New projects

May - June 2002

By joining Group Sponsored R&D Projects TWI Industrial Members gain access to substantial programmes at low cost, with the opportunity to steer work undertaken into areas of specific interest. The following GSPs have been, or are about to be, launched. If you are interested please contact the project leader at TWI.

AUT capability for C-Mn steel and corrosion resistant risers

Deep water steel catenary risers require stringent inspection in manufacture to ensure no failures during service. The acceptance criteria for these girth welded risers has to be determined from knowledge of the defect sizing accuracy of the automated ultrasonic (AUT) methods used for the inspection. There are additional problems for the inspection of risers made from corrosion resistant alloy (CRA) for sour service. This may mean that the performance of AUT systems for CRA girth welds may not be the same as for C-Mn girth welds. This project aims to establish the relevant sizing capability and establish the limitations of standard AUT techniques for inspection of girth welds for CRA risers.

Avoiding intergranular stress corrosion cracking of welds in supermartensitic stainless steels in sweet environments

Laboratory tests have indicated that welds in supermartensitic stainless steels (SMSS) are susceptible to intergranular stress corrosion cracking (IGSCC). This represents an obstacle to acceptance by the oil and gas industry of SMSS as a suitable material for pipelines. This project will establish ways of eliminating sensitivity to IGSCC through control of the welding process and/or brief PWHT cycles. In addition, it will further define the range of environments in which a risk of IGSCC exists and develop understanding of the mechanism of IGSCC.

Rapid curing, precision dispensing and high reliability bonding and encapsulation of medical and implantable devices

Effective bonding and sealing of dissimilar materials and low surface energy substrates ( eg polyolefins) for assembly of multi-component systems in disposable and implantable medical devices are major challenges facing manufacturers. The new generation of polymeric adhesives and encapsulants offers exceptional opportunities for rapid and precision bonding and hermetic sealing (<10 ^-9 mbar litre/sec) for components which have to survive sterilisation processes and service environments. TWI and Queen Mary College (IRC in Biomedical Materials) are proposing a project to exploit these opportunities by adaptation of adhesives and encapsulants and development of novel processing techniques for generic and specific medical device products. The proposed work will provide major cost savings in device assembly and manufacturing by reduced product development time and faster production rates.

Development of an NDT technique for the detection of non-standard butt welds in plastics pipes

Current non-destructive tests for butt fusion welds in plastics pipes, although capable of detecting planar flaws and particulate contamination, cannot detect cold welds ( ie welds which appear visually to be of good quality but which fail in a brittle manner when tested in flexure or tension). A new technique, which involves applying a pre-determined amount of local heat energy to the surface of the weld after removing the bead, has been shown in initial trials to achieve a detection rate of cold welds of over 90%. The objectives of this project are to optimise this NDT technique for different types and grades of plastic pipes and to develop prototype equipment for use in the field.

Weld quality and performance of high strength TRIP steel welds

TRIP (Transformation Induced Plasticity) steels have become of considerable interest in the automotive industry because of their exceptional combination of high strength and ductility. However, their weldability and joint performance have become of concern due to potential brittleness and susceptibility to HAZ cracking. This project seeks to develop practical procedures and guidelines for resistance spot welding and laser welding of TRIP steels to achieve the best weld quality and joint performance. Benefits will include improved weld quality and joint performance of TRIP steels, together with improved understanding of the influence of process factors on the static and dynamic properties of TRIP steel welds.

Hybrid laser-arc processing for improved productivity and quality

Hybrid laser arc welding combines the advantages of both processes resulting in high joint completion rates with increased tolerances to fit up and without compromising joint quality and distortion control. This work aims to develop robust welding procedures which demonstrate the advantages of a range of hybrid laser arc processes. The benefits to industry will include increased productivity, simplified set-up procedures and reduced post weld reworking costs.

Fatigue performance of CRA risers

The design of steel catenary risers (SCR) requires consideration of dynamic loads imparted by the vessel motion and by the wave and current actions. Investigations have been carried out by TWI into fatigue behaviour of welded carbon steel SCRs, but there is little information on fatigue performance of riser fabricated from CRAs. The main objective is to determine the fatigue strength of girth welds in pipes of CRA which are candidate materials for risers under representative conditions both internal (sour) and external (seawater and CP). The project also provides guidelines on the fatigue design of CRA catenary riser girth welds.