SUS, SS and TP Designations: Understanding 304, 304L, 316 and 316L
Dec 05, 2025
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Decoding SUS, SS and TP
Stainless steel designations look confusing because the same material appears under several systems. SUS is the Japanese Industrial Standard prefix for stainless steel, derived from Steel Use Stainless, and appears in JIS G4303 (bar), G4304 (hot-rolled plate) and G4305 (cold-rolled sheet). SS is a general abbreviation for stainless steel used in informal or commercial documents. TP is the prefix used in ASTM A312 for seamless and welded austenitic steel tube: TP304, TP304L, TP316 and TP316L are the tube designations of the grades known as 304, 304L, 316 and 316L in plate and sheet standards such as ASTM A240.
Thus SUS304 and TP304 are the same base composition in different product forms - SUS304 sheet per JIS G4305, TP304 tube per ASTM A312 - while the plain names 304, UNS S30400 and EN 1.4301 are used for the same grade in other contexts.
Grade Equivalents Across Systems
| Grade family | JIS | UNS / AISI | EN number | EN name |
|---|---|---|---|---|
| 304 | SUS304 | S30400 / 304 | 1.4301 | X5CrNi18-10 |
| 304L | SUS304L | S30403 / 304L | 1.4306 / 1.4307 | X2CrNi19-11 |
| 316 | SUS316 | S31600 / 316 | 1.4401 | X5CrNiMo17-12-2 |
| 316L | SUS316L | S31603 / 316L | 1.4404 | X2CrNiMo17-12-2 |
Chemical Composition
| Element | 304 / TP304 (wt. %) | 304L / TP304L (wt. %) | 316 / TP316 (wt. %) | 316L / TP316L (wt. %) |
|---|---|---|---|---|
| C | ≤ 0.08 | ≤ 0.030 | ≤ 0.08 | ≤ 0.030 |
| Si | ≤ 0.75 | ≤ 0.75 | ≤ 0.75 | ≤ 0.75 |
| Mn | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 |
| P | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 |
| S | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
| Cr | 18.00–20.00 | 18.00–20.00 | 16.00–18.00 | 16.00–18.00 |
| Ni | 8.00–10.50 | 8.00–12.00 | 10.00–14.00 | 10.00–14.00 |
| Mo | – | – | 2.00–3.00 | 2.00–3.00 |
Values follow JIS G4305 and ASTM A240 for sheet and plate; ASTM A312 tube uses the same ranges, with a carbon limit of 0.035% maximum permitted for TP304L and TP316L.
Mechanical Properties
| Property | TP304 / TP316 (ASTM A312) | TP304L / TP316L (ASTM A312) | SUS304 / SUS316 (JIS G4305) | SUS304L / SUS316L (JIS G4305) |
|---|---|---|---|---|
| Tensile strength, min | 515 MPa | 485 MPa | 520 MPa | 480 MPa |
| Yield strength, min | 205 MPa | 170 MPa | 205 MPa | 175 MPa |
Elongation minimums are 35% for A312 tube and 40% for JIS sheet above 1.0 mm thickness.
Which Grade for Which Service
304 / TP304: general corrosion service, food equipment, architectural trim and low-cost general engineering
304L / TP304L: welded fabrications where the weld zone cannot be solution annealed, thick sections and corrosive service
316 / TP316: chloride-bearing environments, marine, chemical and pharmaceutical service requiring molybdenum
316L / TP316L: the welded version of 316, preferred for chemical processing, seawater piping and any chloride service with welded joints
The molybdenum in the 316 family is the decisive difference: it raises pitting and crevice corrosion resistance substantially in seawater, brine, de-icing salts and many process acids. Where chlorides are present, 316 or 316L is specified over 304 even though both families have similar strength.
Product Forms and Standards
The same grades are produced in many forms under different standards: seamless and welded tube per ASTM A312 and A269, pipe per A312 and JIS G3459, sheet per A240 and JIS G4305, plate per A240 and JIS G4304, bar per A276 and JIS G4303, and fittings per A403. The TP prefix in the A312 designation specifically identifies tube, and SUS identifies JIS product. When ordering, the grade, product form, size and governing standard must all be stated together.
Frequently Asked Questions
What does SUS stand for in SUS304?
SUS stands for Steel Use Stainless, the JIS prefix for stainless steel. SUS304 is the Japanese designation of the 18-8 austenitic grade known as 304 under ASTM and 1.4301 under EN.
What does TP mean in TP304?
TP is the tube prefix used in ASTM A312 for seamless and welded austenitic stainless steel tube. TP304 is tube made of the 304 composition; the same composition in sheet is called 304 or UNS S30400.
Is TP304 the same as 304?
Yes, in composition and properties. TP304 is the tube form of grade 304 defined in ASTM A312, with the same chromium and nickel ranges and similar minimum mechanical properties as 304 sheet per ASTM A240.
What is the difference between 304L and 316L?
Both are low-carbon austenitic grades with 0.030% maximum carbon. The difference is molybdenum: 316L contains 2.00–3.00%, giving significantly better pitting and crevice corrosion resistance in chlorides, at a higher alloy cost.
How do JIS and ASTM grades correspond?
They are the same materials under different standards. SUS304 corresponds to UNS S30400 and EN 1.4301, SUS316 to S31600 and 1.4401, and the L versions correspond similarly. Mill certificates normally list the grade under all relevant systems.
Which grade is best for seawater service?
316L (UNS S31603) is the minimum practical grade for warm seawater; 304 will pit rapidly. For hot or high-chloride seawater, duplex grades such as UNS S32205 or super duplex UNS S32750 are specified instead.
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