Dish end repair
Dish end repair
(OP)
We are cold forming ellipsoidal dish ends. The problem i am facing is that large dish ends which need to be formed with a joint in it, produces cracks in it after forming. The cracks majorly arise at knuckle radius at joint and adjacent to joint. The material is SA-516 Gr 70 normalized. What could be the possible reasons? And is it ok to repair the cracks by grinding and buildup especially when they are at the both side of dish ends? Any precautionary measures before repair?





RE: Dish end repair
Ensure that the weld seam is flush ground and that there are no undercuts as they may be the starting points for cracks.
Also ensure that the speed of knuckle forming is not too fast
You can always repair the crack and RT it to ensure that the complete defect has been removed.
You should have given additional information like thickness, diameter and post forming heat treatment
RE: Dish end repair
RE: Dish end repair
RE: Dish end repair
Are trying to make the complete dish in one pass? Two? four or more?
Between passes, or after the second pass and before the 3rd, did you re-anneal the head?
RE: Dish end repair
Metengr: Can you please further elaborate?
Racook: By pass you mean flanging of knuckle?
As thickness is not much so we do not go for any heat treatment process
RE: Dish end repair
RE: Dish end repair
RE: Dish end repair
Yes, your experience is showing that is too thick for a single pass (once-through the machine) roll forming for the elliptical head diameters you are trying to roll.
So stop doing that. It is not working, you HAVE to change your process!
RE: Dish end repair
metengr: we do not have facility for hot forming.
RE: Dish end repair
RE: Dish end repair
can you please elaborate the process for forming for our ease.
RE: Dish end repair
in this case Ukmet may have a bigger problem if he's mfg heads w/o proper knowledge,
specially if segmented head, which may require preheatbefore welding and PWHT before forming and hot forming.
RE: Dish end repair
The correct fiber elongation equation must be selected in ASME Section VIII, Div 1 after forming to verify that forming strains have not exceeded a critical value. You can use other methods like marks before and after forming to calculate the tensile fiber strain. In your case, I would suspect formation of the SE head will require thermal treatment because you would exceeded the 5% limit.
This treatment is necessary to avoid work hardened material that can be susceptible to stress corrosion cracking or service-related cracks, like low temperature creep cracking.