Flaws might arise during manufacture and/or operation of pressure vessel and piping components in thermal and nuclear power plants, petrochemical plants, pipelines, etc. If flaws are detected in these components, assessments are needed to determine the cause of flaw formation, the remaining life of the component containing the flaw, whether the flaws should be removed from the components for continued operation, or whether repair/replacement of the component is required. Flaw assessments are performed to not only demonstrate the structural integrity of the degraded components during operation but also to demonstrate quality assurance during production or flaw tolerance in the design phase. Consensus assessment rules on flaw evaluation are needed for industries, utilities, and regulators. These rules require consensus agreement by all stakeholders. Several consensus codes and standards or guidelines of fitness-for-service (FFS) rules for flaw evaluation have been published for inspectors, designers, engineers, fabricators, and regulators.