The inspection of pressure plant, structures and machinery was once determined from custom industry practice based on prescriptive codes and health and safety legislation. The inspection frequency, methods employed and locations examined were determined by the type of equipment with little consideration given to its age, specific duty or likely damage. Increased operational experience and a greater appreciation of ageing and the hazards has led some parts of industry to adopt a more informed approach to inspection planning, specifying an inspection appropriate to manage the risk of failure within regulatory expectations.
Risk based inspection is the process of developing a scheme of inspection based on knowledge of the risk of failure. The essential process is a risk analysis. This is the combination of an assessment of the likelihood (probability) of failure due to flaws damage, deterioration or degradation with an assessment of the consequences of such failure.
The information gained from this process is used to identify (a) the type of damage that may potentially be present, (b) where such damage could occur, (c) the rate at which such damage might evolve, and (d) where failure would give rise to danger. Areas at high risk usually have credible damage mechanisms combined with high consequences from structural failure, the release of hazardous substances or stored energy. A suitable inspection scheme will deploy techniques at a frequency that provides adequate confidence about the condition, taking account of the damage mechanisms and the reliability of the inspection techniques used.
Risk based inspection may be applied in any industry sector, but there has been most interest from the power and petrochemical sectors. In 2006 the UK Health and Safety Executive published a report on best practice for risk based inspection as a part of plant integrity management. In 2000, the European Commission launched the project RIMAP to develop risk based inspection and maintenance procedures for European Industry. The American Petroleum Institute (API) has published recommended practice and a base resource document for risk based inspection relevant to refineries .
Industry sees RBI as a way to obtain economic benefits from extended run lengths and as means of using inspection resources more effectively from the use of automated NDT or non-invasive inspection schemes. Regulatory pressure will ensure that the process of RBI is carried out rigorously so that inspection decisions are based on adequate information and expertise. In some industry sectors (e.g. nuclear) where there very high consequences from failure, an approach to assuring safety based only on RBI may not be entirely tenable.
Jovanovic A, Overview of the RIMAP project and its deliverables in the area of power plants, IntJPVP, vol 81, issues 10 and 11, pp815-824, 2004.
API Recommended Practice 580 and Base Resource Document 581
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