The distinction between general metal loss (Part 4 of API 579) and local metal loss (Part 5 of API 579) is not always clear. API 579, Paragraph 4.3.3.2(b), states, "A minimum of 15 thickness readings is recommended unless the level of NDE utilized can be used to confirm that the metal loss is general." The word "general" implies uniform metal loss with minimum variation of the remaining wall. This fact is supported in Paragraph 4.2.1 where it states that "The assessment procedures in this section [Part 4 Assessment of General Metal Loss] which exceeds or is predicted to exceed the corrosion allowance before the next scheduled inspection." Paragraph 4.1.2 states that if local areas of metal loss are found on the component, the thickness averaging approach may produce conservative results. For these cases, the procedures in Part 5 Assessment of Local Metal Loss, which require detailed thickness profiles, will be utilized to reduce the conservatism in the analysis. The exact distinction between uniform and local metal loss cannot be made without knowing the characteristics of the metal loss profile. Thus general metal loss implies "uniform" metal loss, and the guidelines based on the characteristics of the thickness profile are incorporated into the rules to direct the user to Part 5 when appropriate. API 579 concludes in Paragraph 4.1.2 that for most evaluations, it is recommended to first perform an assessment using Part 4 Assessment of General Metal Loss. Thus, the formulation in Eq. 3-18 is very appropriate...