Stainless Steel > Tubing > 321

Alloys 321 (S32100) and 347 (S34700) are stabilized stainless steels which offer as their main advantage an excellent resistance to intergranular corrosion following exposure to temperatures
in the chromium carbide precipitation range from 800 to 1500°F (427 to 816°C). Alloy 321 is stabilized against chromium carbide formation by the addition of titanium. Alloy 347 is stabilized
by the addition of columbium and tantalum. While Alloys 321 and 347 continue to be employed for prolonged service in the 800 to 1500°F (427 to 816°C) temperature range, Alloy 304L has supplanted these stabilized grades for applications involving only welding or short time heating. Alloys 321 and 347 stainless steels are also advantageous for high temperature service because of their good mechanical properties. Alloys 321 and 347 stainless steels offer higher creep and stress rupture properties than Alloy 304 and, particularly, Alloy 304L, which might also be considered for exposures where sensitization and intergranular corrosion are concerns. This results in higher elevated temperature allowable stresses for these stabilized alloys for ASME
Boiler and Pressure Vessel Code applications. The 321 and 347 alloys have maximum use temperatures of 1500°F (816°C) for code applications like Alloy 304, whereas Alloy 304L is
limited to 800°F (426°C). High carbon versions of both alloys are available. These grades have UNS designations S32109 and S34709.

Alloys 321 and 347 offer similar resistance to general, overall corrosion as the unstabilized chromium nickel Alloy 304. Heating for long periods of time in the chromium carbide precipitation
range may affect the general resistance of Alloys 321 and 347 in severe corrosive media. In most environments, both alloys will show similar corrosion resistance; however, Alloy 321 in the annealed condition is somewhat less resistant to general corrosion in strongly oxidizing environments than annealed Alloy 347. For this reason, Alloy 347 is preferable for aqueous and other low temperature environments. Exposure in the 800°F to 1500°F (427°C to 816°C) temperature range lowers the overall corrosion resistance of Alloy 321 to a much greater extent than Alloy 347. Alloy 347 is used primarily in high temperature applications where high resistance to sensitization is essential, thereby preventing intergranular corrosion at lower temperatures.