Stainless Manifold Repair
 

I have a stainless manifold and it's cracked twice now. The first time it cracked the cracks were welded back up, and some additional metal was added to increase the strength.
Now it is cracked again, in different places.
I was thinking it needed relief cuts, but some hunting around here suggests that those are only required on the cast manifolds. I'm also afraid that if I make any relief cuts, the manifold won't seal against the head anymore.

Do I just need to re-weld the cracks again and try to get better penetration? Add more filler wire? Or do I need to do something to change the stresses?

Was it bolted to a flat plate the first or second time it was repaired?
I would recommend grinding out the majority of the weld that is cracked beyond the cracked section, beveling both sides of the gap, lay a root pass with purge than cover pass.

Relief cuts fixed my welded log manifold.

What wall thickness is that manifold.

Got any closer pictures? In the last picture is the crack in the middle of the weld?

Welds look a little undercut.

What material and filler?

I didn't make the manifold, and am only learning how to weld now so I'll be getting some help to fix this. I also don't know the answers to many of your questions. :-(
The manifold is stainless, I'm assuming 304 but I don't know for sure. I assume the wire is the same, but again that is just my assumption. The material is pretty thick; they are "weld els" but I'm not sure if they are a standard thickness or not.
The cracks are all down the middle of the welds.
What is "undercut" in regards to the welds?

I'm not sure how it was made, as I bought it from somebody who makes them. I believe he has a spare engine or head that he bolts them to when he builds them though. He did the repair as well, so I assume it was bolted to the head then too.
I'm learning to weld at work, so I will be getting help from one of the good welders there when I fix this. I'm not sure we can purge, but I will ask. I do know we only use TIG for stainless steel though.

This sucks, sorry skidude.

304ss, schedule 40, 308 filler. I bolt the manifold to a spare head when I weld them, initially and when I fixed it the first time/added those square support patch things.

I wouldn't worry about the head not sealing if you make relief cuts, especially if you bolt the flange to something flat when you reweld it.

Like noted already, grind out as much of the crack as you can giving you a little channel to add new filler. Go past the current crack somewhat. Back purge with argon can't hurt, same for adding more square overlaps.

Thanks, don't worry about it. I still love the manifold, and you've been very helpful every time I need anything.
Would you recommend fixing the cracks then cutting the flange, or cutting the flange before I weld the cracks? I'm thinking I should weld it first.

Why 309 filler? I've always used 308 or 304-304.

If that was picture is a crack in the weld that's unusual. Most of the time the cracks appear next to the weld in the haz.

If you are going to cut the flange, I would absolutely do so prior to bolting the manifold to a flat plate and re-welding it. This will put the least static stress on the welds after you bolt it to the head.

Ahh shit, you're right. 308 is what I use. I have the 309 for the stainless/mild steel combos which were rare. I'll edit my post.

I think 309 is acceptable for stainless to stainless. But it's usually the go to "different metals" filler.

Skidude. Can you post closer pictures of the cracks?

Undercut is when the weld is slightly under the surface of the 2 joining tubes.

But I didn't realize Tim was the one who built that manifold, and he knows more about welding than I do for sure.

I don't know much about welding, other than the more I step on the pedal, the hotter my hands get.

So my welds are funny, they crack thru the weld instead of the HAZ :dunno: My most recent header for the VP's boat routinely cracks straight thru the reinforcement patch. Crazy.

Could use some @gesso in here.

Regardless of the order of relief cut and weld, after all is done, mill or sand (big belt sander) the flange flat.

preheating that entire assembly prior to welding, could make a huge improvement in weld strength. 300F°?

https://photos.app.goo.gl/fa6134Tvyzdm7ecx7
Does this link work? I took a few more pictures.

1) If its 304, use ER308 or 308L filler.
2) Do not preheat. There is no benefit to preheating an austenitic stainless steel, only detriment.
3) You need to purge the weld root.
4) Your welds are underfilled, and the spacing of your "dabs" of filler is creating pinholes/craters from shrinkage. This is a highly restrained piece, so it's going to crack down the centerline accordingly.
5) You need to completely excavate the cracks for repair, and a bit beyond. Every butt weld there needs additional weld metal. Honestly, given the simplicity of the piece and the fact that it can't be properly repaired without removing the flange, I think you'd be time/effort ahead by re-fabricating the entire piece.