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Type 321 is a standard austenitic 18/8 chromium nickel alloy with the addition of Titanium making it an excellent choice in elevated temperature environments.
The titanium stabilises the material removing its susceptibility to the effects of intergranular corrosion. 321 is therefore the stainless steel material of choice for applications in working environments up to 9000 C.
A drawback of Type 321 is that the titanium does not transfer well across a high temperature arc, so it is not recommended as a welding consumable.
In such instances, 347 is the preferred choice as the Niobium performs the same function as Titanium but can be still transferred across a high temperature arc. Type 347 is therefore the consumable of choice for welding Grade 321. |
The steel has excellent forming and welding qualities and excellent toughness even at cryogenic temperatures. If you are looking for a stainless steel to provide resistance to intergranular corrosion, 304L is the normal choice as it is a more commonly used and supplied steel.
However, 321 is a much better option in operating temperature environments in excess of 5000 C and therefore have its own merits.
Note that Type 321 does not polish well so it is not practical to use this material as cosmetic architectural feature. |
 Product Range
Specifications: ASTM A/ASME SA213/A249/A269/A312/A358 CL. I to V ASTM A789/A790
Sizes (Seamless): 1/2" NB - 24" NB
Sizes (ERW): 1/2" NB - 24" NB
Sizes (EFW): 6" NB - 100" NB
Wall Thickness available:
Schedule 5S - Schedule XXS (heavier on request)
Other Materials Testing:
NACE MR0175, H2 SERVICE, OXYGEN SERVICE, CRYO SERVICE, etc.
Dimensions:
All Pipes is manufactured and inspected/tested to the relevant standards including ASTM, ASME and API etc.
Background of 321 Stainless Steel Pipes and Tubes
Grades 321 and 347 are the basic austenitic 18/8 steel (Grade 304) stabilized 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 425-8500C. Grade 321 is the grade of choice for applications in the temperature range of up to about 9000C, 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 stabilization 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.
Grade 304L is more readily available in most product forms, and so is generally used in preference to 321 if the requirement is simply for resistance to intergranular corrosion after welding. However 304L has lower hot strength than 321 and so is not the best choice if the requirement is resistance to an operating environment over about 5000C. |
Composition of 321 Stainless Steel Pipes and Tubes
Typical compositional ranges for grade 321 stainless steels are given in table 1.
Table 1. Composition ranges for 321 grade stainless steel
| Grade |
C |
Mn |
Si |
P |
S |
Cr |
Mo |
Ni |
N |
Other |
| 321 |
min.
max |
-
0.08 |
2.00 |
0.75 |
0.045 |
0.030 |
17.0
19.0 |
- |
9.0
12.0 |
0.10 |
Ti=5(C+N)
0.70 |
| 321H |
min.
max |
0.04
0.10 |
2.00 |
0.75 |
0.045 |
0.030 |
17.0
19.0 |
- |
9.0
12.0 |
- |
Ti=4(C+N)
0.70 |
| 347 |
min.
max |
0.08 |
2.00 |
0.75 |
0.045 |
0.030 |
17.0
19.0 |
- |
9.0
13.0 |
- |
Nb=10(C+N)
1.0 |
Mechanical Properties of 321 Stainless Steel Pipes and Tubes
Typical mechanical properties for grade 321 stainless steels are given in table 2.
Table 2. Mechanical properties of 321 grade stainless steel
| Grade |
Tensile Strength (MPa) min |
Yield Strength 0.2% Proof (MPa) min |
Elongation (% in 50mm) min |
Hardness |
| Rockwell B (HR B) max |
Brinell (HB) max |
| 321 |
515 |
205 |
40 |
95 |
217 |
| 321H |
515 |
205 |
40 |
95 |
217 |
| 347 |
515 |
205 |
40 |
92 |
201 |
| 321H also has a requirement for a grain size of ASTM No 7 or coarser. |
Physical Properties of 321 Stainless Steel Pipes and Tubes
Typical physical properties for annealed grade 321 stainless steels are given in table 3.
Table 3. Physical properties of 321 grade stainless steel in the annealed condition
| Grade |
Density (kg/m3) |
Elastic Modulus (GPa) |
Mean Coefficient of Thermal Expansion (m/m/0C) |
Thermal Conductivity (W/m.K) |
Specific Heat 0-1000C (J/kg.K) |
Electrical Resistivity (n.m) |
| 0-1000C |
0-3150C |
0-5380C |
at 1000C |
at 5000C |
| 321 |
8027 |
193 |
16.6 |
17.2 |
18.6 |
16.1 |
22.2 |
500 |
720 |
Grade Specification Comparison of 321 Stainless Steel Pipes and Tubes
Approximate grade comparisons for 321 stainless steels are given in table 4.
Table 4. Grade specifications for 321 grade stainless steel
| Grade |
UNS No |
Old British |
Euronorm |
Swedish SS |
Japanese JIS |
| BS |
En |
No |
Name |
| 321 |
S32100 |
321S31 |
58B, 58C |
1.4541 |
X6CrNiTi18-10 |
2337 |
SUS 321 |
| 321H |
S32109 |
321S51 |
- |
1.4878 |
X10CrNiTi18-10 |
- |
SUS 321H |
| 347 |
S34700 |
347S31 |
58G |
1.4550 |
X6CrNiNb18-10 |
2338 |
SUS 347 |
| These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted. |
Corrosion Resistance of 321 Stainless Steel Pipes and Tubes
Equivalent to Grade 304 in the annealed condition and superior if a weldment in these grades has not been post-weld annealed or if the application involves service in the 425-9000C range. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 600C. Considered resistant to potable water with up to about 200mg/L chlorides at ambient temperatures, reducing to about 150mg/L at 600C.
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Heat Treatment of 321 Stainless Steel Pipes and Tubes
Solution Treatment (Annealing) - heat to 950-11200C and cool rapidly for maximum corrosion resistance.
Stabilising - heat to 870-9000C for 1 hour per 25mm of thickness and air cool. Stabilisation is recommended for most severe service conditions (above 4250C) and particularly for material annealed at the upper side of the annealing temperature range.
Stress Relief - Heat to 7000C for 1 to 2 hours and air cool. These grades cannot be hardened by thermal treatment. |
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Steel Pipes & Tubes