Issue 164 January/February 2010

Diary events

February 2010WorkshopLasers in nuclear decommissioning Wed 17Great Abington

March 2010WorkshopLasers in nuclear decommissioning Wed 3Great Abington

WorkshopLasers in nuclear decommissioning Wed 17Great Abington

April 2010Technical Group Meeting Welding ProcessesTitle: tbc Thu 1 Venue: tbc

SkillWeld competition finalsTue 6 – Fri 9 Great Abington

TAGSI Seminar Structural integrity Challenges to new buildTue 20 Great Abington

Technical Seminar Institute of Rail WeldingWed 28 Wolverhampton

May 2010International meeting 8th Friction Stir Welding SymposiumTue 18 – Thu 20 Germany

MaterialsTechnical Group Meeting Materials issues in underwater weldingDate tbcVenue tbc

June 2010ConferenceThe Welding & Joining Society Wed 23 - Thu 24Great Abington

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

w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k

Innovative bed manufacturing and new product development

Joanna Lewis of TWI is working on a two year Knowledge Transfer Partnership (KTP) project on joining technologies for the largest UK bed manufacturer, Silentnight Beds, in Barnoldswick, Lancashire.Partially funded by the UK’s Technology Strategy Board (TSB), this type of project aims to provide British companies with access to cutting edge technology while offering career development to the associate.

The research provider, TWI, provides the KTP associate with advisors and full access to the technologies and laboratory facilities in Cambridge.

Lewis explains, ‘Silentnight Beds provides a commercial mentor, a contribution to the cost of the project and, crucially, a real world industrial need. In this case I will be working to revolutionise the bed industry, developing innovative joining technology specifically in the textile joining and polymer joining aspects of bed design’.

Bed manufacture is based on traditional materials and methods using stitching,

stapling, adhesives and other mechanical fastenings as the joining methods.

There is great potential to reduce costs and increase productivity by introducing high speed textile welding methods such as ultrasonic and laser welding combined with automation and robotic manipulation for many of the tasks.

New materials are also being investigated to reduce waste, enable recycling, end of product life disassembly and to assist with the manufacturing developments.

Progress in the project to date, includes a range of new product concepts, textile joining trials, joining process selection, initial prototypes and the design specification for new textile welding technology to be introduced at a high manufacturing level within Silentnight Beds’ current manufacturing system.

If you would like more information about this project or the KTP scheme, please contact jo.lewis@twi.co.uk

A sample of an ultrasonically welded mattress top design, replacing a ‘tufting’ manufacturing process.

2

January/February 2010

Connect Januar y /Febr uar y 2010 w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k

TWI receives Health and Safety certificate from Lloyd’s Register CEO

AAR Mobility SystemsUSAPallets, shelters and containers for the defence industry

Aker Solutions E & C LtdUKEngineering and construction

Aquilex Welding Services BVThe NetherlandsOil, gas and nuclear energy services

Arvin Meritor LVSFranceAutomotive supplier (latches)

Arvin Meritor HVS (Trailer) LtdUKSuspension and axle systems for trailers

Chevron CorporationUSAEnergy resources

Danfoss Commercial CompressorsFranceManufacturer of compressors for air conditioning and refrigeration

DavyMarkham LtdUKDesign, manufacture and installation of heavy engineering components

ExxonMobil Development Company – UpstreamUSAOil and gas operations

Fusion for Energy (F4E)SpainDevelopment of fusion reactors

Granada Material Handling LtdUKDesign, manufacture, installation and testing of overhead cranes

INPEX Browse LtdAustraliaOil and gas operations

IWE GmbH & Co KGSpainMaterials testing

Libyan Emirates Oil Refining Co Lerco

LibyaOil refining

Matre Instruments ASNorwaySubsea equipment manufacturer

Oil States Industries Inc, HoustonUSAOil and gas industry tools, components and services

PSB Anlagenbau GmbH & Co KGGermanyShipbuilding, marine engineering and offshore construction

Recycled Product Technology LimitedUKProduct development

Rhyal Engineering LtdUKSite-built storage tanks, tank refurbishment, piping and steelwork

SealSkinz LtdUKDesign and manufacture of waterproof gloves, socks and hats

Swenox LtdSwedenExhaust system manufacture

Techlam SAFranceDesign and manufacture of laminated elastomeric components

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

In January 2010, TWI Ltd was presented with a certificate to mark its achievement of certification to Occupational Health and Safety Management System (OHSAS 18001). The certificate was presented to TWI’s Chief Executive, Bob John, by Richard Sadler, CEO of Lloyd’s Register Group and current President of The Welding Institute.

Richard Sadler remarked on the very positive feedback he had heard from the LRQA assessor ‘The attainment of this standard shows TWI’s commitment and desire to take safety to a higher

level. All practical activities which reduce the risk help to take the business forward.’

This standard specifies the requirements for an occupational health and safety management system, taking into account legal requirements and information about occupational health and safety risks.

As an ISO 9001 registered organisation, TWI took the LRQA Prism approach to installing a Safety Management System (SMS). Over approximately 12 months, the TWI team carefully planned and implemented the SMS in stages. Each stage was then reviewed by the assessor over six visits. This new

certificate complements TWI’s existing certificated management systems for Quality (ISO 9001) and Environment (ISO 14001) to demonstrate the company’s commitment to continuing improvement for customers, staff and the environment.

Bob John receiving the OHSAS 18001 certificate from Richard Sadler, CEO of Lloyd’s Register Group

w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k Connect Januar y /Febr uar y 2010

January/February 2010

3

TWI is pleased to announce the introduction of its Thermographic Inspection programme, aimed at those responsible for review and approval of thermographic inspection procedures and qualifications.

Infrared thermography is a non-contact technology where accurate temperature distributions across a surface are used to monitor machine or component condition and in some cases to predict failure. This technique is used in many industries especially in manufacturing, distribution, transmission, retail and various processing worldwide. Over recent years the technology has become more affordable to most industries resulting in the need to carry out new technology training.

There are a number of benefits to this training including reducing failures, improvement in safety standards but

also a reduction in energy usage.

Also, this technology applies to all engineering disciplines and therefore promotes and enhances multi-discipline working and team building.

Thermography inspection is a diagnostic condition monitoring technique operating at three generic levels each taking five days and include practical testing:

- Level One - Thermographic Inspector, where the main responsibility is to collect accurate qualitative condition information and reporting

- Level Two - Quantitative Inspector, as above and in addition to interpret and analyse results, to develop quantitative thermography and produce written instructions

- Level Three - Management and supervisory, where a thermographic programme is designed and managed or where there is a need to carry out internal training.

In addition to these, TWI will be launching new thermographic inspection specialist options such as:

• Medical• NDT

• Buildings• Electrical• Mechanical• Research and development• Plant process.

TWI will be introducing a certification scheme later in the year for those involved in condition monitoring or inspection of plant operation and maintenance and equipment. Anyone with an engineering background is encouraged to attend these new exciting courses.

To find out more and register your interest please contact Customer Services on + 44 (0)1223 899500 or e-mail trainexam@twi.co.uk

QAJoinIT

register now www.twi.co.uk

Whyarefracturetoughnesstestsnecessary?

Whatisthedropweighttest(orPellinitest)?

Howcantackweldingbeusedtominimisedistortion?

Thermographic inspection

New thermographic inspection training at TWI

For further information on TWI, visit the website at

www.twi.co.uk

Connect Januar y /Febr uar y 2010 w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k4

Technology Transfer

The previous Job Knowledge article, No. 103, dealt with the metallurgy of austenitic stainless steels and some of the welding problems that may be encountered.

Austenitic stainless steels can be welded with all the commercially available welding processes. There are matching filler metals available for most of the austenitic range of alloys, the exceptions being that there is no type 304 filler metal available (this alloy is generally welded with type 308 filler metal) and no type 321 filler due to the problems of transferring titanium across the arc. Type 321 steels are usually welded with a type 347 filler.

Also mentioned In Job Knowledge 103 was that the austenitic stainless steels are metallurgically simple alloys and room temperature mechanical properties are not significantly affected by variations in the welding procedure. However, increasing the oxygen and ferrite levels will reduce the toughness at cryogenic (~-196oC) temperatures.

Basic coated manual metal arc electrodes with a controlled short arc length and basic agglomerated submerged arc fluxes are required for best toughness if arc welding processes are used. The steel and filler metal should be selected with as low a ferrite content as possible, say 1 to 3% for best Charpy-V test results.

Conversely, for best creep resistance an ‘H’ grade steel should be selected and rutile or acid/rutile electrodes and acid submerged arc fluxes should

be used. These improve the creep strength by increasing the titanium and niobium content of the weld metal, forming a greater concentration of grain strengthening carbides.

TIG (GTAW) welding of the root pass must always be carried out with an inert gas back purge to prevent loss of chromium (and hence of corrosion resistance), argon being the gas generally used for this purpose. Nitrogen may be used but there is a risk of the weld deposit absorbing nitrogen, thereby becoming fully austenitic and hot crack sensitive.

Two characteristics of austenitic stainless steels that differentiate them from ferritic steels are the coefficients of thermal conductivity and expansion. Austenitic stainless steels have a low coefficient of thermal conductivity, approximately 1/3rd that of ferritic steel at room temperature and a coefficient of thermal expansion some 30% more than that of a ferritic steel.

Higher expansions in a narrower HAZ result in higher residual stresses and more distortion. This is a particular problem with thin sheet fabrications where the achievement of the desired dimensional tolerances can be extremely difficult and costly to achieve. The use of accelerated cooling techniques such as copper chills or a freezing gas (the liquid CO2

low stress-no distortion technique typifies this approach) have been used to reduce distortion to acceptable levels.

One of the main reasons for using an austenitic stainless steel is its corrosion resistance. Whilst this is primarily a function of the chromium content of the steel, carbon also has a major but adverse effect resulting in a form

of corrosion known as intergranular or intercrystalline corrosion (ICC) or weld decay, a localised effect confined to the HAZ.

Carbides present in the HAZ of an austenitic stainless steel dissolve on heating and reform on cooling during the welding heat cycle. Unfortunately, these new precipitates form preferentially as chromium carbides on the grain boundaries, depleting chromium from the region immediately adjacent to the boundary, resulting in a local loss of chromium and a reduction in corrosion resistance. If sufficient chromium carbides are formed this results in a network of steel along the grain boundaries sensitive to corrosion; the steel has been sensitised. This sensitisation occurs in the HAZ region that has seen temperatures between 600 and 900OC and times that may be as short as 50 seconds.

There are several methods that may be used to overcome this difficulty. A solution heat treatment (1050OC followed by a water quench) will re-dissolve the carbides and these will be retained in solution on rapid cooling. Whilst this will eliminate the chromium depleted regions it is rarely practical to solution-treat complex welded structures.

The most obvious alternative technique is to reduce the carbon content. This has two beneficial effects:

• The lower the carbon content, the longer the time required to form the carbides. At 0.08% carbon this time is around 50 seconds; at 0.03% carbon the time required is about eight hours, most unlikely to be achieved during welding!

Job Knowledge104 Welding of austenitic stainless steel. Part 2

w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k Connect Januar y /Febr uar y 2010

Technology Transfer

5

• The lower the carbon content then the fewer carbides there are to form a continuous chromium depleted network. Hence the ‘L’ grades, type 304L, or 316L, are preferred where best corrosion resistance is required.

One other method is the addition of alloying elements that will form carbides in preference to chromium; thus the stabilised type 321 and 347 grades containing titanium and niobium respectively were developed.

Titanium and niobium are very strong carbide formers that precipitate carbides at higher temperatures than those at which chromium carbides will form so there is no carbon available to react with the chromium. However, even these stabilised grades may corrode in a very narrow band close to the fusion line (the so-called knife-line attack) in the presence of hot acids. This is due to the higher and more restricted temperature range at which the niobium or titanium carbides dissolve. The solution, as above, is to limit the carbon to 0.03% maximum.

Welding consumables must also be selected with low carbon content if best corrosion resistance is required. Most arc welding consumables contain less than 0.03% carbon but there are filler metals available with carbon contents of up to 0.10%; these should only be used to weld the ‘H’ grades of steel where good creep resistance is required.

Although MAG (GMAW) welding is often used it should be remembered that carbon pick-up is possible when argon/CO2 mixtures are used, particularly if the welding is carried out in the dip transfer mode. Argon/2% oxygen mixtures are therefore generally preferred where best corrosion resistance is required

but argon/10% CO2/2% oxygen is a good compromise that can be used for a broad range of applications.

The other major service problem encountered with the austenitic stainless steels is that of stress corrosion cracking. This may be caused by strong alkali solutions but it is the halides (chlorides, fluorides and bromides) that are primarily responsible. Cracking takes place in areas of high stress, as the name suggests, and is not therefore confined solely to welds, but it is at and adjacent to welds that stresses approaching the yield point of the metal are found and these present a particular problem.

The cracking is transgranular and propagation rates can be extremely rapid given the ideal conditions. In hot concentrated chloride solutions, for example, penetration can occur in thin, sheet components within a few minutes. However, the lower the temperature and/or the acid concentration then the rate of crack propagation is correspondingly slower. Austenitic stainless steels are therefore not generally used where halides are present. Even here, stress corrosion cracking (SCC)may occur due to contamination, either of the product in the pipe or vessel or externally from sea water, particularly where the liquid is able to concentrate in crevices.

To eliminate any chance of SCC, the only solution is to stress relieve the weld at a temperature of around 700 to 900OC. It should be remembered that:

• this may sensitise the steel so only low carbon grades should be used and

• the steel may embrittle due to sigma phase formation (see Job Knowledge 103) at the lower heat treatment temperatures.

Local stress relief should be approached with caution as the temperature gradients may result in stresses developing outside the heated band; wider heated bands and more stringent control of temperature gradients than required by specifications or codes may therefore be necessary. Solution treatment (1050OC soak followed by very rapid cooling, ideally a water quench) will eliminate all residual stresses whilst avoiding both sensitisation and embrittlement but is rarely practical on a welded assembly.

The alternative is to select a steel that is more resistant; the molybdenum bearing grade type 316 is better than 304 or 321. The ferritic stainless steels (Job Knowledge 101) are not susceptible to chloride SCC.

Stress corrosion cracking (SCC) in Type 316L stainless steel

This article was written by Gene Mathers

Connect Januar y /Febr uar y 2010 w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k6

January/February 2010

An unusual training project has given one of TWI’s Industrial Members a unique insight into low cost non-destructive examination of its assets. Three members of Metalysis staff have been trained by TWI in replicating the surfaces and microstructures of in-service components for laboratory examination.

Replication of microstructures and surfaces allows many industries to derive information on the material condition of their assets without need for sampling and subsequent repair, yet there are very few opportunities to be guided by experts in the art. TWI provides customised training in a wide range of topics.

Metalysis operates a series of high temperature molten salt cells in a highly corrosive environment. It needed a quick and reliable way of examining its vessels’ interiors to determine whether they had reached the end of their practical lives.

The extreme operating temperature, more than 900°C , precluded using most of the popular and available non-destructive testing techniques during operation. However if surface replicas could be made during the brief cool down periods they could be examined, away from the equipment under investigation, in the less frenetic surroundings of a materials laboratory. So Metalysis asked TWI to train its staff in two metallographic techniques.

The first involved making rubber replicas of untreated surfaces. It’s a well developed technique at TWI and has been used successfully on-site for several decades. However this was the first time that TWI had provided training in reproducing rubber surface replicas to a Member company. The work went well.

It allowed Metalysis to obtain accurate three dimensional copies of a critical component’s surface topography without taking it out of service. Pits and cracks were all reproduced in graphic relief in the rubber replica. The detail is sufficiently fine that, with the use of a microscope, it is a simple task to assess the extent and severity of pitting, or

any other form of surface degradation. It’s fast, inexpensive and useable on almost any surface, in any orientation.

The second technique taught to Metalysis involved the in-situ preparation of surfaces to reveal their underlying microstructure. The client was trained in grinding and fine polishing to a mirror finish, using standard metallographic techniques, and then schooled in how to etch the surface accurately to reveal its relevant features.

Modifications in the surface preparation can reveal a variety of different features, so a great deal of information can be obtained from a single site. This is followed by applying a specially prepared acetate which replicates the microstructure in a form that can be subjected to high power light microscopy.

The technique’s versatility was demonstrated on both flat and curved surfaces, so emulating actual site conditions on plate and pipe respectively. TWI’s expertise in handling, storing and interpreting the replicas was also made available to Metalysis.

The training was a complete success and TWI is keen to offer the same service to other Industrial Members. For more information, contact roger.barnett@twi.co.uk or stuart.bond@twi.co.uk

Customised replica training gives insights into material microstructures

Surface of a component after replicas were taken

January/February 2010

7 w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k Connect Januar y /Febr uar y 2010

Negara Brunei Darussalam is a developing nation located in one of the highest growth regions of the world but it relies significantly on imported manpower and skills.

Back in 2006, Joffren Omar Company Sendirian Berhad (JO) and Syarikat Kejuruteraan Sistematik Sendirian Berhad (SKS) embarked on a plan to train and develop local talent in the welding profession. A purpose-built facility was built in Seria with technical advice and guidance from TWI which has been associated with JO/SKS since 2000.

The facility was constructed to provide training facilities not only for welders but also for welding inspectors, painting inspectors and NDT professionals. The new facilities opened in December 2008 and a Senior Supervisor and a Master Welding Instructor were hired with TWI’s help.

On 8 December 2009, JO/SKS headed by Gary Young, presented the first nine home-grown apprentices with a certificate of completion of the Welder Apprentice Scheme.

When these young Bruneians signed on the scheme, they had basic or little knowledge of the standards and competence required to be oil and gas welders.

Yet in a matter of months, through their own dedicated effort and supported by their instructors and supervisors, they have qualified at the highest international standards

acceptable to Brunei Shell Petroleum (BSP) and Brunei Liquefied Natural Gas (BLNG), that is, CSWIP Level 3 oil and gas, 6G and 6GR positions.

Through this initiative, JO/SKS continue to demonstrate their investment in Brunei’s human resources development.

Indeed, it is a strong indicator of the companies’ commitment to BSP’s Local Business Development policy. With the cooperation and support of international organisations such as TWI, and local agencies such as Immigration, Labour, Ministry of Education and others, it is hoped that Brunei will have enough skilled workers to cover its needs in the future.

For more details, please contact: Ibrahim Omar at ibrahimo@josks.com.bn

Welder Apprentice Scheme in Brunei a great success

News in brief

5th International EWI/TWI Seminar Joining Aerospace MaterialsCall for papers – deadline 1 March 201020-21 September 2010, Cincinnati, USATopics will focus on improved or recently developed technologies for welding and joining for a variety of materials. Manufacturing and repair needs will also be addressed. A title and 300 word abstract should be submitted to Brad Hudson, EWI

Events Co-ordinator, at bhudson@ewi.org

Adhesive bonding technical workshopsTWI is holding both theoretical and practical workshops again during 2010 at its headquarters near Cambridge. They are based on the Adhesive Bonder syllabus developed through the European Welding Federation. Theory and practical training can be carried out together or separately depending on the attendees’

requirements. For more information contact trainexam@twi.co.uk or go to www.twitraining.com

TWI in North America We are pleased to announce that TWI has now moved to a new office in Houston, Texas. The address isTWI North America LLC1505 Highway 6 South, Suite 380, Houston, Texas.Tel: +1 281 680 2000E: john.aller@twinorthamerica.comWeb: ww.twinorthamerica.com

8

TWI member companies have free access to MI-21 consumables database

Connect is the bi-monthly magazine of TWI

Editor Penny Edmundson

Photography Simon Condie

Production: Penny Edmundson, John Dadson

© Copyright TWI Ltd 2010

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.

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

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 Technology Centre (Wales) Tel: +44 (0)1639 873 100 Fax: +44 (0)1639 864 679

TWI AberdeenTel: + 44(0)1224 691222

w w w . t w i . c o . u k e - m a i l : t w i @ t w i . c o . u k

Issue 164 January/February 2010

The MI-21 database of ferrous and non-ferrous metals, and welding, brazing, soldering, spraying and surfacing consumables was launched in July 2008.

The aim of the database is to save industry time and money in finding accurate data and sourcing products.

Current products and standard grades are supported by around 60 years’ of archive information. This unique combination allows users to identify old standard grades and products used to build structures which now need repair and maintenance, then to find companies making comparable products today. Some of the most fascinating projects for which the information has been used include the rebuilding of historically important aircraft and steam engines.

Details of source documents are given, plus suppliers, with merger and acquisition information for consumable manufacturers included where known.

At present MI-21 contains almost 50,000 datasheets. Due to the size of the original databanks, TWI and World Metals Index (WMI) have prioritised by inputting the most popular products and standard grades, and are continuing to add items, particularly in response to enquiries and the publication of new standards.

The data is searchable by:

• trade name,• standard grade/classification,• chemical composition,• mechanical and physical properties,• form,• workability (MI-21 Metals),• country of origin,• keywords and free text.

Where appropriate, each product links to its source document, supplier and comparable standard grade(s). Datasheets not only link to the source standard, but to products conforming to that grade, allowing the selection of alternative products. A reporting function can compare products/grades by individual elements and/or other properties, either as a table or as an X-Y chart.

Ten percent of the estimated 500,000 products/grades held by TWI and WMI have now been digitised. Subscribing to MI-21 gives access to both online data, and to non-digitised records via the Support Service; help in searching the database is also provided.

TWI Industrial Members can access the MI-21 database free via the Information Services page of the TWI website www.twi.co.uk

For further information go to www.mi-21.com or contact mi-21@twi.co.uk.