Any welding/metal experts here?
Discussion
Probably is stress. My guess is that the stock headers (or the stock system) had some form of support further down the manifold/downpipe and that now the manifold effectively supports everything down to the first flexi joint. A fair bit of weight plus you've got to factor in expansion/contraction, any movement on the mounts, and so on.
The job itself looks fine. For all that, it's not an exact science -- you might take them back, see what is said/done.
The job itself looks fine. For all that, it's not an exact science -- you might take them back, see what is said/done.
Edited by TheRealFingers99 on Thursday 3rd July 07:30
SEE YA said:
Also how thick is the pipe, itself too thin and with heat it will flex and break at the welds.
I''l bet it's quite a bit thinner than an OEM tubular manifold would be.However if the manifold is not attached to the bottom of the engine somewhere then movement could certainly be assisting the process.
Looks like the upper part of the fillet hasn't penetrated where as the lower part has. The crack seems to start at just that point. You can see a small vertical part on the upper weld, no more tha half a mm, where as the lower part the fillet blends nicely into the parent metal.
Isn't necessarily the actual cause of the problem, just the weakest part which will have failed due to the stress applied. We don't know if that stress would have cracked a perfect weld anyway.
Isn't necessarily the actual cause of the problem, just the weakest part which will have failed due to the stress applied. We don't know if that stress would have cracked a perfect weld anyway.
velocemitch said:
Looks like the upper part of the fillet hasn't penetrated where as the lower part has. The crack seems to start at just that point. You can see a small vertical part on the upper weld, no more tha half a mm, where as the lower part the fillet blends nicely into the parent metal.
Yeah agree with that. The others in the picture all look fine, but the top of that weld hasn't penetrated at all for some reason.doogz said:
buggalugs said:
Being fairly ignorant on such matters, I would have thought the thin pipe would have penetrated and the dirty great thick flange not, rather than the other way around.
If it's a mild flange, stainless CHS, and they used the wrong filler wire, not necessarily.Unless it was stress-relieved by post-weld heat-treatment, the region adjacent to the weld toe is already stressed in tension resulting from post-solidification thermal contraction of the weld metal.
Add a little cyclic stress (engine /exhaust vibrations) to this existing tensile stress and fatigue is a distinct possibility, given that the transition from the weld to the pipe surface, and the roughness of the weld surface itself, both act as stress-raisers.
Of course, it could be that that particular weld contains a defect, such as porosity, lack of penetration/lack of fusion or slag inclusions, but it would probably be necessary to break open the crack and inspect the surfaces to see if that is the case. If exhaust gases have been leaking through the crack these may have damaged evidence of any pre-existing defect/s.
If you have a recurring cracking issue affecting only one pipe and not the others I guess it raises questions about the constraints / degrees of freedom of that particular pipe as the engine moves and as the pipe thermally expands and contracts, as it suggests the stresses are higher in that pipe than the others.
Add a little cyclic stress (engine /exhaust vibrations) to this existing tensile stress and fatigue is a distinct possibility, given that the transition from the weld to the pipe surface, and the roughness of the weld surface itself, both act as stress-raisers.
Of course, it could be that that particular weld contains a defect, such as porosity, lack of penetration/lack of fusion or slag inclusions, but it would probably be necessary to break open the crack and inspect the surfaces to see if that is the case. If exhaust gases have been leaking through the crack these may have damaged evidence of any pre-existing defect/s.
If you have a recurring cracking issue affecting only one pipe and not the others I guess it raises questions about the constraints / degrees of freedom of that particular pipe as the engine moves and as the pipe thermally expands and contracts, as it suggests the stresses are higher in that pipe than the others.
I typed a reply earlier but it didn't post for some reason.
Anyway, the tubular pipe is 1mm thick but I couldn't tell you the grade. I'm told that it's low grade, which is shown by how dull it has gone. I'm no expert on this, so this may be false.
I had runner 4 crack in exactly the same place previously, which was sorted when I took it back for assorted other issues (including other cracks)
Also, the guy who made the mani did make a bracket to support the weight of the turbo. By welding directly onto the compressor housing (but that's another issue entirely). But then one of the welds broke on that too.
Long and short of it....anyone know of a DECENT manifold fabricator in the South? I'm trying to get my money back from this guy so will need a proper one making.
Anyway, the tubular pipe is 1mm thick but I couldn't tell you the grade. I'm told that it's low grade, which is shown by how dull it has gone. I'm no expert on this, so this may be false.
I had runner 4 crack in exactly the same place previously, which was sorted when I took it back for assorted other issues (including other cracks)
Also, the guy who made the mani did make a bracket to support the weight of the turbo. By welding directly onto the compressor housing (but that's another issue entirely). But then one of the welds broke on that too.
Long and short of it....anyone know of a DECENT manifold fabricator in the South? I'm trying to get my money back from this guy so will need a proper one making.
Mr2Mike said:
Would probably have helped if you'd mentioned you had a turbo hanging off it...
1mm is nothing like thick enough for this application, and you certainly need additional supports for the turbo. The cheap Chinese made turbo manifolds you see on eBay crack like this for a passtime.
Yes. 1mm is nothing like thick enough for this application, and you certainly need additional supports for the turbo. The cheap Chinese made turbo manifolds you see on eBay crack like this for a passtime.
That looks like someone has used a n/a performance mani design as a basis for a turbo manifold. It just won't work properly.
Issues are:
- Thickness of tube. For strength and heat retention, you want as thick as you can reasonably go. The cheapest way to do turbo headers is to use what the Americans call Weld-Els. These are pre-bent short sections of pipe (you can get straight sections, too) used by steam engineers and gas engineers. Go for at least schedule 30, 40 would be better. Available in stainless or mild steel. This'll be 3 or 4 times thicker than what you've got. The flange also needs to be something like 1/2" thick. The higher spec the material, the thinner you can go, but 1mm simply isn't enough.
Another cut price solution, assuming the car once had a cast iron manifold, is a cut and shut job to mount a turbo flange on the end. This involves dissimilar welding (something which any welder/fabricator will try to avoid) but can be effective.
- Length of tube. N/A engines rely on exhaust scavenging. Whether you actually get any useful scavenging with a turbo engine is open to debate. Consequently, n/a manifolds will have (or should have!) a carefully calculated length. Turbos are not so fussy, so most folk go for something like 15". This makes for a tougher fitment, and often for an easier/better route for the turbo oil return.
- Hanging the turbo. Ideally, the turbo wants to be hung off a tripod type fitting, so that the weight is supported at all times, but movement for expansion/contraction is allowed.
Lots of good stuff in the "Street Turbocharging" book by Mark Warner, or A Graham Bell's "Forced Induction" book -- maybe the Corky Bell book, too, although I've not got round to reading it.
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