Stainless Steel Pipe Grade 316 fabrication issues 1

[Good_Guy]

Hi all

Attached here are 3 photos of stainless steel pipe (workshop fabricated) that have arrived on site. There appears to be from grinding areas(shiny)
Can anybody advise me for acceptance. What defects should i be looking out for?
Whether passivation has been carried out and how would I know that?
Thank you all

 

[DekDee]

Very poor fabrication.
S/S should never be touched with a grinder or sander unless 100% necessary.
Based on the photographs, no - it has never been passivated.
Spray it with water from a hose - wait a couple of days and see what happens.
Good luck.

 

[CWEng]

The welder is supposed to clean the base metal before he welds on it. Most do it with a grinder/sander rather than a chemical. Nothing wrong with that unless it's a contaminated abrasive. Not sure why the elbows were sanded though. However, if you specified a stainless steel that is so marginal a little sanding would hurt it, you should have picked a more appropriate grade. It is possible the welds have been passivated (or otherwise cleaned) as they have no color on them.

 

[EdStainless]

I am guessing that the grind work was done after welding, in order to remove excessive heat tint.
Such grinding does not restore the corrosion resistance, it actually just re-embeds the oxides into the surface.
And neither will passivation, this is just a cleaning in order to remove free iron from the surface. The appearance of material should not change when passivated.
You need to pickle in order to remove the oxides. This will dull the material.
I would do two things.
First examine the ID for weld penetration and discoloration.
Second do some UT wall thickness measurements.

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P.E. Metallurgy

 

[moltenmetal]

At first glance it just looked like inexpert pre-weld preparation, but on further examination it does look like it was done after welding to remove heat tint. Unless there is severe and obvious material removal, I'm not sure why pickling and passivation wouldn't be an adequate way to restore the surface oxide adequately. EdStainless is right though- the place you need to concern yourself with is the ID...

 

[gtaw]

If the stainless pipe was passivated, I would expect the area of concern to be the ID of the pipe to enhance the corrosion protection offered by enriched chrome and nickel surface layer. Welding destroys the passivated surface where the weld is located, so to be of use, the pipe would have to passivated after welding. As mentioned, wet the ID surface with nitric or citric acid. If you see signs of brown staining, it was not properly passivated.

It looks (to me from the photos) like the exterior was power wire brushed or cleaned with a soft pad. There should be no problem as long as a stainless steel brush/pad was used and it was used exclusively on stainless steel. If you see brown staining after the OD of the stainless pipe, the surfaces are contaminated with "free" iron. That will lead to pit corrosion.

Best regards - Al

 

[Good_Guy]

Thank you all for a wonderful response

 

[LittleInch]

Be sure and let us know what you do next or find out

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Good_Guy]

Thanks to all for the kind responses.
Looks like the supplier has tried to pass on the fabrication as it is to the customer( Govt. agency) who does not have a qualified inspector. They may save money by not calling in a third party inspector.

Will let you know once the site is back in action after the current situation

 

[weldstan]

Power abrasive (tiger paw) cleaning was used to remove heat tint and iron contamination on the elbows and pipe. Spray distilled water on the surface and wait 24 to 48 hours and you should see rust bloom confirming contamination. This is thin material and I expect you will find heat tint and all varieties of root flaws/defects.