Heat EX tubesheet to shell weld repair 2

[Homer2000]

I've been tasked with correcting a leaking Struthers Wells heat exchanger. The problem is the tube sheet (SB-171) to shell (sa-516) weld is leaking, and appears to be a result of welding two dissimilar metals. The Mechanical Engineers think an appropriate fix would be to weld a carbon band around the shell over the existing weld bead (fillet and plug welds) to establish a carbon to carbon weld. I believe re-welding to be another option not yet considered. Would re-welding be a long term, cost effect, and viable solution? Any advice would be GREAT!

 

[stanweld]

Please provide the copper alloy under SB-171. Also provide the leak mechanism; i.e., crack including location (weld metal or HAZ, pitting, etc. Is the weld a full penetration corner weld? Do you have any idea what the welding filler metal is?

 

[Homer2000]

SB-171 alum brnz alloy D (tubesheet) to SA-516-70 (shell). The leak is caused by cracking in the weld metal/incomplete fusion of the weld metal-to-base metal. i do not know the type of weld or the welding filler metal. I am checking...

 

[chicopee]

Is it really a welded joint or a brazed joint?

 

[stanweld]

Aluminum bronze is readily weldable to carbon steel. From your description, weld quality or lack thereof appears to be the problem. Weld repair is recommended over the ring patch method proposed by your Mechanical Engineers.

 

[metengr]

Please note, ring patches are not permitted if your using the NBIC for weld repairs to this Hx.

 

[Homer2000]

thanks guys this helps!

 

[unclesyd]

Concurring with the above post it sure sounds like brazed joint by someone not well versed in the art. We make these type joint using Ampco-Trode 10. We have used brazing for fairly large joints but prefer a TIG first pass and fill in with SMAW.
The secret in your case is to make sure you have as much of residual weld cleaned off unless the existing filler metal is completely bounded to base metals. If there is any doubt take it off. When taking off the existing filler metal don.t dig cavities in the base metal. Over the years I've found out that a well directed chipping gun will strip most of the filler off if there is a lot of lack of fusion.
I would take the time to find a welder who can show their ability to handle Cu alloys.

Conforms to Class CuAl-A2 of Specifications ASME-SFA-
5.6; ASME-SFA-5.7*; AWS-A5.6; AWS-A5.7*, AWS-A5.13*;
MIL-E-23765/3A*.

http://www.ampcometal.com/common/datasheets/ampco_ welding_overview.pdf

 

[stanweld]

The filler metal provided by unclesyd is also recomended by me. Chemical analysis of the current deposited weld metal should be done. I have seen some really, really bad results when similar welds were made using ECuMnNiAl welding filler metals by a manufacturer against my recommendations. The manufacturer finally admitted his mistake, which ended up costing them over 20 million USD (1984 dollars) to correct; poor welding techniques also contributed to the under warranty failures.