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Discussion Starter #1
Developed some cracks around both wastsegates, tubing is 304SS welded with 347 rod.
Wondering whats the best method of repair, lay more 347 over the crack? Anybody use silicon bronze in this area? I have several people that help me out with tig welding but I thought I'd ask some opinions,

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Reweld around the crack and then make a strap that goes across the wastegate protrusion and the main pipe.
 

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The Liquor Makes Me Think
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Looks like a crack from the weld undercut. Re weld with out undercutting.


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If it was not back purged or Solar Flux at a minimum the weld and HAZ will be compromised. This makes the area subject to failure due to what is commonly known as sugar. If it is very black and has an irregular surface with what may look like stelagtites then its sugared. As above, it could have had some undercut or not been full penetration making a thin area again subject to failure. When there's room its nice to use a doubler flange around a saddle weld. This is used a lot in fabrication of pressure vessels where nozzle penetrations are made. In something like an exhaust tube that sees over 1K °F temp delta a rigid gusset can pinpoint stresses and cause them to pull a crack in the tube if they are not run in the direction of the least linear expansion. You could also use a doubler plate under the gusset to spread out the stress over a larger area. Definitely more than one way to skin a cat. Hope this helps.
 

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Discussion Starter #8
Thanks TurboII, it was purged and there is definately some undercutting. The wastegates are the only place I'm having trouble, I didn't give much thought to gusseting when it was built so not being supported well seems to be the biggest problem. I like the idea of a flange, the other gate is way worse and may end up done that way, the way they cracked around the outer toe of the weld leaves a hole thats 1/4" larger than the tubing,
 

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Due to the fact that your on the outside of a reasonably tight looking bend, I would expect the outer wall portion of the bend to be thinner. Myself, I cut a section a second bend, and make a cover plate. I'll weld the cover plate over the outer rad of the bend, tig it 100%, then add my hole and weld in my stud for the WG. Essentially doubling the wall thickness of the outside of the bend. I do everything in my power to not have to weld a WG in those types of locations, for exactly this reason. Sometimes though, that just can't be helped.
 

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When I spec’d weld repairs on APU exhausts last century, Hastelloy was the preferred rod as it was less prone to cracking. That was on 321 and 347 parent material though.
 

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I've got my 38mm wastegates hanging off the outside radius of my 2-1/2 inch collector on each side of my hotside.

As someone stated, take some material and make a doubler plate that spreads the load out over a larger area. I also had it welded with silicone bronze with a wide bead. It's 321SS so that is better but regardless of material is has to be done right or it will fatigue and fail.

Mine has been in service for 10 years, 1300+ passes and over 20,000 street miles so it has proven to be durable. Here is a picture of the exhaust during the original build where you can see the installation of the wastegate flange.

 
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