MAWP limited by bellows expansion joint.

[RonJeremy]

Hello,

I'd be very interested to read your opinions about good practice in the design of a FTS exchanger with a thick walled expansion joint.

Is it acceptable for it be used as the limiting component in MAWP? If so, what is the procedure for calculating MAWP of the element?

I ask because the maximum shellside pressure that a bellows can take depends on numerous conditions including tubeside pressure (for Pt'), temperature difference between shell and tube (for Pd), and even design number of cycles. ALternatively, would it be preferable to calculate AWPs for all the other components and then to run a calculation of the bellows expansion joint using the shellside and tubeside MAWPs as the design pressures?

The problem is a bit like the old thing about MAWP of opening and cone-to-cylingder reinforcement, isn't it?


Thanks for your comments.

Regards,

Chuck Norris

 

[DG72]

First, ASME does not prohibit any part from limiting the MAWP of the equipment.

Standard practice for fixed tubesheet heat exchangers is to limit the MAWP to the design pressure (ie. We don't iterate to find MAWP's based on actual thicknesses for fixed tubesheet exchangers. We set the MAWP equal to the design pressure--We do establish higher MAWP's for u-tube exchangers and floating head exchangers, just not fixed tubesheet heat exchangers. I am very familiar with TEMA member companies in the U.S. and this is standard practice for most).

Differential thermal expansion between the shell and the tubes is based on the operating conditions of the heat exchanger. This differential expansion creates stresses in the shell cylinder, tubes, and the tubesheet. This is why ASME requires that a caution plate be attached to the exchanger (warning that any change in process requires a mechanical design check).

For this reason, most manufacturers will not provide MAWP's for fixed tubesheet exchangers that exceed the design temp. If the equipment was designed for a specific set of operating conditions stated on the data sheet, what purpose would a higher MAWP serve?