API 6HP Process1 API 6HP Example Analysis Project API E&P Standards Conference Applications of Standards Research, 24 June 2008

API 6HP Process2 API 6HP Example Project Objective  Meet the ECS Oversight Committee request  Document a process, not validate a product Scope  Relatively simple HPHT model similar to a C&K valve body  The API 6HP design committee defined the input parameters –Model configuration –Service conditions –Material properties  Document the process in a technical report

API 6HP Process3 User’s Functional Design Spec Design Equipment Design Meets Spec Design Verification Analysis Design Validation Manufacture Equipment No Yes Mfg Design Specification

API 6HP Process4 Design Verification Analysis Applies to pressure containing parts Does not apply to pressure retaining parts Does not apply to closure bolting Does not apply to ring gaskets Design Verification Analysis Plastic Collapse Analysis ASME VIII-2 Par Local Strain Limit Analysis ASME VIII-2 Par Ratcheting Analysis ASME VIII-2 Par LEFM Fatigue Analysis ASME VIII-3 KD-4 Leak Before Burst S-N Fatigue Analysis ASME VIII-3 KD-3 No Yes

API 6HP Process5 LEFM Fatigue Analysis Analysis required for each critical section Assume initial crack size based upon NDE capability Crack aspect ratio should be updated as crack grows Use appropriate material crack growth rate data for environment and loading Allowable crack size based upon ASME Div 3 KD-412 Calculate crack growth for service life requirements LEFM Fatigue Analysis Initial crack size based upon NDE or incremental crack size Calculate stress intensity factor based upon crack depth, a New crack size < allowable No Yes Design meets spec Redesign No

API 6HP Process6 Example Model T M P = 20 ksi T = 105,000 lb M = 10,000 ft-lb Temp = 350°F int, 35°F ext

API 6HP Process7 Process – Plastic Collapse Process per ASME Sect VIII, Div 2, paragraph FEA Model  Geometry –Generate FEA model accurately representing the component geometry, boundary conditions, and applied loads for the pressure containing component –Refinement of the model around areas of stress and strain concentration shall be provided appropriate to good engineering practices –The effects of non-linear geometry shall be considered in the model  Material –Use elastic-plastic material model in accordance with ASME Div 2 Annex 3.D –Use SMYS, SMUTS, and Modulus at max rated temperature  Boundary Conditions –Apply all relevant loads and all applicable load cases per ASME VIII-2 Table 5.5

API 6HP Process8 Process – Plastic Collapse Load Cases  Run all relevant load case combinations per ASME VIII-2 Table 5.5 Analysis  Perform an analysis for each load resistance factor (LRF) case Evaluation  If analysis converges, the component is stable under the applied loads for each load case and meets the Plastic Collapse criteria  If analysis does not converge, either –Reduce load rating –Increase structural design –Increase material strength properties

API 6HP Process9 Process – Localized Failure Process per ASME Sect. VIII, Div. 2, paragraph FEA Model  Use Plastic Collapse model for geometry, material, boundary conditions, and load cases Analysis  Equivalent plastic strain shall be less than triaxial strain limits at each location as per ASME VIII-2 paragraph  Applies to all load cases defined for plastic collapse analysis Evaluation  If analysis meets the triaxial strain limits for all load cases, the component meets the local failure criteria  If analysis does not meet the strain limit criteria, either –Reduce load rating –Increase structural design –Increase material strength properties

API 6HP Process10 Process – Ratcheting Analysis Process per ASME Sect. VIII, Div. 2, paragraph FEA Model  Geometry –Generate FEA model accurately representing the component geometry, boundary conditions and applied loads for the pressure containing component –Refinement of the model around areas of stress and strain concentrations shall be provided appropriate to good engineering practices –The effects of non-linear geometry shall be considered in the model  Material –Use elastic-perfectly plastic material model with kinematic strain hardening –Use SMYS, SMUTS, and Modulus at room temperature for hydro test cycles and at max rated temperature for working pressure cycles  Boundary Conditions –Run using all relevant loads and all applicable load cases

API 6HP Process11 Process – Ratcheting Analysis Analysis  Perform preload of mating flange bolting as necessary  Perform hydro pressure test cycles at room temp as required (normally 2 cycles)  Perform 3 working cycles at max rated temperature Evaluation  After 3 working cycle loads –No plastic action in component is permissible –Must have an elastic core in primary load bearing boundary –No permanent change in overall dimensions between last and next to last cycle is permissible

API 6HP Process12 Input Conditions – Structural Analysis Hydrostatic pressure test – 27.5 ksi (2 cycles)  Based upon ASME Div 3 requirements of 1.25 x rated pressure x material derating factor for 350°F (1 / 91%) Service conditions  Pressure –12 pressure cycles at 20 ksi every two weeks based upon bi-weekly BOP pressure testing  Loads –Pressure end load, plus –Constant external applied tension of 105,000 lb applied along axis of flange neck, plus –Bending moment of 10,000 ft-lb applied to axis of flange neck alternating on a period of 10 sec  Temperature –Material strength reduced to 91% for 350°F service  Environment –Assume air for model

API 6HP Process13 Process – LEFM Analysis Process per ASME Sect. VIII, Div. 3, KD-4 FEA Model  Geometry –Generate FEA model accurately representing the component geometry, boundary conditions, and applied loads –Refinement of the model around areas of stress and strain concentrations shall be provided appropriate to good engineering practices  Material –Use linear elastic material model  Boundary Conditions –Apply all relevant working loads Internal and external pressure External applied loads Thermal gradients

API 6HP Process14 Process – LEFM Analysis Analysis  Superimpose thermal stress with applied loads  Calculate the max principal stresses through the wall at all critical sections (worst case section may not be obvious)  Define the initial crack size based upon NDE criteria –Surface cracks should assume an initial aspect ratio of 1:3 (KD-410) –A surface crack in a stress concentration area, such as cross-bores, can be assumed to have an initial aspect ratio of 1:1  Calculate the stress intensity factor at the crack tip –Apply crack face opening pressure as appropriate  Calculate incremental crack growth with incremental working cycles based upon material properties (da/dN vs. ΔK) –Reference MMS report  Repeat crack growth cycles until crack depth meets the final allowable crack depth

API 6HP Process15 Process – LEFM Analysis Final allowable crack depth  The final allowable crack depth shall be the lesser of: –Half the number of cycle required to grow the crack from initial depth to the depth where the crack stress intensity factor exceeds the material toughness, K 1C, or –Number of cycles required to grow the crack from initial depth to 25% of the section thickness, or –Number of cycles required to grow the crack for initial crack depth to 25% of the critical crack depth Repeat fatigue calculation for each critical section Evaluation  If fatigue life meets criteria, component is acceptable  If fatigue life does not meet criteria –Change inspection intervals –Redesign –Reduce loads

API 6HP Process16 Analysis Summary Materials  Material properties are attainable by testing  Some data is available in existing standards Structural analysis  Max equivalent plastic strain ≈ 0.5% at working loads  Shakedown occurs within 3 working cycles Fatigue analysis  Design life exceeds goal  Consideration of stresses from thermal gradient is important –Thermal stresses may change high stress point and crack initiation from ID surface to OD surface