0. API 17D – Specification for Subsea Trees and Wellheads Differential Pressure Use in Design of Subsea Equipment June 2012

1. API 17D – Use of Differential Pressure in Subsea Equipment Design
Subsea Equipment Pressure Ratings - API TECHNICAL REPORT 17TR4 - JANUARY 2012
design pressure
The maximum differential between internal pressure and external pressure during operating conditions at each cross-section. (API 1111)
rated working pressure
The maximum internal pressure a piece of equipment is designed to contain and/or control. (API 17D, API 6A)

2. API 17D – Use of Differential Pressure in Subsea Equipment Design
Document objectives:
define the framework for the use of differential pressure as well as broadly definition of paths to:
determine standards for designing equipment using differential pressure;
how to rate the equipment for differential pressure service; and
determine how to validate (test) the design of the equipment.

3. API 17D – Use of Differential Pressure in Subsea Equipment Design
VME stress = f(∆P); not magnitude of Pi or Po
Principal stress or individual stress component failure criteria = f(Pi and Po)

4. API 17D – Use of Differential Pressure in Subsea Equipment Design
Summary of TR4
All loads and conditions that may realistically occur must be considered (including accidental )
Limits must be defined for materials and loads to provide protection against the appropriate types of failure.
Limit load failure based upon VME stress is affected by differential pressure and external applied loads.
Localized stress concentration areas, such as areas of discontinuity and areas of high mean and alternating stresses, are normally where fatigue failures occur.
Principal stresses are important in analyzing failure from cyclic loading.
Other system failures, such as non-metallic seals, may be the weak link in the system instead of the pressure vessel body.

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