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When engineers size a JIS G3463 steel tube for a boiler, condenser, or heat-exchanger bundle, the most common short-list comes down to two names: SUS304TB and SUS316TB. They look similar on a spec sheet, they both ship as seamless or welded austenitic tubes, and they cost differently. This guide walks through the chemistry, mechanical properties, corrosion behavior, fabrication, and code limits that actually separate them in service — so you can match the right grade to the right fluid.
1. What JIS G3463 Actually Covers
JIS G3463 is the Japanese Industrial Standard for stainless steel boiler and heat-exchanger tubes. It defines seamless (TB) and welded tubes used in pressure-bearing service where the metal is exposed to hot water, steam, or aggressive process fluids. The standard lists a family of austenitic grades, including SUS304TB, SUS304LTB, SUS309TB, SUS310TB, SUS316TB, SUS316LTB, SUS317TB, SUS321TB, and SUS347TB, with specified chemical composition, tensile strength, elongation, hardness, flattening, reverse flattening, and hydrostatic or eddy-current test requirements.
Both SUS304TB and SUS316TB sit inside that family. They are austenitic, non-magnetic in the annealed condition, and supplied in the solution-annealed (bright annealed or pickled) state for optimum corrosion resistance.
2. Chemical Composition: Where the Two Grades Actually Diverge
The practical difference between these two grades starts with chemistry. The published JIS G3463 limits are summarized in the table below (values are maximum unless a range is shown).
| Element | SUS304TB (typical limits) | SUS316TB (typical limits) |
|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.08 |
| Silicon (Si) | ≤ 1.00 | ≤ 1.00 |
| Manganese (Mn) | ≤ 2.00 | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.040 | ≤ 0.040 |
| Sulfur (S) | ≤ 0.030 | ≤ 0.030 |
| Chromium (Cr) | 18.00 – 20.00 | 16.00 – 18.00 |
| Nickel (Ni) | 8.00 – 11.00 | 10.00 – 14.00 |
| Molybdenum (Mo) | — | 2.00 – 3.00 |
Read that table closely and the real story is two-fold:
- 316 trades chromium for nickel and adds molybdenum. The 2 – 3 % Mo is the headline difference. Molybdenum is what gives 316 its edge in chloride-rich and acidic environments.
- 304 has a wider Cr window. With up to 20 % Cr, 304 forms a slightly more robust passive film in purely oxidizing, low-chloride media — but it loses that advantage the moment chlorides enter the picture.
3. Mechanical Properties and Dimensional Envelope
Under JIS G3463 the two grades share the same minimum tensile and yield targets because both are standard austenitic 18 Cr-type compositions. The headline mechanical limits are:
- Tensile strength: ≥ 520 MPa
- 0.2 % proof stress (yield): ≥ 205 MPa
- Elongation: ≥ 35 % (for the standard 50 mm gauge length on most sizes)
- Hardness: typically ≤ 90 HRB in the solution-annealed condition
Where 316 has a real engineering edge is at elevated temperature. Molybdenum-bearing austenitic stainless steels retain strength and creep resistance slightly better than 304 in the 500 – 700 °C window, which is one reason 316TB shows up in superheater sections and refinery heater coils.
Both grades are produced to the same dimensional envelope under JIS G3463, with outside diameters typically from about 15.9 mm up to 139.8 mm and wall thicknesses tied to the ASME B36.19M size schedule. Tubes can be supplied as seamless (hot- or cold-finished) or as welded and solution-annealed, with the suffix "TB" denoting the boiler / heat-exchanger tube use-case rather than a separate dimensional class.
4. Corrosion Behavior in Real Service
If the chemical table looks almost interchangeable, the corrosion section is where SUS304TB and SUS316TB clearly separate. Three service conditions matter most for boiler and heat-exchanger duty:
4.1 Pitting and Crevice Corrosion in Chloride Media
Molybdenum stabilizes the passive layer against chloride attack. The widely used pitting resistance equivalent (PREN = %Cr + 3.3 × %Mo + 16 × %N) gives 304 a value near 18 and 316 a value near 24 – 25. In practice that means:
- Cooling water with even modest chloride content (a few hundred ppm) starts to pit 304 long before it pits 316.
- Seawater-cooled condensers and plate-heat-exchanger bundles almost always specify 316 or higher.
- White rust and under-deposit attack in storage or hydrostatic test water are far less common on 316.
4.2 General Corrosion in Acidic Process Streams
In dilute sulfuric, phosphoric, and many organic acids, the Mo addition lets 316 outperform 304 by a noticeable margin at low and mid temperatures. 304 remains adequate for clean steam, demineralized water, and atmospheric condensate, but for chemical processing lines SUS316TB is the safer default.
4.3 Stress Corrosion Cracking (SCC)
Both grades can suffer chloride-induced SCC above roughly 60 °C, and neither is immune. In practice, 316 does not eliminate SCC risk; it shifts the failure mode. If SCC is the dominant concern, the usual upgrade path is to a higher-nickel grade (e.g., 321, 347) or a duplex stainless rather than another step up within the 300 series.
5. Fabrication, Welding, and Bending
Both grades behave predictably in tube fabrication:
- Forming and bending. Both are suitable for U-bend heat-exchanger tubes; 316 is slightly more work-hardening, so spring-back is marginally higher per pass.
- Welding. Both weld cleanly by TIG, plasma, and laser. For 304, an over-alloyed filler such as ER308L is typical. For 316, ER316L filler is used. 316L variants (extra-low carbon) are often preferred where the tube will see post-weld sensitization risk in the 450 – 850 °C range.
- Pickling and passivation. Both grades need a proper pickling and passivation step after fabrication to restore the chromium-rich surface layer. 316 benefits more visibly from this step in chloride service.
6. Common Application Snapshots
Pulling the above into a quick reference, the most common service placements are:
- SUS304TB — saturated steam lines, hot-water boilers, instrument air and gas lines, food and dairy heat exchangers, general chemical piping in low-chloride service, HVAC and district heating condensate.
- SUS316TB — seawater-cooled condensers, brine heaters, pharmaceutical and biotech process lines, pulp-and-paper digesters, refinery overhead condensers, marine and offshore process piping, and any chloride-bearing cooling circuit.
7. Cost, Availability, and Lead Time
Because both grades are produced on overlapping production lines, the price gap is driven almost entirely by the nickel and molybdenum content of 316. Expect a noticeable, but not dramatic, premium for SUS316TB over SUS304TB. Lead times are similar for standard sizes, but 316 in thick walls or tight B36.19M sizes can stretch out because of the extra mill capacity that 304 takes in commodity boiler service.
For project buyers, the right approach is usually to dual-source both grades through one supplier that controls the mill. A single mill certificate (MTC) per heat, with traceable chemical and mechanical data, simplifies the quality package for EPC, ASME U-stamp, or PED audits.
8. Specification Checklist Before You Order
- Confirm JIS G3463 edition and any project-specific addenda.
- Pin down size: outside diameter, wall thickness, length (random, fixed, or U-bend).
- State delivery condition: solution annealed, pickled, bright annealed, or polished.
- List the test package: hydrostatic, eddy current, ultrasonic, PMI, intergranular corrosion (e.g., ASTM A262 Practice E for 316L if sensitization is in scope).
- Request EN 10204 3.1 or 3.2 mill certificates with full chemical and mechanical results.
- For chloride service, ask for a measured PREN value rather than a nominal composition callout.
9. Frequently Asked Questions
Is SUS316TB always better than SUS304TB?
Not always. In clean steam, hot water, and atmospheric service, 304 performs identically to 316 and is more economical. The advantage of 316 is in chloride, acid, and marine exposure, not in routine boiler duty.
Can I weld SUS304TB to SUS316TB tubes?
Yes. Use a 316L filler (ER316L) for the joint to match the more corrosion-resistant side, and run a post-weld passivation to restore the surface film.
Do both grades meet ASME equivalent specifications?
SUS304TB is the JIS equivalent of ASTM A213 / A249 TP304, and SUS316TB aligns with TP316. Procurement documents often accept dual certification, which is useful for international projects.
What temperature ceiling applies to each grade?
Both grades are suitable for continuous service up to about 870 °C in dry air, but for sustained pressure-bearing service the practical limit is closer to 600 – 650 °C. 316 retains slightly more strength in that upper band.
10. Sourcing JIS G3463 Tubes From a Single Supplier
Whether the project calls for SUS304TB, SUS316TB, or both within the same heat-exchanger bundle, the most efficient path is to work with a mill that holds the full JIS G3463 size range and ships complete MTC packages. That removes the risk of mixed-quality lots and shortens the inspection loop for EPC and ASME U-stamp projects.
EZ Steel Industrial supplies JIS G3463 stainless steel tubes across STB340, SUS304TB, SUS316TB, and other grades from a Yangzhou production base, with optional U-bend forming, finning, and project-level bundling for heat efficiency tube assemblies. For tube-only inquiries, the stainless steel tube catalog covers boiler, heat-exchanger, and general-service sizes, and full alloy steel tube lines are available where higher-temperature creep strength is required.
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