What TP321 / 321H is
Type 321 is 18Cr-10Ni stainless stabilized with titanium at roughly five times the carbon content. In service between about 800 and 1500 degrees F, unstabilized 304 precipitates chromium carbides at grain boundaries and becomes vulnerable to intergranular attack. Titanium carbides form first in 321, keeping the chromium in solution. TP321H carries slightly higher carbon and a minimum grain size for elevated-temperature strength under ASME Section VIII and Section I.
Chemical composition
| Element | Requirement |
|---|---|
| Carbon | 0.08% max (321); 0.04 to 0.10% (321H) |
| Chromium | 17.0 to 19.0% |
| Nickel | 9.0 to 12.0% |
| Titanium | 5 x (C + N) min to 0.70% max |
| Manganese | 2.00% max |
Mechanical properties
| Property | Minimum |
|---|---|
| Tensile strength | 75,000 psi (515 MPa) |
| Yield strength | 30,000 psi (205 MPa) |
| Elongation in 2" | 35% |
Where it is used
- Refinery heater convection tubes and transfer lines.
- Hydrogen reformer and FCC unit exchangers.
- Aircraft and gas turbine exhaust components.
- High-temperature chemical process exchangers and expansion joints.
321 or 347
Both are stabilized grades for the same temperature range. 347 uses columbium (niobium) and is often preferred for welded construction and slightly higher creep strength; 321 is more readily available in tube. Specifications usually decide. We supply both.
321 or 321H, OD, minimum wall, length, quantity, design temperature, grain size requirement, and the licensor or customer specification. State whether stabilizing heat treatment is required.