Selection of AISI 316Ti Vs AISI 321 as materials of construction for bellows seals for Thermic fluid application (such as Santhotherm-66, dow therm ,therminol etc) for high temperature application +200 to +300 Degree C)
Generally both the materials are recommended for selection of bellows seals so long maximum temperature is below the creep range.
AISI 321 is Titanium stabilized Austenetic Stainless steel. It is very good corrosion resistant material for high temperature environment where presence of chloride is negligible.Presence of Ti has tendency to suppress the formation of Chromium carbide under elevated temperature specially at welded construction .Thus depletion of Cr is avoided due to presence of Ti.
But it has less resistance to Pitting-Corrosion as compared to AISI 316 Ti
On the other hand AISI 316 Ti is having 'Mo' in addition to 'Ti:'. Therefore it has very good resistance to Pitting corrosion and has all property of AISI 321.
Obviously AISI 316 Ti shall be comparatively costlier than AISI 321
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