Technical Achievements

Full-scale variable amplitude testing of pipe joints

Fatigue qualification testing of girth welds for offshore pipes and risers has to be carried out full-scale in order to ensure that results are representative. TWI has extensive facilities for such full-scale tests up to a maximum pipe diameter of 36 inches (914mm). Tests are conducted under rotating bending at the resonant frequency of the pipe, typically 25-30Hz. Until recently, a limitation of the equipment was that tests could be conducted only under constant amplitude loading, but new control equipment and software developed by TWI now allows simulation of the variable amplitude loading seen in service. Current work is examining the accuracy of cumulative fatigue damage predictions for joints in 16 inch (406mm) diameter pipe subjected to a range of different loading spectra.

Revisiting 'wet welding' for offshore repair

Wet welding has been used as an option for minor repairs of offshore structures for many years but because of the inherent risk of defects, such as porosity and cracking, has until recently been considered as unsuitable for major structural repairs. Stimulated by the increasing demand to extend the life of offshore structures, TWI has recently carried out an extensive literature study, the results of which allowed TWI to dispel myths regarding underwater processes and evaluate the true potential for wet welding for structural repair.

Weld strength reduction factor for advanced 9-12%Cr creep resistant steels

A relationship between weldment to parent metal creep strength ratio (WPCSR) and the test duration/service life has been identified for advanced 9-12%Cr creep resistant steels without boron additions. A linear extrapolation suggests that the WPCSR appropriate for a 30 year design life at 650°C for such steel is of the order of 0.27, 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 weldments.

Ultrasonic phased array inspection of high-performance fillet welds

TWI was asked to design a procedure for the inspection of fillet welds in high-performance, double-walled tubular products used in drilling operations. The fillet welds are between inner and outer tubes and the procedure designed was to detect cracking and lack of fusion notches in the weld root area. An ultrasonic phased array procedure was developed and demonstrated successfully on a test block, proving 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. This system was then used for the inspection of some 800 pipes over a four-month period. This work was the first application of phased array ultrasonics to the inspection of such components.

Additive manufacture by linear friction welding (LFW)

Significant improvements have been made at TWI in the application, control, and monitoring of LFW. LFW of metals was pioneered by TWI in the 1980s, and is now established as a high-quality welding process for aeroengine blisks. Recent work has concentrated on expanding the range of potential applications with particular interest in the manufacture of high-value aerospace components. Recent developments include LFW for additive manufacture of Ti-alloy parts, the design, build and installation of a new in-plane force measuring system for LFW, high-speed video recording of trials to improve understanding of the mechanisms involved and the development of a novel concept for a new generation of LFW machines.

Carbon footprinting of manufacturing operations for construction equipment

There is increasing interest in applying carbon footprinting to assess the greenhouse gas impact of manufacturing and industrial processes. TWI carried out an evaluation of the different approaches used for carbon footprinting as applied to the processes used by a Member company in the production of construction equipment. The selected approach was first validated by external peer review and then applied to calculate the carbon footprint of an example product. The results were used by the Member company as decision support to determine where to focus its process improvement activities.

High-brightness electron beam facility

Developments on TWI's high-brightness electron beam facility have reduced the focused spot size to allow fine-scale welding, melting, drilling and machining of metals and ceramics. Such processing is presently carried out by lasers, but the high-brightness EB system has been developed to allow processing at dimensions below 10µm, previously not possible with lasers or electron beams. Real-time viewing of the processing has been enabled using an electron back-scattered imaging technique resolving features of 10µm in size. Applications for this new technology are in the medical devices field, semi-conductor industry and micro-fluidic devices.

Sealed seams in textiles for protective garments using laser welding

Currently, seams for protective garments are made using stitching followed by tape sealing. The process is labour intensive and the reliability of the sealing is not good. Developments by TWI experts and a collaboration of manufacturers in textiles, laser welding and process equipment now allow sealed seams to be made in a single step without the need for seam taping and without putting holes into otherwise fluid- and gas-tight fabrics. The welded seams are up to three times the industry required strength for waterproof garments and easily exceed the requirements for resistance to water penetration. Additionally, 2 and 3D shaped joints have been demonstrated and the seams are less bulky and of lower weight than those traditionally produced.

Further developments in TWI's Surfi-Sculpt^® technology

Surfi-Sculpt is a power beam process, invented and patented by TWI, which enables controlled surface features to be developed on a range of substrates, including metals, polymers and ceramics. Recently, several additions to this technology have been developed: Laser Surfi-Sculpt: High-brightness, fibre-delivered laser beams and galvanometer-driven scanning mirrors have produced a rapidly moving spot of laser energy to demonstrate the process. Laser Surfi-Sculpt of plastics: This has been demonstrated on plastics such as polypropylene, nylon and polyethylene. There is potential to use the reconfigured surfaces to enhance the adhesive bonding between dissimilar polymers or to act as 'scaffolds' for electronic or medical implant applications. Macro and Micro Surfi-Sculpt: Through further process development, individual features as large as 40mm across and of similar height have been produced - making this a technique capable of near-net shape manufacture. In parallel, the process has been scaled down, and features of 20µm width have been produced.

Development of diagnostic tools for electronic systems

Electronic components are becoming smaller and more powerful. There is therefore a push to increase the heat dissipation efficiency ('thermal management') because thermal cycling and the associated stresses are a major source of reliability problems. TWI has developed experimental and modelling techniques to investigate the performance of electronic materials and systems. A wind tunnel facility has been established with infrared temperature and flow speed measurement capability to characterise and compare the thermal conductivity of a range of die attach and heat sink attachment methods and materials. Modelling methods based on commercially available computational fluid dynamics software are being developed in parallel, verified using analytical solutions.