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Up Topic Welding Industry / Metallurgy / Effect if root oxidation of stainless steel welds
- - By Shaju K. Albert Date 09-23-2012 00:58
We found due to improper purging of the Ar shielding gas, some oxidation of the root pass in stainless steel piping (316L steel containing nitrogen typically in the range of 0.03-0.07 wt.%). The filler wire employed is 16-8-2. What would be consequences using these welds with root oxidation in high temperature service (typically at 500 degree C).

Thanking you in advance

Shaju
Parent - By Lawrence (*****) Date 09-24-2012 10:49
Some images and description of the extent of oxidation might be helpful along with information on what type of service (other than temp)
Parent - By G.S.Crisi (****) Date 09-24-2012 19:55
How many welds show the oxidation you're talking about? Two or three? Four perhaps? In this case, I suggest to grind the oxidation by means of an aluminum oxyde grinding disk and reweld again. You won't spend that much manhours. Do not use a silicon carbide (Carborundum is the brand name) disk, because it will leave traces of carbon on the ground surface that will promote intergranular corrosion.

If the oxidized welds are, say, 15 or 20, I would consider acid pickling. Don't use hydrochloric acid because it corrodes 316L SS. Don't use neither nitric acid, it's difficult to handle due to the harmful fumes it releases. Use dilute sulfuric acid (say 20% acid and 80% water). It doesn't corrode 316L SS. Warning! When preparing the solution, add the acid onto the water, never the water onto the acid.

Don't be afraid, 20% sulfuric acid doesn't corrode SS, but if you're still in doubt, add a corrosion inhibitor to the solution. The corrosion inhibitor will let the acid to dissolve the oxydes but not the metal. Get in touch with a reputable chemicals supplier and ask him to  recommend  a good inhibitor. 

Giovanni S. Crisi
Sao Paulo - Brazil
Up Topic Welding Industry / Metallurgy / Effect if root oxidation of stainless steel welds

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