Trboatworks
Diamond
- Joined
- Oct 23, 2010
- Location
- Maryland- USA
A question about why welds fail on a exhaust.
Ok- a pair of exhausts ran through my buddies marine fabrication shop for repairs.
I didn't get a photo of the damage but the weld cracked right down the middle on that shoulder where the 3" was stepped up to 4".
Both exhausts had the same crack
We were talking about what caused the crack and he was thinking that the heat got to the weld and was the cause.
I am thinking more a vibration thing.
So... I tend to overthink these things at times
My thinking has a vibration frequency dropping as one moves away from the turbo where this bolts up to the lowest frequency out at end where soft hose is hooked up.
I am seeing a vibration node caused by that step up from 3" to 4" on that shoulder which has a sudden shift in frequency and loads up the metal causing fatigue failure.
So the frequency is dropping as we move away from the flange but that drop is not linear.
The crack is found where the greatest change in frequency occurs at that shoulder.
I would love to see a heat map on a part like this to show stress risers but am betting I am right- that shoulder is one and the crack has more to do with that vibration being concentrated there than heat.
I guess my next question is why it wouldn't crack right at the flange where the stress is greatest and not the shoulder..
This sort of question makes me wish I had some engineering theory under my belt..
Thoughts?
I drew a line where the crack was on the second photo:
.
Ok- a pair of exhausts ran through my buddies marine fabrication shop for repairs.
I didn't get a photo of the damage but the weld cracked right down the middle on that shoulder where the 3" was stepped up to 4".
Both exhausts had the same crack
We were talking about what caused the crack and he was thinking that the heat got to the weld and was the cause.
I am thinking more a vibration thing.
So... I tend to overthink these things at times
My thinking has a vibration frequency dropping as one moves away from the turbo where this bolts up to the lowest frequency out at end where soft hose is hooked up.
I am seeing a vibration node caused by that step up from 3" to 4" on that shoulder which has a sudden shift in frequency and loads up the metal causing fatigue failure.
So the frequency is dropping as we move away from the flange but that drop is not linear.
The crack is found where the greatest change in frequency occurs at that shoulder.
I would love to see a heat map on a part like this to show stress risers but am betting I am right- that shoulder is one and the crack has more to do with that vibration being concentrated there than heat.
I guess my next question is why it wouldn't crack right at the flange where the stress is greatest and not the shoulder..
This sort of question makes me wish I had some engineering theory under my belt..
Thoughts?
I drew a line where the crack was on the second photo:
.
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