Pulsed eddy current testing and digital radiography, what they are and are not able to do

In the last few months, I have been privileged to witness advances in the use of two inspection methods due to the expansion of specific techniques in each. Both methods and techniques are available to purchase now and are in use in industry, but the full appreciation of what they are and are not able to do is yet to be explored.

One of these methods is pulsed eddy current testing, which is being used for the detection of corrosion under insulation. IMechE Engineering Training Solutions has been running training courses using this equipment and has manufactured both specimens and associated insulation types. The instructor, Howard, is able to show the positive aspects of the equipment, which include its ability to locate significant areas of corrosion without the need to remove the insulation, thus allowing rope access inspection of piping systems and other applications to be carried out. The disadvantages include the marking up of the piping system, especially elbows, and the limited detection of small areas of corrosion, which may have significant areas of wall loss. However, as an initial screening method the advantages can been seen. It would be interesting to compare ultrasonic guided wave inspection results against the pulsed eddy current testing results.

The second method is digital radiography and Rex from NFW Inspection has the advantage of an enquiring mind and the time to explore the potential of this method. He has found that by taking multiple identical images and overlaying them, the resultant final image quality is exceptional whereas conventional wire image quality indicators (IQIs) can generate their own issues, with the plastic used to keep the wires spaced apart affecting the image. The exposure times are still short compared to conventional film-based radiographic testing (RT). One of the disadvantages is the storage of the digital files due to their size and also who owns them. Customers that are used to conventional film are often not ready to store large digital files. In one instance, Rex was able to identify that a component had been manufactured by the additive layer process just by the resultant digital image. This was later confirmed by the manufacturer, who did not initially supply this information.

Both situations demonstrated to me how interesting and important it is to be aware of the advances being made in inspection and how they are being used in industry, plus it is valuable continuing professional development (CPD).

For the UK, specifically at MT 2017, J Taylor from the Health and Safety Executive (Radiation Team) gave a session on the Ionising Radiation Regulations 2017. Further information and a draft of the document can be found at: www.hse.gov.uk/consult/condocs/cd282.htm

The web page offers the following text:
CD282 – The implementation of Directive 2013/59/EURATOM laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation

HSE is consulting on changes to the Ionising Radiation Regulations 1999 (IRR1999), the majority of which are brought in by the implementation of the EU Basic Safety Standards Directive (BSSD).

Briefly, the main changes are:
  • Dose limit for exposure to the lens of the eye and implementation of the Directive – the Directive introduces a reduction of equivalent dose from 150 mSv to 20 mSv in a year. Currently, exposure to ionising radiation is calculated and assessed on a calendar year basis. This would require individual dose limits to be recalculated for the remainder of the year. HSE propose to transpose the BSSD early, on 1 January 2018, to avoid confusion and any additional cost burden to businesses.
  • Graded approach – introduction of a new three-tiered risk-based system of regulatory control. The Directive refers to these levels as notification, registration and licensing – the higher the radiation protection risk associated with the work, the greater the requirements.
    It requires HSE to have in
    place a positive system of authorisation whereby permission is granted to duty holders for higher risk activities through registration and licensing.

The date of 1 January 2018, which is approaching rapidly, was reiterated by Mr Taylor.


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