For pressure equipment containing clean, dry and non corrosive products under stable and benign conditions, there may not be any degradation mechanisms affecting the containment material over a considerable length of time. Taking account of the low risk of failure, it may then be possible to justify a longer interval between shutdowns for internal examination. Nonetheless, it is important that this judgement has been made carefully and correctly, and that adequate safeguards are in place so appropriate action may be taken if the expected conditions are subject to change. This is the theme of a recent report by TWI [1] commissioned by the UK Health and Safety Executive (HSE), which has outlined a six-step approach for assessing and justifying internal examination requirements for process plant at high hazard sites. The work has been developed partly through consultation with leading UK petrochemical companies and inspection bodies that are proactive in developing risk-based inspection methodologies.

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