Validation testing of subsea equipment designed for high pressure/high temperature (HP/HT) applications is necessary but can be extremely expensive and infeasible. The complete paper presents a practical approach for validating design-verification analysis for subsea equipment, using a representative pressure valve block to correlate finite-element analysis (FEA) predictions for strain changes with actual measured changes. The design methods use the guidelines in technical report API 17TR8, and load cases per API 17TR12.
Introduction
Current editions of API standards covered in API Subcommittee 17 (API SC 17) for subsea production equipment are geared toward designing the equipment for its absolute internal working pressures. Also, on the basis of previous regulatory requirements for the offshore industry, until 2014 it was not advised to take advantage of the external seawater hydrostatic head and other external pressures to design certain types of subsea equipment covered under API SC 17. Thus, equipment per its corresponding API standards was designed to have an absolute rated working pressure always greater than the well shut-in tubing pressures.
Three API technical reports published in 2014 and regulatory guidelines for the Gulf of Mexico published in 2017–2018 provide design guidelines for depth-adjusting subsea equipment specific to its working seawater depths, and detailed verification and validation guidelines for designing HP/HT equipment—that is, with absolute internal pressure rating exceeding 15,000 psi and temperatures exceeding 350°F. These guidelines can be used to develop subsea equipment rated to working pressures greater than 15,000 psi.
