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Overpressurization of heat exchanger tube side
2

Overpressurization of heat exchanger tube side

Overpressurization of heat exchanger tube side

(OP)
Can anyone tell me which code governs the tube (primary) side of heat exchangers?  Is it B31.1 or ASME Section VIII?

By how much are we allowed to overpressurize??

Thanks.

RE: Overpressurization of heat exchanger tube side

Section VIII governs both sides of the heat exchanger (shell side and tube side).

Not sure what you mean about overpressurization...during service?  ASME has requirements for safety relief valves.

RE: Overpressurization of heat exchanger tube side

(OP)
Occasionally we exceed the design pressure by up to 5%. In our application, the relief valve setpoint equals the design pressure. Our relief valves lift and usually reseat. Is that a violation of the code?
Somewhere in ASME VIII it says that the relief valve should be set up to relieve pressures up to 10% of max allowable pressure. SO does that mean we are allowed to increase the pressure up to 10% above design pressure?

RE: Overpressurization of heat exchanger tube side

(OP)
Occasionally we exceed the design pressure by up to 5% during service. In our application, the relief valve setpoint equals the design pressure. Our relief valves lift and usually reseat. Is that a violation of the code?
Somewhere in ASME VIII it says that the relief valve should be set up to relieve pressures up to 10% above max allowable pressure. SO does that mean we are allowed to increase the pressure up to 10% above design pressure?

RE: Overpressurization of heat exchanger tube side

overpressurized:
I'm afraid that the answer to your question is NO.
In order to cover all aspects of your inquiry, I would suggest you review ASME VIII-1 / UG-125 and UG-134.

VIII-1 / UG-125 (c) says that: "All pressure vessels other than unfired steam boilers shall be protected by a pressure relief device that shall prevent the pressure from rising more than 10% or 3 psi, whichever is greater, above the MAWP…"

Please highlight these words: "prevent the pressure from rising more than 10% or 3 psi". The important issue is pressure rising, NOT your set point!
As you may see at the following, pressure rising is not stopped at set pressure point.

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/safety-valves/introduction-to-safety-valves.asp

Go down to "Basic Operation of a Safety Valve". You may see that max. discharge point is 10% higher than set pressure point. Thus, if your set point will be increased to 10% above MAWP, it means that your total pressure rising is about 20% above MAWP.

RE: Overpressurization of heat exchanger tube side

Why not install a vessel that has a MAWP to handle the spikes?

You risk burst or collapsed tubes, seal failures, vessel failure.

Sounds like a poor practice to me.

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