Strange skin-like pattern on the ID of a SS pipe ID 2

[Spoonful]

Dear All,

Found this strange skin-like pattern on the ID of a SS pipe ID, please see attached. Seeking for a bit of expert explanation, of why and how?

Cheers

 

[Compositepro]

I've not seen that before, but I would guess that it is centrifugally cast pipe.

 

[Spoonful]

It is a A312 316L Pipe

 

[metengr]

Remove a small cross section and have reputable metallurgical lab perform an examination of the ID surface using a stereomicroscope (and possible SEM examination) and metallographic examination of the tube wall thickness to determine the cause.

 

[IRstuff]

What happens when you scrape it?

TTFN
faq731-376

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[EdStainless]

My guess is that this pipe has been cold drawn, and that the last draw pass was a sink only (on internal tooling).
This looks like the puckering that you get from a heavy sink on soft tubes.
It also looks like the surface was pickled. perhaps over pickled creating more texture.

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Plymouth Tube

 

[moltenmetal]

Typical sh*tty ID found on much of the seamless pipe we buy in my experience. Cool-looking pattern this time, but nothing unusual.