Why apply seperated head front closures in hair pain type heat exchangers

[Maarten73]

Hello everyone, I am new to this site so please forgive me any beginner stupidities.

For a current running project we have to design a hair pin heat exchanger which operates in hydrogen service.
The design shall be according the ISO 12212/ API 663.
According to this standard the front closure shall have separate shell side and tube side bolting in hydrogen service.
Now I am wondering what the philosophy is behind this requirement. I have asked several colleagues but no one can convince me.

Can anyone assist me?

Many thanks in advance.

 

[MikeHalloran]

Well, it's in the standard, and the standard is invoked, so no one should have to convince you.

If you're still curious, call API, and ask to speak to the crankiest old timer they've got. I'd be suspicious that the requirement may reflect a good defense against a single actual incident that happened long ago, and had really unfortunate consequences.

I can conjecture other reasons, too.
Imagine you're trying to assemble such a heat exchanger with a single row of bolting; you have to align the shell, the head and tube assembly, and the cap(s), with two gaskets, N studs, 2N nuts, and get everything nicely aligned, torqued down, and sealed. I'd bet you couldn't do it right on the first try.

Additionally, separate bolting allows you to remove the shell, and do a leak test on the tubes, head, and caps, without opening the process envelope or disturbing the process gaskets. Or conversely.

... but I'm just conjecturing. Please do come back and let us know if you find an actual historical reason.


Mike Halloran
Pembroke Pines, FL, USA