Since we are on the topic of RSF, it may be helpful to delve into how this parameter is connected to other problem parameters. The RSF concept is very useful, especially for local thin areas. In FFS, one may know if a component is "acceptable" or "not acceptable," and API 579 is very clear about acceptance criteria. What is not evident is how long it will remain acceptable once it is found to be acceptable. This question is fair and will inevitably be asked by the organization inspectors and managers alike. To answer this question, we will "jump through some hoops" and get ahead of ourselves since we are talking about RSF and its relevance.

The API 579 mentions maximum allowable working pressure. This term is sanctioned for use with piping by API 570 Piping Inspection Code. It is defined in Paragraph 3.21 as "The maximum internal pressure permitted in the piping system for continued operation at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service." The term "design pressure" is used in ASME B31.3 and ASME B31.1 and is subject to the same rules relating to allowances for variations of pressure or temperature or both. The pressure design of piping components is based on design conditions. Because piping systems are made of standardized components, often there is significant pressure capacity in the piping system beyond the conditions imposed on the system (with vessels one...