Expansion Joint THK

Dear Sirs,

I have designed one BEM heat exchanger (337 ID, shell side fluid is air at 200 degree celcius & tube side fluid is water at 65 degree celcius) in which the compressive stresses in the tubes are exeeding the allowable stresses, so i have used a thick expansion joint to reduce these stresses.
But mine doubt is, can i use thick expansion joint (single convolution) in which the thickness of joint is 10 mm however thk of shell is only 6 mm?

Hello Mak

It is difficult to comment without seeing the model you built. Please send me the PV Elite file at techsupport@coade.com for my attention.

Dear Mak

Typically the expansion joint nominal thickness is same as the shell thickness. You do not want to introduce a stiff exp. jt, as the whole purpose is to introduce more flexibility.

Are encountering problem with a thinner joint, is the pressure case failing the joint? If that is the case then you may also try to use the Kopp and Sayre method to design the exp. jt. they are less conservative for pressure stress than TEMA 8th ed.

If you have to use TEMA 8th ed. then I have seen engineers adding more convolutions.

You should also enter the nominal exp. jt. thickness (not minimum) in PV Elite and CodeCalc.

Another option is to perform FEA of the exp. jt, per the suggestions of TEMA 9th ed.

as you guys know, expansion joints was too difficult to be analyst. Its too 'sensitive' if compared to other pressure parts. Eg. 8mm will be a pass result but 8.1mm will propably turn out a fail result. The hard part is you do not have any idea how this expansion final thickness after forming.

Dear KK,

We investigated this last year and came to conclusion that the nominal thickness of the expansion jt should be used. As you said that it is very difficult to know the minimum thickness.

TEMA 8th ed. shows the thickness of the exp. jt. at the straight portion which is where thinning will not occur. So one can deduce that nominal thickness of the jt. is needed.

This was also confirmed by some experienced heat exchanger fabricators.

Hope this helps.