Public Funded Projects
TWI has been involved with several public-funded, collaborative projects related to or using digital radiography, including the development of an automated digital radiography system for the inspection of plastic electronics. The PlastronicsSpec project developed a system that performs real time, online, and 100% volumetric inspection by digital, real-time radiography (Figures 1-2).
Our experts also provided input to the AutoInspect project, which involved the creation of a digital radiographic system for the online inspection of sintered powder metallurgy and metal injection moulded parts (Figures 3-4).
Elsewhere, the HedRad project developed digital computed radiography technology for the volumetric examination of large scale safety critical pressure components for the detection of in-service defects, corrosion and malfunctions.
Using digital radiography to deliver improved quality assurance for powder metallurgy (PM) manufacturing, the Dira-Green project delivered higher-level quality assurance alongside savings in material, time and energy.
Working for the benefit of the nuclear power and petrochemical industries, the TOMOWELD project developed quantitative radiographic tomography technology for the in-situ inspection of welded austenitic safety critical pipework.
Core Research Programme (CRP) Projects
Our CRP projects aim to deliver benefits for industry across a range of disciplines and applications, including digital radiography. One example was the ‘Laser Profiling for Image Enhancement of Digital Radiographs’ project, which demonstrated the feasibility of using laser profiling to digitally remove the effect of the weld-cap thickness profile from a digital radiograph of a weld. The outcome was aimed at assisting radiographic interpretation and improving the applicability of automated defect recognition (ADR) software.
Joint Industry Programme (JIP) Projects
Digital radiography was one of the methods used within a JIP project aimed at providing an impartial assessment of handheld laser welding technology. With the goal of supporting industrial adoption of the process, TWI developed weld quality/operator protocols and guidelines for handheld laser welding, as well as supporting data around welding parameters and process tolerances for a range of materials, joint configurations and thicknesses that are representative of the needs of the project sponsors. Radiography was used to assess the welded specimens used in this example project.
Other Projects
Much of our work is conducted on behalf of specific Industrial Member companies, to solve challenges or provide new innovations.
One such project saw us contacted by a structural steel fabricator who were using plates coated with an iron oxide epoxy primer for fabricating box girders. However, overlapping passes of the spray gun had led to localised excess coating that had caused porosity in fillet welds. An inspector asked that all of the welds were ground out and replaced, which would have been time-consuming so, instead, the fabricator persuaded the inspector to accept radiography of the welds in question (Figure 5).
Digital radiography was also used for a failure investigation of welded moulded plastic components. As the automotive industry identifies new materials and processes such as advanced engineering thermoplastics there has also been an increasing number of premature in-service failures have been reported by the automakers. TWI’s experts provided support through an assessment of weld integrity on a moulded plastic vapour separator welded with linear vibration welding (Figure 6). Visual inspection and microtoming were supplemented with computed tomography scans (Figures 7-10), showing evidence of poor welding procedures. In addition to the inspection work, TWI provided a three-day training course and assessment to improve understanding of material selection, design and fabrication of moulded plastic components. We also helped to set up and develop a new British Standard, BS 89100; “Joining of thermoplastic moulded components,” providing a specification of variables for thermal joining processes to produce components to a consistent level of quality.
The 1952 failure of a crude oil storage tank at Fawley, Hampshire was also investigated by TWI. The tank failed during a hydrotest due to a small defect associated with a repair weld that probably produced strain ageing embrittlement in the surrounding material, leading to a brittle fracture failure (Figure 11). The failure raised concerns over the API Code’s weld inspection method that relied on taking boat samples from the welds. Since the failure initiated from a poorly repaired boat sample site and a significant defect was missed by the inspection method, it was decided that radiography should be used for the weld inspection of storage tanks. The failures also highlighted the importance of material toughness for storage tanks, and the introduction of the use of materials with minimum Charpy V properties greatly improved the safety of these structures.
Digital radiography has also been used as a back-up technique to check other inspection methods, such as a project to use thermography to inspect metal under coating. The aim was to use thermography to detect surface-breaking defects in metallic structures without having to remove any coating first. Previously, magnetic particle inspection (MPI) and liquid penetrant inspection (LPI) had been used for this purpose, but neither of these methods are completely automated and also rely on skilled operators. Pulsed thermography was deemed a potential automated solution to test a painted sample with realistic defects. One defect, a toe-crack that was sub mm in width and around 40mm in length was visible with sufficient contrast even without post-processing. The results were validated with the radiograph of the plate, which clearly showed the presence of the toe crack at the same location (Figures 12-13).
Our digital radiography experts were also called upon by the Royal National Lifeboat Institution (RNLI) to assist with the factory-based inspection of their Shannon-class lifeboats. These boats have been produced at the RNLI’s All-weather Lifeboat Centre (ALC) in Poole, Dorset since 2016. The RNLI already used several non-destructive testing (NDT) techniques on critical areas of the boats during construction but traditional factory based techniques, such as ultrasonic testing, were found to be unsuitable for evaluation of the hull-to-deck joint as the composite structure was found to be too attenuative to support ultrasonic propagation. Therefore, TWI developed a specific radiography technique for inspection of the hull-to-deck joint and conducted onsite digital radiography at RNLI’s premises through deployment of portable digital radiography kit (Figure 14). Digital radiography proved to be an appropriate method of inspection for the complex composite hull-to-deck joints of a lifeboat in the process of manufacture. It allowed a speedy and versatile evaluation of the bond-line, providing information regarding construction that had never been available before. The process was rapid enough that the entire boat could be inspected in an out-of-hours period, providing high quality images that could resolve down to small imperfections in the manufacturing process. These images could then be evaluated as to their criticality in terms of size and location in relation to the design intent, thereby enabling improvements to be made in the future as necessary.
Finally, in one of the more unusual requests made of TWI, our experts used X-ray inspection to investigate a horseshoe found in the grounds of St Catharine’s College, Cambridge, near to where Thomas Hobson (1544-1631) ran a lucrative livery stable from where he would arrange delivery of mail between Cambridge and London as well as renting his horses out to students and staff from the University of Cambridge. Although it is possible to date horseshoes based on their design, this one was so badly corroded that it was impossible to discern features such as the shape and nail holes. The X-ray tests (Figures 15 – 17) showed the shape of the horseshoe beneath the corroded outer layer, including an arrangement of at least six nail holes with two seeming to still contain square headed nails. The results offered a number of clues that showed the horseshoe could have come from the late sixteenth or early seventeenth century, placing it squarely within Thomas Hobson’s lifetime. While it is impossible to be absolutely certain, TWI helped conclude that there is definitely a good chance that the St. Catharine’s College horseshoe may have once been worn by one of Thomas Hobson’s horses.