TWI Annual Review - July 2008

Technology Groups

• Advanced Materials and Processes
• Electron Beam, Friction and Forge Processes
• Laser and Sheet Processes
• Manufacturing Support Group
• Metallurgy, Corrosion and Surfacing
• NDT Technology
• Structural Integrity

Advanced Materials and Processes

Ceramics

• Ceramic to metal joining for high performance applications.
• Development of bespoke sol-gel solutions to coating problems in the oil, aerospace and renewable energy sectors.
• High temperature diffusion bonding of complex structures
• Product and manufacturing route developed for Vitolane^TM technology in hard-coat applications.
• Bespoke brazing and heat treatment solutions for metallic and ceramic components
• Use of nano-indentation to study failure mechanisms in thin coatings

Microtechnology

• A Precision Reliability facility is being installed at TWI.
• A new wind tunnel facility for evaluation of thermal management methods in microelectronics has been developed and used.
• Endoscopy equipment has been successfully developed in a collaborative European project.
• Completion of two major projects, LEADOUT and FLEXNOLEAD, to evaluate the performance of the new lead-free solders in electronic assemblies.
• Ionic liquids, a new class of solvents with potential for safer and environmentally friendly usage, have been explored in a successful collaborative project.
• TWI are a Hub Partner in the UK Photonics KTN which is helping companies to obtain funding for development of photonic-based products.
• A programme with Cambridge University, which explored copper wire bonding to electronic devices instead of gold, has been carried out.

Polymers

• Development of design approaches to convert two-dimensional laser welded fabric into fashionable three-dimensional garments.
• Laser welding of polyethylene sheet up to 10mm in thickness using carbon nanotubes as the heating susceptor.
• Laser surface pretreatment on oil pipe insulation systems to enable bonding in-field joints in pipelines is attracting much industrial interest.
• Enhanced in-house capability established to test representative oil field conditions to qualify new polymer materials for an oil and gas operator.
• First e-learning modules on composites joining and inspection were developed.
• Smallest joint ever made at TWI (less than 10µm) between carbon nanotubes via a tin-gold solder.

Case Study The Microtechnology Group has successfully completed FLEXNOLEAD, a three-year EU Framework 6 collaborative project to assist SMEs in electronics assembly as lead-free soldering is introduced. The project assessed the current materials available for flexible-circuit assembly and how they performed under lead-free processing conditions. It also helped the materials suppliers develop adhesive materials compatible with the new lead-free processes. Overall the project provided the electronic assemblers with a better insight into the new techniques and materials required for the assembly of flexible circuits with lead-free solders in compliance with the new legislation. It also specifically developed the profile prediction and reliability modelling techniques that will increase the process window and improve the process yields and long term reliability of flexible-circuit systems.

Electron Beam, Friction and Forge Processes

Electron Beam

• Specification, purchase and commissioning of a mobile seal reduced pressure welding machine and a dedicated Surfi-Sculpt^® machine for installation in the REMTEC facility in North East England for use in renewable energy projects.
• Further development of equipment and procedures for non-vacuum electron beam welding of thick section ferrous materials in the flat and vertical positions.
• Use of modelling to predict and manage residual stresses when joining thick section materials using high power electron beam welding
• Further development of Surfi-Sculpt^® to extend the range of application to very fine features of <10 microns and very large features at a scale of tens of millimetres.
• Demonstration and optimisation of electron beam probing equipment for use in quality assured manufacture of critical components.

Friction and Forge Processes

• Further development of the stationary shoulder variant of friction stir welding for high quality welding of Ti-6Al-4V alloy in thicknesses in excess of 10mm
• Extension of thick section friction stir welding capability in high strength aluminium alloys through developments in tool design and understanding of welding parameters with targets of 150mm welded in two passes in 6000 series alloys and 100mm in the higher strength alloys
• Investigation of linear friction welding for production of near-net shape preforms in Ti alloys as well as Ni-based alloys, high strength steels and dissimilar material combinations
• Development of enhanced techniques for real-time monitoring and control of the friction stir welding process to aid process understanding and procedure development and to provide quality assurance on welded components

Case Study A medical implant manufacturing company approached TWI after seeing some early Surfi-Sculpt® developments. Their interest was in using the process to enhance the growth of bone on to metallic implants, such as orthopaedic hip replacements. Feasibility trials at TWI gave encouraging results, but it was identified that to enable this process to be used in products sold into the demanding medical market, a number of issues concerning productivity and control of quality would need to be tackled. TWI was able to build a consortium of companies and organisations either with similar needs, or which could develop solutions, and this consortium won substantial funding from the UK Technology Programme to take the process forward to be ready for production. In 2007, as part of this project, a prototype Surfi-Sculpt® production machine was delivered to TWI and is currently carrying out trials. It is anticipated that this project will de-risk the adoption of Surfi-Sculpt® for the manufacture of a wide variety of products.

Laser and Sheet Processes

• High speed, low distortion, gap tolerant hybrid Yb fibre laser-MIG welding of aluminium alloys for lightweight construction
• Laser Surfi-Sculpt^®
• Direct laser metal deposition of tall free-form Ti alloy components
• High-brightness laser processing development
• Laser powder bed deposition to create parts using additive layered manufacture

Case Study Aluminium alloys are widely used in transportation applications due to their combination of mechanical properties and low density. However, depending upon the application, a number of joining processes can be considered in welded fabrications. Recently, TWI has been working with Nippon Sharyo in Japan on the manufacture of future designs of high speed train bodies, and one of the possible joining processes being considered is hybrid laser-MIG welding. This joining method combines laser welding and MIG welding in the same process zone. Traditional MIG welding has its disadvantages, being a high heat input process that can lead to strength loss and distortion. However, hybrid welding has advantages over both laser and MIG welding in terms of higher productivity, and results in significantly lower distortion than MIG welding. Hybrid welding also scores higher than friction stir welding in some areas, notably in terms of flexibility of joint design, clamping forces required during welding, and productivity for thinner sections. The work in this project was carried out using an ytterbium fibre laser source. Ytterbium fibre lasers are attractive as they are compact, high power, efficient solid state lasers with the flexibility of fibre optic delivery. Results from this project were very positive in terms of tolerance to fit-up and low distortion, and further work is being undertaken to maximise the advantages gained by using the hybrid laser-MIG joining process.

Manufacturing Support Group

Achievements in 2007

• Analysis of the carbon footprint in the production of construction equipment
• Demonstration of the potential for using a novel TIG welding system for high productivity, high quality line-pipe welding
• Detailed analysis of the potential to mass-produce wind turbines to meet predicted demand
• Optimisation of welding parameters in 9%Ni steels to achieve consistent mechanical properties
• Review of the potential for using underwater wet-welding techniques for offshore repairs
• Provided best practice manufacturing advice to over 50 supply-chain companies in the North of England and Wales
• Collected in excess of 200 field measurements of electromagnetic fields from production equipment in support of forthcoming EMF legislation
• Facilitated technology translation between the medical health technology industry and the Innovative Manufacturing Research Centres

Future Plans

• High productivity, high quality clad pipeline fabrication
• A systems approach to wet-welding for structural repair
• Further engagement with UK supply-chain companies
• Building an expert project management capability
• Enhancement of welding engineering services including EN ISO 3834 support and turnkey repair
• Increased activity for overseas welding engineering support
• Leverage of medical sector activities
• Leverage of new REMTEC facilities

Case Study The demand for renewable energy sources, particularly wind turbines, is set to continue to increase over the next 20 years. One limiting factor to widespread implementation is the relatively low rate of production of these large fabricated structures. Members of the Manufacturing Support Group carried out an analysis of the various options to increase the rate of wind turbine tower fabrication which involved moving from a manual approach producing a few tens of units per year to high volume automated production. In the analysis, MSG modelled the production sequence of traditional fabrication routes and then went through a systematic iteration process of improving the throughput by introducing new technology for welding, positioning and finishing operations. The results of the analysis showed that production rates of 50 wind towers per year could be increased by 100%. This could be achieved using a combination of optimised and balanced flow-through production and the adoption of high-speed production operations such as reduced pressure electron beam welding and thermal spraying of corrosion protection treatments.

Metallurgy, Corrosion and Surfacing

• TWI has established the first commercial cold spray facility in the UK and successfully deposited dense coatings of metals on to other metallic materials, polymers and polymer composites and ceramics.
• In partnership with fabricators and end users, TWI has developed coating systems that offer improved high temperature corrosion and slagging resistance. These coatings have been tested successfully in small- and large-scale biomass plant.
• Effect of HAZ hardness on corrosion fatigue in sour service. Fatigue tests in a sour environment have shown that crack growth is dependent on microstructure. This is important for girth welds in C-Mn steel catenary risers, where maximising sour service performance is essential to avoid using corrosion resistant alloys.
• Testing under simulated service conditions has demonstrated the difficulty of identifying worst case conditions for corrosion fatigue. Project-specific testing is advisable, and knowledge of the principal environmental variables and how they change during service is essential. Unique data have been generated that are critical for the safe operation of steel catenary risers in sweet service.
• Complex failure investigations require increasingly more detailed microstructural analysis. TWI has developed methods based on its advanced electron backscattered diffraction (EBSD) system that enable determination of the cracking mechanism by characterisation of texture, phase distribution and strain local to the crack.

Case Study Efforts to improve the creep performance of high-chromium ferritic steels for high temperature power plant are generally concentrated on the development of the parent steel. Weldments, however, are often the weak link and so-called 'type IV' creep failures may occur in the outer region of the visible HAZ of welds, leading to premature failures and associated forced outages. Despite this, relevant weldment creep rupture data are not commonly available and the relevant weldment creep rupture 'strength reduction factor' or 'weldment-parent creep strength ratio' (WPCSR), ie the reduction in creep life associated with type IV creep failure, is not always known. TWI is undertaking cross-weld creep tests on a range of welds in creep-resistant 9%Cr steel, and has reviewed existing weldment creep data. Published results show that the WPCSR does not have a single value but decreases with increasing service life for advanced 9-12%Cr creep-resistant steels without an appropriate boron addition. A linear extrapolation, which might not be conservative, suggests that the WPCSR appropriate for a 30-year design life at 650°C for such steels would be of the order of 0.3, which is lower than the widely-accepted values. Hence, where the deployment of new steel grades is concerned, long term (>10,000 hour) test results should be taken into account, not only for the parent steel but also for the weldments, and care should be taken in extrapolating WPCSR values to the appropriate service life.

NDT Technology

Non-Destructive Testing

Achievements in 2007

• Applied advanced NDT techniques, such as digital radiography and computed tomography, automated and phased array ultrasonics, eddy current arrays, and thermography, to deliver innovative inspection solutions to industrial engineering challenges.
• Provided inspection solutions for challenging material combinations, adverse joint geometries, and novel joining processes through application of world-class breadth and depth of NDT knowledge and experience.
• Increased inspection reliability, consistency and repeatability through NDT modelling and analysis, and technique and procedure development, supported by thorough experimental design.

Long Range Ultrasonics and Structural Health Monitoring

Achievements in 2007

• Advanced guided-wave phased array focusing technique for plates and pipeline
• Time reversal focusing technique for guided waves
• Novel transducer for guided wave generation
• Advanced signal processing techniques for noise reduction and ultrasonic signal improvement
• Marinised long range ultrasonic system for offshore application
• Developed guided wave inspection techniques for rail, large plates, sea defence, lampposts, aircraft wiring and wind turbines
• New type of guided wave system using magnetostrictive approach
• Conducted workshops and working group for long range ultrasonic inspection and application
• Conducted acoustic emission test on duplex stainless steel

The NDT Validation Centre

Achievements in 2007

• Provided UKAS accredited, independent and impartial consultancy support to NDT operators and end-users to optimise inspection effectiveness in specific applications.
• Transferred inspection technology to Objective 1 SMEs to support growth in employment and turnover.

Case Study TWI was called upon to design an innovative procedure for the inspection of fillet welds in high-performance, double-walled tubular products used in drilling operations. These fillet welds are situated between inner and outer tubes and the procedure was designed to detect weld root area cracking and lack of fusion notches that may give rise to structural weaknesses. An ultrasonic phased array procedure was developed and demonstrated on a test block containing representative artificial flaws, these having approximately 2mm through-wall extent and a circumferential length of 10mm. The procedure was successfully demonstrated for the client and a third party observer and showed the technique to be capable of detecting and resolving 2mm through-wall flaws. Further, the demonstration showed that the technique could correctly position and characterise the flaw indications. Subsequently this system was used for the inspection of some 800 pipes over a four-month period. This was the first time that phased array ultrasonics had been applied for the inspection of such components. TWI is able to provide innovative solutions to inspection challenges within all industry sectors at any stage of plant or equipment life.

Structural Integrity

Asset Integrity Management

• Production of a robust integrity management system for wind turbine blades, to minimise the risk of blade failures at a client's wind farm in a safety critical location.
• Asset Integrity Management assisted one of the world's biggest energy companies when they discovered corrosion in a safety critical area of one of its petrochemical plants during a planned shutdown.

Fracture Integrity Management

• TWI contributed to FITNET, the European consortium project to help establish a European fitness-for-service procedure.
• The development of a reference stress (or limit load) model for use in failure assessment diagram-based fracture assessments of circumferential embedded girth weld flaws.

Fatigue Integrity Management

• Experimental fatigue tests on welded joints have shown that Miner's rule of linear cumulative damage was non-conservative for certain stress histories.
• Fatigue testing of 20 inch pipelines for deepwater use comprising 50 full scale fatigue tests were completed ahead of schedule. Results showed that the pipe wall thicknesses exceeded the project fatigue requirements.

Numerical Modelling and Optimisation

• A software package, Weld Set-up and Optimisation Tool (WSOT) was developed to simplify modelling of conventional and low stress, no distortion welding in an Al alloy.
• A novel and effective algorithm was developed for focusing guided waves on one region of a pipe.

Case Study BAPCO's refinery in Bahrain selected TWI to conduct an RBI pilot study on a representative selection of their plant. All fixed equipment within a vacuum distillation unit (VDU) A process piping circuit within this VDU Two above-ground storage tanks and two off-site pipelines A utility water-tube boiler The VDU was commissioned in 1973 and has since experienced eight major inspections, at intervals varying between three and four years. Recently, following a comprehensive internal study, an extended run-length of five years between turnaround and inspections (T&I) had been approved within BAPCO. The two tanks were for naphtha and diesel storage and were commissioned in 1948. The selected pipelines are a crude feed and a medium straight run product line, which run between the tank farms and associated process units. The 100,000 lbs/hr boiler was commissioned in 1944 and has been subject to biennial mandatory T&I, in accordance with Bahrain's Ministry of Labour regulation for fired steam generating plant. All the equipment was found to be non-critical in terms of remaining life indicator (RLI). The calculated RLIs indicated that the proposed T&I interval of five years was entirely acceptable. This proved the scope for large possible increases in run lengths between inspections without the need for additional inspection.