STAINLESS STEEL TUBE & PIPE   

Room Temperature Tensile Properties
Minimum mechanical properties of the stabilized Alloy 321 and 347 chromium-nickel grades in the annealed condition (2000°F [1093°C], air cooled) are shown in the table.

Elevated Temperature Tensile Properties
Typical elevated temperature mechanical properties for Alloys 321 and 347 sheet/strip are shown below. Strength of these stabilized alloys is distinctly higher than that of non-stabilized 304 alloys at temperature of 1000°F (538°C) and above.

High carbon Alloys 321H and 347H (UNS32109 and S34700, respectively) have higher strength at temperature above 1000°F (537°C). ASME maximum allowable design stress data for Alloy 347H reflects the higher strength of this grade in comparison to the lower carbon Alloy 347 grade. The Alloy 321H is not permitted for Section VIII applications and is limited to 800°F (427°C) use temperatures for Section III code applications.

Creep and Stress Rupture Properties
Typical creep and stress rupture data for Alloys 321 and 347 stainless steel tubing are shown in the figures below. The elevated temperature creep and stress rupture strengths of the stabilized steel are higher than those of unstabilized Alloys 304 and 304L. These superior properties for the 321 and 347 alloys permit design of pressure-containing components for elevated temperature service to higher stress levels as recognized in the ASME Boiler and Pressure Vessel Code.

Impact Strength
Alloys 321 and 347 have excellent toughness at room and sub-zero temperatures. In the following table are Charpy V-notch impact values for annealed Alloy 347 after holding the samples for one hour at the indicated testing temperatures. Data for Alloy 321 would be expected to be similar.

Fatigue Strength
The fatigue strength of practically every metal is affected by corrosive conditions, surface finish, form, and mean stress. For this reason, no definite values can be shown which would be representative of the fatigue strength under all operating conditions. The fatigue endurance limits of Alloys 321 and 347 are approximately 35% of their tensile strengths.

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