valveguy580437
Petroleum
- Mar 16, 2016
- 1
Hi All,
Working on some subsea valves that are to be installed in a manifold. Output loads from the piping analysis of the manifold (seismic) have been used as inputs to verify the pup piece on the valves via FEA. These loads gave stresses that were high but within allowables according to ASME VIII Div. 2 (in accordance with API 6A).
The manifold design has since changed and the piping analysis has been re-run with the end result being that the stresses observed in the pup pieces via FEA exceed ASME VIII allowables. My question is, can I design the valve pup piece to B31.8 which is less conservative on maximum allowable stresses?
In ASME VIII D2 it is minimum of SMYS/1.5 and SMTS/2.4, while in the B31.8 code it is only the yield strength that is used. For Hoop stress the allowable stress is 0.72 x SMYS, longitudinal stress is 0.80xSMYS and combined (Von-Mises) stress is 0.90xSMYS. As you can see the approach in determining the allowable stresses varies hugely. Another difference between the two standards are that ASME VIII D2 divides loads into primary (weight and pressure) and secondary (thermal and forced displacements), most of the operational loads can be determined as secondary, which again will increase the allowable stresses substantially.
(SMYS=Specified Minimum Yield Strength, SMTS=Specified Minimum Tensile Strength)
My proposal is that the pup-piece is to be treated as a part of the pipe and therefore the B31.8 Chapter VIII code stresses apply to bring the results within allowable stress limits.
Working on some subsea valves that are to be installed in a manifold. Output loads from the piping analysis of the manifold (seismic) have been used as inputs to verify the pup piece on the valves via FEA. These loads gave stresses that were high but within allowables according to ASME VIII Div. 2 (in accordance with API 6A).
The manifold design has since changed and the piping analysis has been re-run with the end result being that the stresses observed in the pup pieces via FEA exceed ASME VIII allowables. My question is, can I design the valve pup piece to B31.8 which is less conservative on maximum allowable stresses?
In ASME VIII D2 it is minimum of SMYS/1.5 and SMTS/2.4, while in the B31.8 code it is only the yield strength that is used. For Hoop stress the allowable stress is 0.72 x SMYS, longitudinal stress is 0.80xSMYS and combined (Von-Mises) stress is 0.90xSMYS. As you can see the approach in determining the allowable stresses varies hugely. Another difference between the two standards are that ASME VIII D2 divides loads into primary (weight and pressure) and secondary (thermal and forced displacements), most of the operational loads can be determined as secondary, which again will increase the allowable stresses substantially.
(SMYS=Specified Minimum Yield Strength, SMTS=Specified Minimum Tensile Strength)
My proposal is that the pup-piece is to be treated as a part of the pipe and therefore the B31.8 Chapter VIII code stresses apply to bring the results within allowable stress limits.
