Overview
This type 321 Seamless tube is a standard austenitic which is basically a chromium-nickel alloy. Some amount of titanium is added to it to make it suitable for the atmosphere of elevated temperature. The titanium also provides it the effects of the intergranular corrosion. 321 is that grade of stainless steel which is basically used for the applications which have the temperature up to 9000 Celsius. These tubes have excellent forming and welding qualities and also provide excellent toughness at cryogenic temperatures. This 321 stainless steel is used in the intermediate heating which is from 800 Celsius to 1650 Celsius.
Grades 321 and 347 are the basic austenitic 18/8 steel (Grade 304) stabilised by Titanium (321) or Niobium (347) additions. These grades are used because they are not sensitive to intergranular corrosion after heating within the carbide precipitation range of 425-850°C. Grade 321 is the grade of choice for applications in the temperature range of up to about 900°C, combining high strength, resistance to scaling and phase stability with resistance to subsequent aqueous corrosion.
Grade 321H is a modification of 321 with a higher carbon content, to provide improved high temperature strength. A limitation with 321 is that titanium does not transfer well across a high temperature arc, so is not recommended as a welding consumable. In this case grade 347 is preferred - the niobium performs the same carbide stabilisation task but can be transferred across a welding arc. Grade 347 is therefore the standard consumable for welding 321. Grade 347 is only occasionally used as parent plate material.
Like other austenitic grades, 321 and 347 have excellent forming and welding characteristics, are readily brake or roll formed and have outstanding welding characteristics. Post-weld annealing is not required. They also have excellent toughness, even down to cryogenic temperatures. Grade 321 does not polish well, so is not recommended for decorative applications.
Specification
ASTM A213/A213M-21a Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes.
| Specifications | ASTM A213 / ASME SA213 |
| Dimensions | ASTM, ASME and API |
| Range | 1/2"OD - 12"OD |
| Outside Diameter | 3.00 mm - 219.10 mm, 6.35 mm O.D to 114.3 mm O.D |
| Length | Single Random, Double Random & Required Length |
| Thickness | 0.40 mm - 12.70 mm, 0.8 mm to12.7 mm |
| Schedule | SCH20, SCH30, SCH40, STD, SCH80, XS, SCH60, SCH120, SCH140, SCH160, XXS |
| Type | Seamless |
| Form | Round Tube, Square Tube, Rectangular Tube |
| End | Plain End, Beveled End, Treaded |
ASTM A213 SS 321 Equivalent:
Grade | UNS No | Old British | Euronorm | Swedish SS | Japanese JIS | ||
| BS | En | No | Name | ||||
| SS 321 | S32100 | 321S31 | 58B, 58C | 1.4541 | X6CrNiTi18-10 | 2337 | SUS 321 |
Chemical Composition
| Grade | C | Mn | Si | P | S | Cr | N | Ni | Ti |
| SS 321 | 0.08 max | 2.0 max | 1.0 max | 0.045 max | 0.030 max | 17.00 - 19.00 | 0.10 max | 9.00 - 12.00 | 5(C+N) – 0.70 max |
Mechanical Properties
Grade | Tensile Strength | Yield Strength | Elongation | Hardness | |
| Rockwell B (HR B) max | Brinell (HB) max | ||||
| 321 | 515 | 205 | 40 | 95 | 217 |
Physical Properties
Grade | Density (kg/m3) | Elastic Modulus (GPa) | Mean Co-eff of Thermal Expansion (µm/m/°C) | Thermal Conductivity (W/m.K) | Specific Heat 0-100°C (J/kg.K) | Elec Resistivity (nΩ.m) | |||
| 0-100°C | 0-315°C | 0-538°C | At 100°C | At 500°C | |||||
| 321 | 8027 | 193 | 16.6 | 17.2 | 18.6 | 16.1 | 22.2 | 500 | 720 |
SS 321 Tube ASTM A213 Tolerances
Specification | Allowable Outside Diameter Variation in mm | Allowable Wall Thickness Variation | Exact Length Tolerance in mm | Testing | ||||
| Nominal Diameter | Over | Under | %Over | %Under | Over | Under | ||
ASTM-A213 TP321 | Under 25.4 | .1016 | .1016 | +20 | -0 | 3.175 | 0 | Flattening Test |
| 25.4-38.1 incl | .1524 | .1524 | +22 | -0 | 3.175 | 0 | Tension Test | |
| 38.1-50.8 excl | .2032 | .2032 | +22 | -0 | 3.176 | 0 | Flare Test | |
| 50.8-63.5 excl | .254 | .254 | +2 | -0 | 4.46 | 0 | Hardness Test | |
| 63.5-76.2 excl | .3218 | .3218 | +22 | -0 | 4.76 | 0 | 100% Hydrostatic test | |
| 76.2-101.6 incl | .381 | .381 | +22 | -0 | 4.76 | 0 | Refer to ASTM A-450 | |
Applications
- 1. Food preparation equipment particularly in chloride environments.
- 2. Laboratory benches & equipment.
- 3. Coastal architectural panelling, railings & trim.
- 4. Boat fittings.
- 5. Chemical containers, including for transport.
- 6. Heat Exchangers.
- 7. Woven or welded screens for mining, quarrying & water filtration.
- 8. Threaded fasteners.
- 9. Springs.
