6 replies to this topic

[aider94]

Dear everyone, 

My case is heat exchanger - shell&tube type wax/wax+solvent. 
Parameters (only pressure considered):
Shell design pressure: 14 bar(g),

Shell side operating pressure (in/out): 4,0/2,5 bar(g),
Tube design pressure: 9,5 bar(g),
Tube side operating pressure (in/out): 6,0/4,5 bar(g).
Tubes diameter 20 mm.
Density is needed too I suppose...

My knowledge of PSV devices tells me that if lower pressure side to higher pressure side is equal to 10/13 ratio, then I don`t need to consider PSV (ASME/API says condition that hydro test pressure of lower pressure side has to be higher or equal to higher pressure side).

In my HX I have lower design pressure side on the tube side and higher design pressure on the shell side. A ratio isn`t enough to meet the 10/13 rule (9,5/14 bar(g)). 

Questions:

1) Is a tube rupture case is taken under consideration in case that shell side has higher design pressure than the tube side?

2) How to calculate such PSV relief (I`m asking for advice for calculating PSV relief for tube rupture case for both sides when shell side/tube side pressure ratio is higher than 10/13 and inversely). When calculating relief do I use design pressure or operating pressure?

Regards,
Aider

[Bobby Strain]

Is the shellside protected by a relief device? And for what cause? If so, what is the set pressure. Which side is being cooled?

 

Bobby

[aider94]

Bobby,
Thanks for your response.

I'm considering if I need to protect SS or TS by a relief device such as PSV. Shellside isn`t protected by a relief device, because I see no sense in securing shell side (design pressure of SS is higher than TS. A situation when tube ruptures and tube side fluid flows into SS won`t be able to crack/break SS).

I have hot fluid on the shell side (in/out temperature 202/129 degC) and cold fluid on the tube side (in/out temperature 96/126 degC).

[latexman]

A P&ID would help us help you.  Is hot fluid liquid or gas/vapor?  Is cold fluid liquid or gas/vapor?

[aider94]

Both sides contain in/out liquid phase. Sorry, but P&ID is covered by a confidentiality clause and I can`t upload... Basing on my descriptions, it is possible to imagine my case.

Both questions #1 and #2 could be answered based on all the information I wrote I think.

Regards

[Pilesar]

My answers to your questions:

1) Is a tube rupture case is taken under consideration in case that shell side has higher design pressure than the tube side?

The engineer must consider all reasonable scenarios that would result in exceeding the maximum pressure of the vessel. The evaluation of the tube rupture case may or may not result in vessel overpressure.

2) How to calculate such PSV relief (I`m asking for advice for calculating PSV relief for tube rupture case for both sides when shell side/tube side pressure ratio is higher than 10/13 and inversely). When calculating relief do I use design pressure or operating pressure?

Relief valves should be calculated by those who are trained and competent. At a minimum, you should read and try to understand API 520 and API 521. For additional explanation I recommend the Crosby Engineering Handbook https://www.emerson....-us-3923290.pdf

Sizing relief valves is serious business. Vessel overpressure has resulted in thousands of deaths.

[diogovalente]

In my understanding the shell side do not need to be protected for tube rupture since it is the high pressure side. The tube side would need since the hydrotest pressure is lower than the shell side pressure. Again, that is for tube rupture, other scenarios (like fire or blocked outlet) still might need to be considered on the shell side.

 

The relief load calculation for this one could be done several ways, the most common would be the following:

• Two orifices flow based on the tube diameter;
• An orifice and a tube flow based on the tube diameter and length.

With more data I could provide a more accurate help.

 

Regards,

Diogo