31 replies to this topic

[fallah]

Fez,

 

As per the submitted info the pressure inside the shell of the exchanger A while relief load of tube rupture in exchanger A is relieving through the PSV B on exchanger B at 324.5 (295*1.1) psig pressure, would be 338.5 (324.5+14) psig that cannot be acceptable due to passing the relevant MAWP. Then you can go to investigate about decreasing the set pressure of the PSV B as much as the pressure inside the exchanger A wouldn't pass 295 psig as its MAWP (almost a value between 250 to 260 psig as new set pressure). Of course, at the conditions of lower set pressure, the capacity of the PSV B would be decreased that should be investigated to be acceptable on new rated capacity standpoint and wouldn't be less than the required relief load...

Edited by fallah, 16 January 2014 - 03:01 AM.

[seeker_of_knowledge]

Thanks Fallah for your feedback. I will investigate further based on your comments. 2 quick questions I have:

1. As per API 521 section 5.19, can we ignore tube rupture case if pressure during tube failure is less than corrected hydro test pressure? I looked at pump shutoff head( source of over pressure on tube side) and it's less than corrected hydro test pressure on shell side.

2. What is normally done when PSV has to be taken out for service while the equipment is running if there is no Spare PSV installed and there is no bypass around PSV designed to handle full relief load?

Any comments please,

Fez

[fallah]

Fez,

 

1- If the pressure in shell side; here as low pressure side; during the tube rupture doesn't exceed the corrected hydrotest pressure you cannot ignore the credibility of tube rupture case. Then you should investigate which pressure would be exist in the shell side during tube rupture case. You might take the operating pressure of the tube side as a basis for this investigation.

 

2- Installing a spool pipe for removed PSV, operator to present there to open the inlet or outlet valve based on reading a PG at upstream of the inlet isolation valve...

[seeker_of_knowledge]

Thanks Fallah. Sorry I dont understand your reply in point 1. Why I cannot ignore tube rupture case in light of API 521 section 5.19 since my corrected hydrotest pressure is higher than the maximum pressure expected (which is shutoff head of cooling media pump). PSV will be removed for about 8 hrs or so and relief flow path will be locked open and will be under continuous monitoring for the duration PSV is removed.  

 

Thanks again,

 

Fez

[fallah]

Sorry I dont understand your reply in point 1. Why I cannot ignore tube rupture case in light of API 521 section 5.19 since my corrected hydrotest pressure is higher than the maximum pressure expected (which is shutoff head of cooling media pump). 

If maximum expected pressure in the shell side as low pressure side during tube rupture doesn't exceed the corrected hyrotest pressure you can ignore the credibility of the tube rupture case...

PSV will be removed for about 8 hrs or so and relief flow path will be locked open and will be under continuous monitoring for the duration PSV is removed.  

No need the relief path to be locked open during such a bit long time PSV removal because it will lead to huge loss of inventory. You can continuously monitor the vessel pressure and open the isolation valve in case of any opverpressure to conduct the relief to relevant detination...

 

Fez,

 

My answers are as red color....

Edited by fallah, 22 January 2014 - 03:40 AM.

[seeker_of_knowledge]

Thank you Fallah.

 

Regards.

 

Fez

[eliealtawil]

1.) MAWP tube side is 650 psig. If the max historical pressure in the tube side (say last 5 years) never exceeded 440 psig, then you are ok. A PSV is not required.

2.) Your calculated inlet losses to PSV are 12+2= 14 psig or 14/295 x 100 = 4.7% of PSV set pressure. Code allows only 3% pressure drop in the PSV inlet line unless you have a statement from the PSV manufacturer stating that the PSV blowdown is > 5% of PSV set pressure.

 

Regards,