Manual ultrasonic testing (UT) is a common non-destructive testing (NDT) technique that uses a high frequency mechanical energy, such as high frequency sound waves, to examine a test area.
The inspection system used typically comprises an ultrasonic transducer, pulser/receiver, and display unit. The pulser/receiver produces high-voltage electrical pulses that the transducer turns into high frequency ultrasonic sound energy in the form of sound waves that act as an ultrasonic flaw detector. When discontinuities are detected the sound waves are reflected back to the transducer where they are transformed back into an electrical signal and shown on the display unit. The time taken for the reflected sound waves to reach the transducer can be related back to the distance that the signal travelled allowing the location of the defect to be ascertained.
TWI has undertaken a number of projects involving manual ultrasonic testing over the decades, as follows…
Core Research Programme (CRP)
Through the core research programme (CRP), TWI conducts projects to address challenges faced by our Industrial Members, advancing technologies and processes, and finding new solutions for industry problems. These projects are jointly funded by our Industrial Members, with the outcomes made available to all our Members.
- Manual Ultrasonic Inspection Characterisation
This 1998 CRP project aimed to develop a neural network method capable of classifying ultrasonic signals according to flaw type. Manual ultrasonic inspection requires a degree of experience to be able to accurately predict flaw types based on the signals shown on the flaw detector display screen. This project sought to make it easier to interpret the results, with any solution needing to be capable of being implemented using standard manual digital flaw detection equipment to discriminate between different types of welder-induced flaw, using a neural network-based classifier.
- Probability of Detection Curves for Ultrasonic Testing
This 2012 project investigated probability of detection (POD) curves which are used to establish the ability of an inspection to detect flaws. These curves show the likelihood of detection (along the y-axis) against the size of the flaw (along the x-axis), with the likelihood of detection by the inspection system increasing as the size of the flaw grows. POD estimations typically rely on the manufacture of large numbers of defect specimens followed by practical trials of the inspection procedure. This project aimed to replace this costly and time-consuming process with a theoretical simulation, providing it proved to be accurate, consistent and repeatable. Working with Rolls Royce and British Energy Generation Ltd (now EDF Energy), we devised a case study which was based on EDF Energy's Capability Statement for manual ultrasonic testing (UT). The case study was used in a previous project to identify limitations to an earlier prototype POD model and recommend improvements to two models, with the aim of establishing the feasibility of generating realistic POD curves theoretically.
Public Funded Projects
Our expert teams are also called to participate in public funded projects in partnership with other organisations from industry and academia. These are designed to solve specific challenges, typically for particular industry sectors, including those that require the use of manual ultrasonic testing.
- An ICT Enabled Approach to Optimising the Reliability of Manual Ultrasonic Non-destructive Testing
The European Commission-funded project, called ‘ICARUS,’ sought to develop a system wide approach to improve the performance and functionality of the procedure, equipment and personnel to deliver a step-change in the reliability of manual ultrasonic testing.
- An Ultrasonic Non-destructive Testing System for Detection and Quantification of Early-Stage Subsurface Creep Damage in the Thermal Power Generation Industry
Also funded by the European Commission, the CreepUT project was created to address the problem of creep damage detection in pressurised steam line components used by the power generation industry. At the time of the project, replica metallography was commonly used to inspect such components, but this technique was only able to detect surface defects, whereas evidence showed that creep damage develops first inside the pipe wall and does not show at the wall surface until the pipe is almost ready to fail. The resulting failures were costing the industry more than €500,000 in lost revenue per day out of operation.
- Development of an Ultrasonic Testing Technique to Characterise Diffusion Bonds in Layered Structures
Manual ultrasonic testing was also used as part of the European Commission-funded ‘BondTest’ project, which was created to find a suitable NDT technique for detecting defects of the required dimensions and size in diffusion bonded joints both during manufacture and in service. Experts from TWI worked to help develop a validated NDT technique and system to meet appropriate detection criteria, before the system was to be commercialised and made available to industry.
- Radiation Resilient Ultrasonic Sensor
Funded by Innovate UK, aimed to provide the nuclear industry with a reliable ultrasonic testing solution for prolonged inspection and monitoring. Ultrasonic testing methods were the go-to non-destructive testing solution for the nuclear industry, where limited access and high thickness components limit the number of potential solutions. However, the radiation endurance of commercially-available ultrasonic testing sensors were limited to cumulative doses of 1 to 2 MGy, even for models branded as radiation resistant. Unexpected sensor failure and the need for replacements are both expensive and time-consuming, so, to solve this problem, TWI worked to help explore the construction and testing of novel, radiation resilient probes manufactured from exotic materials and a variety of assembly techniques. A series of prototype probes were manufactured and tested to suit both high and low radiation environments. Ultimately, TWI was able to develop and manufacture an ultrasonic transducer that remained functional after a total radiation dose of ≈12MGy (Figure 1).
- Non-Destructive Evaluation of Sandwich Composite Structures
As interest grew across industry in the use of sandwich composite structures, there grew a need to find a reliable non-destructive inspection solution. These structures posed an inspection challenge as the energy that is applied for the inspection is highly attenuated due to absorption and scattering, causing difficulties in the interpretation of received energy and sizing. Ultrasonic testing techniques were tested on artificially-induced flaws in a composite structure (Figure 2). The inspection was performed underwater in an ultrasonic immersion tank (Figure 3) with the ultrasonic wave generated by a probe passing through the water to propagate inside the specimen. Any obstacles inside the specimen reflected the wave. Analysis of these reflected waves allowed for a 2-dimensional image of the reflections (called a C-scan) to be created (Figure 4) while a flaw detector allowed for the detection of the flaws (Figure 5). This project showed that sandwich composite structures with glass fibres can be successfully inspected using ultrasonic techniques.