tr1ntx
Mechanical
- Jul 20, 2010
- 285
I searched and didn't find a thread similar enough on rapid decompression.
For a trunnion ball valve, 8" port, 15000psi rating, during testing the valve is cycled Open under full test pressure differential, 16500psi. My topic here is the seat ring (the steel ring which houses the actual polymer seat). It is 9.340" OD on the large end where the seat is, and 8.120" ID. The length of this large OD is 0.830" and then the OD steps down where the seals are.
The actual sealing material, the polymer insert, is 8.540" OD x 8.270" ID x 0.435" H. It is PEEK, produced by extrusion. The afore-mentioned seat ring can be 4130 NQT or 17-4PH Cond H-1150.
When pressure is applied in the port with the valve in the Closed position, the OD of the seat ring will expand ~0.012", having contacted the valve body and been restrained from further expansion (this is including the concurrent expansion of the valve body, insofar as approximations/assumptions/methods allow a truly accurate calculation). As the ball is rotated toward the Open position, the "void" of the ball bore begins to be located over the angled sealing face of the PEEK seat. The pressure in the ball bore is atmospheric and vented. At some point, flow begins. The rotation of the ball is continuous due to the actuator. Needless to say, the rate of depressurization in the valve bore is rapid, whatever fraction of a second, 0.1, 0.3, whatever, maybe faster. The test fluid is water + antifreeze.
I have found some tables of strain rate vs. tensile properties, but don't know about what happens going the other way, i.e., the relaxation of the tension & how fast does the seat ring contract? In this case, we're dealing with 2 different materials, the PEEK insert and the steel ring, plus the loading condition is all sorts of asymetric due to the fact that the ball bore leaves a crescent of the seat out-of-contact with the ball OD.
I'm putting this up hoping someone might come back with some experienced examples or other insight/general discussion into rapid decompression and thought the pressure vessel forum was more likely than the materials forum to get results.
For a trunnion ball valve, 8" port, 15000psi rating, during testing the valve is cycled Open under full test pressure differential, 16500psi. My topic here is the seat ring (the steel ring which houses the actual polymer seat). It is 9.340" OD on the large end where the seat is, and 8.120" ID. The length of this large OD is 0.830" and then the OD steps down where the seals are.
The actual sealing material, the polymer insert, is 8.540" OD x 8.270" ID x 0.435" H. It is PEEK, produced by extrusion. The afore-mentioned seat ring can be 4130 NQT or 17-4PH Cond H-1150.
When pressure is applied in the port with the valve in the Closed position, the OD of the seat ring will expand ~0.012", having contacted the valve body and been restrained from further expansion (this is including the concurrent expansion of the valve body, insofar as approximations/assumptions/methods allow a truly accurate calculation). As the ball is rotated toward the Open position, the "void" of the ball bore begins to be located over the angled sealing face of the PEEK seat. The pressure in the ball bore is atmospheric and vented. At some point, flow begins. The rotation of the ball is continuous due to the actuator. Needless to say, the rate of depressurization in the valve bore is rapid, whatever fraction of a second, 0.1, 0.3, whatever, maybe faster. The test fluid is water + antifreeze.
I have found some tables of strain rate vs. tensile properties, but don't know about what happens going the other way, i.e., the relaxation of the tension & how fast does the seat ring contract? In this case, we're dealing with 2 different materials, the PEEK insert and the steel ring, plus the loading condition is all sorts of asymetric due to the fact that the ball bore leaves a crescent of the seat out-of-contact with the ball OD.
I'm putting this up hoping someone might come back with some experienced examples or other insight/general discussion into rapid decompression and thought the pressure vessel forum was more likely than the materials forum to get results.
