What are the mechanical properties specified for JIS G3461 steel tube at room and elevated temperatures?

When selecting carbon steel tube for a boiler or heat exchanger service, the first specification engineers usually open is JIS G 3461. The standard lays down the mechanical properties that the tube must satisfy at room temperature and also defines the elevated-temperature test that confirms the material is still safe once it enters the steam or process side. This guide explains exactly what JIS G 3461 requires at room temperature, what the high-temperature test clause actually proves, and how the three grades — STB340, STB410 and STB510 — compare when the design temperature rises.

What JIS G 3461 covers

JIS G 3461 is the Japanese Industrial Standard for carbon steel tubes used in boiler and heat exchanger service. The latest revision (JIS G 3461:2023) covers seamless and electric-resistance-welded (ERW) carbon steel tubes in outside-diameter range 15.9 mm to 139.8 mm, in three grades: STB340, STB410 and STB510. Tubes are intended for water tubes, smoke tubes, superheater tubes, air-preheater tubes, condenser tubes, catalyzer tubes, and similar heat-transfer service in chemical and petroleum plants. The standard is not applied to fired-heater tubes or to low-temperature heat-exchanger tubes, which are covered by separate specifications.

Within our pressure tube portfolio, JIS G 3461 sits between the lower-temperature ASTM A179/A192 range and the higher-strength ASTM A335 alloy steel tube family, and it is the standard most often called out for utility boiler and refinery exchanger packages.

Room-temperature mechanical properties

The room-temperature table in clause 6 of JIS G 3461 specifies the minimum tensile strength, minimum yield point (or 0.2% proof stress Rp0.2 when the upper yield point is not pronounced), and the minimum elongation measured on No. 11 test pieces parallel to the tube axis.

Symbol of grade	Tensile strength, min. (N/mm²)	Yield point or proof stress, min. (N/mm²)	Elongation, min. % (OD < 10 / 10–20 / ≥ 20 mm)
STB340	340	175	27	30	35
STB410	410	255	17	20	25
STB510	510	295	17	20	25

A few practical points that often get missed in specifications:

Unless otherwise specified, the yield point to be reported is the upper yield point ReH. When the stress-strain curve does not show a pronounced upper yield, the 0.2% proof stress Rp0.2 is used instead.
For tubes of wall thickness below 8 mm tested on No. 12 pieces, the elongation is reduced by 1.5% for every 1 mm reduction in wall thickness, rounded to an integer in line with JIS Z 8401 Rule A.
For heat-exchanger tubes, the purchaser may specify a maximum tensile strength; the agreed ceiling is the minimum value in the table plus 120 N/mm².

These three grades also carry a hardness ceiling. The Rockwell B hardness (HRBW, average of three indentations) shall not exceed 77 for STB340, 79 for STB410, and 92 for STB510. The hardness test is not performed on tubes with wall thickness 2 mm or under, and for ERW tubes the indentation is taken outside the weld and heat-affected zone.

The elevated-temperature clause

Clause 6.2 of JIS G 3461 is the part of the standard that engineers most often ask about. The clause states that the standard specifies a high-temperature test in addition to the room-temperature tensile, flattening, flaring and impact tests. In other words, JIS G 3461 is written to confirm that the tube retains the mechanical behavior the designer is counting on once the wall metal reaches operating temperature, even though the standard does not publish a tabulated high-temperature allowable-stress list the way ASME does.

What this means in practice is that the elevated-temperature suitability of JIS G 3461 tube is established in three layers:

Material pedigree. Tubes are made from killed steel, with a defined chemical composition and a defined heat treatment for each combination of grade and manufacturing route (S-H, S-C, E-H, E-C, E-G). For example, STB510 in any route is supplied in the normalized condition, while STB340 and STB410 in the as-electric-resistance-welded (E-G) route are also normalized. Normalizing restores a uniform fine-grain structure that resists creep better than the as-rolled condition.
Room-temperature mechanical envelope. Because the room-temperature yield and tensile values are minimum values, the actual elevated-temperature strength envelope can be estimated from the room-temperature properties using the well-known Larson-Miller or ISO 9330 type relationships for carbon steel. A tube that meets 175 N/mm² at room temperature will retain roughly 60–70% of that value at 400 °C, which is the temperature range most JIS G 3461 superheater and water-wall tubes operate in.
High-temperature tensile or proof-stress test. When the purchase order specifies it, a hot tensile test is performed at the agreed temperature, and the result must meet the value agreed between purchaser and manufacturer. The clause explicitly leaves the elevated-temperature acceptance value to the order rather than fixing it in the standard, because the operating temperatures of utility boiler, refinery hydrocracker, ethylene cracking and other heat-exchanger services differ widely.

How the three grades behave as temperature rises

Carbon steel loses strength as temperature rises; this is true for every grade in JIS G 3461, but the absolute value of strength retained differs significantly. The room-temperature minimum yield strengths are 175, 255 and 295 N/mm² for STB340, STB410 and STB510 respectively. As a rule of thumb for killed carbon steel of these compositions:

Temperature	Typical retention of room-temperature yield for STB340 / STB410 / STB510
200 °C	≈ 90% / 88% / 87%
300 °C	≈ 78% / 75% / 73%
400 °C	≈ 65% / 62% / 60%
450 °C	≈ 55% / 52% / 50% (creep becomes significant above this point)

STB340 is the preferred choice for lower-temperature water-wall and economizer service where weldability and formability matter more than strength. STB410 is the workhorse grade for superheater tubes and most refinery exchanger shells operating up to about 400 °C. STB510 is reserved for the highest-temperature carbon steel service, typically final-stage superheaters and reheater lines; for sustained operation above 450–500 °C, designers normally step up to GB/T 5310 or ASTM A213 alloy tubes rather than relying on a carbon steel grade.

Manufacturing route and its effect on properties

The combination of tube-making method and finishing method is shown on every JIS G 3461 tube through the process symbol. The five standard routes are:

S-H – hot-finished seamless
S-C – cold-finished seamless
E-G – as electric-resistance-welded
E-H – hot-finished electric-resistance-welded
E-C – cold-finished electric-resistance-welded

The route matters for elevated-temperature service. Hot-finished seamless (S-H) gives the most uniform grain structure and the most predictable elevated-temperature behavior. Cold-finished seamless (S-C) tubes are usually supplied in the low-temperature-annealed, normalized or full-annealed condition, which restores the as-rolled grain before the tube enters high-temperature service. ERW tubes, particularly in the E-G and E-H routes, are normalized to dissolve the heat-affected zone of the weld and bring the weld metal and parent metal back to a similar microstructure. Without that normalize, an ERW tube would show a soft band in the weld on a high-temperature test.

For projects where the elevated-temperature certificate must be traceable, the mill test report should always list the route symbol, the heat-treatment condition, the room-temperature tensile/yield/elongation/hardness results, and (when ordered) the high-temperature tensile result at the agreed test temperature. This is standard practice in every carbon and carbon alloy steel tube shipment we issue for utility and EPC clients.

What the high-temperature test tells you — and what it does not

A JIS G 3461 high-temperature tensile test is a short-duration strength test at temperature. It does not directly measure creep rate or creep-rupture life. For services where the tube is expected to operate for 100,000 hours or more above about 400 °C, the engineer still needs to apply the elevated-temperature allowable-stress tables from ASME BPVC Section I or Section VIII, or the equivalent values from EN 12952, before the JIS G 3461 tube is accepted for the design. The JIS G 3461 elevated-temperature test is best understood as a quality-control check that the lot of tube matches the metallurgical pedigree expected for that grade and route; it is not by itself a long-life creep rating.

If you are evaluating JIS G 3461 against ASME or EN, it is worth knowing the cross-reference: JIS G 3461 is broadly equivalent to ASTM A192 (high-pressure boiler) and ISO 9329/ISO 9330, and is the basis of GB/T 5310 (China) and DIN 17175 (Germany) in terms of property envelope. Forged fittings that match these tubes are covered in our butt-weld fittings range, so the full piping package can be specified against one mechanical-property baseline.

Practical checklist for procurement

When you order JIS G 3461 tube for elevated-temperature service, the purchase order should clearly state the items below so the mill test report answers every question an inspector will ask:

Grade (STB340, STB410 or STB510) and route symbol (for example S-C, E-H)
Outside diameter, wall thickness, length and length tolerance class
Required heat-treatment condition (as-manufactured, low-temperature anneal, normalize, full anneal)
Room-temperature test requirements: tensile, flattening, flaring, hardness, impact if applicable
Elevated-temperature test temperature and acceptance value, if required
Hydrostatic test pressure or, by default, the value calculated from P = 2st/D with s = 60% of the minimum yield point
Non-destructive test method (UT per JIS G 0582 class UD, or ET per JIS G 0583 class EY) and acceptance level
Mill test certificate type (JIS G 0321 Table 1 is the standard 3.1-style certificate; higher levels available on request)

With those items locked down, JIS G 3461 tube is a robust and well-documented choice for utility boiler tubing, refinery heat-exchanger tubing, and petrochemical process service up to the carbon-steel temperature limit. Where the design pushes into alloy territory, the ASTM A335 P-series and GB/T 5310 ranges from the same mill extend the same documentation discipline to higher temperatures and pressures.

FAQ

Does JIS G 3461 publish an elevated-temperature yield strength table?

No. JIS G 3461 publishes only the room-temperature minimum tensile, yield, elongation and hardness values. The standard requires a high-temperature test to be performed when specified in the order, and the acceptance value is agreed between purchaser and manufacturer rather than being fixed in the standard. Engineers usually obtain elevated-temperature allowable stresses from ASME, EN or the corresponding national pressure-vessel code.

Which grade is the right choice for a 400 °C superheater?

STB410 is the usual selection. It gives roughly 250 N/mm² of room-temperature minimum yield and retains about 60–70% of that at 400 °C, which covers most saturated and slightly superheated steam duties. STB510 is used for higher final-steam temperatures, but above about 500 °C an alloy tube is normally more cost-effective than a thicker carbon steel tube.

Is a JIS G 3461 ERW tube acceptable for elevated-temperature service?

Yes, provided the tube is supplied in the normalized condition (route E-H or E-G with a normalize) and the purchaser has ordered the high-temperature test. The normalize erases the heat-affected zone of the weld and gives a uniform ferrite-pearlite microstructure across the wall section.

How does JIS G 3461 compare with ASTM A192?

JIS G 3461 and ASTM A192 cover the same product type (seamless carbon steel boiler and heat-exchanger tube) at similar strength levels. STB340 is close to ASTM A192 in minimum tensile, while STB410 and STB510 sit above it. For mixed ASME/JIS projects the two are routinely cross-referenced, with the choice driven by the design code rather than by metallurgy.