How Much Stress Needed To Induce SCC?
How Much Stress Needed To Induce SCC?
(OP)
Let me start my question by stating that I am fully aware that austenitics SS are not the best selection for seawater applications - use of 316/316L was decided by others against the advice of many.....now to the question:
When welding a series of branch connections (typically weldolets or similar boss attachments) to a thin wall 316/316L SS pipe, we will perform cold straightening operations to the pipe to take out the distortion that occurs during welding. The distortion can be considerable, as much as ~2 1/2 inch bow in a 10 ft length of 3.5 inch O.D. x .125" wall thickness pipe.
I am wondering how to quantify the amount of stress induced by this bending (straightening) operation? To straighten the bowed pipe, we bend it in the opposite direction beyond it's yield point so that it restores and retains straightness. Insodoing, are there residual stresses now built in? Or have all stresses been relieved once yielding begins? In any event, I would guess some areas of the pipe is no longer in it's solution annealed condition as it was when delivered from the mill.
A second likely area of residual stress is that induced around the solidifying weld puddles which supposedly can be taken as equal to the yield stress of the base metal or weld metal.
We perform no pwht to the SS weldments. We will passivate.
How valid is any of the above concerns and if valid, are they sufficient to cause SCC in a corrosive (warm seawater) environment?
Thankyou for your interest.
When welding a series of branch connections (typically weldolets or similar boss attachments) to a thin wall 316/316L SS pipe, we will perform cold straightening operations to the pipe to take out the distortion that occurs during welding. The distortion can be considerable, as much as ~2 1/2 inch bow in a 10 ft length of 3.5 inch O.D. x .125" wall thickness pipe.
I am wondering how to quantify the amount of stress induced by this bending (straightening) operation? To straighten the bowed pipe, we bend it in the opposite direction beyond it's yield point so that it restores and retains straightness. Insodoing, are there residual stresses now built in? Or have all stresses been relieved once yielding begins? In any event, I would guess some areas of the pipe is no longer in it's solution annealed condition as it was when delivered from the mill.
A second likely area of residual stress is that induced around the solidifying weld puddles which supposedly can be taken as equal to the yield stress of the base metal or weld metal.
We perform no pwht to the SS weldments. We will passivate.
How valid is any of the above concerns and if valid, are they sufficient to cause SCC in a corrosive (warm seawater) environment?
Thankyou for your interest.





RE: How Much Stress Needed To Induce SCC?
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: How Much Stress Needed To Induce SCC?
Just because the original pipe was annealed doesn't mean that it has low stress.
I would wager that the residual tensile stress in the pipe equals the yield strength.
to your original question, in 316 my testing has shown that you don't get a reduction in SCC sensitivity until the stress is below 20% of the UTS or 33% of the Yield.
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