Abstract: Operators should conform whether a pipeline in corroded flaw situation could maintain its service, for corrosion may leads to lower pipeline strength. Current assessment methodologies are ASME B31G and API 579 series. Theory foundation for remaining strength assessment methodology is presented and assessing formula for relative assessment methodology is educed based on individual basic assumption. Thus deep comparison is made for this purpose. Significant conclusion obtained is that API 579 is more conservative than ASME B31G. Authors suggest that under single load and simple flaw situations, remaining strength assessment should be carried out according to ASME B31G criterion.