Re-Rating of Piping and Pressure Vessels Using API 579 Section 3

As data on actual failures of metals, becomes available from various industries, advances are made in understanding behaviour of materials under different conditions. This leads to refinement of published characteristics for materials in general. Further, changes in manufacturing technology, improved measurement techniques and analytical capabilities of software, all contribute in their own way in defining boundaries for a broad category of materials. This manifests itself in a challenge for design engineers to continue to let some chemical processes operate in their normal range using existing equipment that needs to be re-rated based on improved understanding. One such example is the minimum temperature limit, without impact testing, for ordinary carbon steels that has been revised upwards in recent years. This has resulted in rendering piping systems and pressure vessels unsuitable for low temperature conditions that they might have been certified for based on earlier knowledge and Standards. This challenge can be dealt with in a number of different ways by revisiting both process and mechanical design variables. This paper/presentation discusses the approach adopted by Santos for their gas processing plant at Moomba, to review and adjust the process in light of latest knowledge on resistance to brittle failure.