be used to provide additional grain refinement and hence an increase in tensile strength and toughness. TMCP is carried out at a temperature about or just below the recrystallisation temperature of the steel ie below about 900°C, resulting in elongated crystals of austenite. Accelerated cooling from the rolling temperature then causes very fine grained ferrite to form on the austenite grain boundaries.

Despite the improved weldability of these steels there are some fabrication problems. Firstly, hydrogen induced cold cracking.

The low carbon content – and hence low carbon equivalent, sometimes less than 0.30CEv - means that these steels have a low sensitivity to hydrogen

cold cracking (see Job Knowledge 45 but note that the standard IIW carbon equivalent formula is not valid for all of these steels and cannot always be relied upon when calculating preheat temperatures).

The HSLA steels can therefore be welded with lower preheats than would be permitted for conventional carbon-manganese steels, despite their higher strength. The highest risk of cold cracking in these types of steels is therefore in the weld metal, rather than the HAZ. There are several reasons for this; a) The high strength of the parent metal means higher residual stresses during welding, b) To match the tensile strength and toughness of the parent steel, the filler metals need to be more highly alloyed and therefore will have a higher CEv,

Job Knowledge98 Welding of HSLA steels

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Technology Transfer

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perhaps as high as 0.6CEv(IIW) if matching the tensile strength of a 700MPa yield steel with an E11018-G electrode. c) The weld metal transforms from austenite to ferrite at a lower temperature than the parent steel (it is generally the other way round in a conventional carbon-manganese steel) meaning that any hydrogen in the HAZ is rejected into the still austenitic weld metal which has a high solubility for hydrogen. A preheat based on the weld metal composition is therefore advisable and low hydrogen techniques must be used. The exceptions to this rule are those HSLA pipeline steels specifically designed to be welded with cellulosic electrodes. Advice regarding the preheat temperature for specific steels should be sought from the steel manufacturer.

Secondly, even though steels generally have very low levels of sulphur, the steels containing less than 0.05%C

may suffer from solidification cracking in the root pass of butt joints, particularly if the root bead is deposited at a high welding speed. The reason for this is that high dilution of the filler metal produces a weld metal low in carbon. This low carbon content in its turn leads to excessive grain growth of the austenite during welding and these large grains increase the risk of centre line solidification cracking in the root bead. This problem appears to be most prevalent in pipe butt joints welded using cellulosic electrodes, probably due to it being possible to use a fast, vertical-down welding technique.

Thirdly, toughness and strength in the HAZ can be an issue. The steel manufacturer takes great care to control rolling temperatures and cooling rates to provide the desired properties. The component is then welded, producing a heat affected zone that has experienced an

uncontrolled cycle of heat treatment. The microstructure in the HAZ will vary with respect to the composition of the steel and the welding process heat input. A high heat input will promote grain growth and this will have an adverse effect on both strength and toughness. As a rule of thumb, heat input should be restricted to around 2.5kJ/mm maximum and the interpass temperature maintained at 250°C maximum, although some of the steels containing titanium and boron can tolerate heat inputs as high as 4.5kJ/mm without undue loss of strength. For a definitive statement on heat input control the advice of the steel manufacturer should be sought.

These steels must under no circumstances be normalised or tempered although post weld heat treatment (PWHT) is often a requirement when the component thickness is greater than some 35 to 40mm. Care needs to be taken if PWHT is applied that the soak temperature does not exceed 600°C – a temperature range of 550°C to 600°C is often specified. The reason for this is that many of the TMCP steels are accelerated cooled to a temperature of around 620°C; heat treating at or close to this temperature will result in a substantial reduction in tensile strength due to over-tempering. The same restriction applies to any hot working activity; plate must not be hot rolled and the temperature of local heating for correction of distortion must not be allowed to exceed 600°C.

Further advice on the welding of these steels can be found in the trade literature and in the specification EN 1011 Part 2. Recommendations for welding of metallic materials: arc welding of ferritic steels.

This article was written by Gene Mathers.

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January/February 2009

Engineers from one of TWI’s Industrial Members delivered the

remains of a welded manifold valve to TWI’s defect characterisation and interpretation experts. They needed to know the reason the component cracked.

The valve was a substantial forging made from F22 alloy steel. A central hole had been machined around which a stub had been welded. Cracking occurred at the toe of this weld.

TWI took a methodical approach to solving the problem:

visually examined and photographed it in intensive detail

inspected it using liquid penetrant, magnetic particle inspection and ultrasonic testing

cut it open to allow one of the dye penetrant indications to be broken open, then examined the fracture

surfaces using light microscopy and scanning electron microscopy

re-assembled the remaining parts of the fracture surfaces and took a metallographic section for examination using light microscopy. Features of particular interest were photographed at high magnification and hardness measurements were made in the parent material and heat affected zone

analysed the chemical composition of the parent material using optical emission spectrometry

The results of these examinations focused attention on the discovery of a flaw about a half millimetre in depth. Examination of the metallographic section through the flaw revealed products of oxidation and corrosion on the flaw surface.

This indicated that the flaw was present when the component was at elevated temperature, ie during postweld heat treatment (PWHT), but it was not consistent with a forging defect. Original features of the flaw had been destroyed during PWHT and subsequent corrosion but close examination allowed TWI to rule out reheat cracking as a possible cracking mechanism.

Detailed discussion took place

between TWI and its client based on the findings and TWI was able to advise that the defect formed due to hydrogen cracking, primarily as a result of inadequate control of preheating.

Five recommendations were made related to the importance of pre-heating control, post weld heat treatment and consumable drying to allow the client to overcome the problem.

To learn more about TWI’s defect characterisation services, contact HYPERLINK “mailto:fer@twi.co.uk” mcs@twi.co.uk

Manifold failure in service ...but why?

QAJoinIT

register now www.twi.co.uk

How can I avoid local brittle zones?What is the place of automation and control in welding?Are there any differences between fracture toughness tests?

For further information on TWI, visit the website at

www.twi.co.uk

January/February 2009

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News in brief

• Metallography of heat-affected zones in carbon-manganese steels

• Quality assurance in welded fabrication • Visual inspection of welded joints • Introduction to welding processes - 1 • Introduction to welding processes - 2 • Safe working with arc welding • Safe working with gas cutting and welding

Individual posters are priced at £15 (ex VAT and P&P) or the full set of seven posters at £90 (ex VAT and P&P) and can be bought on-line from the shop area of the training website: www.twitraining.comNew posters will become available throughout 2009. If you wish to be kept updated, please e-mail: nadine.earp@twi.co.uk

Following a successful launch in October 2008, TWI Training & Examination Services is now running a second course aimed at managers and engineers involved in fabrication or metal components or those interested in the research and development of materials joining. A mixture of classroom work and practical demonstrations,

the course will provide the knowledge to make confident decisions about the process when involved with equipment suppliers or process providers. The next course will run from 21-23 April 2009 in Rotherham. Further details may be found at http://www.twitraining.com/world/courses/index.jsp?coursecode=ATC210%20

TWI has updated seven of its technical posters:

An introduction to friction stir welding

Welding engineering courses taught at TWI have been assessed by the Open University (OU) for the national Credit Accumulated Transfer Scheme (CATS) points. These courses start from a level designed for the practical person, and success in the examinations gives the candidate points towards an OU degree. Furthermore, the OU is developing Foundation Degrees in engineering, one specifically designed around the TWI courses that will make the steps to higher qualification more manageable.

The initiative is part of a wide-ranging effort by TWI to stimulate growth in engineering qualifications. It has an agreement with Cranfield University for exemption of part of the Welding Engineering MSc course for those who hold a Diploma from TWI. TWI is also instrumental in the establishment of a new chair in the OU engineering department, the Lloyd’s Register Educational Trust Chair in Materials Fabrication and Engineering.

TWI and the Open University join forces

In October 2008 TWI’s Structural Integrity Group held technical

seminars in Japan and China, both of which proved to be very popular and successful events.

Presentation topics included amongst others fatigue, fracture, modelling, distortion, residual stresses and risk based inspection.

The Japanese Seminar in Tokyo is a well established annual event which has been successfully running since 1989. The British Embassy was once more a very welcoming and most hospitable partner and many of TWI’s

longstanding business friends attended the event. The idea to hold a seminar in a similar format in China was a first try this year and we were overwhelmed by the response! About 100 attendees from a large variety of companies were present at the event which was held at the Jiaotong University in Shanghai.

Plans for 2009 are already being developed and TWI is looking

forward to continuing the close relationship with its Industrial Members in Japan and China.

Seminars in Japan and China prove a hit

Attendees at the TWI seminar in China which was held at Jiaotong University in Shanghai

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Connect is the bi-monthly magazine of TWI

Editor: Penny Edmundson

Photography: Simon Condie,

Production: Penny Edmundson, John Dadson

© Copyright TWI Ltd 2009

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.

Designed by: Jenny May

Printed by: Fisherprint Ltd Tel: 01733 341444

Published by: TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK Tel: +44 (0)1223 899000 Fax: +44 (0)1223 892588 E-mail: twi@twi.co.uk www.twi.co.uk

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Issue 158 January/February 2009

TWI is now ideally placed to use its new high pressure hydrogen facilities and expertise as European industry moves towards a hydrogen economy. Already two collaborative calls have been made relating to materials performance which necessitates use of high pressure equipment and TWI is seeking industrial partners for projects in response to these calls..

Careful design and build has been undertaken and commissioning of TWI’s new facility is nearly complete. The equipment will allow mechanical testing to be carried out in hydrogen pressures of up to 1000bar, under dynamic tensile and fatigue loading regimes.

Material will be tested dynamically in the environment allowing the effect of hydrogen environmental embrittlement on tensile, low cycle fatigue and toughness properties of materials to be quantified. The equipment will be able to operate over a temperature range of –150 to +85°C and at pressures of up to 1000 bar.

Development of safe, cost effective materials and fabrication routes are priorities for TWI. TWI is represented on the ISO 11114-4 committee for which is concerned with testing methods to allow selection of metallic materials resistant to hydrogen embrittlement.

Two forthcoming collaborative calls are relevant to this subject area.

The first is part of Framework 7 through the Hydrogen and Fuel Cells Joint

Technology Initiative. Details of the calls are described in the Implementation Plan and can be downloaded at: www.hfpeurope.org/hfp/keydocs

The second call is from the Technology Strategy Board (TSB) which is a UK based initiative, and is entitled: Environmental sustainability: fuel cells and hydrogen technologies.

It is anticipated that demand for the TWI facilities will be high and testing programmes are already planned. Industrial Members requiring more information should contact hydrogen@twi.co.uk

High pressure H2 equipment - partners now sought for European and UK collaborative projects