Issue 166 May/June 2010

Diary events

June 2010

Materials Technical Group MeetingMaterials issues in defence and securityWed 9Great Abington

The WJS conferenceSOS! Specification or Standard: Sink or SwimWed 23 – Thu 24Great Abington

Technology Awareness DayTue 29Great Abington

September 2010

Advanced Structures Technical Group MeetingMilau ViaductThu 9Great Abington

5th Joint TWI/EWI SeminarJoining of aerospace materialsTue 21 – Wed 22USA

November 2010

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

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Safe under pressure - new test chamber now completedExtremely high pressure testing at TWI’s Cambridge laboratories took a step forward recently with the completion of a large subterranean pressure test pit. Serving the engineering needs of the oil and gas sector in particular it is believed to be one of the best equipped facilities of its type in Europe.

The establishment of the new test facility is linked with the start of a Group Sponsored Project on strain based assessment of pipeline girth welds. The specimen under test will be both axially strained and pressurised simultaneously.

‘The idea is not necessarily to take it to destruction’ explains project consultant Henryk Pisarski. ‘But we are applying very high loads at extremely high pressure, up to 1000 bar. The pipe will be strained considerably, in a four point loading test or in tension in a modified wide plate rig. In each case it will be strained beyond its yield point. There will be an intentional crack within it so the potential exists for things to go wrong. Without a remote pit like this you run the risk of damaging adjacent laboratory equipment, so we decided now is a perfect opportunity to build a dedicated facility’.

What makes the TWI facility so special is the back-up support offered behind any test work it performs; ‘We will pressurise it of course, but perhaps the client will want it to

be strain gauged and instrumented. We can do that. Perhaps the client even wants the event to be filmed. We are able to say “this is what we recommend”. And then we can carry out all the material behaviour analysis, if and when it fails. Whatever happens, we can do all the post-test investigation under one roof because we have all the metallurgists and engineers and equipment we need here at TWI. We can also compare the reality of the test with the results of numerical modelling, which can also be conducted at TWI’.

QAJoinIT

register now www.twi.co.uk

What are the main properties of a sound wave relevant to ultrasonic testing??

What are local brittle zones (LBZs)?

What is pulsed MIG/MAG welding and what are its advantages over conventional MIG/MAG processes?

For further information on TWI, visit the

website at www.twi.co.uk

continued on page 2

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May/June 2010

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Safe under pressure - new test chamber now completed

Aircelle LtdUKAerospace component manufacturer

BMT Fleet TechnologyUKEngineering research, development and consultancy

Caterpillar IncUSAConstruction and mining equipment, engines and engine systems

Delphi Electronics & SafetyUSAManufacturer of automotive injection and electrical systems

Dongkuk S&C Co LtdKoreaSteel structure and wind tower fabricator

GE Aviation Systems - NewmarketUKDesign, manufacture and testing of custom electronic components

Guangdong Xingfa AluminiumCo LtdPeople’s Republic of ChinaManufacturer of industrial aluminium profiles

Iranian Offshore Oil CompanyIranCrude oil production

Moog Insensys LtdUKHigh performance, low cost, fibre optic load measurement technology

Momentum Engineering LLCDubai UAEOffshore installation contractor

NRGThe NetherlandsServices for design and safety of operational and new generationnuclear power plant

Odenberg Engineering LtdRepublic of IrelandOriginal equipment manufacture for the food industry

Pertamina Hulu Energi ONWJ LtdIndonesiaExploration and production of oil and gas

Plasma Giken Co LtdJapanThermal spraying and cold spray systems design

Radiografias de Campeche SA de CVMexicoNDT inspection

RTS – InternationalUKWind turbine installation and maintenance

SC Grup Servicii Petroliere SARomaniaOffshore drilling, offshore constructions and well service

Shaanxi Guode Electric Co LtdPeople’s Republic of ChinaHigh voltage switchgear

Vibro-Meter UK Ltd UKEngine controls and sensors for the aerospace industry

Weldex SASouth AfricaFriction welding, specialised repairs and coding

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

continued from page 1

Measuring eight metres by three in plan, the 2.5m deep reinforced concrete bunker comprises a metre thick floor with 700mm thick walls. The multi-plate flat roof is made from eight 25mm thick steel plates, each individually removable.

Specimens will be craned into the chamber using a pair of 3t capacity A-framed gantries. Provisionally the pit will be able to accept specimens up to 6t in weight. Both hydraulic and pneumatic tests will be possible in either static or dynamic loading regimes.

Above ground the entire installation is housed within a large steel

fabricated out-house, equipped with mains and communication services. These include video monitoring and recording equipment dedicated to receiving digital signals from in-chamber cameras and test piece instrumentation.

Inside the pit two large diameter conduits have been installed at mid-height in the northerly wall to allow access for all instrumentation and communication services to be run between the specimen and the control centre.

‘Since this construction has been underway we have been approached about testing a sample from a pipeline

containing in-service damage to assess its fitness for continued operation.’

Now that there is an established controlled facility, rather than building a temporary structure for each new project, it is expected that a number of short notice projects related to internal pressure testing and external loading will be undertaken. Already there are half a dozen jobs on the waiting list related to last year’s destructive testing of electrical resistance welded pipe.

To learn more about TWI’s new pressure test facility contact: henryk.pisarski@twi.co.uk or phil.robinson@twi.co.uk

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May/June 2010

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Risk based, direct assessment of pipelines coupled with TWI Inspection Services

TWI has applied its direct assessment service to a network of 250km of buried, non-piggable gas and condensate pipelines in the south of Iran. The project provided a complete service to plan and perform inspection and also assessed the inspection results in terms of the pipeline fitness for continued service. The approach combined three main elements:

• Risk-based inspection (RBI)• Inspection services• Fitness for service assessment

With the recent release, development and adoption of direct assessment standards (eg NACE) for buried pipelines, TWI put together a service to maintain and prove the integrity of pipeline networks.

Direct assessment is a four step method to determine the condition of a pipeline. The methodology assesses the threat from external and

internal corrosion and stress corrosion cracking for both liquid and gas carrying lines. The approach consists of the following:

• Phase 1 - Pre-assessment (risk based study - using TWI RISKWISE for Pipelines)

• Phase 2 - Indirect inspection (above ground inspection and flow modelling)

• Phase 3 - Detailed examination (excavation and inspection)

• Phase 4 - Post-assessment (fitness for service assessment)

Phase 1 was a desktop study using RISKWISE for pipelines and identified external and internal locations most susceptible to damage. The result was a plan for above ground inspection and flow analysis recommendations.

Phase 2 carried out the plan recommended by Phase 1, focusing resources to areas highlighted as at highest risk of failure. Above ground inspection techniques such as direct current voltage gradient (DCVG) and close interval survey (CIPS) were used

to look for problems with the coating and cathodic protection system to screen for external damage areas. For internal damage, prediction flow modelling was used to highlight potential locations for build-up of water. The result of Phase 2 was a refined inspection plan for areas that required additional inspection by excavation.

Phase 3 was direct inspection by way of excavation. By this phase, the prior screening phases had filtered out areas where excavation would

have been unnecessary, so that only the highest risk areas were excavated based on evidence that there was potentially a problem. TWI’s long range ultrasonic system was used for inspection of key areas of the pipeline along with other inspection methods.

Phase 4 examined the inspection data and performed a fitness-for-service assessment to determine the safety of the pipelines and where necessary make run, repair, re-rate or replace recommendations.

The process allowed for an optimised condition assessment to be performed on the entire network of pipelines which could not be otherwise inspected without complete excavation.

For more information, please contact aim@twi.co.uk

The damage to the pipe under the coating.

Detection of a coating defect

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Technology Transfer

The previous article highlighted some of the problems encountered when welding duplex and superduplex stainless steels, in particular the need to control closely the heat input if an undesirable phase balance or the formation of brittle intermetallic phases are to be avoided.

This requirement has implications with respect to quality control. Variations in weld preparations which would be compensated for by the welder changing his welding technique, wide root gaps for example, may result in a significant change in heat input. Weld preparations therefore need to be more closely controlled than for a conventional stainless steel.

It is recommended that weld preparations are machined for greatest accuracy but, if hand-ground, close attention must be paid to the weld preparation dimensions. Welding supervisors and inspectors also need to understand the importance of heat input control, ensuring that welding is not allowed to take place outside the limits of the qualified procedures with regular checking of welding parameters and interpass temperature.

Hot cracking is rarely a problem due to the high ferrite content but has been observed, particularly in submerged arc welds. Cleanliness of the joint is therefore still important. Machining or grinding burrs and any paint should be removed and the joint thoroughly degreased and dried prior to welding. Failure to do so can affect corrosion resistance and joint integrity.

Hydrogen cold cracking, whilst unusual, is not unknown and can occur in the

ferrite of weld metal and HAZs at quite low hydrogen concentrations. It is recommended that the hydrogen control measures used for low alloy steel consumables should apply for duplex consumables. Submerged arc fluxes and basic coated electrodes should be baked and used in accordance with the manufacturer’s recommendations; shield gases must be dry and free of contaminants.

Most commercially available welding consumables will provide weld metal with yield and ultimate tensile strengths exceeding those of the parent metal but there is often difficulty in matching the notch toughness (Charpy V) values of the wrought and solution treated base metal.

TIG welding gives very clean weld metal with good strength and toughness. Mechanisation has substantially increased the efficiency of the process such that it has been used in applications such as cross-country pipelining.

Gas shielding is generally pure argon although argon/helium mixtures have given some improvements by permitting faster travel speeds. Nitrogen, a strong austenite former, is an important alloying element, particularly in the super/hyper duplex steels and around 1 to 2% nitrogen is sometimes added to the shield gas to compensate for any loss of nitrogen from the weld pool. Nitrogen additions will, however, increase the speed of erosion of the tungsten electrode. Purging the back face of a joint is essential when depositing a TIG root pass. For at least the first couple of fill passes pure argon is generally used although small amounts of nitrogen may be added and pure

nitrogen has occasionally been used.

TIG welding may be performed without any filler metal being added but is not recommended on duplex steels as the corrosion resistance will be seriously impaired. Filler metals are be selected to match the composition of the parent metal but with an additional 2 to 4% nickel to ensure that sufficient austenite is formed. Any stray arc strikes will be autogenous and must be removed by grinding.

MMA welding is carried out with matching composition electrodes overalloyed with nickel and either rutile or basic flux coatings. Basic electrodes give better notch toughness values. Electrodes of up to 5mm diameter are available with the smaller diameters providing the best control when welding positionally.

MAG welding is generally carried out using wires of 0.8 to 1.2mm diameter, rarely exceeding 1.6mm and of a similar composition to the TIG wires. Shielding gases are based on high purity argon with additions of carbon dioxide or oxygen, helium and perhaps nitrogen. Because of the presence of carbon dioxide or oxygen the weld metal notch toughness (Charpy V values) are less than can be achieved using TIG. Microprocessor-controlled pulsed welding gives the best combination of mechanical properties. Mechanisation of the process is easy and can give significant productivity improvements although joint completion times may not be as short as anticipated due to the need to control interpass temperatures to below the recommended maximum.

Flux-cored arc welding (FCAW) is used extensively with major productivity gains being possible in both manual and mechanised

Job Knowledge106 Duplex stainless steel. Part 2

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Technology Transfer

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applications. The flux core is generally rutile; the shielding gas CO2, argon/20%CO2 or argon/2%O2. The presence of carbon dioxide or oxygen leads to oxygen,and, in the case of CO2, carbon pickup in the weld metal, thus notch toughness is reduced. Metal cored wires are also available that require no slag removal; better suited to mechanised applications than flux-cored wires. Because of differences in flux formulation and wire composition between manufacturers it is recommended that procedure qualification is carried out using the specific make of wire used in production even though the wires may fall within the same specification classification.

Submerged arc welding (SAW) is generally confined to welding thick wall pipes and pressure vessels. Solid wires, similar to those available for TIG welding, are available. Fluxes are generally acid-rutile or basic, the latter giving the best toughness values in the weld metal. As with any continuous mechanised welding process the interpass temperature can rapidly increase and care needs to be taken to control both interpass temperature and process heat input. Because of the need to control heat input the wire diameter is normally limited to 3.2mm permitting a maximum welding current of 500A at 32V although larger diameter wires are available. However, any productivity gains from the use of a large diameter wire and high welding current may not be realised due to the need for interpass cooling.

There is often the need to weld duplex/superduplex steel to lower alloyed ferritic steel, a 300 series stainless steel or a dissimilar grade of duplex steel. The 300 series stainless steels are generally welded to duplex

steels with a 309MoL (23Cr/13Ni/ 2.5Mo) filler metal. Low carbon and low alloy steels may be welded to duplex steels using either a 309L (23Cr/13Ni) or a 309MoL filler metal.

These two filler metals, however, have yield and ultimate tensile strengths substantially less than most low carbon/low alloy steels and all duplex steels. This means the designer has to take this reduction of strength into account by increasing the component thickness or the welding engineer has to select a filler metal that both matches the strength of the weaker steel and is compatible with the two parent metals. These considerations narrow the choice to one of the nickel-based alloys such as alloy 82 or, for higher strength, a niobium-free high alloyed nickel filler, such as C22. or 59. Alloy 625 has been used but problems with reduced toughness due to the formation of niobium nitride precipitates along the fusion boundary have resulted in the alloy falling out of favour.

Duplex steel welds are seldom post-weld heat treated. Due to sigma phase formation they cannot be given a heat treatment at the low temperatures

of 600-7000C, the normal range for stress relief unless a qualification programme has been undertaken to demonstrate that the loss of toughness is acceptable. If PWHT is required then ideally the whole component must be given a solution anneal at 1000-11000C followed by a water quench; an impractical operation with most welded structures.

Lastly, any process that heats the steels above 3000C will affect the mechanical properties. Heat straightening to control distortion should therefore not be carried out. The HAZs produced by hot cutting processes like plasma or laser may contain undesirable microstructures. Cut edges that will enter service ‘as-cut’ must be ground or machined back for a minimum of 2mm to remove the HAZ and ensure there is no loss of toughness or corrosion resistance.

If the cut edges are welded after cutting then the HAZs are generally sufficiently narrow that the effects of the cutting operation are lost although it is recommended that, as above, the edges are ground or machined back 2mm.

This article was written by Gene Mathers

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May/June 2010

First CSWIP thermographic inspection certificate issued

TWI was approached by ROVision Ltd for advice on training. The company operates unmanned aerial vehicles (UAV) technology to supply inspection services to many different areas including oil and gas refineries, pipeline inspection and construction support for major building projects. ROVision recently purchased new infra red

cameras to carry out detailed aerial thermal inspection from their SR30 helicopter but getting certified training was becoming a problem as infra red inspection is still in its infancy.

Ian Hogarth, TWI’s Business Development and Training Manager suggested that the delegates come on TWI’s

new Thermographic Inspection Level 1 course held in Middlesbrough. Three students including company Managing Director Tony McConnell and Technical Director Bob Furness attended.

The course, although only Level 1, covered in detail the theory and application of thermography. The equipment

used was cutting edge technology and there were plenty of different models and makes to practice with. Professor Rod Thomas, one of the UK’s leading experts in the field of thermography was the course lecturer,.proved excellent, holding the attention of the class throughout. Tony McConnell of ROVision spoke of the course and the facilities at TWI Middlesbrough.

‘I have been in inspection for many years but this has to be the most interesting course I’ve ever attended’. He continued ‘the applications for thermography are incredible; I can see it overtaking many of the conventional forms of NDT in the next few years. I’m happy to be getting in at the very beginning. It’s an exciting time for ROVision and we are all looking forward to returning to TWI for the Level 2 course in the near future’.

TWI’s Thermographic Inspection Level 1 course (duration five days) is aimed at all engineering disciplines especially people involved with any maintenance or reliability issues including management, engineers, technicians and craft personnel.

The CSWIP scheme for those involved in condition monitoring, inspection of plant operation, maintenance and equipment has now been launched.

Anyone working in an engineering background environment is encouraged to attend this exciting new course. To find out more and register your interest please contact trainexam@twi.co.uk

Tony McConnell received the first CSWIP thermographic inspection certificate from EurIng Chris Eady, Chief Executive of TWI Certification Ltd

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May/June 2010

Adhesives and adhesion knowhowTWI’s Adhesive Bonder training is a modular course based on the Adhesive Bonder syllabus developed through the European Welding Federation. In response to the needs of industry, theory and practical training are now offered together or separately depending on attendees’ time constraints.

Focused workshops will help the user understand the underlying science and provide an opportunity to exploit the benefits of this versatile technology. Newcomers to the field will gain a sound knowledge of the area and practical hands-on experience. More experienced users will be able to expand and refine their knowledge.

Each workshop will finish with

an end of course assessment and all candidates will receive a TWI Certificate of Attendance.

For full details of dates, venues and prices, please visit www.twitraining.com

11th National Conference of The Welding & Joining SocietySOS! Specification or Standard: Sink or Swim!An update on directives and standards23-24 June 2010, TWI, Granta Park, Great Abington, Cambridge, UKBuilding on the highly successful events held in past years, this conference will provide the latest expert information and advice on current and emerging EU Directives related to welding and joining. Also covered will be European and International Standards and

their implementation and how to achieve compliance as cost effectively as possible. This conference is a recognised CPD event

Register online at www.eventsforce.net/10WJS

boom! Engineering the stars of tomorrowNorth East Engineering Show 2010Newcastle upon TyneWed 14 - Fri 16 July 2010This event, aimed at young people aged 11-17, will be the venue for TWI’s exciting ‘Welding with Chocolate’ stand. Attendees can try their hand at welding chocolate box girders, testing them to destruction and then eating their broken bridges!

News in brief

PEDITO – a unique plasma generation processTWI and Plasma Quest Limited (PQL) are partners in an exciting collaborative project part-funded by the Technology Strategy Board (TSB), for plasma enhanced (sputter) deposition of indium tin oxide and other transparent conducting compounds (TCCs).

The PEDITO project’s key differentiator is PQL’s unique plasma generation process that enables the sputter deposition of high rate, high quality coatings of many different materials at ambient temperatures.

After only three months, this one year project is significantly ahead of the original plan, with some exceptional early stage results.

Outside the PEDITO project, but potentially for further inclusion, other materials deposited at ambient temperatures include a wide range of dielectrics. Such materials can enable the fabrication of transparent semiconductors suitable for flexible electronics applications.

With the progress made thus far the project will concentrate more of its activities in developing a large area deposition process. The project’s technical leader, Dr Peter Hockley of PQL, is already developing a revolutionary system that will offer a fully integrated source and target solution capable of even greater widths whilst being readily retrofittable

to a variety of tools. With an initial deposition width of 1m, future developments to 3m widths are planned.

For further information see www.plasmaquest.co.uk or www.twi.co.uk

ITO on a flexible substrate

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IMPCOAT – a new project to extend the life of coatings

Connect is the bi-monthly magazine of TWI

Editor Penny Edmundson

Photography 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.

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 165 May/June 2010

TWI has been very active in developing thermally sprayed aluminium (TSA) coating applications since 2000 through work which includes three Joint Industry Projects (JIPs) on its use for the protection of welded components and structures in offshore locations. A widespread need has recently been identified for improved coating formulations to mitigate splash and tidal zone corrosion and to extend structural design life. As a result, a new JIP has recently begun which will provide support both to the oil and gas sector and the wider offshore community.

Current coating systems are vulnerable to mechanical and environmental damage and commonly fail well within structural design life. More than 25 years of oil sector experience indicates TSA coatings provide long-term protection. Improved coating formulations based on TSA, modified TSA compositions, novel sealants and leading organic coatings systems will be evaluated.

Quantitative coating corrosion measurement techniques will be used and a ruggedised coating performance monitoring unit will be trialled at an offshore site. It is expected that the data generated will provide confidence that coatings can achieve the desired 40 year life. A successful

outcome will bring several benefits to the industrial partners through:

• Reduced on-site coating repair and maintenance costs and lower life cycle costs

• Extended corrosion design life with extended maintenance intervals

• Reduced structural mass and lower material costs

• Reduced coating costs during fabrication

• Increased foundation production rates• Lower electricity unit pricesThe project is being funded not only by TWI Members, but also through the Northern Wind Innovation Programme (NWIP). NWIP partners comprise International Paint, Monitor Coatings, McNulty Offshore Construction, Vattenfall Wind Power and the University of Manchester. This approach utilises expertise throughout the supply chain ranging from R&D, product development and fabrication to asset operation.

For more information please contact dave.harvey@twi.co.uk