Case Study on the Design of HPHT Components Using ASME Section VIII Division 2 and 3

Abstract

Design margins in high pressure / high temperature (HPHT) equipment vary throughout the various Codes and Standards. This paper is an overview of the design standards which can be applied to HPHT service or are currently under development. This paper will provide a case study of the design philosophies referred to in API 17TR8 which refers heavily on ASME Section VIII Division 2 and Division 3. This will demonstrate the difference in design margins, and how the life of the components may be affected. Design approaches such as "Design-by-Rule" or "Design-by-Analysis" are included in the standards used today. Implementation of the "Design by Analysis" methods can be very complex and require a significant amount of analytical rigor, compared to traditional "Design-by-Rule" analyses. However, the benefits of the additional rigor can be significant to allow the use of lower design margins which will minimize material while providing equal or increased theoretical design lives. HPHT equipment is entering into operating pressure ranges that have rarely been experienced before by similar equipment. API 17TR8 does not have approved industry guidance that would support a traditional "Design-by-Rule" process. The lower design margins used by some codes can have the unintended consequence of leading to significant areas of potentially high stresses due to thinner sections and stress concentrations, which can lead to fatigue issues. A combined approach which includes lower design margins and rigorous analytical methods for the determination of the cyclic life of components can lead to robust designs which both minimize cost while improving manufacturability and reliability.