Strange discontinuity near SS pipe surface 3

[Liuk]

Hello,

We have examined SS pipe surface condition. There are some stress corrosion cracks on OD surface. But this subsurface discontinuity (please see attached file) is very strange. What is your opinion? I see the shape of defects like this in the first time in my practice.

Thank you in advance for any idea.

 

[EdStainless]

Do you have any other pictures?
Does the part of the pattern follow forming flow lines?
I would suppose that it is SCC connecting with inclusions.
Can you take the piece that was adjacent to this and section it longitudinally?

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

I see locally deformed material along the surface, and at this interface are indications. This could be SCC that was present and during forming smeared over to appear subsurface.

 

[Liuk]

This pipe was damaged during removal from service. There are strong deformation line near OD surface and mechanical damage (like notching)of surface so identification of discontinuity isn't clear.

I have attached other photo (with deformation lines, notching and cracks like SCC).

 

[EdStainless]

That is a lap (or fold) from the manufacturing process.
Corrosion started as crevice corrosion in the lap, and then progressed as SCC.
That would be my call.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

Agree with Ed.