Aspects of Design Verification Analysis for HP/HT Applications

Abstract

Abstract Design verification analyses for high-pressure/high-temperature (HPHT) environments, as defined in the annexes of the American Petroleum Institute (API) codes (11D1 and 14A) as well as by the Bureau of Safety and Environmental Enforcement (BSEE), require some basic definitions and interpretation of code requirements. One of the basic definitions is the global collapse load in accordance with ASME BPVC VIII Division 2 or 3 (ASME BPVC VIII-2 2015 or ASME BPVC VIII-3 2015, respectively). There is confusion with respect to what this load really means in relation to actual failure load and maximum load (critical load) allowed for safe operation. Fatigue life assessment is necessary in design verification analysis if cyclic loading is expected during the life of the well. Several approaches to conducting fatigue analysis have been proposed by various codes. A detailed examination of the three load types (global collapse, catastrophic failure, and maximum loads) is provided. The differences between the load types are highlighted conceptually first, then illustrated through finite element analysis (FEA) and published test data in the literature. The ASME BPVC VIII Division 2 and Division 3 load factors for global collapse analysis are evaluated, and factors that affect the conclusions are delineated. Various fatigue analysis approaches are evaluated to help illustrate the difference and effect of these approaches on design verification analysis for HPHT applications. Theoretically, the global collapse load, as defined in ASME BPVC VIII Division 2 or 3, is greater than or equal to the catastrophic (theoretical or physical) failure load, and the catastrophic failure load is larger than the maximum load. The global collapse analysis is a verification analysis against the global collapse load definition; therefore, questions are raised when load ratings are derived from global collapse load predicted from FEA. However, uncertainties remain regarding which fatigue evaluation approach is most suitable for HPHT applications. This study provides a clear basis for load assessment, highlighting how industry-wide consensus is necessary for precise HPHT design verification analysis.