need ANSI600 outlet flange on pilot PSV but only ANSI150 available
need ANSI600 outlet flange on pilot PSV but only ANSI150 available
(OP)
The suction pressure of the triplex pump can be as high as 845 psig.
The PSV set at 1440 psig on the discharge relieves to the suction.
Because of the potential of high backpressure we believe a pilot PSV is required.
However, the vendors only have ANSI-150 outlet flanges for pilots with ANSI-600 inlet flanges.
One vendor refers to API 526 table 17 that we will not be able to find ANSI-600 outlet flanges on a pilot with ANSI-600 inlet.
Does anyone have advice to accommodate the high backpressure on this PSV?
The PSV set at 1440 psig on the discharge relieves to the suction.
Because of the potential of high backpressure we believe a pilot PSV is required.
However, the vendors only have ANSI-150 outlet flanges for pilots with ANSI-600 inlet flanges.
One vendor refers to API 526 table 17 that we will not be able to find ANSI-600 outlet flanges on a pilot with ANSI-600 inlet.
Does anyone have advice to accommodate the high backpressure on this PSV?





RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
PSV for class 600 inlet valve will be class 150. For class 900 and above 300 class flanges are available. Other class flanges can be provided as a special case. But this will require a modification of the valve casting and can be provided only if there are no other dimensional conflicts. Also please note that in this case the valve body chest portion will be designed to base class ie. 150 or 300, and only the flange is modified. So the modified valve with different class flange can take only the original pressures it is designed for though it can be physically fitted on to a higher class flange.
Also with high back pressure the valve performance will be affected. Valve can chatter, and its capacity will be affected.
Regards.
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
Question to All - Here's a fundamental question: How can a pilot PSV be used for one of it's main intended purposes (i.e. back pressure greater than 40% of set pressure) if the discharge flange rating only allows up to 20% of set pressure (285 psig for ANSI-150 divided by 1440 psig)? We thought we could specify a pilot PSV with ANSI-600 inlet and ANSI-600 outlet because the back pressure is greater than that for ANSI-300 (740 psig). But we have not been able to find a pilot PSV that allows it to function any better than would a balanced PSV. A PSV manufacturer tells us they can custom make one for us but it will not be ASME UV certified. I get the feeling I'm missing something obvious.
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
As I understood your application looping the PSV discharge back to a pressure source is not correct. Please review.
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
Other than blocked flow, what are your relieving scenarios? Did you include Fire?
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
Duwe6 - the governing case in blocked flow. The thermal expansion and fire cases have much lower required flow-rates.
Moltenmetal, does a back-pressure regulator on a PD pump satisfy the ASME VIII and API 521 requirements for last line of defence for overpressure, for example from blocked flow? I've seen several clients and EPCM put PSV protection on PD pumps that already have manufacturers' internal back-pressure regulation. Are you saying the PSV is not required if a back pressure relief valve is in place?
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
One can typically route the relief device back to the suction side without experiencing such high pressure. The fact that this isn't true for your application means that you need to consider routing the discharge elsewhere, to another vessel, if indeed you choose to use a relief valve.
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
, you are not allowing the PSV to reseat. I agree with don1980. If you are intent is only to protect pump, PSV is not required. You are the better judge as you know the condition better. All the best!
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
What I think the system should have is a re-circulating control valve / ARV set below your design pressure as your primary operational control to prevent over pressure in the event of locked in flow. Then the PSV becomes a more straightforward PSV which I set at your piping design pressure in the event that the re-circulation valve fails to open for blocked flow. where you send this potential flow to is a different matter as it can't go back to the separator, but this instance I would suspect it would need to be an ESD trip of the pump (2oo3 pressure switches)and probably the whole system.
As don 1980 says look at the system you're protecting and what it's design limits are and what the max pressure the pump can put out before it stalls. Piping has some fairly high potential over pressure allowances for short duration (30% from memory for < 10 hrs a year).
I think you need to have a discussion about your protection philosophy and how the plant protects itself (ESD trips etc) and where PSV discharges go to.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: need ANSI600 outlet flange on pilot PSV but only ANSI150 available
ASME B31.3 doesn't say that all piping has to be protected according to Sec VIII. If it did, you'd see a relief device on all segments of piping. Instead, B31.3 says that the piping must be designed to either safely contain or relieve the pressure to which it may be subjected. So, for piping the owner has a broad range of discretion. In the application you describe, you have a range of design options for preventing overpressure. For PD pumps, a relief valve is commonly used, but in this specific application a relief valve doesn't look like a realistic option. What I am saying (and others too) is that you don't have to use a relief valve - you have other options.