HPHT Subsea Equipment Verification & Validation: Understanding Operational Limits
Authors: Vaclavik Matthew 
Published: April 2019

Practices for engineering, design, qualification, and implementation of drilling, completions, production, and intervention equipment for high-pressure high-temperature (HPHT) developments have matured sufficiently to enable the next frontier of projects in the Gulf of Mexico (GoM). Per the code of federal regulations, the Bureau of Safety and Environmental Enforcement (BSEE) regulates oil and gas exploration, development, and production operations on the Outer Continental Shelf (OCS). Unlike historical OCS projects with pressures less than 15,000 psi and temperatures less than 350°F where subsea production equipment is governed by codes and standards referenced in 30 CFR 250.804(b), equipment required for well completion or well control in HPHT environments in most instances exceeds the ratings prescribed in these established codes and standards. Industry's initial attempt to address all wellbore issues and challenges associated with HPHT from sand face to pipeline in a holistic manner was through API TR PER15K, 1st Ed. which was released in March 2013. API PER15K was never intended to serve as a guideline for HPHT design verification and validation, thus additional direction was needed.

To address the need for extension of industry codes and standards to ratings needed for HPHT equipment, the 1st Edition of API 17TR8 was released in February 2015 and represented Industry's initial guideline for HPHT subsea equipment development. Through use of the guideline, key lessons learned, and technical gaps were identified and incorporated into the document, which is now reflected in the 2nd Edition released in March 2018.

As industry-led equipment development programs have progressed to a mature stage, Chevron has identified two topics in API 17TR8 which serve as the fundamental drivers for defining equipment operational limitations: Extreme/Survival ratings for equipment designed according to Elastic-Plastic (E-P) design methods as prescribed in ASME Section VIII Div. 2 & Div. 3,Equipment serviceability criteria.

The current guidance in 17TR8 is quite clear as it relates to defining equipment capacity via FEA but puts the onus on the Offshore Equipment Manufacturer (OEM) and Operator to define how serviceability can impact operational limits.

Industry has presented work to validate the normal, extreme, and survival load factors for E-P analysis (Ref. Dril-Quip OTC-27605-MS), but most of this work has been performed on non-complex, single body geometries. Similarly, the industry is wrestling with a consistent view of how to address serviceability. This paper discusses the following: 1.) Recommended design codes in API 17TR8 and an Operator's perspective on application of these codes; 2.) How to address uncertainties that exist in the design, qualification, and manufacturing process; 3.) Using the aforementioned guidelines when performing a component-based verification & validation process; 4.) How to define system operational limits and ensure system integrity by addressing and mitigating gaps when all the qualified components are integrated into a system.