tubular exhaust manifold, collector keeps cracking!

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So I had to modify the exhaust manifold on my car, ill save the details since most arent interested.basically, I drilled out a 1.75 diameter hole in the collector of my tubular exhaust manifold and welded a pipe to it with a flange. After I finished the welding, I noticed there were two spots that had cracked. They were not my new welds that cracked, but two old welds right near where I had worked. I tried to run a new bead over them, and as soon as the bead cools off, it cracks again. I am a novice tig welder, and am unsure what I am doing wrong. Help please
Reply:I had this happen on an intercooler I did, someone called it hot cracking. Something to look up, still no idea how to fix it though.Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Adding an external wastegate to the manifold, ehh?Tell us about the manifold.  What material and thickness is it made of?  And what filler was used to weld it up."There are two types of people in America - those who try to classify everyone into two types and those who don't."
Reply:Those are the two pictures I had taken before I welded it, unfortunately I havnt taken pictures of the crack yet since Im at work. The material is stainless, and im not sure what thickness, whatever is typical for exhaust manifolds. This was a mass produced manifold.Where the big flange on top welds to the collector, is where the two cracks are, right in the corner that I was working to add that new pipe.
Reply:Maybe the material is too thin? Or maybe it's not 321 SS and can't handle the heat?Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:you need to clean the pipe better before you weld anything to it. the build up of the black soot on the inside of the pipe will get into your welds....Miller Dynasty 200Millermatic 211Instagram?.... find me @ WELD_MEDIC
Reply:Hmmmmm being a production part I really don't see any secret stuff being done there...  As mentioned what filler are you using and is the new pipe stainless or just muff pipe?   Try 308 filler and run the beads close together to keep the heat down....maybe 80 amps on the machine and use the pedal......  Gas lens 3/32 tungsten045  to 060 filler  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:So the weld at the top between the collector tubing and the turbo flange cracked?  I wouldn't be surprised if someone got overzealous with smoothing the welding in that area inside (when port matching the ID of the flange to the collector), and caused the tubing near the weld, or the welds to get excessively thin.  Check that out.  I've repaired a cracked stainless turbo header with this problem.Anyhow, you could build the fillet weld up wider on the outside of the tubing, where it would not impede flow on the inside.  You should clean the material, especially on the back side if yo are fully penetrating (as you should be for repairing a crack), and even if possible inside the crack, before you weld it.  You need it to be contaminant free.Also, consider adding some support to the turbocharger if it's heavy, or adding a flex joint in your exhaust system if that is otherwise rigid and applying "stress" to this location as the engine rocks during deceleration and acceleration.  It's hard to determine if that's the case based on the info you've provided, but it's a possible root cause.PS - scotch brite works great for cleaning stainless.  Nice to have a die grinder for something like this.One more thing - it's a good idea to back purge with Argon, or use solar flux (mix up as a paste and brush on the back side in the area to be welded) to prevent oxidation of the back side when TIG welding stainless tubing.
Reply:Hey guys so update, I actually got a little fed up and gave the manifold to a shop to repair. I guess they found out that the manifold is actually some sort of mild steel, and has been ceramic coated. They said that using mild steel filler worked much better.I think between me using SS filler rod, and overheating, I caused it myself. The manifold has been repaired and finished and is now back on the car and doesnt leak! The same spot is already starting to crack again unfortunately, but Im going to leave it alone unless it starts leaking.
Reply:Originally Posted by Tim1137Hey guys so update, I actually got a little fed up and gave the manifold to a shop to repair. I guess they found out that the manifold is actually some sort of mild steel, and has been ceramic coated. They said that using mild steel filler worked much better.I think between me using SS filler rod, and overheating, I caused it myself. The manifold has been repaired and finished and is now back on the car and doesnt leak! The same spot is already starting to crack again unfortunately, but Im going to leave it alone unless it starts leaking.
Reply:yeah. most of those mass produced turbo manifolds, if coated from factory, are mild steel. cheaper to make and coat than use stainless.Hobart EZ-Tig newbie.
Reply:The cracking problem would have been caused by not grinding off the ceramic coating from the material before you tried to weld it. Stainless filler or overheating would not cause those issues.Have we all gone mad?