5 replies to this topic

[Alfreedo]

Our pipeline group is suggesting PSVs on new launcher receiver being installed on 14" existing natural gas pipeline. The sales gas is fairly clean (not anticipating any liquids but I guess I can't rule it out) and the only case for a PSV I can think of is a thermal case when the launcher/receiver is blocked in. Normal pressure is 6000 kpag and max operating about 9500. The design pressure is 9930 kpag.

Do we need a PSV on these launcher/receivers? We are in a cold northern climate but the temperature could limb to 38C a couple days of the year. Still, I don't anticipate much pressure rise in the trap due to gas heating. Perhaps if some volatile liquids precipitated out of the gas and were subsequently boiled in the traps by the heat of the sun, the pressure could rise some but this is a highly unlikely case.

If I do provide PSVs just to be sure, what do I use for a sizing basis?

Thanks for any help you can provide.

[shan]

You may have to consider "fire" case.

[demank]

I agree with shan.
If its can be considered as being possibly exposed to fire, the fire case PSV shall be installed.

A TSV is not required as ambient temperature (or sun radiation) may not lead to pressurized exeeding piping design Pressure.

[Mac Adam]

I agree with shan.
If its can be considered as being possibly exposed to fire, the fire case PSV shall be installed.

A TSV is not required as ambient temperature (or sun radiation) may not lead to pressurized exeeding piping design Pressure.

Yup.. the most credible case for launcher / receiver must be considered is fire case.

[ogpprocessing]

PSV which is sized for fire case may not be a good protectin for pig traps because the heat transfer coefficient of gas is small and the heat will be accumulated at pig trap body. So you should think about additional fire protection equipment in excess of PSV.

[ankur2061]

A vapor expansion case as given in section 5.15.2.2.2 of API STD 521 due to external fire may be considered however personally I don't believe that a PSV for a fire case on a gas-filled vessel would be of much help. This is simply due to the fact that the walls of the vessel filled with gas / vapor and exposed to a fire would become weak even before the pressure in the vessel rises up to the design pressure of the vessel due to the fact that very little heat transfer is occuring to the gas inside the vessel. The reason for relatively less heat transfer is that gases inherently have lower thermal conductivities or in other words the heat transfer coefficients are low for gases.

In the above mentioned scenario the probability that the vessel wall ruptures even before the vessel pressure rises to the setpoint of the PSV is very high. That the pressure already existing inside the vessel along with the fire impinging on the vessel walls hastens the weakening of the vessel walls is also a known fact.

In my opinion a BDV or emergency depressurization valve would serve better to protect the vessel from rupture by rapidly reducing the pressure in the vessel as per the guidelines provided in API STD 521.

Regards,
Ankur.