A wide range of engineering plant is subject to periodic in-service inspection in order to ensure continued safe and economic operation. The inspections are often performed by traditional NDT methods such as routine ultrasonics, magnetic particle inspection, dye penetrant inspection, visual inspection and radiography. These can be highly sensitive but the rate of coverage is often slow, so that full coverage can be prohibitively expensive, and extensive preparation for inspection may be required (eg access for internal visual inspection, removal of insulation for external inspection etc.) There are also many situations where geometry or access prevents the use of conventional inspection methods.
Over recent years a wide range of advanced NDT techniques has evolved. These techniques provide large area screening of a component for significant degradation. Some of the techniques can be rapidly applied, much quicker than a more detailed, conventional inspection. Generally, the screening techniques are less sensitive than the more traditional methods. They also provide a means of inspecting areas which would otherwise be ‘uninspectable’. Examples include long range ultrasonics, pulsed eddy current techniques and saturated low frequency eddy current techniques.
There is a lack of objective information on the capability and limitations of screening techniques which is needed in order to allow judgement on their suitability for a particular application. Information is required on how to select a particular technique, what it can detect (as well as what it can miss), and what the level of confidence is in no degradation being present if none is detected.
The aim of this document is to provide an objective source of information on the capability and limitations of screening techniques and to provide information on their use to those involved in plant operation and maintenance.
This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.
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