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Updated Recommended Practice/Guidelines for in-situ inspection of Corrosion Under Insulation (CUI) within the oil and gas industry. (HOIS-G-023 Issue 2)

Project Summary

The primary aim of this two-year project was to update and develop a HOIS/Net Zero Technology Centre Recommended Practice/Guidelines for in-situ inspection of corrosion under insulation (CUI).

There is a lack of independently assessed information on inspection performance and sizing accuracy for many of the non-destructive testing (NDT) methods available for CUI inspection. Without this information, there may be over optimism on the capabilities of NDT to detect CUI. One of the main deliverables of this project was to assess independently the capabilities of existing NDT methods for CUI inspection by means of blind trials.

The project provided enhanced facilities for the evaluation of advanced NDT equipment to manage CUI. Insulated test samples were used, both manufactured and ex-service, to simulate real world site conditions. A series of 10” test pipes and assemblies were manufactured for the trials using an advanced computerised numerical control (CNC) machining process to create areas of wall loss with realistic CUI morphologies.

In addition, samples were created with genuine corrosion in a controlled environment and an internal ultrasonic testing corrosion mapping scanner tool was designed and built to allow benchmarking of the test samples prior to carrying out the blind trials.

Industry value:
The Recommended Practice document provides guidance on a wide range of current NDT methods available for corrosion under inspection, by detailing the strengths, limitations and areas of applicability for each one. This work should provide operators and NDT service providers with current relevant information on the best methods for this challenging application and lead to a more consistent approach across the industry.

Key results:
Trials were hosted using pulsed-eddy current (PEC) equipment from three different manufacturers for comparison against scans made from using three different advanced electromagnetic inspection techniques.

This data was used to inform a major revision of the Industry Best Practice HOIS CUI inspection guideline (HOIS-G-023 Issue 2).

The project has substantially moved the guidance document forward both in terms of:

  • the trial sample pieces providing much more varied and realistic real-world samples to test inspection equipment on
  • to trial new technology available on the market to improve plant operator’s management of CUI

In addition, the trial also helped support the development of new Recommended Practice – “Guidance on inspection of uninsulated external corrosion scabs”. (HOIS-G-028 Issue 1)

Lessons learned:
It is important that any users of NDT for corrosion under insulation are fully aware of the capabilities of the different methods available as these may make them suitable for application to a certain set of components under specified conditions, but not for general usage across a site. It is unrealistic to expect reliable results to be obtained if the methods are applied outside their range of applicability.

Next steps:
The project outcomes and results are publicly available through the two Recommended Practice documents that raise awareness within the oil and gas industry of technologies available to carry out CUI mitigation inspections.

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