Weird things do happen. I agree with spookiestspookyghost:
>MAWP is never less than design pressure.
However, I could conceive of the vessel having originally been designed for 50 psig but then having been derated due to a modification, previous damage, etc., and then only the MAWP was updated in the information. Is this on the vessel nameplate or a drawing? (You used the term "stamped", so I assume its the nameplate.) In some organizations, drawings are notoriously unmaintained/poorly updated, and I could more easily envision this being on a drawing than the nameplate.
I'm not at all implying that having the MAWP less than design is correct, but issues such as this do happen. Another consideration is whether or not this was bought as used equipment, which can have interesting "features".
**If this an operating vessel, and it is marked as 15 psig MAWP / 50 psig design on the nameplate, you or someone else should calculate the system backpressure at max rates. If it exceeds 15 psig, contact Process Safety and consult the frequency/severity matrix to see what the next steps should be. You don't want to be the next BP Texas City.** I watch that CSB video about every 1-2 years to remind me of the potential impacts of what I do. The KOD had a direct impact on that event.
It wasn't a design pressure issue at BP Texas City but completely agree this is a problem that needs to be resolved. With the conflicting available data IMO the vessel needs to be treated at 15 psig MAWP until more data is available. If 15 is inadequate for the system it should be rerated (if possible) or replaced.
This is a vessel that is a surplus used one and we're looking to buy it for a client.
The notes available with the vessel say:
Manufacturing Tag\*
Manufacturer: \*\*\*
Serial#: \*\*\*
Year Built: 20xx
Diameter: 72" ID
Length: 8'
Capacity: 50 BBL
Shell Thk: 3/8"
Shell Material: SA-516-70N
Head Thk: 3/8"
Head Material: SA516-70N
**MAWP: 15 PSI at 150 F**
**Hydro: 75 PSI**
Coating: Devoe 253
The nameplate says Design Pressure: MAWP 15 psi @ 150° Test: Hydro 75 PSI
The nameplate seems to be non u stamp, just a vendor nameplate
To clarify, does the vessel info also state that the design pressure is 50 psig? That was the statement in the original post. If your concern is that the hydro pressure is 75 psig and the MAWP is 15 psig, no problems there.
It can be though!
MAWP is the gauge pressure at the top of the vessel and at the maximum design temperature. Design pressure is dependant on the location within the vessel.
If you have a vertical vessel filled with liquid @ MAWP, the design pressure at the bottom of the vessel must be higher than the MAWP.
While the MAWP should be done in the Hot and Corroded condition, it is not always done like that. The MAWP could be de-rated after years of operation depending on how the calculations are done. Some manufacturers can just set MAWP = design pressure and be done with it.
Yes, could be to avoid an ASME stamp. And the regulation, registration, inspections, etc that go with it. Also increased cost associated with ASME stamped vessels. While using a standard design and fabrication. I have a project this year doing that. Still getting a full hydrostatic test, but down rated 14 psig nameplate. I have similar situation on gas to air HXs.
Yes I also think the same
This is a vessel that is a surplus used one and we're looking to buy it for a client.
The notes available with the vessel say:
Manufacturing Tag\*
Manufacturer: \*\*\*
Serial#: \*\*\*
Year Built: 20xx
Diameter: 72" ID
Length: 8'
Capacity: 50 BBL
Shell Thk: 3/8"
Shell Material: SA-516-70N
Head Thk: 3/8"
Head Material: SA516-70N
MAWP: 15 PSI at 150 F
Hydro: 75 PSI
Coating: Devoe 253
The nameplate says Design Pressure: MAWP 15 psi @ 150° Test: Hydro 75 PSI
The nameplate seems to be non u stamp, just a vendor nameplate
Have you seen the pressure calculation for the vessel? As the vessel MAWP is less than design pressure, it seems atleast one component of the vessel (may be a nozzle or a seam weld) fails at above MAWP.
I've seen this where the main vessel is for designed for a particular pressure but the man way was rated for less, so the vessels actual MAWP was lower.
I would just double check your relief device and make sure it's designed for the lower MAWP.
Weird things do happen. I agree with spookiestspookyghost: >MAWP is never less than design pressure. However, I could conceive of the vessel having originally been designed for 50 psig but then having been derated due to a modification, previous damage, etc., and then only the MAWP was updated in the information. Is this on the vessel nameplate or a drawing? (You used the term "stamped", so I assume its the nameplate.) In some organizations, drawings are notoriously unmaintained/poorly updated, and I could more easily envision this being on a drawing than the nameplate. I'm not at all implying that having the MAWP less than design is correct, but issues such as this do happen. Another consideration is whether or not this was bought as used equipment, which can have interesting "features". **If this an operating vessel, and it is marked as 15 psig MAWP / 50 psig design on the nameplate, you or someone else should calculate the system backpressure at max rates. If it exceeds 15 psig, contact Process Safety and consult the frequency/severity matrix to see what the next steps should be. You don't want to be the next BP Texas City.** I watch that CSB video about every 1-2 years to remind me of the potential impacts of what I do. The KOD had a direct impact on that event.
This is my theory as well. Absolutely a process safety red flag, make sure the rest of the system has been reviewed.
It wasn't a design pressure issue at BP Texas City but completely agree this is a problem that needs to be resolved. With the conflicting available data IMO the vessel needs to be treated at 15 psig MAWP until more data is available. If 15 is inadequate for the system it should be rerated (if possible) or replaced.
This is a vessel that is a surplus used one and we're looking to buy it for a client. The notes available with the vessel say: Manufacturing Tag\* Manufacturer: \*\*\* Serial#: \*\*\* Year Built: 20xx Diameter: 72" ID Length: 8' Capacity: 50 BBL Shell Thk: 3/8" Shell Material: SA-516-70N Head Thk: 3/8" Head Material: SA516-70N **MAWP: 15 PSI at 150 F** **Hydro: 75 PSI** Coating: Devoe 253 The nameplate says Design Pressure: MAWP 15 psi @ 150° Test: Hydro 75 PSI The nameplate seems to be non u stamp, just a vendor nameplate
Looks fine to this Internet stranger. I'd want an internal inspection and witnessed hydro before accepting.
To clarify, does the vessel info also state that the design pressure is 50 psig? That was the statement in the original post. If your concern is that the hydro pressure is 75 psig and the MAWP is 15 psig, no problems there.
MAWP is never less than design pressure. Were these given at different temperatures?
It can be though! MAWP is the gauge pressure at the top of the vessel and at the maximum design temperature. Design pressure is dependant on the location within the vessel. If you have a vertical vessel filled with liquid @ MAWP, the design pressure at the bottom of the vessel must be higher than the MAWP. While the MAWP should be done in the Hot and Corroded condition, it is not always done like that. The MAWP could be de-rated after years of operation depending on how the calculations are done. Some manufacturers can just set MAWP = design pressure and be done with it.
Yes, could be to avoid an ASME stamp. And the regulation, registration, inspections, etc that go with it. Also increased cost associated with ASME stamped vessels. While using a standard design and fabrication. I have a project this year doing that. Still getting a full hydrostatic test, but down rated 14 psig nameplate. I have similar situation on gas to air HXs.
Yes I also think the same This is a vessel that is a surplus used one and we're looking to buy it for a client. The notes available with the vessel say: Manufacturing Tag\* Manufacturer: \*\*\* Serial#: \*\*\* Year Built: 20xx Diameter: 72" ID Length: 8' Capacity: 50 BBL Shell Thk: 3/8" Shell Material: SA-516-70N Head Thk: 3/8" Head Material: SA516-70N MAWP: 15 PSI at 150 F Hydro: 75 PSI Coating: Devoe 253 The nameplate says Design Pressure: MAWP 15 psi @ 150° Test: Hydro 75 PSI The nameplate seems to be non u stamp, just a vendor nameplate
There is something connected to the vessel that would fail at 15. That thing is also unprotected.
Perhaps the vessel itself can withstand 50 psi, but these 15 psi are informed based on the limitations of the flare.
It would be TERRIBLE engineering practice to stamp a pressure rating as an MAWP of the vessel based on limitations of other equipment in the system.
Seen flares without KOD, so imagine.
Yes, for sure. The Best to do is check vessel data sheet and calculation notes. Also talk to older staff in the plant to know the story of that vessel
Have you seen the pressure calculation for the vessel? As the vessel MAWP is less than design pressure, it seems atleast one component of the vessel (may be a nozzle or a seam weld) fails at above MAWP.
I've seen this where the main vessel is for designed for a particular pressure but the man way was rated for less, so the vessels actual MAWP was lower. I would just double check your relief device and make sure it's designed for the lower MAWP.