304/304L stainless steel seamless pipe is presented here as two distinct ASME SA-312 grades, not as one interchangeable commercial label. TP304 is UNS S30400 and TP304L is UNS S30403; the matching ASTM document is A312/A312M. Both are austenitic 18Cr-8Ni pipe grades for high-temperature and general corrosive service, but their carbon limits and guaranteed strength levels differ.
Site A’s pipe focus is the purchase-order chain: grade and UNS, actual OD and wall, manufacturing route, solution anneal, and the tests needed to connect the delivered length to its heat record. NPS is a size designation, not a measured bore. Pressure capability must be calculated from the ordered wall and the governing piping code rather than inferred from ‘Schedule 40’ alone.
Grade, UNS and Specification
| Grade | UNS | ASME / ASTM designation | Carbon route | Minimum tensile / yield |
|---|---|---|---|---|
| TP304 | S30400 | SA-312 / A312 TP304 | 0.08 % max | 75 / 30 ksi (515 / 205 MPa) |
| TP304L | S30403 | SA-312 / A312 TP304L | 0.035 % max | 70 / 25 ksi (485 / 170 MPa) |
Chemical Composition (ASME SA-312 Table 1)
| Element, weight % | TP304 (S30400) | TP304L (S30403) |
|---|---|---|
| Carbon, max | 0.08 | 0.035 |
| Manganese, max | 2.00 | 2.00 |
| Phosphorus, max | 0.045 | 0.045 |
| Sulfur, max | 0.030 | 0.030 |
| Silicon, max | 1.00 | 1.00 |
| Chromium | 18.0–20.0 | 18.0–20.0 |
| Nickel | 8.0–11.0 | 8.0–13.0 |
| Molybdenum / titanium / nitrogen | No requirement | No requirement |
Tensile Requirements (ASME SA-312 Table 4)
| Grade | Tensile min, ksi (MPa) | 0.2 % yield min, ksi (MPa) | Elongation longitudinal / transverse, min % |
|---|---|---|---|
| TP304 | 75 (515) | 30 (205) | 35 / 25 |
| TP304L | 70 (485) | 25 (170) | 35 / 25 |
Size Range and OD × Wall
| NPS | OD, in. (mm) | Sch 5S wall, in. (mm) | Sch 10S wall, in. (mm) | Sch 40S wall, in. (mm) | Sch 80S wall, in. (mm) |
|---|---|---|---|---|---|
| 1/2 | 0.84 (21.34) | 0.065 (1.65) | 0.083 (2.11) | 0.109 (2.77) | 0.147 (3.73) |
| 3/4 | 1.05 (26.67) | 0.065 (1.65) | 0.083 (2.11) | 0.113 (2.87) | 0.154 (3.91) |
| 1 | 1.315 (33.4) | 0.065 (1.65) | 0.109 (2.77) | 0.133 (3.38) | 0.179 (4.55) |
| 1-1/2 | 1.9 (48.26) | 0.065 (1.65) | 0.109 (2.77) | 0.145 (3.68) | 0.2 (5.08) |
| 2 | 2.375 (60.33) | 0.065 (1.65) | 0.109 (2.77) | 0.154 (3.91) | 0.218 (5.54) |
| 3 | 3.5 (88.9) | 0.083 (2.11) | 0.12 (3.05) | 0.216 (5.49) | 0.3 (7.62) |
| 4 | 4.5 (114.3) | 0.083 (2.11) | 0.12 (3.05) | 0.237 (6.02) | 0.337 (8.56) |
| 6 | 6.625 (168.28) | 0.109 (2.77) | 0.134 (3.4) | 0.28 (7.11) | 0.432 (10.97) |
| 8 | 8.625 (219.08) | 0.109 (2.77) | 0.148 (3.76) | 0.322 (8.18) | 0.5 (12.7) |
| 10 | 10.75 (273.05) | 0.134 (3.4) | 0.165 (4.19) | 0.365 (9.27) | 0.5 (12.7) |
| 12 | 12.75 (323.85) | 0.156 (3.96) | 0.18 (4.57) | 0.375 (9.52) | 0.5 (12.7) |
Selected rows from ANSI B36.19 Table 1 as reproduced in the ASME library. NPS is a designation; the OD shown is the controlling outside diameter. Other schedules and sizes are subject to the specification and enquiry. Wall tolerance is governed separately by SA-312 Table 3.
Manufacturing Route and Heat Treatment
SA-312 permits seamless, straight-seam welded and heavily cold-worked pipe; this page addresses the seamless route. Hot piercing or extrusion is followed by hot or cold finishing and solution heat treatment. TP304 and TP304L fall under Table 2’s general 1900 °F [1040 °C] minimum row, followed by water quench or rapid cooling. Section 6.1.7 does not make pickling mandatory after bright annealing; the required surface route should therefore be stated on the order.
Inspection, Testing and Certification
- Heat and product verification: review heat number, UNS/grade, chemical analysis and the specified mechanical result against the named standard, not against a generic grade datasheet.
- Pipe tests: SA-312 Sections 11 and 13 cover tension/flattening and hydrostatic or nondestructive electric examination as applicable. Additional UT, eddy current, impact, PMI or hardness requirements must be defined on the order.
- Dimensions and surface: confirm actual OD, wall, length, end preparation and surface condition. Hydrostatic P = 2St/D is not a design-pressure calculation.
- Documentation: request the MTC route at enquiry stage. EN 10204 3.1 or 3.2, purchaser witnessing and third-party inspection are order-specific options to be confirmed in the quotation, not an automatic certificate bundle.
Packing & Delivery
Plastic end caps; steel frames or wooden crates for larger diameters; VCI protective wrapping where required. Beveled or plain ends are confirmed with the order. Marking should maintain the link between each length, standard, grade/UNS, size and heat number. Delivery schedule, quantity, MOQ and price are confirmed only against a specific enquiry.
Applications
General chemical and petrochemical utilities, food and beverage process lines, pharmaceutical non-sanitary utilities, water and brine systems, structural pipework, heat-transfer auxiliaries, and fabricated manifolds where the designer has qualified 304-series corrosion performance. For hygienic or instrumentation tubing, use the product-specific tubing standard rather than assuming A312 pipe covers it.
Technical Notes
1. The L grade changes more than carbon. SA-312 lowers TP304L carbon to 0.035 % max but also changes its nickel window to 8.0–13.0 %, compared with 8.0–11.0 % for TP304. Its guaranteed tensile and yield minima fall from 75/30 ksi to 70/25 ksi. A substitution approved only on corrosion grounds can therefore still be wrong on design strength or certificate review.
2. Sensitization control is a time-temperature question, not a slogan. Lower carbon reduces the amount available for chromium-carbide formation during welding, but it does not make every heat input or every service cycle harmless. SA-312 Table 2 note C links the cooling requirement to Practices A262 Practice E, while the test itself is invoked only when Supplementary S7 is ordered. If intergranular-corrosion verification is project-critical, write S7 and the test condition into the purchase order.
3. Filler and wall belong in the same technical review. SA-312 Table 6 lists ER308 for TP304 and ER308L for TP304L. Separately, Table 3 controls wall-thickness variation and SA-999 uses P = 2St/D for the hydrostatic relationship. That hydrostatic formula is a mill-test relationship, not a substitute for B31 design rules, corrosion allowance, weld-joint factors or a project pressure-temperature rating.
Related: 316/316L seamless pipe for the Mo-bearing alternative, and the B36.19 dimensions guide.
Frequently Asked Questions
Are 304 and 304L the same under ASME SA-312?
No. TP304 is S30400 with 0.08 % carbon max and 75/30 ksi minimum tensile/yield. TP304L is S30403 with 0.035 % carbon max and 70/25 ksi minimum tensile/yield.
What solution anneal applies to 304/304L seamless pipe?
SA-312 Table 2 places both in the general 1900 F [1040 C] minimum requirement, followed by water quenching or rapid cooling.
Does the page give a working-pressure rating?
No single rating is valid without the ordered OD, wall, temperature, corrosion allowance and design code. SA-999’s P = 2St/D is a hydrostatic-test relationship, not a complete service-rating calculation.
Which filler metals are listed for the two grades?
SA-312 Table 6 lists ER308 for TP304 and ER308L for TP304L. Welding procedure qualification and project requirements still apply.
Can an EN 10204 3.2 certificate be requested?
State EN 10204 3.1 or 3.2 and any third-party inspection requirement in the enquiry so the inspection route can be confirmed in the quotation; do not assume 3.2 is automatic.
