Air Cooled Heat Exchanger Plug Torque Calculation
Air Cooled Heat Exchanger Plug Torque Calculation
(OP)
All,
I have been asked to provide a torque value for an air-cooled heat exchanger's plugs. Thus far I have not had much exposure to air-cooled heat exchangers. We have internal company standards that specify header plug torque values but the table in our standard does not utilize the same k value or include the appropriate plug size for my application.
I am looking for some guidance on how to calculate the appropriate torque. I have already checked API 661 and did not find anything to suit my needs. Can anyone point me in the right direction?
I have been asked to provide a torque value for an air-cooled heat exchanger's plugs. Thus far I have not had much exposure to air-cooled heat exchangers. We have internal company standards that specify header plug torque values but the table in our standard does not utilize the same k value or include the appropriate plug size for my application.
I am looking for some guidance on how to calculate the appropriate torque. I have already checked API 661 and did not find anything to suit my needs. Can anyone point me in the right direction?
-Blue
Mechanical Integrity Engineer
5 Years Experience (Refinery)
2 Years Experience (Chemical Plant)





RE: Air Cooled Heat Exchanger Plug Torque Calculation
As a check I calculated the plug tensile area and used the calculated preload to check the tensile stress in the bolt. Since it was suffeciently low I doubled the torque to account for any unknowns I had missed and rechecked the stress using the new preload.
Bolt stress was about 10 ksi so I assumed this would be good.
Any holes in my method?
Gasket OD: 2.1875
Gasket ID: 1.890
Stud Size: 1.875 (n=12tpi)
K Factor: 0.16
Target Seating Stress: 18,000 psi (Lamons Handbook)
Calculated Target Preload: 13306 lbs. (Gasket Area*Target Stress)
Calculated Target Torque: 330 ftlbs. (T=kFd)
Bolt Tensile Area: 2.527 in^2 (pi/4 * (d-0.9743/n)^2)
Bolt Stress: 5265 psi (Bolt Stress=Preload/Tensile Area)
Doubled torque value as a safety factor yielding a stud preload of 26611 lb requiring a torque of 660 ftlbs.
This would produce a bolt stress of about 10.5 ksi.
Thanks in advance for your help.
-Blue
Mechanical Integrity Engineer
5 Years Experience (Refinery)
2 Years Experience (Chemical Plant)
RE: Air Cooled Heat Exchanger Plug Torque Calculation
Perhaps you could check against your company standards, see if you (they) are in the range.
Regards,
Mike