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Heating element mfgr. encounters rust of 321SS coils

2003

Hi,

We manufacture industrial heating elements and of late we have been experiencing rusting on our heaters made of Stainless Steel (SS321).We are unable to point into one root cause for this problem. We do weld at the end of the heater area which we call the cold section and then we coil the heated area on a hardened stainless steel.



My concerns are

1:Why is it rusting all around the coiled area and the cold area?
2:We have been manufacturing these type of heaters since 1998 and we have not experienced any rusting issue before?
3: Rusted heaters are not used and kept in bags with desiccants for the last 6 months, why does it rust just being in the bag with desiccants?

I would appreciate if some one could answer me at the earliest possible.

Thank you,

Arun Divakar
Heating Elements - Battle Creek, Michigan

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2003

Rusting (red) is definitely abnormal for 321 SS. Your supplier may have furnished a lower grade material, or else the parts are getting contaminated, probably during heating or bending. Also, I cannot tell from the photo, is there some bluish heat tint (oxidation)?

1) Check the material.
2) Welding should be arc welding (not oxy-acetylene, which causes carbon contamination), using E/ER437 filler if necessary.
3) Verify no contact with non-stainless material during heating.
4) Clean and passivate both your parts and the hardened mandrel. Citrisurf« from Stellar Solutions [a finishing.com supporting advertiser] is a suitable product.
5) Desiccant should not be necessary for passivated 321.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.