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RE: welding weird stainless steel

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In the case of (some) austenitic stainless steels, chromium carbides may
precipitate at grain boundaries when cooling, e.g., from welding
temperatures. This leads to chromium-starved areas adjacent to the
chromium-rich carbides (i.e., at and around the grain boundaries) - the
phenomenon called "Sensitization". These depleted areas are highly subject
to corrosion attack, especially in acid service. The chromium carbides that
are formed tie-up the chromium preventing it from forming a passive chromium
oxide layer on the material.  The chromium oxide layer, though only a few
atoms thick, prevent corrosion from occurring.

To restore the corrosion protection the material must be SOLUTION ANNEALED
(same as CARBIDE SOLUTION ANNEALED).  Summarizing the process; heating a
finished fitting to over 1,850 degrees F. and cooling it quickly, usually in
water, so carbon content goes back into the stainless solution.


Rich

Richard M. Beldyk, PE, CPEng, NSPE, MIEAust, AIT, CWEng, CPE

Professional Engineer - Delaware, Maine, Maryland, Michigan,  New Hampshire,
Ohio, Pennsylvania, Virginia, West Virginia
Chartered Professional Engineer - MIEAust, NPER
Registered Member - International Registry of Professional Engineers
(USCIEP)
NASP Certified Accident Investigation Technician
AWS Certified Welding Engineer
AFE Certified Plant Engineer


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