head exchanger leak repair 1

[gfernan]

Hi
It is posibble to weld a clamp on the flange connection in a head exchanger?. We have a vapor leak and the vapor is also leaking through the bolts. We are going to replace the entire heat exchanger soon so we are thinking that mean while we can put a entire clamp that cover the flange connection and weld it to the head and the shell in order that even the bolts keep inside. What do you think?

 

[SnTMan]

Well, that's one way to go about it, I guess. Acceptable to owner / insurer / jurisdiction, I dunno.

Much else is not known here, metals, service, size, configuration, and what exactly is meant by "clamp".

Regards,

Mike

 

[gerhardl]

Could soft sealings, either as discs or a series of different sized o-rings, be placed on the outer side of each flange and rim of flanges, and clamped in place by two metal plates? Metal plates larger than flanges and screwed together in a diameter larger than flanges, distance pieces between the plates at outer rim of plates to give correct pressure at flanges?

 

[jte]

Hi gfernan-

For future reference, you'll reach a more targeted audience at forum794. After all, you are talking about repairing a pressure vessel.

To answer your question, yes, a welded encapsulation can be engineered which would land on either side of the flange pair.

However, this is easier said than engineered. This type of repair can get complicated in a hurry. One source of information is ASME PCC-2, Repair of Pressure Equipment and Piping. The currently available edition is 2011; the 2013 2014 edition will allegedly be published late this year. The info in PCC-2 is good, but light on this particular topic. I'd strongly suggest involving people who have experience with designing this type of repair. There are multiple issues to consider, ranging from simple statics (frequently not considered, believe it or not) to materials and welding issues to field practicalities.

This type of repair has the potential to cause a major incident; the pressure equipment industry had a multiple fatality event last year that related to a bolted box style temporary repair. Take it seriously, involve qualified and experienced engineers for the design work, and remember that a failure can cost far more than using a good consultant.

 

[chicopee]

About seal welding around the bolts as the temporary measure? Seal welding is exhaustively discussed in the boiler and pressure vessel engineering forum.

 

[PVPguy]

That is not normally a good solution. The design of the clamp (leak box) becomes very cumbersome, since you have to clear the OD of the flange and there is rarely enough space to use dished heads, so then the end plates must be flat, which means very thick, which means lots of distortion when welding, etc...

More typically you would use an injectible external clamp that seals the OD of the flange and has sealing washers under each nut. There are many companies that will provide this service (Furmanite, TEAM, etc...).

However, before you do that, you need to try other alternatives to get the joint to seal - increasing the bolt load using turn-of-nut or hot bolting the joint. Even if you do eventually need the external clamp, you need to redesign the joint so the leakage doesn't occur again. Look for papers on turn-of-nut in ASME PVP conference proceedings and reference both ASME PCC-1 and PCC-2. Beware of placing your bolts in a corrosive or stress corrosion cracking environment, there have been many failures associated with this (including fatalities).