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321 Stainless Steel Tubing and Seamless Pipe

321 stainless steel tubing is the titanium-stabilised austenitic grade for service between about 425 and 815 C, where 304 and 316 sensitise and lose corrosion resistance. Titanium is added at a minimum of five times the carbon plus nitrogen content, so it ties up carbon as titanium carbides and leaves chromium in solution where it maintains the passive film. Walmay supplies 321 and 321H as seamless tube to ASTM A213, seamless and welded pipe to ASTM A312, and instrumentation tube to A269, in sizes from 6 mm OD to 273 mm and 1/8 inch to 10 inch NPS.

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  • Radiation Resistance

    Maintains ductility after 10⁶ Gy, elongation ≥35%, superior to 304 (≤20% after radiation).

  • Intergranular Corrosion Resistance

    Ti stabilization prevents grain boundary corrosion under high-temperature, high-pressure nuclear conditions.

  • High-Temperature Resistance

    Long-term use at 800℃; oxidation film remains intact for superheated steam.

Product Specifications

Specification
ItemDetail
Grade321, UNS S32100, and 321H, UNS S32109
Tube standardsASTM A213 seamless boiler and heat exchanger, ASTM A269 instrumentation
Pipe standardsASTM A312 / SA312 seamless and welded, ASTM A358
Size range, tube6-114 mm OD, 0.7-8.0 mm wall
Size range, pipe1/8 in to 10 in NPS
Schedules5S, 10S, 40S, 80S, and to order
Length6 m random, or cut to length
ConditionSolution annealed, or stabilise annealed on request
CertificationEN 10204 3.1 with titanium reported, hydrostatic or NDT per standard
Chemical Composition
Element321321H
Carbon0.08 max0.04-0.10
Chromium17.0-19.017.0-19.0
Nickel9.0-12.09.0-12.0
Titanium5 x (C + N) min, 0.70 max4 x (C + N) min, 0.60 max
Manganese2.00 max2.00 max
Silicon1.00 max1.00 max
Nitrogen0.10 max-

Always ask for titanium and carbon as reported figures, not just as specification limits. A heat where titanium falls below five times carbon plus nitrogen is not effectively stabilised and will behave like plain 304 in the sensitisation range, whatever the grade marking says.

Mechanical Properties
Property321321H304 for comparison
Yield strength minimum205 MPa205 MPa205 MPa
Tensile strength minimum515 MPa515 MPa515 MPa
Elongation35 percent35 percent35 percent
Maximum continuous serviceAbout 815 CAbout 870 CAbout 870 C oxidation, but sensitises far lower
Oxidation resistance limitAbout 900 C intermittentAbout 900 CAbout 870 C
Creep strength above 550 CHighHigher, the reason for the H gradeLow
Density8.0 g/cm38.0 g/cm38.0 g/cm3

321H is the same alloy with a deliberately raised carbon range, because carbon improves creep strength. It is specified where the part carries load at temperature, typically superheater and reheater tubing, and it is the version ASME code work usually calls for above 540 C.

Equivalent Designations
System321321H
UNSS32100S32109
AISI / ASTM321, Type 321321H
EN material number1.45411.4878
EN steel nameX6CrNiTi18-10X8CrNiTi18-10
JISSUS 321SUS 321H
GB0Cr18Ni10Ti1Cr18Ni9Ti
DIN old1.45411.4878

The nearest functional alternative is 347, EN 1.4550, which uses niobium instead of titanium as the stabiliser. 347 is preferred where the material will be welded in aggressive service, because titanium is partly lost across the arc while niobium is not, and 347 filler is what is used to weld 321 for exactly this reason.

Ordering
ItemDetail
Minimum order500 kg from stock, 2 tonnes for a mill run
Lead time from stock12-18 days
Lead time mill run40-60 days
TestingHydrostatic, eddy current or ultrasonic per standard, PMI, grain size and intergranular corrosion test on request
DocumentationEN 10204 3.1 with titanium and carbon reported, elevated-temperature data on request
PackingHexagonal bundles, end caps, crated for small tube
IncotermsFOB, CIF, DAP

Tell us the operating temperature and whether the component is load bearing, because that determines whether 321 or 321H is correct, and whether a stabilise anneal should be added.

Pricing Calculation

Workshop & Manufacturing Machine

Stainless Steel Tubes Packed in Truck

Wooden Crate Packaging in Factory

Neo-Mac Machine with Stainless Steel Tubes

Factory Tube Packaging Process

Industrial Manufacturing Equipment

Stainless Steel Composition Analyzer

Bundled stainless steel pipes of varying diameters racked in a mill warehouse
Close-up of a stainless steel pipe end showing the weld seam and polished bore

321 stainless steel tubing is the titanium-stabilised austenitic grade for service between about 425 and 815 C, where 304 and 316 sensitise and lose corrosion resistance. Titanium is added at a minimum of five times the carbon plus nitrogen content, so it ties up carbon as titanium carbides and leaves chromium in solution where it maintains the passive film. Walmay supplies 321 and 321H as seamless tube to ASTM A213, seamless and welded pipe to ASTM A312, and instrumentation tube to A269, in sizes from 6 mm OD to 273 mm and 1/8 inch to 10 inch NPS.

What the Titanium Addition Does

Every austenitic stainless steel that is held in the 425 to 815 C band precipitates chromium carbides at its grain boundaries, leaving those boundaries chromium depleted and open to intergranular attack. Low-carbon grades such as 304L and 316L avoid this by having too little carbon to form the carbides, but that only works up to a point: at sustained high temperature carbon continues to diffuse and even an L grade eventually sensitises. It also costs strength, which matters most at temperature.

321 takes the other route. Titanium has a stronger affinity for carbon than chromium does, so titanium carbides form preferentially and chromium stays where it is needed. The result is a grade that can sit at 600 C indefinitely without losing its corrosion resistance, and that retains far better creep strength than 304L at the same temperature.

ApproachGradeWorks toCreep strength at 600 C
Standard carbon304, 316Sensitises in the 425-815 C bandModerate
Reduced carbon304L, 316LShort exposure onlyLow
Titanium stabilised321, 321HContinuous service to 815 C, oxidation to 900 CHigh
Niobium stabilised347, 347HSame band, better in aggressive weld serviceHigh
High chromium and nickel310SContinuous to 1,150 CVery high
Bundled stainless steel pipes strapped and tagged for export shipment on a warehouse dock

Welding and Heat Treatment

  • Filler: use ER347 or ER347Si. Titanium oxidises and is lost in the arc, so a 321 filler cannot reliably deliver a stabilised weld bead; niobium survives the transfer and stabilises the deposit instead.
  • Stabilise anneal: for severe service, a stabilise anneal at 870 to 900 C after solution annealing puts remaining carbon into titanium carbides before the part enters service. Specify it where the line will operate above 550 C in a corrosive medium.
  • Heat input: keep it moderate. 321 is more prone to hot cracking than 304, and high heat input widens the affected band.
  • Post-weld: pickle and passivate. Heat tint on a high-temperature line is chromium depleted and becomes the first scaling site.
  • Forming: elongation of 35 percent allows normal cold bending and tube forming. Work hardening is slightly higher than 304.

Our welding, cutting, bending and heat treatment capabilities cover these steps, described on the fabrication page.

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Stainless steel pipe being cut to length on a bandsaw in a fabrication shop
Technician checking stainless steel pipe wall thickness with an ultrasonic gauge

Applications

  • Superheater, reheater and economiser tubing in energy production plants, normally 321H
  • Refinery and petrochemical heater tubes and transfer lines
  • Expansion joints and bellows, where the grade's combination of formability and temperature resistance is hard to match
  • Exhaust manifolds, ducting and flexible sections in high-temperature service
  • Aircraft and gas turbine exhaust components for aerospace manufacturing bases
  • Chemical process lines carrying hot organic acids
  • Furnace and heat-treatment plant piping in machinery manufacturing workshops

Related products: 321 sheet, 321 coil, 310S pipe, 316Ti pipe, seamless pipe, and the full pipe and tube range.

FAQs

What is 321 stainless steel equivalent to?
The same material is designated UNS S32100, EN 1.4541 with steel name X6CrNiTi18-10, JIS SUS 321 and GB 0Cr18Ni10Ti. The H version is UNS S32109, EN 1.4878, JIS SUS 321H. Functionally the closest alternative is 347, EN 1.4550, which is stabilised with niobium rather than titanium and is often preferred for welded service. In terms of base composition, 321 is essentially 304 with a titanium addition, so it sits in the same 18-10 family.
Is 321 stainless better than 304?
Above about 425 C, decisively yes. 304 sensitises in the 425 to 815 C band, losing corrosion resistance at the grain boundaries, while 321's titanium addition prevents it and gives much better creep strength at temperature. Below 425 C, 304 is the better buy: the two have identical room-temperature strength, 304 is cheaper and more widely stocked, and the titanium brings no benefit. Choosing 321 for an ambient-temperature application spends money on a property that will never be used.
Is 321 stainless better than 316?
They solve different problems. 316 has 2 to 3 percent molybdenum and resists chlorides, seawater and reducing acids far better; 321 has no molybdenum and is not a chloride grade. 321 resists sensitisation and retains creep strength in the 425 to 815 C band, where 316 does not. Choose 316 for wet chloride service and 321 for hot service. If a line is both hot and chloride bearing, 316Ti, which is 316 with a titanium addition, or a duplex or nickel alloy is usually the answer.
What is 321 stainless steel?
It is an austenitic stainless steel with 17 to 19 percent chromium, 9 to 12 percent nickel and a titanium addition of at least five times the carbon plus nitrogen content. The titanium is the point: it combines with carbon to form stable titanium carbides so that chromium carbides do not form at grain boundaries when the metal is held between 425 and 815 C. That makes it the standard grade for superheater tubing, exhaust systems, expansion joints and heater tubes, in continuous service to about 815 C.
What is the difference between 321 and 321H?
Carbon content, and therefore creep strength. 321 allows up to 0.08 percent carbon with no minimum; 321H specifies 0.04 to 0.10 percent, deliberately keeping carbon higher. More carbon in solution means better strength under sustained load at high temperature, which is why ASME code work above about 540 C calls for the H grade. For non-load-bearing hot service, standard 321 is sufficient and slightly easier to weld.
Why is 321 welded with 347 filler?
Because titanium is lost across the welding arc. It oxidises readily and much of it does not survive the transfer from the filler wire into the weld pool, so a nominally 321 filler produces a bead that is not reliably stabilised. Niobium, the stabiliser in 347, transfers efficiently, so ER347 filler leaves a stabilised weld deposit on a 321 parent metal. This is standard practice and does not compromise the joint.
Do I need a stabilise anneal?
Only for severe service. A stabilise anneal, typically 870 to 900 C after solution annealing, forces remaining free carbon into titanium carbides before the component enters service, and it is worth specifying where the line will run above about 550 C in a corrosive medium, or where an intergranular corrosion test is part of the acceptance criteria. For general high-temperature use, solution-annealed material is standard.

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Walmay will help match the right stainless product form and specification for your application, confirm quantities and packing needs, and provide requested documents based on order requirements.

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