Phased array ultrasonics inspection of wind turbine aluminium blade roots

Issue 180 September/October 2012

TWI Events

Materials Issues in the Power Sector

Power

6 November 2012Great Abington

Technical Group Meeting and BSI Standards Meeting

Offshore oil and gas

19–20 November 2012

Aberdeen

NDT and Condition Monitoring Technical Group MeetingPower and oil and gas12 February 2013Glasgow

Advanced Structures Technical Group MeetingConstruction and engineering7 March 2013Great Abington

Linear Friction WeldingAerospace14 March 2013Great Abington

Exhibitions

Fabtech

All technologies

12-14 November 2012 Las Vegas, Nevada, USA

Structural Integrity Management Conference

All technologies

27-28 November 2013

Aberdeen Workshops and seminars are recognised Continuous Professional Development events

T h e m a g a z i n e o f T W I

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High temperature test facility assesses material performance in HCl environments

The test facility is located within the Trevor Gooch Corrosion Laboratory to comply with safety requirements. Concentrations >200ppm HCl can only be provided as a gas from cylinders containing a maximum of 1%HCl requiring additional safety measures including gas detection sensors and restricted access to personnel because the short term exposure limit for HCl gas is 5ppm.

The facility has been used on a current Group Sponsored Project on the development of coating technologies for high temperature, chlorine-induced, corrosion mitigation in biomass, waste to energy and other process plants to evaluate the performance of coated superheater tubes for boiler applications. It comprises two, 10kW, front-loading kilns which incorporate corrosion test cells (335mm internal diameter x 470mm long), manufactured from 316 stainless steel. These can support testing of samples for months at a time with continuous temperature monitoring. Samples can be tested with and without molten salt mixtures which can be introduced using alumina crucibles containing the appropriate salt mixtures and samples. Due to the capacity of the cells, the facility can be used for testing other materials subject to gaseous HCl attack in other industrial applications.

Contact mcs_contact@twi.co.uk for further details.

TWI has designed and constructed a new high temperature test facility for assessment of material performance in environments containing up to 1000ppm HCl in air, at ambient pressure and temperatures up to 600°C.

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Engineers from the research and manufacturing divisions of the Wuhan Iron and Steel (Group) Corporation (WISCO), China, have completed a valuable three month training and awareness secondment to TWI – returning home with deeper knowledge, and practical experience, across a range of joining, surfacing and related technologies. The time spent with TWI experts, has also demonstrated how, as an Industrial Member of TWI, they can best use our resources to add value to their own technology development services and manufacturing operations.

WISCO is a major steel producer in China and the secondment, the first of such duration, was established as a three month project. Content and activities were tailored to the technical and commercial profile of

WISCO and its continuous development as a solutions provider to a multi-sector customer base.

Wuhan Iron and Steel (Group) Corporation celebrates valuable technology secondment

ACAL Energy LtdUKPower - renewable

Anadarko Petroleum CorporationUSADeveloping, and exploring for oil & gas resources

Black Cat Engineering & Construction W.L.L.QatarEngineering, procurement and construction for O&G

Borealis GroupBelgiumPolyethylene (PE) and polypropylene (PP) plastics

Bouygues TP/ Laing O’Rourke,UKCivil engineering and infrastructure

Camcon Technology LtdUKDevelopment of gas lift technology for oil industry

Cytec Surface Specialties SA/NVBelgiumAerospace composite resins

Dhuruma Electricity CompanySaudi ArabiaConstruction and operation of power plant

FCC Environment - Allington Integrated Waste Management Facility Co LtdUKLandfill: Waste to energy

Kolon IndustriesRepublic of KoreaSports, leisure clothing and textiles

Laser Technology Centre RussiaResearch and development in natural sciences and engineering

Peerless Europe LimitedUKSuppliers of filtration/separation equipment for oil and gas industry

Spiral Weld LtdUnited Arab EmiratesEngineering, welding and machining

Teledyne Corman LtdUKCorrosion monitoring services and equipment - subsea

Time CorporationJapanPrecision machining for LCD and semi-conductor industry

Weir Engineering Services Ltd - Turbomachinery EngineeringUKService of rotating machinery

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

We are always open to applications from Materials Scientists, Metallurgists and Welding Engineers, in particular experts in corrosion and ferritic steels with knowledge of the oil and gas sector.

For current vacancies, please see our careers page www.twi.co.uk/careers or to apply speculatively email your CV and covering letter to recruitment@twi.co.uk

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The research programme includes the production of P92 pipe welds with the narrow gap TIG (NG TIG), TOPTIG, variable polarity submerged-arc (VP SAW), flux-cored (FCAW) and electron beam (EB) welding processes. The soundness of the experimental welds is verified via non-destructive testing (NDT) and mechanical testing. Following these, an extensive creep testing programme is planned to determine their high temperature properties.

The preparation and NDT/mechanical testing of the narrow gap TIG has been recently completed with successful results. Before commencing the welding activities, Polysoude reviewed their database of welding procedure to determine the process parameters to be applied when welding P92. The following were selected:

• Single-pass layer welding technique

• Narrow groove joint 9mm wide with a 2° slope, accounting for cross-seam shrinkage enabling the maintenance of a constant groove width after each welding pass

• The use of pure argon welding gas known for its universal availability

At the same time, the various phases of the heating cycle, such as pre- and post-heating, as well as the post-weld heat treatment (PWHT) conditions were agreed by the project partners based on current practice. A grade 92 matching filler metal was supplied by Metrode. The heating cycle is a key factor in obtaining optimum results when welding P92 to ensure the required high temperature properties.

Polysoude prepared a preliminary test weld to develop then optimise all welding variables, in particular the operational weldability of the selected welding wire and the cross-seam shrinkage curve obtained with the consumable.

A P92 weld was produced on a spare pipe to confirm the welding parameters and make the necessary adjustments. Considering that high magnetisation had been observed for this test weld (± 15 gauss or 1200A/m), the pipe pieces to be used for the final weld were de-magnetised prior to welding. The final weld was then carried out according to the developed procedure and conforming to the required

heating cycle. The soundness of this weld was confirmed through radiographic testing (RT).

The total arc time was two hours and eighteen minutes, whereas approximately six hours would be expected for a conventional weld groove which shows the high productivity obtainable with the narrow gap hot wire TIG process.

Following RT, the test piece was heat treated at 760°C ± 10°C for 4 hours. Four monitoring thermocouples were installed at different locations on the inside and outside surface of the welded pipe to verify that a uniform temperature could be reached and maintained throughout the pipe wall thickness.

Prior to delivery to TWI and the other project partners, Polysoude carried out the NDT and mechanical tests typically required by international standards for the qualification of welding procedures, namely penetrant testing, RT, macroscopic examination, transverse tensile testing, hardness survey, impact testing, bend testing as well as weld metal chemical analysis and all weld metal tensile testing. No defects were detected and the mechanical test results were in compliance with the acceptance criteria established for the project. This allowed progression to creep testing which is currently underway at the Doosan Power Systems and E.ON laboratories.

For information contact marcello.consonni@twi.co.uk

Narrow-gap TIG welding of P92TWI is managing a TSB collaborative project; verified approaches to life management and improved design of high temperature steels for advanced steam plants – VALID, a three year research programme focused on the application of advanced processes for P92 pipe welding, which started in March 2011.

Project partners: TWI Ltd, Polysoude SAS, Air Liquide UK Ltd, Centrica Energy plc, Doosan Power Systems Ltd, E.ON New Build & Technology Ltd, Metrode Products Ltd and SSE plc. The project is managed by TWI Ltd and is partly funded by the TSB.

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Technology Transfer

Job Knowledge

120 Structural Steel, CE Marking and ISO 3834

ISO 3834, Quality Requirements for Fusion Welding of Metallic Materials was first published as an EN specification, EN 729, almost 20 years ago, becoming an ISO specification in 2005. Parts 2 - 4 is regarded as best practice for the control of welding and its associated activities. Not being a mandatory specification it has been ignored by welding fabricators with the attitude that they will implement the requirements when they have to. That point has now been reached for many companies with the publication of the Construction Products Regulations (CPR) and a number of related specifications that reference ISO 3834 and will therefore directly affect the structural steel industry.

The CPR is the UK version of the European Construction Products Directive and requires structural steel work placed on the market to be CE marked. CE marking may be applied to the steel work provided that the manufacturer can demonstrate that the components comply with the relevant harmonised standards; a harmonised standard being one regarded by the European Commission as satisfying the essential safety requirements set out in the Directive. The CE marking of construction products becomes mandatory in the summer of 2014 when fabricators must be able to demonstrate compliance with BS EN 1090, Execution of Steel Structures and Aluminium Structures, the harmonised standard for construction products.

The CPR requires that the manufacturer implements a factory production control (FPC) system to ensure that products comply with the design and service criteria by means of written procedures and inspections and tests. BS EN 1090

Part 1 clause 6.3 states that an FPC system conforming to EN ISO 9001 and made specific to the requirements of BS EN 1090 is regarded as acceptable. Welding is identified in ISO 9001 as a special process and additional controls are

RequirementComprehensive Quality

Requirements Part 2

Standard Quality Requirements

Part 3

Elementary Quality Requirements

Part 4

Contract review Full documented review Less extensive review Establish that capability and informa�on is available

Design review Design for welding to be confirmed

Design for welding to be confirmed As above

Sub-contractor Treat like a main fabricator Must comply to standard

Welders/Operators Qualified to EN 287/1 or ISO 14732

Welding co-ordina�onWelding co-ordina�on personnel with appropriate technical knowledge according to ISO 14731, or persons with similar knowledge

Not demanded but responsibility of manufacturer

Inspec�on personnel Sufficient and competent qualified personnel to be available

Produc�on equipment Required to prepare, cut, weld, transport, li�, together with safety equipment and PPE No demands

Equipment maintenance Has to be carried out. Maintenance plan necessary

No specific demands - must be adequate No demands

Produc�on plan Necessary More restricted plan necessary No demands

Welding Procedure Specifica�ons (WPS) Instruc�ons to be available to Welder. See ISO 15609/1 No demands

Weld Procedure Qualifica�on

To appropriate part of ISO 15614 - qualified as applica�on standard or contract demands No demands

Work instruc�ons Welding Specifica�on or dedicated instruc�ons to be available (WPS) – see ISO 15609/1 No demands

Batch tes�ng of consumables Only if specified in contract Not specified No demands

Storage and handling of welding consumables As per supplier recommenda�ons as minimum

Storage of parent materials Protec�on required from influence by the environment, iden�fica�on shall be maintained No demands

Post Weld Heat Treatment Specifica�on and complete record

Confirma�on to Specifica�on necessary No demands

Inspec�on before - during -a�er welding As required by specifica�on and/or contract As specified in contract

Non-conformances Procedures must be available

Calibra�on Procedures must be in opera�on Not specified Not specified

Iden�fica�onRequired when appropriate

Required when appropriate

Required when appropriate

Required when appropriate

Not specified

Traceability Not specified

Quality recordsAs required by contract and product liability,

retained for 5 years minimum

Table 1 summarises the requirements contained in Parts 2 - 4.

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Technology Transfer

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required to ensure that welding and its related activities are competently managed; compliance with the relevant part of ISO 3834 satisfies this requirement so is specified in BS EN 1090. The CPR also requires that the FPC system is accredited by a notified body (NB), an independent third party approved by the government. In the UK this is via the UK Accreditation Service (UKAS).

BS EN 1090 Part 2 – Steels – divides construction products into four Execution Classes (EXC). EXC1 includes unwelded items, welded items not subject to dynamic loading and items in steels with a specified minimum yield strength below 355MPa. EXC2 - 4 are for increasingly onerous service conditions and for all steels of S355 grade and above. Manufacturers working to EXC1 are required to comply with ISO 3834 Part 4 Elementary Quality Requirements: EXC2 with ISO 3834 Part 3, Standard Quality Requirements and EXC classes 3 and 4 with ISO 3834 Part 2 Comprehensive Quality Requirements.

Because of the requirement with respect to S355 steels it is likely that most fabricators will need to comply with ISO 3834 Part 3 as a minimum. In addition to the parts mentioned above ISO 3834 has a further three parts. Part 1 Criteria for the selection of the appropriate level of quality requirements; Part 5 Documents with which it is necessary to conform to claim conformity and Part 6 Guidelines on implementing ISO 3834.

Most of the work in achieving compliance is in the production and implementation of written procedures and the qualification of welding procedures. Whilst there is no mandatory requirement either in the CPR or EN 1090 for the fabricator to have independent accreditation to ISO 3834 it is inevitable that self-certification will not be acceptable and that purchasers will demand third party accreditation.

The implementation of a competent FPC system, whilst time-consuming, is relatively straightforward there is one area with which fabricators may have difficulty complying. EN 1090 Part 2 clause 7.4.3 requires welding co-ordination personnel as specified in ISO 14713, Welding Co-ordination – Tasks and Responsibilities, to be appointed when welding EXC2 - 4 components.

Any individual involved in any way with welding activities is regarded as a welding co-ordinator - from the chief designer to the storeman. It is, however, the appointment of an individual called the Responsible Welding Co-ordinator (RWC) that may be problematic.

International Welding Specialist (IWS), International Welding Technologist (IWT) and International Welding Engineer (IWE) are quoted in ISO 14713 as examples of qualifications regarded as fulfilling the requirement of B, S and C respectively. Other qualifications of the RWC may be accepted by the accrediting body auditor following a formal interview but the appointment of a suitable qualified and experienced RWC is a potential problem area for many fabricators.

In addition to the requirements of the CPR and EN 1090 there are several additional specifications that require the implementation of ISO 3834 and its related specification ISO 14713. To be included in the Register of Qualified Steelwork Contractors (RQSC), administered by UKAS, it is necessary to comply with the National Highways Sector Scheme for Quality Management in Highway Works document 20 - The Execution of Steelwork in Transportation Infrastructure Assets, fortunately known as NHSS 20.

This document is mandated in Appendix A of the Specification for Highway Works and describes the quality management system requirements for fabricators providing transportation infrastructure assets; this includes roadside furniture, overhead gantries, crash barriers, bridges, etc. NHSS 20 specifies that the quality systems shall comply with both ISO 9001 and the appropriate part of ISO 3834 including the appointment of an RWC with qualifications and experience in accord with the execution class of EN 1090.

One final specification EN 15085 - Railway Applications - Welding of Railway Vehicles and Components. This specification is in four parts and adopts a similar approach with respect to the classification of railway components and the quality assurance systems for the control of manufacture as EN 1090. Fabricators are required to be independently third party certified and to comply with ISO 3834 Part 2, Part 3 or Part 4 depending on the certification level (execution class in EN 1090).

There are numerous specific requirements regarding welding and its related activities in EN 15085 (far more that can be covered in a brief article) reference to the specification is essential. The requirements of EN 15085 apply not only to the main contractor but also to any sub-contractors - this includes the repair welding of items such as forgings and castings.

This article was written by Gene Mathers.

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September/October 2012

Following widespread acceptance by the aerospace, shipbuilding, train making and automotive industries for manufacturing aluminium structures, TWI is developing friction stir welding (FSW) for application to steel. Recent work at TWI Technology Centre, Yorkshire has shown that welds in steel made by FSW have considerably better mechanical properties than those made by conventional arc welding, for example significantly improved toughness and fatigue lives. The lack of melting and thus low heat input – characteristic of the FSW process – reduces distortion in the welded structures.

Results just published show that for 6mm thickness, high strength shipbuilding steel, FSW reduces distortion along a 2m welded plate from 115 to15mm

while tripling weld toughness and increasing fatigue life compared with submerged arc welding. As up to 40% of the costs of building a ship are associated with correcting distortion of welded plates, this new technique has the potential to introduce considerable cost savings during manufacture. Contact stephen.carter@twi.co.uk for further information.

Ground breaking developments for friction stir welding of steel

The 6th TWI-EWI Seminar on Joining of Aerospace Materials, with 60 people (not all shown) from 11 countries attending supported by MTU was held in Munich. There was a wide range of presentations from major industrial and academic organisations on TIG, hybrid laser MIG, laser, linear friction, friction stir and electron beam welding processes and simulation techniques, as well as talks on additive manufacturing (wire + arc and laser), coatings development, laser and shot peening, laser paint stripping and laser brazing.

The conference dinner was held in the aircraft museum (Flugwerfth Oberschleissheim) and the proceedings finished with a tour of the MTU facility and their engine museum. Richard Freeman and Becki Parratt of TWI would like to thank Karl-Hermann Richter and his colleagues at MTU for their support of the event. The 7th TWI-EWI

Seminar on Joining of Aerospace Materials is scheduled to take place in the USA in September 2014 and is likely to take place on the West Coast.

More details will follow and for more information on TWI’s aerospace activities contact richard.freeman@twi.co.uk

Munich venue for aerospace meeting

Q

Aregister now www.twi.co.uk

Are there any fatigue design rules for bolted joints?

How can I minimise electrode wear in resistance spot welding?

How can I use metal powder additions to increase the productivity of SA (Submerged Arc) welding?

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September/October 2012

News in briefTWI develops essential metallography training to ensure best practice

Understanding the relationship between the properties and microstructures of metallic materials is extremely important in quality control, failure investigation and development of new materials and alloys. Many properties of metallic materials like corrosion resistance, yield strength, hardness, elongation, conductivity and tensile strength are closely related to the microstructure.

As such, microstructure examination is an extremely important test method that can be used to determine the possible failure mode of a component, detect fabrication defects and confirm correct material selection.

Welsh Minister for Business, Enterprise, Technology and Science visits TWI Wales

TWI Wales, based in Port Talbot, was pleased to welcome Edwina Hart, Minister for Business, Enterprise, Technology and Science to its laboratories on 1 October 2012. The visit marked the start of a new exchange of ideas between the Welsh Government and TWI to support ‘applied research and development’ to aid the advancement and growth of both Welsh and wider UK industry.

During the meeting with Philip Wallace, Regional Manager for TWI Wales, and Peter Oakley, Associate Director, TWI, discussion took place about the challenges of finding and retaining competent qualified engineering staff and how new initiatives to strengthen the links between industry and the Welsh universities could drive a programme to generate top quality Masters and Doctorate graduates underpinning research advances and presenting new opportunities for technical growth in Wales.

For further information on TWI visit the website at www.twi.co.uk

As a founder research partner of the Materials Technology Centre (MTC), TWI announced that a new generation of rotary friction welding machines will augment existing facilities at TWI’s Cambridge laboratories and be available to Industrial Members for research purposes.

The first of two new state-of-the-art tri-mode machines (rated at 125 tons and capable of operating in direct drive, inertia welding and hybrid welding modes) is already in place at the MTC.

The machines enable precise weld cycle programming and management through advanced software and hardware control techniques. The functionality allows the user to target a desired weld upset and provides the ability to manage overall part length, orientation and weld quality. The new capability enables a step change in product dimensional accuracy and consistency while maintaining the benefits of rotary friction welding as a proven, reliable, solid state welding process. Contact chris.dungey@the-mtc-org for further information

Advanced rotary friction welding facilities launch

An Industrial Member company contacted TWI about wind turbine components to detect suspected cracking. This followed an earlier component failure, where a number of phased array ultrasonic inspections conducted by the wind turbine manufacturer had reported cracking within the blade root area. The exact location of flaws and specific details of the technique applied were not available, so the Member company asked TWI to devise a phased array ultrasonic technique (PAUT) to replicate the manufacturer’s inspection of the aluminium blade root and determine the location of any cracking.

The TWI team worked to:• Develop a suitable inspection technique

for the blade root; an aluminium ring glued in the composite which allows the mounting of the blade onto the wind turbine rotor. This blade root contained 60 bolt holes, measuring about 1m in diameter and giving an external circumference of around 3m

• Report any cracks within the aluminium ring main body

• Validate the results provided by the inspections carried out by the manufacturer’s personnel

TWI began by making a number of visits to wind farms to collect information about blade configuration, geometry and accessibility. The team was then able to develop a PAUT inspection programme and start a number of trials.

The programme succeeded first in the detection of cracks within the ring –

confirming the results of the manufacturer’s inspections. TWI carryied out an encoded inspection to achieve accurate measurement of crack length and through-wall extent.

In terms of acceptance criteria and applicability to any future work on this component, the inspections appear to lie outside the scope of current codes. With over 40 years’ experience in the engineering critical assessment (ECA) approach or fitness-for-purpose analysis widely accepted by a range of engineering industries, TWI considers it more appropriate to adopt ECA. This allows NDT results to be interpreted against tolerable flaw sizes and enable classification of the root in terms of safe remaining life (eg Class 1: Unfit for purpose, Class 2: One year remaining life, Class 3: Two years remaining life, etc). The approach will use information from the inspection results on size (length and through-wall extent), position and orientation of flaws within the ring rather than just their circumferential extent.

Contact ndt_dept@twi.co.uk for further information

Phased array ultrasonics inspection of wind turbine aluminium blade roots

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Connect is the bi-monthly magazine of TWIEditor Candy SmelliePhotography Simon Condie Production Candy Smellie © Copyright TWI Ltd 2012

Articles may be reprinted with permission from TWI. Storage in electronic media is not permitted.

Articles in this publication are for information only. TWI does not accept responsibility for the consequences of actions taken by others after reading this information.

This publication is also available in alternative formats. Please contact 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 E-mail: twi@twi.co.uk www.twi.co.uk

TWI Technology Centre (North East) Tel: +44(0)1642 216320 Fax: +44(0)1642 252218

TWI Technology Centre (Yorkshire) Tel: +44(0)114 2699046 Fax: +44(0)114 2699781

TWI NDT Validation Centre (Wales) Tel: +44(0)1639 873100 Fax: +44(0)1639 864679

TWI AberdeenTel: +44(0)1224 691222

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Issue 180 September/October 2012