Industrial Member and Research Projects
Much of the work we conduct for our Industrial Members is understandably confidential, however, here follows some examples of eddy current testing project work undertaken at TWI…
- Eddy Current Non-Destructive Technique of Pipelines
TWI developed a novel NDT technique for the inspection of contaminated stainless steel welds in liquefied natural gas plants. Eddy current testing was used to detect defective welds in wall thicknesses up to 8mm. The inspection procedure was developed through the manufacture of stainless welds at TWI with known amounts of ferritic consumable in the weld root. When applied to a production plant in the Middle East the method was able to achieve around 100 weld inspections per day (Figures 1-2).
- Qualification of Reeled Mechanically Lined Pipes for Fatigue Service
Eddy current testing (ECT) was part of a programme of work supporting TWI Industrial Member company, Technip, who had designed mechanically lined pipes (MLPs) that enabled reel-lay installation under atmospheric pressure without the risk of wrinkling the corrosion-resistant alloy (CRA) lining. We conducted tests to qualify the reelable MLPs and provide further evidence that a high fatigue performance can be reached without breaching the CRA liner. This involved full scale resonance fatigue testing and non-destructive testing (NDT) including dye penetrant inspection (DPI) and ECT (Figure 3).
- Two-Year Project to Convert a Tanker to an FPSO
TWI acted as the technical authority for all welding-related matters on a two-year project to convert a shuttle tanker to a $1 billion floating production, storage and offloading vessel (FPSO). The conversion was a joint venture between Odebrecht Oil and Gas and Teekay Petrojarl to convert the Navion Norvegia, a tanker built in 1995, into the FPSO Pioneiro de Libra (Figure 4). TWI’s work on the conversion, which was carried out at four shipyards in South-East Asia, including ensuring the correct welding procedure qualifications were in place and in accordance with both welding standards and internal specifications. Two experienced welding engineers from TWI supported the attachment of the FPSO turret head to the vessel while we also carried out an audit of the four shipyards to make sure all contractors were following sound working practices. Our experts also used phased array ultrasonic and eddy current testing, advised on inspection and assessed results. The TWI team assessed over 250 welding procedures, providing frequent feedback to the clients.
- External Thread Crack Detection using Eddy Current Testing
An Industrial Member operating in the sub-sea industry asked TWI to inspect the external threads on a composite valve block body (CVB) for any potential cracks in the component. This work involved the application of ECT and alternating current potential drop (ACPD) testing on-site in Agotnes, Norway (Figures 5 and 6). The inspection determined that no deposits were visible on the inspected composite valve block and the threads themselves were in a good surface condition, although we did detect two indications below the reportable level.
- NDT Inspection of Mooring Chain Links
Bringing together expertise in metallurgical theory with non-destructive testing (NDT), TWI was asked to inspect mooring chain links for surface-breaking defects. The client had procured mooring chains for an upcoming project but discovered shallow, crack-like indications on the crown region of two links, which were believed to have originated by the steel manufacture. Due to our impartial operating stance, TWI was able to inspect the links, review the root cause analysis and report the findings. Eddy current array (ECA) testing was chosen as the most suitable NDT technique to use for the on-site inspections, supported by magnetic particle inspection (MPI) for defect confirmation. Because the two NDT methods were equally sensitive, with both demonstrating a good probability of detection, they were able to detect surface cracks as small as 2mm long and 0.6mm deep (Figures 7-8). However, on occasion the ECA picked up some crack like indications, which MPI did not, and vice versa. Our experts were able to use impartial and qualitative judgment to assist the client and providing confidence by deciding that the chain was acceptable.
- Integrity Management of Buried Cooling Water Pipelines
Fitness for service was also the focus of a project to assess the integrity of two pipelines that were buried beneath three metres of concrete coating, which prevented the external surfaces from being accessible and created concerns over the likelihood and severity of external corrosion damage. Working to a combination of industry codes. Full coverage testing to address the integrity of external corrosion damage on the pipelines beneath the concrete coating was conducted using pulsed eddy current (PEC) inspection, followed by an ultrasonic thickness measurement of any reported anomalies. The reported anomalies were subjected to a fitness for service assessment, providing peace of mind that the pipes were both safe to continue service (Figures 9-14). TWI also provided the client with an inspection strategy for the future, to ensure the most efficient use of resources and reduced inspection costs going forward.
- Quick Response to a Contamination Problem
Our experts reacted quickly when TWI was contacted by an oil and gas contractor who had detected ferritic contamination in pipework welds during commissioning for a liquid natural gas tank. Our experts were on site within five days where they performed inspection of around 100 welds per day in the pipework, which ranged from 50 to 600mm in diameter. The client had already performed simple inspection using magnets to reveal that some of the welds were ferritic, despite the pipeline material being a 304L stainless steel. TWI used ECT to back up the original findings and to position the flawed areas accurately. The contamination had been introduced accidentally as sub-contractors, unfamiliar with the specific requirements of a job, occasionally pick up the wrong consumable. TWI was able to identify the troubled regions on time and to budget to the satisfaction of the client, saving potential costs and ensuring safety.
- Bridge Fatigue Crack Inspection
Another project that provided peace of mind for the client began when we were contacted by a civil engineering operator who were charged with maintaining one of the UK's most notable bridge structures. TWI was contacted to detect and size any service induced fatigue cracks across the bridge structure, including the hanger boxes, A-frame assemblies and lighting, as well to inspect the deck structure's welds from within the box sections. Our team developed inspection procedures for each task, involving the use of ultrasonic and eddy current techniques, and was able to provide assurance that there was no evidence of service induced planar flaws in the deck welds, the lighting column bases or the A-frame assemblies, while detailed inspection of the hanger box welds in regions where the paint had cracked showed no associated fatigue related flaws.
- Assessment of Electroslag Welds for London 2012 Olympics
As the UK prepared to host the 2012 Olympic Games, TWI was contacted by a UK-based highways maintenance company to provide independent advice on the on the structural integrity of ES welds in a critical part of UK infrastructure, required to support unprecedented levels of tourism during the London 2012 Olympics. TWI engineers led the multidisciplinary non-destructive inspection of the welds, comprised of teams of specialists from different UK-based inspection companies. The materials characterisation was performed by TWI engineers investigating weld quality, materials properties, residual stresses, fatigue crack growth rates (FCGR) and cyclic response. ECT was among the non-destructive testing techniques employed for inspecting the ES welds contained within 965m of steelwork, over 17 spans of plate girder flanges and lattice (truss) box girders (Figure 15). Rope access was used for locations that were inaccessible by platforms, with around 600 ES welds inspected and critical locations highlighted for cyclic response measurement across the structure over a period of three weeks. In other instances, welds were removed for in-house tensile, fracture toughness, FCGR, Vickers hardness, and chemical analysis testing as well as macro sectioning (Figure 16). The results of the various tests were used as engineering critical assessment input parameters using TWI’s CrackWise™ integrity management software, to confirm the integrity of the welds.
Joint Industry Projects
In addition to conducting projects for the benefit of individual Industrial Members, we also create joint industry projects (JIPs) that are designed to meet the needs of a group of Member companies. These Member companies act as sponsors for the project in return for exclusive access to the results and the opportunity to have input into the direction of the research.
- Best Practice Guide for the Use of Eddy Current Arrays
One such JIP saw our experts create a best practice guide for the use of eddy current arrays (ECAs). The project involved a study of the essential variables that should be controlled during inspection and a benchmarking of the performance of ECA systems relative to that of other existing, recognised surface inspection methods. The outcomes of this research were then used for the production of the best practice guide.
Public Funded Projects
TWI has also lent our expertise to public-funded projects over the course of our history both for the benefit of industry and for wider society. Examples of public-funded projects related to ECT include:
- Advances in Rail Inspection Technology
TWI developed several different inspection technologies, including ECT, for the inspection of rail and, in particular, the London Underground system which contained around 200 miles of track. To aid inspection, TWI assisted with the European Commission-funded RAIL-INSPECT project to develop techniques to improve the probability of detecting significant defects, while reducing the incidence of false positive indications ('false calls') and mechanising the process so inspection can be carried out at up to 80km per hour. Eddy current testing was applied to the detection of shallow surface-breaking cracks as well as for measuring lift-off between the inspection device and the rail surface. The ECT sensor assembly consisted of two pairs of probes, with each pair consisting of an absolute probe, sensitive to changes in lift-off and a double differential probe sensitive to defects. All four probes are positioned in a single housing which was contoured to suit the rail head (Figure 17). The project was not intended to provide a total industrial solution, but to provide additional ideas to the complex problem of rail inspection by combining phased array ultrasonic, eddy current, and magnetic flux leakage testing into one system (Figure 18).
- Eddy Current / Thermography for Robotic Aircraft Inspection
TWI was a partner in the ROBAIR project, which commenced in 2001 with the aim of deploying aircraft structure eddy current and thermographic inspection solutions via a mobile vehicle and/or scanner (Figure 19). One of the challenges was the detection of cracks around fasteners because the parent/fastener interface is in effect a large crack, and if the fastener is steel, then the magnetic properties are detected by the probe. This meant that the probe needed to be moved directly around the centre of the rivet, so that the contribution of the eddy current signal from the fastener or its interface are kept constant. The ROBAIR scanner was designed to be capable of x/y/z movement, with the eddy current signal actually proving to be a convenient way of locating fastener coordinates, making inspections easier.
The combination of phased array ultrasonic and eddy current testing were used on another aerospace-focussed challenge with the Qualiti project, a European Commission-funded project to develop a new and novel quality control system for the inspection of titanium components in safety critical applications in the Aerospace industry
These are just a few of the projects conducted by TWI that have involved the application of eddy current testing. However, ECT is frequently used in support of other capabilities in projects undertaken at TWI for the benefit of our Industrial Members and industry. By combining different areas of expertise, and because we act as an impartial and independent source of technical excellence, TWI delivers the most appropriate solution for your industrial challenges. To find out more about eddy current testing at TWI and how we can help you, please email contactus@twi.co.uk.