Tube leak sealing under external pressure?

[mjpetrag]

I have a column overheads condenser, product on shell and cooling water on tubes, that began leaking a few weeks ago. The shell side pressure is near full vacuum and tube pressure around 50 psig. The leak appears to be real since we are showing water in the product, and the only source found is cooling water (calcium and sodium found in high amounts in the product). We took the exchanger down, took off the heads, and put water pressure up to 75 psig on the shell and found 2 leaking tubes. Buttoned up the condenser, and restarted. The leak persisted, but in a smaller amount (leak calculated from the water in the product went from 200 GPH to about 20 GPH). We took the exchanger down again, pressured up the shell side with water and found no leaks.

Is it possible that the external pressure is closing up a crack in a tube, and when we put it back online, the internal pressure opens up the crack and comes out?

If so, what is the easiest way to find the leaking tube? I have had bad experiences with individual testing of tubes giving false positives due to bad sealing.

This is a straight tube fixed sheet heat exchanger, 6 pass, 304 SS tube and shell. Operating temperature is 140 C on shell, 30-50C on the tubes.

-Mike

 

[georgeverghese]

Strange why no one has responded so far - many caught up in the Standing Rock discussion...

I can see the dilemma you're in and though I dont know how to help, all I can say is you've got one or both of the following :

a)There are tube to tube sheet joint leaks
b) What you suspect of hidden tube leaks that you've not been able to catch with shellside pressurisation could be true.

Can also see the difficulty with picking up the right leaking tubes / tube sheet joints with pressuring up the entire tubeside.

Will a low pressure helium or N2 injection into each tube / tube sheet joint unit with a custom made injection assembly help?

 

[bimr]

It is possible, you may be experiencing differential expansion of the materials from the temperature. Have you pressure tested at the higher temperatures?

 

[jte]

Strange why no one has responded so far...

Well, one reason would be that the OP is asking a heat exchanger related question in a piping forum. Shifting to forum794 would reach a more targeted audience.