MDMT coincident pressure
MDMT coincident pressure
(OP)
I'm working on a carbon steel ASME VIII-1 vessel where the design pressure and temperature are up around 200psi/300°F. This design pressure has been chosen as an upset case, and the tank will actually be operating at around -5psig/-45°F, with potential upsets taking us down to around -70°F at deeper vacuums. In this application we're working with a saturated fluid, so the temperature/pressure curve is very well defined.
As I understand for MDMT the fabricator will be required to stamp the MDMT at the vessel MAWP, in which case the rated MDMT will be well above the required -70°F.
That said, they are also free to stamp additional MDMT values at lower coincident pressures to bring down the MDMT using the rules of UCS-66.
My question is this: are we allowed to specify a coincident pressure for a MDMT case that is lower than the vessel design pressure (200psi)?
As an example, could I set a MDMT case at: -70°F @ 50psi for a vessel designed for 300°F/200psi if the process shows that I could never exceed 50psi at -70°F?
If I could, then the coincident ratio of 0.35 from UCS-66 would be met, and the vessel would be exempt from impact testing.
Thank you!
As I understand for MDMT the fabricator will be required to stamp the MDMT at the vessel MAWP, in which case the rated MDMT will be well above the required -70°F.
That said, they are also free to stamp additional MDMT values at lower coincident pressures to bring down the MDMT using the rules of UCS-66.
My question is this: are we allowed to specify a coincident pressure for a MDMT case that is lower than the vessel design pressure (200psi)?
As an example, could I set a MDMT case at: -70°F @ 50psi for a vessel designed for 300°F/200psi if the process shows that I could never exceed 50psi at -70°F?
If I could, then the coincident ratio of 0.35 from UCS-66 would be met, and the vessel would be exempt from impact testing.
Thank you!





RE: MDMT coincident pressure
RE: MDMT coincident pressure
Agree with TomBarsh (Structural); Also check ASME B31T 2010
RE: MDMT coincident pressure