SS321 Tube Sheet
Titanium-stabilized stainless that resists carbide precipitation at high temperature — the grade to reach for when service runs hot enough that standard 304/316 would sensitize over time, without moving to a nickel alloy.
Chemical Composition
| Element | Min % | Max % |
|---|---|---|
| Chromium (Cr) | 17.0 | 19.0 |
| Nickel (Ni) | 9.0 | 12.0 |
| Titanium (Ti) | 5×%C min | 0.70 |
| Carbon (C) | — | 0.08 |
Mechanical Properties
| Property | Typical Value |
|---|---|
| Tensile Strength | 515 MPa min |
| Yield Strength (0.2% offset) | 205 MPa min |
| Elongation | 40% min |
| Max. Practical Service Temp. | ~870°C (oxidation-limited) |
Equivalent Grades
| Standard | Designation |
|---|---|
| ASTM / UNS | S32100 |
| EN / DIN | 1.4541 |
| JIS | SUS321 |
SA-965 / F321 Specification
When a drawing or RFQ cites SA-965 / F321 (or ASTM A965 Grade F321) with UNS S32100, it is pointing at an austenitic stainless-steel forging path — not a universal “tube sheet standard.” Confirm the ordered product form, grade designation and purchaser requirements against the drawing before procurement.
| Element | Reference |
|---|---|
| Specification | ASTM A965 / A965M |
| ASME designation | SA-965 / SA-965M where applicable (edition-dependent; confirm Code context) |
| Grade designation | F321 |
| UNS | S32100 |
| Product form | Austenitic stainless-steel forging |
| Application context | Pressure and high-temperature parts, subject to project requirements |
A965/SA-965 covers austenitic stainless-steel forgings for boilers, pressure vessels, high-temperature parts and associated equipment. F321 is the listed grade designation that corresponds to UNS S32100 (SS321). The finished tube-sheet geometry, machining, hole pattern and inspection scope remain purchaser / drawing requirements — they are not defined by naming A965 or SA-965 alone.
Do not treat A240, A182 and A965 as interchangeable. A practical procurement path when SS321 / F321 / S32100 appears on a drawing:
| Specification | Product form / role | How to read it for tube sheets |
|---|---|---|
| ASTM A240 / SA-240 | Plate, sheet and strip | Common plate path when the blank is machined from flat product |
| ASTM A182 / SA-182 | Forged / rolled piping components (F321 context) | Relevant when the callout is piping-component forging scope; confirm against the ordered part — do not assume A182 purchases a large forged tube-sheet blank |
| ASTM A965 / SA-965 | Austenitic stainless-steel forgings (F321) | Investigate when the material is specified as a forging for pressure/high-temperature parts |
For RFQ clarity, include where known: grade (SS321), UNS (S32100), ASTM/ASME + edition, F-grade (F321), product form (plate / forging / clad), drawing + revision, OD/thickness, hole pattern, quantity, and inspection/testing.
Continue from grade identity into product form and machining:
Why Stabilization Matters
Available Product Forms
SS321 is most often specified as a U-Tube Tube Sheet for high-temperature boiler and process heater service, where its stabilization matters most.
Applications
High-temperature process heaters, exhaust and flue gas equipment, and any welded application cycling through the sensitization temperature range where 304/316 aren't stabilized. See also SS347 for the niobium-stabilized alternative.
Advantages & Limitations
Advantages
- Resists sensitization through the critical temperature range
- Good oxidation resistance to ~870°C
- Widely available compared to more exotic high-temp grades
Limitations
- No chloride advantage over standard 304 — still no molybdenum
- Titanium carbides can be less stable than niobium (347) in some weld conditions
- Cost premium over standard 304/316
FAQ
If a proper post-weld solution anneal is reliably part of your fabrication process, standard 304/316 can be adequate. 321 exists precisely for the many real-world cases where full post-weld heat treatment isn't practical or verifiable in the field.
321's titanium stabilization is specifically a high-temperature benefit; for cryogenic service, standard austenitic grades like 304L are generally preferred since low-temperature toughness isn't affected by the sensitization mechanism 321 addresses.
321 is more often sourced to order than 304/316L given lower demand volume — send your specification and quantity for a confirmed lead time.