Schematic of canister repository

Issue 168 September/October 2010

Diary events

November 2010

Joint TWI/DVS ConferenceLatest developments in joining plastics in mass production and fabricationTue 2Düsseldorf

FESI SeminarStructural integrity of welded structures – what have we learnt?Wed 3Great Abington

Pressure and Process Plant Technical Group MeetingNuclear new build in the UKThu 4Great Abington

TWI Annual DinnerTue 9London

Structural Integrity Technical Group MeetingStrain based fracture assessmentTue 23Great Abington

December

18th IoRW Technical SeminarDevelopments in rail inspectionWed 1 Great Abington

WJS SeminarStandards for offshore power and low carbon energyWed 8Middlesbrough

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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The safe and effective storage and disposal of high level waste (HLW) and spent fuel (SF) arising from nuclear power generation is a global issue, posing major technical challenges. When TWI was asked by Nagra to advise on suitable welding technologies for hot cell encapsulation of HLW and SF, TWI was able to establish a multi- disciplinary team to investigate the best choice of welding processes. Nagra is the Swiss national co-operative for the disposal of radioactive waste and is responsible for final disposal of all types of radioactive waste produced in Switzerland.

TWI was selected for the project due to significant experience with other long term

dry cask and repository storage projects for the global nuclear industry such as the successful development of friction stir welded copper canisters for SKB and the hot cell welding procedures for closure of the canisters to be stored in Yucca Mountain.

From the outset it was clear that the Nagra approach to encapsulation would pose entirely new challenges to the welding processes. The chosen material for the canister construction was to be carbon steel, 190mm thickness with a minimum lifetime of 1000 years. The timescale for development also added challenges. With the weld production not scheduled until 2035, all processes had to be considered.

After brainstorming, literature reviews and preliminary investigations TWI engineers reduced the list of potentially viable welding processes from over thirty to two: electron beam welding (EBW) and narrow gap tungsten inert gas (NG-TIG) welding. These processes were then researched and investigated extensively and all details of advantages, disadvantages and the technology readiness level were reported. This included in-depth analysis of potential metallurgical and residual stress issues arising from each of the potential techniques. In addition to the welding process technology, methods of non destructively testing the welds in a hot

Selection of welding processes for high level nuclear waste encapsulation

continued on p. 2

CSWIP Welding QC Co-ordinator – a popular new scheme

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September/October 2010

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Aker Solutions (Drilling Risers)USAOil and gas engineering

Cytec Industries UK LtdUKCoatings and composites

Fotolec Technologies LtdUKShatterproof coatings application to standard lamps

ILVA SpAItalySteel production of flat products and welded pipe

ITER Organisation - Magnet Division FranceDevelopment of magnet technology for the ITER programme

Johnson & Starley LtdUKManufacturer of heating and ventilation products

Swagelining LimitedUKProvision of integrated lining systems

TATA Steel LtdIndiaDesign, manufacture and supply of plant equipment and cranes

Woodside Energy LtdAustraliaOil and gas exploration, production and development

Welding Alloys LtdUKWelding consumables, machines and service

New Members of TWI

TWI is pleased to welcome the following as Industrial Members

Aerospace Industry PanelTWI held its 35th Aerospace Panel Meeting on 15 September 2010, with attendees from the UK, Japan, USA, Brazil, Germany, France and Sweden.

There were TWI presentations on microwave curing of composites, cold spray forming for additive manufacture, developments in high brightness laser processing and EB welding of crack sensitive materials.

This was supplemented by excellent presentations from MTU, GKN Aerospace and BAE Systems.

Two Group Sponsored Meetings took place the previous day and there were several meetings between Industrial Members and TWI staff during the week.

The next Aerospace Panel Meeting is scheduled for 16 March 2011, with two Group Sponsored Project Meetings due to take place on 15 March and a linear friction welding seminar planned for 17 March.

Details will follow in due course and more information can be obtained by contacting Richard Freeman, the Aerospace Industry Sector Manager at richard.freeman@twi.co.uk

cell environment were also investigated and reported.

The results of TWI’s work were published in a Nagra report and presented at a meeting in Wettinngen, Switzerland. TWI’s report was subsequently issued

publicly along with a previously published material selection report. This work formed a precursor for a multi-year study to develop designs for carbon steel canisters, which was issued as an open tender in March 2010.

TWI (with Hitachi Zosen Corporation as a subcontractor) successfully bid for this competitive tender. Nagra evaluated the offers received on the basis of the financial offer, qualification and experience of the bidder, qualification and experience of the experts, proposed project work plan and an oral presentation made to Nagra. For more information about this project and TWI’s services to the nuclear industry please contact: simon.pike@twi.co.uk,rajesh.patel@twi.co.uk chris.punshon@twi.co.uk or colin.walters@twi.co.uk

Cross-section of hot wire, narrow gap gas tunsten arc welding in180mm P91 steel

Single pass, fully penetrating electron beam weld in 280mm thickness C-Mn steel

continued from p.1

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September/October 2010

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The TSB collaborative project Advanced Design Partitioning and Test for System in Package electronics (ADEPT-SiP) has now come to a close. Partners within the project were:

• TWI: lead partner, assembly, reliability, environmental research

• Filtronic Broadband: RF communications end-user

• Zarlink Semiconductor: medical modules end-user

• Zuken: design flow, partitioning, supply chain management

• AWR: RF design flow, Process Design Kits (PDKs)

• Leeds University: RF simulation, models, PDKs

• Mentor Graphics: thermal design

• QuantumCAD: design rules, layout

• Wurth Elektronik: process architectures, manufacture

The partners formed a complete supply chain for production of a SiP module.

The objective of the ADEPT-SiP project was to develop and demonstrate a rigorous, right-first-time design and supply chain management methodology for novel SiP electronics. The ADEPT-SiP module architecture involved a high density interconnect (HDI) printed circuit board with integrated passive components. One face of the HDI substrate was allocated for RF functions and the other for digital functions. Active devices were mounted by wire bonding or flip chip bonding on both the upper and lower faces of the module substrate.

A design kit has been successfully produced that can select which passives to integrate according to cost and other priorities. Models have been integrated into the design kit, to show RF performance of the passive components and interconnect. Resistors, capacitors and inductors have been successfully printed onto a HDI substrate and achieved close to design values. Thermal cycling, humidity testing and highly accelerated stress testing has been used to test the reliability of the embedded passives.

Demonstration medical and RF modules were produced, showing promising results for commercial products.

For further information, please contact helen.goddin@twi.co.uk.

ADEPT at System in Package – collaborative project draws to a successful close

Active devices

ADEPT-SiP module

HDI substrate

Mother board

Encapsulation

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Technology Transfer

In Part 1 the importance of cleanliness, particularly the removal of all sulphur containing compounds, was mentioned. With respect to defect free welding of nickel and its alloys this cannot be over-emphasised.

As well as sulphur, however, there are several other substances that can lead to embrittlement of the nickel alloys when they are exposed to high temperatures. Amongst these are lead, phosphorus, boron and bismuth.

These may be present in oils, grease, cutting fluids, paints, marker pen inks, temperature indicating crayons, etc; it may not be possible to avoid using these during fabrication so it is essential that these are removed if the component is to be welded, heat treated or is to enter high temperature service.

Fuel gases frequently contain sulphur and it may be necessary to use radiant gas heaters or electrical elements for local heating or in heat treatment furnaces.

Nickel alloys can be welded using all the conventional arc welding and power beam processes, the commonest processes being TIG or MIG with pure argon, argon/hydrogen or argon/helium mixtures as shield gases and MMA where basic flux coatings provide the best properties.

However, if argon/helium mixes are used it is only when there is more than 40% helium that any significant benefits with respect to penetration and improved fusion will be noticed. Submerged arc welding is restricted to welding solid solution alloys using basic

fluxes. Matching welding consumables are available for most of the nickel alloys. See Job Knowledge 22 for recommendations for a range of alloys.

Slag from MMA welding and particularly submerged arc welding can be difficult to remove from the nickel alloys and often needs to be ground between runs to remove it completely. It is also often necessary to grind the surface of each run when welding with the gas shielded processes to remove oxide scabbing, wire brushing simply polishing these oxides.

Failure to remove slag or oxide scabs will result not only in weld metal inclusions but also reduce corrosion resistance if left on exposed surfaces. Total welding times can therefore be substantially longer than the equivalent joint in stainless or carbon steel and welders need to be fully acquainted with these differences when converting from welding steels to nickel alloys.

Comments regarding the recommended weld preparations were included in Part 1. Although the weld preparations are similar to those used for steel it is worth considering the use of double V or U type preparations at thicknesses less than would be considered with steels. The additional cost of the preparation is offset by savings in consumable costs (nickel being an expensive metal) and welding time.

The majority of nickel alloys are best welded in the annealed or solution treated condition, particularly if the alloys have been cold worked. As mentioned in Part 1, preheat is not required except to remove condensation or if the ambient

temperature is below about 5OC when a moderate preheat of 40-50OC is recommended.

Interpass temperature should not be allowed to rise above 250OC although some alloy suppliers recommend an interpass as low as 100OC for certain alloys such as Alloy C276.

Remember the potential hot crack problems if thermal crayons are used to measure this temperature! For most alloys heat input should be controlled to moderate levels (say 2kJ/mm maximum) to limit grain growth and HAZ size although for some Alloys 718, C22, and C276 for example, a maximum heat input of 1kJ/mm is recommended.

Conversely if too fast a travel speed is used in an attempt to maintain a low heat input this can result in a narrow weld bead sensitive to centre line cracking. Adequate testing during welding procedure development should be used to optimise the range of acceptable welding parameters.

The solid solution alloys such as Alloy 200 or 625 do not require post weld heat treatment to maintain corrosion resistance but may be subject to PWHT either to reduce the risk of stress corrosion cracking if the alloy is to be used in caustic soda service or in contact with fluoro-silicates or to provide dimensional stability.

A typical stress relief treatment would be 700OC for ½ an hour for Alloy 200; 790OC for four hours for the higher chromium content alloys such as Alloy 600 or 625.

The nickel-molybdenum alloys are identified with the prefix B eg B1, B2, etc. and are used in reducing environments, such as hydrogen

Job Knowledge108 Welding of nickel alloys Part 2

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Technology Transfer

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chloride gas and sulphuric, acetic and phosphoric acids. Alloy B2 is the most frequently encountered alloy and matching filler metals are available. Unlike Alloy B1, Alloy B2 does not form grain boundary carbide precipitates in the weld heataffected zone, so it may be used in most applications in the as-welded condition.

Alloy 400, a 70Ni-30Cu alloy, has good corrosion resistance when exposed to hydrofluoric acid, strong alkaline solutions and sea water.

A matching filler metal, Alloy 190, is available but this can become anodic in salt solutions, leading to galvanic corrosion and it is recommended that one of the Ni-Cr alloy fillers such as Alloy 600 or 625 is used in this environment.

The age hardened alloy K-500 does not have a matching filler metal and is generally welded using the Alloy 190 filler, the reduction in strength being taken into account during the design phase.

Precipitation hardened alloys are best welded in the solution treated condition; welding these alloys in the age hardened condition is likely to result in HAZ cracking.

The ageing process in the alloys is sufficiently sluggish that the components can be welded in the solution treated condition and then aged at around 750OC without the mechanical properties being degraded.

A solution treatment of the welded item followed by ageing will provide the highest tensile strength.

The sensitivity of the age hardened alloy to cracking causes problems when attempts are made to repair

items, particularly when these have been in high temperature service and additional precipitation on the grain boundaries has occurred.

Little can be done to overcome this problem apart from a full solution heat treatment but this is often not possible with a fully fabricated component. If repair is to be attempted, small weld beads and controlled low heat input welds are recommended.

If the design permits, a low strength filler metal, eg Alloy 200 or 600, may be used to reduce the risk. Buttering the faces of the repair weld preparation, sometimes combined with a peening operation, has been successful.

Many of the nickel alloy filler metals have been used for making dissimilar metal joints with excellent results; dilution when welding joints between ferritic, stainless and duplex steels being less important than when using a type 309 stainless steel filler.

Nickel also has a coefficient of thermal expansion between that of ferritic and austenitic steels and therefore suffers less from thermal fatigue when high

temperature plant is thermally cycled. Alloy 625 has been a popular choice, the weld tensile strength matching or exceeding that of the parent metal.

There are limitations to this approach, and caution needs to be exercised when selecting a suitable filler.

For example, Alloy 625 has been extensively used for welding dissimilar joints in austenitic and duplex steels.

Use of this filler metal has resulted in the formation of niobium rich precipitates adjacent to the fusion line and has been discontinued. Alloy 59 or C22 filler metals has replaced Alloy 625 as the filler of choice.

The moral of this is, if there is any uncertainty, ask an expert!

This article was written by Gene Mathers

Erratum:In the table included in Job Knowledge 107, the percentage of Fe in Alloy 825 should read 28% and not 38%.

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September/October 2010

In-service inspection

In general terms, inspection may be applied to three main sectors of industry: manufacturing, fabrication and in-service.The manufacturing and fabrication sectors have developed inspection regimes specific to their products. These products are in many ways repetitive, predictable and inspection procedures have been proven to be effective when applied by competent inspection personnel.

In-service has not been subject to the same level of development and scrutiny.

With ageing assets and capital investment at a premium, it is necessary to try and develop non-

invasive inspection techniques to locate and quantify failure mechanisms at an early stage in order to manage and control the possible interruption to production and possibly safety and revenue.

By identifying the defined possible failure modes and mechanisms in a timely manner, it is then possible to re-schedule planned maintenance shutdown of plant to accommodate repair and if necessary replacement of components.

TWI recognises the importance of this sector of industry and

has the necessary knowledge, resources and experience to assist in the management, control and development of relevant and appropriate inspection processes and procedures.

These include:

• Integrity management• Appropriate research and development facilities• NDT Validation Centre• Appropriate and relevant personnel training and certification, including Employer Specific Schemes

in accordance with BS EN 473 and ISO 9712.

Recent developments include:

• Specific training and certification in corrosion monitoring using manual ultrasonic techniques

• Training and CSWIP certification scheme for personnel inspecting drillstem components (rotary tool and drillpipe).

For more information, please contact: bill.brown@twi.co.uk

QAJoinIT

register now www.twi.co.uk

Why is preheat used when arc welding steel and how is it applied?

Are duplex and superduplex steels fit for purpose under conditions of cathodic protection?

Are there any standard tests for plastics welds?

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September/October 2010

WJS/DVS Conference on Joining Plastics International Conference on the latest developments in joining plastics in mass production and fabrication 2 November 2010 Handwerkskammer, Düsseldorf, Germany This event, which will be conducted in English, is organised jointly by the WJS of The Welding Institute and the German Welding Society (DVS).

Twenty papers will be presented in two parallel sessions. Areas covered will include new developments in laser welding, infrared welding, ultrasonic welding and adhesive bonding; welding of thermoplastic tanks and pipes; joining of composites; testing of welded joints; and qualification of plastics welders.

For further information please contact simone.mahlstedt@dvs-hg.de or visit www.dvs-ev.de/joiningplastics2010.

Advanced manufacturing and engineering in the US Midwest and Indiana. New opportunities for the UK businesses.Joint event organised by UK Trade & Investment East and the State of IndianaThursday 11 November 20109:00-14:00 TWI, Granta Park, Great Abington, CambridgeThe United States is the world’s largest manufacturing economy, employing nearly 12 million Americans and producing manufactured products worth up to $1.6 trillion. The US market represents 18%of the world’s manufactured goods, largely due to Midwestern manufacturing companies that have a strong orientation toward knowledge- intensive manufacturing.

The state of Indiana and the UK Trade & Investment East would like to ex-tend an invitation to join UK specialists and an Indiana business delegation and explore new

opportunities in the Midwest advanced manufacturing and engineering sector.

For the full programme or to book your place at this FREE event, please call 01707398382 or email bookevents@uktieast.org.uk

Appointment of new TWI DirectorsWith the significant growth in TWI’s research and technology business during recent years, we have strengthened the executive team to lead this key area into the future. Separate Research and Technology functions have therefore been established. Dr Paul Woollin has been appointed Director, Research to focus on research strategy and quality to ensure the maintenance and enhancement of TWI’s technical reputation and Professor Aamir Khalid has taken up the post of Director, Technology to concentrate on commercial technology development to drive profitable business growth.

News in brief

Over the last sixty years TWI has been pioneering welding and associated engineering technologies.

TWI Services North America was founded to extend the services the TWI Group could offer to engineering companies, from a local base, within the North American region.

The new office in Houston primarily supplies advanced engineering services to the oil, gas, chemical and

power generation sectors.

The services supplied range from complex structural integrity studies to manufacturing and fabrication support.

If you are based in the North American region, you can now find out about the local news and events via our new website: www.twinorthamerica.com

Don’t forget to add it to your favourites.

TWI North America

For further information on TWI, visit the website at

www.twi.co.uk

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Connect is the bi-monthly magazine of TWIEditor: Penny EdmundsonPhotography: Simon Condie Production: Penny Edmundson

© 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.

This publication is also available in alternative formats. Please contact marketing@twi.co.uk to request a copy.

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

TWI AberdeenTel: + 44(0)1224 691222

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Issue 168 September/October 2010

The first CSWIP Welding Quality Control Co-ordinator course took place in Great Abington, UK on 23 August. At the end of this five-day course, candidates were invited to a cake cutting ceremony to celebrate the official launch of this new programme!People holding CSWIP welding inspection certification with several years’ experience often asked us about the next logical step on their career ladder.

In addition, the modern inspector’s roles have changed in the last few years and often the title of QC Engineer is thrust upon them or they are expected to be equally proficient in several disciplines.

The Welding QC Co-ordinator programme is designed to bridge the

knowledge gap between welding inspection and quality control.

A highly subscribed second course has been held in Middlesbrough and will be followed by a furthercourse in Great Abington starting on 22 November. Further courses will be available in 2011

This new scheme is proving to be very popular so don’t delay enrolling!

For further information, please visit www.twitraining.com call +44(0)1223 899500 or e-mail trainexam@twi.co.uk

CSWIP Welding QC Co-ordinator – a popular new scheme