4 replies to this topic

[curious_cat]

Is it possible to re-tube a vertical Heat Exchanger with long tubes on site without having to remove it from its structure to the shop?

 

This is a long tube forced circulation evaporator with SS316 tubes approx. 20 feet in length and 1.5" diameter. Some of the leaking tubes were initially plugged but we want to replace them eventually. 

 

The tubes are welded to the tubesheet and not rolled. The tubesheets can be accessed via removable bolted heads but the tube bundleis not accessible from the shell side.

 

If this can indeed be achieved on site I'm wondering if anyone has any tips, warnings, pitfalls etc. 

Edited by curious_cat, 26 July 2015 - 01:02 PM.

[Art Montemayor]

Curious:

 

I’ve had the misfortune of having to replace a lot of heat exchanger tubes in the field and it has never been a picnic.  Everytime I’ve done it in the past, I resorted to using the same technique my mentor taught me: contract the job out to a fab shop.  The first two times I tried doing it on site, I almost ruined the exchangers.  Yes, it is possible to re-tube a vertical heat exchanger in its field location.  But I wouldn’t do it.

 

The best proven way to remove the welded tubes is in a shop with a movable lathe turret head.  Some heat exchanger shops even have a special design available for their contracted maintenance work.  Unless I’m mistaken you have fixed carbon steel tube sheets and you don’t want to ruin them by removing the tube welds with non-precision grinding or cutting tools.  You mess up one of the tube sheets and you have bought yourself a new heat exchanger.  A shop-controlled turret cutter can remove the tube-tube sheet weld material with precision and allow for the removal of the tubes with just a few “thous” (thousandths of an inch) of tube sheet metal removed.  Re-aligning and installing the new tubes through both tube sheets and the associated baffles can be nightmare if not done properly.  An experienced shop does this in a fraction of the time you or your crew could ever accomplish for the simple fact that they do this every day, while your maintenance shop does this technique once in a blue moon.

[Bobby Strain]

Conventional wisdom suggests that you buy a new heat exchanger. This way there are no surprises. And it might even cost you less than a field re-tube.

 

Bobby

[curious_cat]

Thank you Art for those tips!

 

To clarify: I wasn't thinking of doing it myself or from our shop crew to save costs etc. I'd definitely stick to someone who has experience doing this operation.

 

But I was wondering about the feasibility of there being a skilled team who could come and do it on site with their specialized tools to avoid the difficulty of removing this HEX from its location. Of course, you cannot lug around a lathe. But I was hoping there's a specialized portable tool that someone has come up with to do it. 

 

Due to some questionable design decisions it has become a nightmare to move this HEX from its position. 

[curious_cat]

Conventional wisdom suggests that you buy a new heat exchanger. This way there are no surprises. And it might even cost you less than a field re-tube.

 

 

Update: This is what ended up happening like Bobby had astutely predicted. The hassle & cost of re-tubing (whether on site or off site) wasn't deemed worthwhile. 

 

We did end up reusing the shell & end closures though. Just are getting a new tube bundle inserted.