Heat exchanger pipe welding


I am an experienced welder but recently ran onto a couple of new things to me.

A heat exchanger pipe from a local dive boat. I cleaned off the corrosion and found the extent of the crack which extended from the square mounting flange about an inch and a half longitudinally along the pipe. I tried initially to TIG this crack using si-bro filler rod and dcen. But I got immediate burn through as the pipe was very thin from electrolysis, a lot of hissing and fumes. I backed off. Contacted a friend of mine who ran a radiator shop for 15 years and we cut a piece of copper plate and soldered it into place to cover the crack.

This pipe appeared to be brass or some alloy of copper.I was concerned about the excessive hissing, etc. Any ideas if this material is weldable and how? Perhaps a/c instead of dcen? I could not afford to play with this as it was an only piece and it was an emergency repair. No second chances here.

I have also run into some conflicting information on welding bronze. Seems as though some folks us dcen and others prefer a/c. What I have is a bronze strut. The part of a vessel that holds the propeller shaft in a straight line after it exits the hull of the vessel. The strut has a horizontal crack in it and will continue to crack if not repaired.

Grinding out the crack to bevel it out is generally the first step here as with many crack repairs. But I have never welded on bronze.
I bought si-bro rod from the local weld supply store for this job.
Maybe you could enlighten this old dog a little about this repair and the proper weld procedure.
Thanks. Doug


You sound like you have been around the block a few times.

The hissing sounds like you might need to make sure you have a vent somewhere so pressure doesnt build on you and hiss and mess up your weld.

Corrosion is a problem. if the thing is full of stress corrosion cracks, it aint gonna work and you probably did the best thing in soldering a doubler.

The strut may be nibral bronze...a popular marine alloy.
AC or DC works. you are right that it seems conflicting, but AC flows cleaner and wets easier, dc pinpoints a little better but welds a little dull and if there is any aluminum in the bronze DC will not work as well.

Helium mixed with the argon helps too.

There is a web site that offers pretty good information on welding propellers and stuff.

here is the page with propeller and skeg welding


good luck


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Sep 21, 2009
Cast aluminum filler rod.
by: DL Kipp

The Rundquist site proposes that the 4145 alloy makes a better metallugical consistent weld. Is this alloy also a better match for repairing the housing and skegs of most cast alluminum outboards. And for that matter, most cast aluminum anything?

Sep 21, 2009
Hissing on heat exchanger pipe.
by: DL Kipp


We had removed the pipe from the system and tried welding it on the bench. It was dry when this action occured. No way to really get to to the inside to clean it though. So I suppose it could have been from the contamination inside the pipe. Th solder and patch held and the dive operation made both trips. Saved them several thousand in lost revenue. One small score for the good guys. Kinda makes you feel like Robin "Hood".

Sep 21, 2009
re. Heat exchanger pipe welding
by: Dave Naisuler

Great link to the prop welders, Jody!

Pipe- definitely sound like you did the best thing to me, to, nothing worse than lighting up thin, dirty, cracked metal, right? The hissing would be from no vent/ water condensation in the crap in the pipe, fumes would be from zinc in the base alloy, bronze rod flows like butter no matter what for me, but nothing will cure the zinc fumes. If copper and must be welded try CuP rods w/ the tig, great stuff, won't make paper thin contaminated metal weld magically, though.

If the strut is silicon bronze, imho grind it tight (pencil wheel to root w/ tight V grind), hit it hot and fast w/ dcen for penetration, top up generously and especially at weld endings to prevent hot-short cracking especially if the metal is firmly backed up/ under significant torsion. All I do is art foundry welding, not like I'm certified, but I need full pen welds that don't crack (1/4" average for single pass) w/ single side access (can't weld from the inside) just so I don't have to worry about grinding through crappy welds when chasing metal, plus patina is like a dye check for cracks.....

Recently I accidentally hoisted well over 1000 lbs of bronze, positioning stand, rolling platform, an assistant and me on 4 heavy spot welds on an edge w/ proper prep (37.5 deg walls, 3/32 land, 3/32 gap); I was trying to straighten the part w/ the hoist by hinging it on the welds, but those little tacks denied me, I was stunned when i realized we were dangling! Not much of a spec, but there ya go...

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