A Design Combining API and ASME Codes for Subsea Equipment in HP/HT Conditions

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 23928, ’A Design Method Combining API and ASME Codes for Subsea Equipment in High-Pressure/High-Temperature Conditions,’ by Parth D. Pathak, Christopher G. Kocurek, and Samuel L. Taylor, Cameron International Corporation, prepared for the 2013 Offshore Technology Conference, Houston, 6-9 May. The paper has not been peer reviewed. The design of subsea equipment for pressures greater than 15,000 psi and temperatures more than 250°F is a substantial challenge. The current standard from the American Petroleum Institute (API), Specification17D, for designing subsea equipment provides little guidance on conditions exceeding these measurements. This work has been performed to demonstrate the acceptance of existing methods for high-pressure/high-temperature (HP/HT) conditions and introduce advanced American Society of Mechanical Engineers (ASME) methods for designing subsea equipment. Introduction The design methods given in API 17D refer to the design methods of API 6A, which are valid for working pressures up to 20,000 psi and temperatures up to 650°F. The ASME Boiler and Pres-sure Vessel Code (BPVC), Section VIII, Division 2 and Division 3, provides design methods for high-pressure vessels. These design methods must meet the API allowable limits and material and test requirements. ASME BPVC has its own design material and test requirements to be used along with the design methods outlined in the ASME codes. A design method combining the ASME design techniques with API material and test requirements that satisfies both the codes is desirable. An example evaluation is presented of an API 17D (API 6A, 4-in. 20K) flange flow loop for a design pressure of 20,000 psi and a temperature of 350°F with external tension and bending loads. The ASME BPVC was a result of a committee set up in 1911 to formulate standard rules for the construction of steam boilers and other pressure vessels. This code is formulated for pressure vessels in the nuclear industry, and for designing storage and transportation tanks. API 17D was formulated for standardization of subsea production systems. The ASME and API codes differ in material, hydrostatic-test, and nondestructive-examination (NDE) requirements in particular. The API codes provide temperature derating factors for elevated-temperature design. The standard hydrostatic-test requirement per API 17D is 1.5 times the rated working pressure, whereas in BPVC, Section VIII, Division 2, the hydrotest requirement is 1.43 times the working pressure. Additionally, the hydrostatic test pressure in ASME varies between divisions and has also fluctuated over time.