Published on 22 January 2013
The owner/operator of an ethylene facility in North Africa required assessment of the 10-year-old plant, so that a future inspection strategy could be developed. The project scope covered:
- review of inspection records, NDT and quality assurance systems
- identification of previous and potential failure mechanisms
- condition assessment of the critical plant components using NDT inspection and metallurgical techniques
- detailed engineering criticality assessments on defects present
- risk-based assessment of optimum time between planned shutdowns and evaluation of alternative materials and designs. Equipment items covered all pressure vessels and interconnecting pipework associated with the plant.
The site work was undertaken in two phases. The first phase consisted of two engineers visiting the plant for one week to review inspection records, site NDT equipment, QA system and enter into discussions with key personnel. One important aspect of this visit was to identify previous failure mechanisms, consider other potential failure mechanisms and draw-up an inspection list of vessels and interconnecting pipework in the high pressure envelope, cold blow down system and storage tanks. Given the component geometry and potential failure mechanism, a new set of NDT procedures was written for the client.
The second visit coincided with a planned shutdown and included two engineers and three NDT technicians. The site team inspected the critical components using a combination of magnetic particle/dye penetrant, ultrasonic flaw sizing, site metallography and hardness survey, in addition to the more standard NDT carried out by a contractor.
As defects were located, the engineers were able to make fitness for purpose evaluations using TWI staff at Abington with engineering critical assessment (ECA) expertise. Furthermore, where the defects were considered unacceptable, repair and renovation techniques were developed and implemented. Other failed components were returned to TWI, where structural and materials engineers were able to investigate the cause(s) of failure and recommend alternative materials or designs.
Conclusions and recommendations were drawn on the future inspection strategy for each component examined, as well as plant inspector training and equipment needs. In addition, it was concluded that the time between shutdowns could be safely extended from 2 to 3 years.
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