Accumualtion Pressure

[Process879]

Dear all,
can any onr tell me that the accumualtion pressure considered for thermal expansion case.
My case is , there is heat exchanger shell side hydrocarbon and tube side cooling water. i wanted to have thermal expansino valve on tube side. my exhanger is designed for blocked outlet condition 10/13 rule is applied. so i have set the PSV at tube side design pressure 10 kg/cm2(g) . my query is what shoul be the maximum accumualation pressure to considered.

 

[Latexman]

10%

Good luck,
Latexman

 

[Latexman]

or some folks think of it as 110% of MAWP.

Good luck,
Latexman

 

[JoeWong88]

Ha ha...this could be an interesting discussion if Phil is in...


I hope your case is cooling water blocked in tube side and maximum hydrocanbon flow on shell side.

If the tube head is designed per ASME Section 8, Div II, then maximum 10% accumulation or 110% of MAWP as advised by Latexman.

 

[Process879]

some says 25% ... they explanied me that it has been designed for fire case . liquid expansion ... they will allow 25%.

 

[Latexman]

"They" are wrong. ASME allows 21% for fire exposure. If the thermal expansion is due to a fire, fine. If it's due to heat from anything else but a fire, like ambient heating, blocked in with steam on, etc., ASME allows 10%.

Good luck,
Latexman

 

[djack77494]

You said, "my exhanger is designed for blocked outlet condition 10/13 rule is applied. so i have set the PSV at tube side design pressure 10 kg/cm2(g) ."

This statement worries me and I have to ask if you know what you are doing. What you did NOT say is that you have designed the exchanger such that the tube side design pressure is >= 10/13 of the shell side design pressure. That would have indicated a good design. Instead, to me you are just saying that you'll set the tube side PSV at 10/13 of the shell side (...unknown). If you mean what I said would be a good design, then no problem. If not, then I'd like to know what the TS & SS design pressures are.
Doug

 

[JoeWong88]

Process879,

Can you advise the heat exchanger design code ?

 

[Process879]

this exchnager is designed as per ASME 1 code.

 

[sheiko]

Does the 10/13 rule superseeds the 2/3 rule? because i had always heard that tube rupture is considered a viable contingency if the design pressure of the LP side is less than 2/3 the design pressure of the HP side. Could you please clarify?

"We don't believe things because they are true, things are true because we believe them."
"Small people talk about others, average people talk about things, smart people talk about ideas and legends never talk."

 

[JoeWong88]

Process879,

Your response make this thread interesting.

First, I understood "ASME 1 code" mean "ASME Section I Power Boilers". If so please check ASME Section I,

- Paragraph PG-67.2 it defines the 6% ,maximum Boiler Overpressure requirement.

- Para. PG-67.3, One or more Safety Valves on the boiler proper shall be set at or below MAWP. If additional valves are used the highest pressure setting shall not exceed MAWP by more than 3%.

I hope above statement still valid with latest ASME (i don't have latest ASME Section I with me).

So in many event, the overpressure shall be mentioned together with the design code.



sheiko,

Hope this post "Two-third (2/3) rule or Ten-thirteen (10/13) rule ?" and associate links answer your question.

 

[Process879]

Dear Sheiko,

2/3 =0.666 and 10/13 =0.769 . 10/13 will give you a higher design pressure and API 521 also recommends. 10/13 only...