In-service inspection and maintenance assessment of plant and equipment to reduce the risk of failure and hazardous release have been used for many decades as cost-effective procedures in concert with design, material selection, defect criteria, fabrication, and operation/use. Codes and standards have, more recently, sought to provide hazardous release protection as an additional means of reducing risk by means of criteria based on risk (event probability and consequences), including maintenance and inspection. These criteria use risk-based methods for prioritizing inspection and maintenance. In a power station or refinery, for example, the risk of unplanned shut-down is related to the failure or malfunction of a relatively small number of items. Risk-based maintenance and inspection allows efforts to be concentrated on items involving the highest risk, with a proportionate reduction in effort for low-risk items. Hence, base-load operating times can generally be increased, while maintaining the same or reduced level of risk. Maintenance and inspection inspection play a vital role to reduce risk by more accurately quantifying event probability. Where there is a possibility of high-risk catastrophic failure, the consequences and risk to personnel, environment and equipment can be rendered tolerable to negligible if appropriate protective systems are in place with reduced maintenance and inspection. This paper reviews several cases in which the authors have been involved and in which failures would have been prevented if proper risk assessment procedures had been in place or in which assessment of risk was made to prevent failure. [S0094-9930(00)02203-4].
