CS Tubesheet, 304 Tubes, 500degF

[DivideByZero]

Fellows,
I am replacing an exchanger that has a carbon steel tubesheet and 1" 304 tubes. The shell side operates at 500degF. Besides service/corrosion concerns (we have those lined out), are there mechanical issues with the tube to tubesheet joint?

I feel the difference in thermal expansion between the CS and 304 may cause an issue with joint leaks or perhaps elevated stress at the rolled joint. If I were to strength weld the TTS joint, there is a dissimilar weld issue to deal with...perhaps with a 309 tubesheet overlay and a 309 to 304 strength weld.

Any experience with these dissimliar bundle materials and these temperatures? If this is not an issue for these temperatures, is there a calculation that can be performed to verify other instances with different materials, tube diameters, etc will perform reliably?

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[DG72]

You will likely want to weld the tubes to the tubesheet. It is difficult to get a tight seal with this combination of metallurgies when roller expanding only. It takes a lot of force to expand stainless steel tubes, and this often moves (yields) the carbon steel ligament between the tube holes. In other words, you expand one tube and the carbon steel ligament moves one direction, then you expand the adjacent tube and the ligament moves again. The result...you don't have a tight seal.

 

[MJCronin]

Divide....

What is the TEMA type of your heat exchanger ?

BEM.. AEU ????

Is there an ASME plate with allowable temperatures and pressures....... or is this a older HX to be reused in a new service ?


-MJC

 

[rmw]

You haven't told us much about the Hx or the service. And, the TS thickness or the tube gage.

I have had lots of experience with high pressure Hx's with SS tubes expanded (rolled, explosively and hydraulically) into thick CS tubesheets and seal welded at a typically 309 overlaid tubesheet. The shell side temps ranged up as high as 8-900F.

Your service, on the other hand might have to do with detrimental effects to the above configuration.

We need to know more to help with any tips.

rmw

 

[DivideByZero]

TEMA R and AES type. This is a section VIII hxer, I believe 300# @ 650F.

In the end, I'm looking for general guidance on how to put numbers to this issue in the future. Any thermal expansion/tubesheet calcs that help
with this assessment?

I wul have to reconfirm the service with process, but I don't know how that will affect the tubesheet joint design. Also, don't have the tubesheet thickness ATM, but would guess 3.5 to 4"

Thanks gents!

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