Stainless Steel Pipe: Grades 304, 316, ASTM A312 Specifications & Applications
When carbon steel cannot survive the service environment — corrosive chemicals, seawater, high-purity process fluids, sanitary applications, or extreme temperatures — stainless steel pipe is the specification. It costs 3–5 times more than carbon steel pipe, so getting the grade right is critical: specifying 316 where 304 would work wastes money, while specifying 304 in a chloride environment guarantees pitting failure within months.
ASTM A312 is the standard that governs stainless steel pipe for industrial, chemical, and process applications. This guide covers the grades, seamless vs welded options, sizes, schedules, and selection criteria you need to specify stainless steel pipe correctly.
ASTM A312: The Standard
ASTM A312 (and its ASME equivalent SA312) is the specification for seamless, welded, and heavily cold-worked austenitic stainless steel pipe intended for high-temperature and general corrosive service. It is the most commonly referenced specification for stainless steel process piping worldwide.
What A312 covers:
Seamless pipe (SMLS) — manufactured without welding, from solid billet
Welded pipe (WLD) — manufactured by automatic welding without filler metal addition, then solution annealed
Heavily cold-worked pipe (HCW) — welded pipe that is cold-worked to increase wall thickness uniformity
Size range: NPS 1/8" (DN 6) to NPS 30" (DN 750). Larger sizes are covered by ASTM A358 (electric fusion welded pipe for high-temperature service) and ASTM A778 (welded pipe for general corrosive service).
Schedules: SCH 5S, 10S, 40S, and 80S are the most common. Schedule 10S is standard for most process piping applications up to approximately 10 bar. Schedule 40S is used for higher pressures. Schedule 80S for the highest pressures or where extra wall thickness is needed.
Grades: 304 vs 316 and the L Variants
Grade | UNS | Key Feature | Primary Application |
|---|---|---|---|
TP304 | S30400 | General purpose austenitic SS | Broad industrial and architectural |
TP304L | S30403 | Low carbon 304 — prevents sensitization in welds | Standard for welded process piping |
TP316 | S31600 | Contains 2–3% molybdenum — chloride/pitting resistance | Marine, chemical, coastal |
TP316L | S31603 | Low carbon 316 — best weldability + corrosion resistance | Standard for corrosive/welded service |
TP321 | S32100 | Titanium-stabilized — resists intergranular corrosion at high temp | Refinery, exhaust, high-temp process |
TP310S | S31008 | High chromium/nickel — oxidation resistance to 1,100°C | Furnace tubes, high-temp equipment |
TP347 | S34700 | Niobium-stabilized — similar to 321 for high-temp | Nuclear, aerospace, high-temp process |
The 80/20 rule: TP304L and TP316L account for approximately 80% of all stainless steel pipe ordered for industrial projects. TP304L is the default unless chlorides are present. TP316L is specified whenever chlorides, seawater, or aggressive chemicals are involved.
Always specify the L grade for pipe that will be welded. The low carbon content (0.03% max vs 0.08% for standard grades) prevents chromium carbide precipitation during welding, which protects against intergranular corrosion in the heat-affected zone. The cost difference between L and standard grades is negligible. There is no practical reason to specify TP304 or TP316 (without L) for welded piping.
Chemical Composition
Element | TP304L | TP316L | TP321 |
|---|---|---|---|
Carbon (C) max | 0.035% | 0.035% | 0.08% |
Chromium (Cr) | 18.0–20.0% | 16.0–18.0% | 17.0–19.0% |
Nickel (Ni) | 8.0–12.0% | 10.0–14.0% | 9.0–12.0% |
Molybdenum (Mo) | — | 2.0–3.0% | — |
Titanium (Ti) | — | — | 5×C min |
Manganese (Mn) max | 2.0% | 2.0% | 2.0% |
Silicon (Si) max | 0.75% | 0.75% | 0.75% |
The difference that matters: 316L has molybdenum. 304L does not. Molybdenum provides pitting and crevice corrosion resistance in chloride-containing environments. If your process fluid contains any chloride (seawater, brackish water, hydrochloric acid, chlorinated solvents, even chlorinated tap water in some cases), specify 316L.
Mechanical Properties (ASTM A312)
Property | TP304L | TP316L | TP321 |
|---|---|---|---|
Tensile strength, min | 485 MPa (70 ksi) | 485 MPa (70 ksi) | 515 MPa (75 ksi) |
Yield strength (0.2%), min | 170 MPa (25 ksi) | 170 MPa (25 ksi) | 205 MPa (30 ksi) |
Elongation in 50mm, min | 35% | 35% | 35% |
Hardness, max | 192 HBW | 192 HBW | 192 HBW |
Seamless vs Welded Stainless Steel Pipe
Factor | Seamless (SMLS) | Welded (WLD) |
|---|---|---|
Manufacturing | Extruded from solid billet — no weld seam | Plate/strip rolled and welded — visible weld seam (ground smooth after) |
Strength | Uniform wall — no weak point | Weld seam is tested and annealed — approaches seamless strength |
Wall thickness uniformity | Slight eccentricity possible | Very uniform (from flat strip) |
Surface finish | Good | Excellent (from cold-rolled strip) |
Available sizes | NPS 1/8" to 24" (limited above 16") | NPS 1/8" to 30"+ (easier in large diameters) |
Cost | Higher — 20–40% premium over welded | Lower — standard for most process piping |
Lead time | Longer (specialty production) | Shorter (widely stocked) |
When required | High-pressure, critical service, code requirements | Standard process piping, general corrosive service |
For most industrial projects: Welded pipe (ASTM A312, solution annealed and pickled) is the standard specification. The weld seam is made without filler metal by automatic welding, then the entire pipe is solution annealed (heated to 1,040–1,100°C and quenched) to dissolve any carbides and restore full corrosion resistance. After annealing, the weld is virtually indistinguishable from the parent material in terms of corrosion resistance.
Seamless pipe is specified when: the design code requires it, the service is critical (nuclear, high-pressure steam), or the application involves severe cyclic fatigue where a weld seam could be a crack initiation point.
Common Sizes and Schedules
NPS | OD (mm) | SCH 10S Wall (mm) | SCH 40S Wall (mm) | SCH 80S Wall (mm) |
|---|---|---|---|---|
1/2" | 21.3 | 2.11 | 2.77 | 3.73 |
3/4" | 26.7 | 2.11 | 2.87 | 3.91 |
1" | 33.4 | 2.77 | 3.38 | 4.55 |
1-1/2" | 48.3 | 2.77 | 3.68 | 5.08 |
2" | 60.3 | 2.77 | 3.91 | 5.54 |
3" | 88.9 | 3.05 | 5.49 | 7.62 |
4" | 114.3 | 3.05 | 6.02 | 8.56 |
6" | 168.3 | 3.40 | 7.11 | 10.97 |
8" | 219.1 | 3.76 | 8.18 | 12.70 |
10" | 273.1 | 4.19 | 9.27 | 12.70 |
12" | 323.9 | 4.57 | 10.31 | 12.70 |
16" | 406.4 | 4.78 | 12.70 | — |
20" | 508.0 | 5.54 | 12.70 | — |
24" | 609.6 | 6.35 | 14.27 | — |
Schedule 10S is the workhorse for stainless steel process piping. It provides adequate wall thickness for most low-to-moderate pressure applications and is the most commonly stocked schedule. Schedule 40S is used for higher pressures or where the piping code requires additional wall thickness.
Grade Selection Guide
Application | Recommended Grade | Why |
|---|---|---|
General chemical processing | TP304L | Cost-effective, broad corrosion resistance |
Chloride-containing chemicals | TP316L | Molybdenum resists pitting and crevice corrosion |
Food and beverage processing | TP304L (or 316L for dairy/brewing) | Hygienic, easy to clean, FDA compliant |
Pharmaceutical manufacturing | TP316L (electropolished) | ASME BPE compliant, superior cleanability |
Seawater / marine applications | TP316L minimum | Chloride pitting resistance mandatory |
Water treatment (chlorinated water) | TP316L | Chlorinated water attacks 304 |
Pulp and paper | TP316L or TP317L | Bleaching chemicals contain chlorides |
Refinery process piping | TP321 or TP347 | Stabilized grades resist polythionic acid SCC |
High-temperature service (500–800°C) | TP321 or TP310S | 321 resists sensitization; 310S resists oxidation |
Cryogenic service (-196°C) | TP304L or TP316L | Austenitic structure retains toughness at cryo temps |
Steam systems | TP304L or TP316L | Good oxidation resistance to ~800°C |
Potable water | TP304L | Standard for drinking water contact |
Desalination | TP316L or duplex 2205 | High chloride concentration demands Mo content |
Nuclear applications | TP304L or TP316L (nuclear grade) | Per ASME Section III requirements |
Related Standards
Standard | Scope |
|---|---|
ASTM A312 / SA312 | Seamless and welded austenitic SS pipe (primary standard) |
ASTM A358 / SA358 | Electric fusion welded austenitic SS pipe (large diameter) |
ASTM A778 | Welded austenitic SS pipe for general corrosive service |
ASTM A269 | Seamless and welded austenitic SS tubing (small diameter instrumentation) |
ASTM A213 | Seamless austenitic SS boiler/heat exchanger tubes |
ASTM A182 | Forged SS fittings and flanges (matching pipe grades) |
ASTM A403 | Wrought austenitic SS butt-weld fittings |
ASME B36.19 | Stainless steel pipe dimensions (schedule wall thicknesses) |
How to Order Stainless Steel Pipe
1. Standard: ASTM A312 (or SA312 for ASME code work)
2. Grade: TP304L, TP316L, TP321, or other — specify with UNS number if needed
3. Type: Seamless (SMLS) or Welded (WLD)
4. Size: NPS (e.g., NPS 4") or DN (e.g., DN 100)
5. Schedule: SCH 10S, 40S, or 80S
6. Length: Random lengths (typically 5.8m or 6.0m single random), double random, or cut-to-length
7. End finish: Plain end (PE), beveled end (BE) for butt welding
8. Surface: Solution annealed and pickled (SA&P) — standard for A312
9. Documentation: EN 10204 Type 3.1 MTC with heat number, chemical composition, and mechanical test results
10. Additional testing: PMI (Positive Material Identification), intergranular corrosion test (ASTM A262 Practice E for critical service), hydrostatic test certificate
Example order:
500m — ASTM A312 TP316L, Welded, NPS 4" SCH 10S, Solution annealed & pickled, Random lengths 6.0m, Beveled ends, EN 10204 Type 3.1 MTC, PMI tested.
Supply from Kasko Makine
Kasko Makine supplies stainless steel pipe in all common grades, sizes, and schedules:
Grades: TP304, TP304L, TP316, TP316L, TP321, TP310S, TP347, duplex 2205, super duplex 2507
Standard: ASTM A312 / ASME SA312, ASTM A358, ASTM A778
Type: Seamless and welded
Sizes: NPS 1/8" to NPS 30" (DN 6 to DN 750)
Schedules: SCH 5S, 10S, 40S, 80S
Surface: Solution annealed and pickled (standard), electropolished (for pharma/biotech)
We also supply stainless steel plate (A240), stainless steel fittings (A403), stainless steel flanges (A182), and stainless steel fasteners (A193 B8/B8M) — complete stainless steel material packages for your piping project.
All pipe supplied with EN 10204 Type 3.1 mill test certificates. PMI testing, intergranular corrosion testing, and third-party inspection available on request.
FAQ SCHEMA
Q: What is ASTM A312 stainless steel pipe?
A: ASTM A312 is the standard specification for seamless, welded, and heavily cold-worked austenitic stainless steel pipe intended for high-temperature and general corrosive service. It covers grades TP304, TP304L, TP316, TP316L, TP321, and others in sizes NPS 1/8" to NPS 30" and schedules 5S through 80S. The ASME equivalent is SA312.
Q: What is the difference between TP304L and TP316L pipe?
A: TP316L contains 2–3% molybdenum, which provides significantly better resistance to chloride pitting and crevice corrosion. TP304L has no molybdenum. Specify TP304L for general corrosive service without chlorides. Specify TP316L whenever chlorides are present — seawater, coastal environments, chlorinated water, or chemical plants handling chloride-containing solutions.
Q: Should I use seamless or welded stainless steel pipe?
A: Welded pipe (ASTM A312, solution annealed and pickled) is the standard for most industrial process piping. It is lower cost, more readily available, and has excellent wall thickness uniformity. Seamless pipe is specified for high-pressure critical service, nuclear applications, or where the design code specifically requires seamless construction.
Q: What schedule is standard for stainless steel pipe?
A: Schedule 10S is the most common schedule for stainless steel process piping. It provides adequate wall thickness for most low-to-moderate pressure applications and is the most widely stocked. Schedule 40S is used for higher pressures. Schedule 80S for the highest pressure requirements. Always verify the required schedule with your piping design engineer.
Q: Why specify the L grade (304L, 316L) instead of standard (304, 316)?
A: The L grades have lower maximum carbon content (0.035% vs 0.08%), which prevents chromium carbide precipitation during welding. This protects the weld heat-affected zone from intergranular corrosion. For any stainless steel pipe that will be welded, the L grade should always be specified. The cost difference is negligible.
Request stainless steel pipe pricing — send us your grade, size, schedule, quantity, and any special requirements to info@kaskomakine.com or WhatsApp +90 (537) 521 1399. We respond within 24 hours and deliver to projects across Africa, the Middle East, Central Asia, and beyond.
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