Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
(OP)
Dear all,
the point is: one pipeline is to be designed according to B31.8 and is protected by an upstream PSV.
Knowing that usually the PSV overpressure is 10 % of the set pressure, how can I correctly define the design pressure of the pipeline, i.e. should I use as design pressure the PSV set point or should I increase that value by 10%?
Let me make an example: Suppose that the pipeline is expected to operate normally up to 91 bar g, with high pressure alarm at 93 bar g and high high pressure shut down at 96 bar g with the PSV set point at 100 bar g: can, as per ASME B31.8, the pipeline be designed for 100 bar g or the design pressure must be 100 x 1.1 = 110 barg, as actually, once the PSV is fully open, the pressure in the pipeline can be higher than 100 bar g up to 110 bar g?
In other words, with ref. to this example, does the code B31.8 require to consider in the design pressure also the increase of pressure due to the PSV relief?
Thanks to all.
Thanks to all.
the point is: one pipeline is to be designed according to B31.8 and is protected by an upstream PSV.
Knowing that usually the PSV overpressure is 10 % of the set pressure, how can I correctly define the design pressure of the pipeline, i.e. should I use as design pressure the PSV set point or should I increase that value by 10%?
Let me make an example: Suppose that the pipeline is expected to operate normally up to 91 bar g, with high pressure alarm at 93 bar g and high high pressure shut down at 96 bar g with the PSV set point at 100 bar g: can, as per ASME B31.8, the pipeline be designed for 100 bar g or the design pressure must be 100 x 1.1 = 110 barg, as actually, once the PSV is fully open, the pressure in the pipeline can be higher than 100 bar g up to 110 bar g?
In other words, with ref. to this example, does the code B31.8 require to consider in the design pressure also the increase of pressure due to the PSV relief?
Thanks to all.
Thanks to all.





RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
Why do even use a PSV, they are not required, you can use a ESD or MOV valve.
RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
A MOV needs power.
A ESD usually need instrument air or gas, unless you go with a self-contained hydraulic (in which case you need to refile the hydraulic fluid once in a while).
"Do not worry about your problems with mathematics, I assure you mine are far greater."
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RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
My gas is usually wet, sour, and with solids.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
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RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
If I can rephrase the problem as an example:
1. On-plot compressor normal operating discharge pressure (ANSI B31.3 piping) = 90 barg (say)
2. Compressor discharge piping design pressure = 100 barg
3. Hence PSV set pressure on piping is 100 barg. (Alarms and trips hopefully act before these lift, but are not relied on)
4. Hydrotest pressure is 1.5x piping design pressure = 150 barg
5. Note that PSV "accumulated" pressure (API521 and Process engineering term for when PSV will be fully open under relief case) = will be 1.1x set pressure, ie. 110 barg.
Question:
Following the ANSI B31.8 code for the export scraper/launcher and export pipeline, what is deemed the design pressure of:
A. Scraper Launcher (100 or 110 barg?)
B. Export pipeline (100 or 110 barg?)
C. What is the set pressure of the scrapers PSV (which is normally installed in ANSI B31.3 piping? (100 or 110 barg?)
RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
That is an excellent re-statement of the problem, and the basic question only matters if you are designing to very close to the design conditions.
In my world, I would design the pipe at 100 bar. The flange could be ANSI 600, material group 1.1 at 50C for a flange rating of 100.2 bar, but I would use ANSI 900 material group 1.1 at 50C for a flange rating of 153 bar. I'd pick my pipe for hoop stress around 50% of SMYS. Some might call this overkill, but when you look at the percentage difference in cost between arbitrarily limiting your hoop stress and allowing 100% you'll see its pretty small.
In short, if you're designing to the limits of the material then this is an important question. Otherwise it is just words.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
looking4advice
RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
The overpressure protection must fully stop the pressure from exceeding 110% of the design pressure which is the MAOP or 75% of the SMYS, which ever is lower.
RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8
thank you for your reply. This is also my interpretation of B31.8, that is, a pipeline can be designed for a pressure that then will be the MAOP for that pipeline and, in addition, it is in full compliance with B31.8, the fact that the PSV protecting the pipeline and therefore set at the MAOP (which is the highest allowable value for the PSV set point), will protect the pipeline with an increase of pressure over the set point value but not higher than 10 % of the set pressure.
This is to say :
a) PSV set point must be < or = MAOP of the pipeline.
b) Actual pressure of the pipeline with PSV fully open can
be < or = 110 % (max) of MAOP
RE: Maximum operating Pressure (MOP) for a pipeline as per ASME B31.8