1、Consideration of External Pressure in the Design and Pressure Rating of Subsea EquipmentAPI TECHNICAL REPORT 17TR12 FIRST EDITION, MARCH 2015Special NotesAPI publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and re
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6、practices. These publications are not intended to obviate the need for applying sound engineering judgment regarding when and where these publications should be utilized. The formulation and publication of API publications is not intended in any way to inhibit anyone from using any other practices.A
7、ny manufacturer marking equipment or materials in conformance with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. API does not represent, warrant, or guarantee that such products do in fact conform to the applica
8、ble API standard.Users of this Technical Report should not rely exclusively on the information contained in this document. Sound business, scientific, engineering, and safety judgment should be used in employing the information contained herein. All rights reserved. No part of this work may be repro
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10、rican Petroleum InstituteForewordNothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be c
11、onstrued as insuring anyone against liability for infringement of letters patent.Shall: As used in a standard, “shall” denotes a minimum requirement in order to conform to the specification.Should: As used in a standard, “should” denotes a recommendation or that which is advised but not required in
12、order to conform to the specification. Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW, Washington, DC 20005, standardsapi.org.iiiContentsPage1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Normative References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Terms, Definitions, Acronyms, and Symbols. . . . . . . . . . .
14、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.1 Terms and Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.2 Acronyms and Abbreviations . . . . . . . . . . . . .
15、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33.3 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Rating and Design Conside
16、rations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.
17、2 Definition of “Rated Working Pressure”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.3 Design Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18、. . . . . . . . . 64.4 Considerations for API 17TR12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Procedures for Consideration of External Pressure in Subsea Equipment Designs . . . . . . . . . . . . . . . . . 75.1 Gener
19、al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75.2 Functional Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20、 . . . . . . . . . . . . . 85.3 System-Level Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105.4 Design Assessment Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21、 . . . . . . . . . . . . . . . . . . . . 115.5 Additional Consideration for Design Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155.6 Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22、. . . . . . . . . . . . . . . . . . . . . . . . 175.7 Verification of External Pressure at Different Water Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Design Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23、 . . . . . . . . . . . . . . . . . . . . . . . . . 186.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186.2 Validation Testing . . . . . . . . . . . . . . . . . . . . . . . . .
24、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196.3 Validation of Finite Element Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196.4 Validation Testing of Seals . . . . . . . . . .
25、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Factory Acceptance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208Conclusion. . . . . . . . . . . .
26、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Annex A (informative) Analysis Example for Pressure-Containing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 22Annex B (informative) Analysis Example fo
27、r Pressure-Controlling Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 24Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Figures1 External Pressure Design Asses
28、sment Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9A.1 Depth Adjusted Working Pressure (DAWP) for “XX-YYY Product Name” . . . . . . . . . . . . . . . . . . . . . . . . . 23B.1 15 ksi API RWPGate Valve Pressure-Controlling Equipment. . . . . . .
29、 . . . . . . . . . . . . . . . . . . . . . . . . . . . 24B.2 15 ksi API RWPGate Valve, Case 1: API RWP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25B.3 15 ksi API RWPGate Valve, Case 2: DAWP SWD. . . . . . . . . . . . . . . . . . . . . . . . . . . .
30、. . . . . . . . . . . . . . 25B.4 15 ksi API RWPGate Valve, Case 3: External Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26B.5 15 ksi API RWPGate Valve, Case 2a: DWP SWD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26B
31、.6 15 ksi API RWPGate Valve, Pressure-controlling Equipment, Load Case Verification Summary . . . . 27TableA.1 DAWP at Specified Water Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22vviIntroductionFor pressure-containing
32、equipment, as defined by API 6A and API 17D, where external pressure is constant and acting on the outside of the component, it is reasonable to include the external pressure effects when designing and rating the equipment. Examples would be piping, valve body, bonnet, and similar items, which are a
33、lways wetted by the seawater or fluid, resulting in an external pressure equal to ambient seawater pressure at the installed water depth.For pressure-controlling equipment (see API 6A and API 17D), external pressure (or in some case, backpressure) may not always be present downstream of the pressure
34、-controlling element (closure mechanism), or the backpressure pressure magnitude may fluctuate. Example of this scenario is a closed valve or choke where downstream pressure of the closure mechanism may not always be equal to external ambient seawater pressure (e.g. a subsea flowline is blown-down t
35、o low pressure during a system shut-in to avoid hydrate formation in the flowline as its contents cool down). Another example of external pressure assessment is equipment containing one-atmosphere pressure (or 14.7 psia) voids such as spaces between dual seals where the inner seal does not benefit f
36、rom the external pressure effects. Pressure in trapped spaces between closed valves can decline significantly due to thermal effects when a hot system is shut-in and begins to cool down. In certain cases where dual barriers are designed into the equipment (i.e. dual packings on valve stems, connecto
37、r gaskets with primary and secondary seals, penetrators with internal and external seals, etc.), the effects of external ambient seawater pressure may not be present behind the primary seal during subsea operation, nor present during shop testing operations. If the pressure equipment is designed wit
38、h consideration of external pressure due to ambient seawater pressure at depth, it may not be possible nor practical to perform FAT pressure test of the primary seal (inboard) for the dual barrier sealing arrangement to the maximum pressure that it will see in operation at depth without overstressin
39、g the pressure equipment since external pressure in the shop is only one-atmosphere. It is a proper quality assurance practice to test all seals to at least the differential pressure they will see in service, or higher. If such testing cannot be conducted, the manufacturer and equipment purchaser/en
40、d-user should address the associated risk of the utilizing external pressure in the design with dual barrier sealing configuration, and the potential risk of a seal defect not being detected during the FAT. As illustrated above, the evaluation of pressure-controlling equipment and equipment containi
41、ng trapped one-atmosphere void spaces can be more complicated than for pressure-containing equipment with consideration of external pressure. In all cases, a full system analysis is necessary, along with HAZID/HAZOP and FMEA/FMECA studies to ensure that external pressure conditions during all potent
42、ial operating modes and scenarios are properly identified and evaluated. Additionally, equipment with trapped voids or dual barrier seals configuration may not have the beneficial effects of external pressure and this must be taken into consideration when assessing pressure ratings. 1Consideration o
43、f External Pressure in the Design and Pressure Rating of Subsea Equipment1 ScopeThis technical report addresses issues related to the effects of external pressure acting on API Subcommittee 17 (SC17, Subcommittee on Subsea Production Equipment) subsea equipment installed in deepwater for containing
44、or controlling wellbore fluids. External pressure at deepwater can significantly reduce the differential pressure acting on the wall of subsea equipment, and therefore, this can improve its internal pressure containment capability. External pressure is typically ambient seawater pressure, but in som
45、e cases, external pressure may be due to the hydrostatic head of drilling mud, completion fluids, or other fluids contained within risers or other conduits that connect the subsea equipment to surface facilities.There is a need for guidelines on the application of external pressure during the design
46、, validation and operation of subsea equipment. Guidelines are also needed to calculate and/or determine a modification to the working pressure limits at the installed water depth, using the selected equipment API rated working pressure (RWP).API Technical Report 17TR12 (hereafter API 17TR12) provid
47、es guidance for subsea equipment designers/manufacturers to properly account for external pressure (or in some cases, differential pressure) when designing and validating subsea equipment. Additionally, this technical report provides guidance to equipment purchaser/end-user to appropriately select r
48、ated equipment for their subsea systems with consideration to the effects of external pressure in addition to internal pressure, including differential pressure across a closure mechanism, and other applied mechanical or structural loads under all potential operating scenarios and functionality crit
49、eria.NOTE API Technical Report 17TR4 (hereafter API 17TR4) provides additional information on the effects of external pressure on stresses generated within subsea equipment for the equipment designer.API 17TR12 applies specifically to API SC17 equipment. API 17TR12 is to be used as a supplement to the equipments applicable API product specification (e.g. API 6A, API 17D, API 17G), depending on its specific application, associated regulations, and project requirements. Other API product specifications may elect to adopt this technical report, subject to their component hardware
