JIS G 3461 Steel Tube Application Guide: Matching STB340, STB410 and STB510 to Your Boiler, Superheater and Heat Exchanger Service

Two procurement engineers, one datasheet, two answers

A procurement engineer at a Southeast-Asian refinery writes a tube RFQ for a waste-heat boiler. The datasheet says “carbon steel boiler tube, JIS standard, 50.8 mm OD x 4.0 mm wall, 6 m random length, hydrostatic test, MTC EN 10204 3.1.” She emails it to two approved suppliers. One quotes STB340-S-H, the other quotes STB410-S-C at a 22% premium. Both meet the datasheet. Both are technically right. Neither is more helpful than a price list.

JIS G 3461 is unusually permissive in three places: three strength grades (STB340, STB410, STB510), five manufacturing routes (S-H, S-C, E-G, E-H, E-C), and a negotiable heat-treatment condition for two of the three grades. The standard is not ambiguous — it is silent on which combination a given service needs. The selection work is on the buyer, not the standard.

This guide walks through how a B2B buyer turns a one-line JIS G 3461 datasheet into a specific grade, forming route and heat-treatment call, using only information that already lives in the operating envelope of the equipment.

1. What JIS G 3461 actually covers — and what it does not

JIS G 3461 is the Japanese Industrial Standard for carbon steel tubes used in boilers and heat exchangers — a jis g3461 steel tube order is the default code call for any carbon-steel boiler or exchanger tube on a JIS-spec datasheet. The current published edition is the 2023 revision, which tightened chemical limits, clarified the heat-treatment table, and aligned the test methods with the rest of the JIS G 3460 family. The standard covers both seamless and electric-resistance-welded (ERW) carbon steel tubes for service at elevated temperature and pressure — typically economizer inlet lines, superheater tubing, water-wall panels, air-preheater connections, and the tube bundle of shell-and-tube exchangers. These tubes are part of the broader pressure tubes family at EZ Steel Industrial, sitting alongside the alloy and stainless variants in adjacent JIS standards.

Three boundary conditions matter when a buyer first meets the standard:

In other words, the moment the datasheet says “boiler,” “superheater,” “economizer” or “shell-and-tube heat exchanger” and the tube-side medium is water or steam, JIS G 3461 is the standard the tube should be quoted to.

2. The three grades: where STB340, STB410 and STB510 actually fit

JIS G 3461 defines exactly three strength grades, and the number in the grade name is the minimum tensile strength in MPa. There is no “STB360,” no “STB420” — these are the only three options the standard offers. The reference STB340 datasheet from ljgjxt.com gives a clean view of how the standard structures the chemical and mechanical table for the lowest-strength grade; the same structure applies to STB410 and STB510, with progressively higher strength floors and progressively tighter heat-treatment discipline.

2.1 STB340 — the workhorse for low-to-medium pressure boilers

STB340 is the most common grade in the family. With a minimum tensile strength of 340 MPa and a minimum yield of 175 MPa, it covers the bulk of fire-tube boilers, auxiliary heat exchangers, economizer outlet sections, and lower-temperature superheater coils. It is the grade most stockists carry on the shelf and the grade most “carbon-steel boiler tube” RFQs in the Asian market default to. The JIS G 3461 datasheet for STB340 caps carbon at 0.18%, manganese at 0.30-0.60%, phosphorus and sulfur at 0.035% each, with optional silicon 0.10-0.35%.

2.2 STB410 — for higher-pressure and higher-temperature service

STB410 lifts the minimum tensile to 410 MPa and the minimum yield to 250 MPa, with a wider manganese range (0.30-0.80%) to reach the higher strength floor without raising carbon. It is the grade typically specified for water-wall tubes, economizer inlet headers, and the higher-pressure side of industrial boilers. When a Japanese utility or EPC writes “JIS G 3461” without a grade suffix on a power-plant RFQ, it is almost always STB410 they actually mean.

2.3 STB510 — for high-temperature headers and severe service

STB510 takes the minimum tensile to 510 MPa and is reserved for high-temperature headers, superheater outlet sections, and other locations where the combination of internal pressure and elevated metal temperature would over-stress an STB340 or STB410 tube. STB510 is the least-stocked of the three and is almost always a mill-direct inquiry rather than a stockist call.

3. The five manufacturing routes and why they matter

JIS G 3461 lets the buyer order the same grade in five different process routes, and the way the tube is made has real consequences for surface finish, dimensional tolerance, and price. The reference STB340 datasheet from ljgjxt.com lists the symbol convention used throughout JIS G 3461:

For boiler and heat-exchanger service above Class 300 / PN 50 equivalent, most JIS-spec buyers stay with seamless (S-H or S-C). ERW routes (E-G, E-H, E-C) are commonly accepted for lower-pressure economizer and air-preheater service where the project specification does not explicitly require seamless.

4. Heat-treatment: the most-overlooked line in the PO

The JIS G 3461 heat-treatment matrix is one of the few places where the standard gives the buyer an explicit choice rather than a default. For STB340 and STB410, the route-and-condition combination is negotiable; for STB510, normalize is mandatory across all routes. The reference STB340 datasheet captures the full STB340 matrix; the same structure applies to STB410:

A practical note for cold-worked ERW tubes that have been normalized before cold drawing: the standard requires a low-temperature anneal or full anneal after the final cold-working step. If the mill skips this post-cold-work anneal, the tube will have residual stress and is more prone to stress-corrosion cracking in hot water service — confirm the anneal in the MTC.

5. Cross-walking to ASTM, EN and GB so the same job is not quoted twice

JIS-spec plants often sit inside a multi-standard project. A Southeast-Asian combined-cycle power plant built under a Japanese EPC license will frequently have JIS G 3461 datasheets for the boiler island and ASTM A178 / A179 / A192 / A210 datasheets for the balance of plant. If the same tube can be sourced against either standard, the buyer can keep one batch in inventory and avoid ordering two production runs for what is essentially the same material.

These are cross-walks for procurement consolidation, not for code substitution. A JIS-stamped boiler still has to use JIS G 3461 tubes in the JIS-stamped sections; the cross-walk matters for the spare stock and for the non-JIS sections of the same plant. If the datasheet allows either JIS or ASTM, a mill-direct supplier can quote a single dual-certified heat that meets both, with both standard markings on the tube.

6. What the MTC should actually say

For a JIS G 3461 tube, the mill test certificate (MTC) is the buyer's only objective evidence that the order matches the datasheet. A useful MTC answers these six questions without the buyer having to ask:

MTC format should be EN 10204 3.1 for the standard project order, and 3.2 (with independent witnessing) for the high-pressure or nuclear-adjacent order. The MTC must be in English or bilingual, with the test methods referenced to the JIS G 3461 clauses or to the equivalent ISO / ASTM method.

7. Sourcing pattern: why a mill-direct JIS G 3461 order is different from a stock call

Three sourcing differences from a stock-line carbon-steel tube order:

7.1 Stockists carry STB340-S-H, almost nothing else

The default shelf item in the Asian market is STB340 in the hot-rolled seamless route, usually 25.4-76.2 mm OD and 2.0-6.0 mm wall. STB410, STB510, cold-drawn, ERW, or unusual sizes are mill-direct inquiries with a 4-8 week lead time. Plan the procurement calendar accordingly.

7.2 Heat-treatment is a separate line on the quotation

Stock quotations typically include the cheapest compliant heat treatment (often “as manufactured” for STB340-S-H). If the datasheet calls for normalize, low-temperature anneal, or full anneal, the mill cost and the lead time both go up. Write the heat-treatment condition into the RFQ explicitly — do not let the supplier pick the cheapest compliant option.

7.3 Bundled items ride along with the tube

A boiler retube or heat-exchanger rebuild never ends with the tubes alone. The same RFQ usually needs the matching pipe fittings, the matching pipe flanges, and the gasket / stud-bolt & nut set. Sourcing all from one mill-direct supplier with one combined MTC saves inspection time, logistics cost, and the inevitable argument about which lot is the “rogue” one when a leak shows up at start-up.

8. The 8-line RFQ that gets the right quotation the first time

A JIS G 3461 RFQ that arrives without these eight pieces of information will produce three different quotations from three different suppliers, all technically compliant, none directly comparable. The minimum RFQ for a clean JIS G 3461 quote is:

9. Common selection mistakes that cost weeks at site

Five recurring errors that show up in JIS G 3461 procurement, in order of how often they appear in the field:

10. Where EZ Steel Industrial fits in a JIS G 3461 procurement

EZ Steel Industrial supplies jis g3461 steel tube for boiler and heat-exchanger service across all three grades (STB340, STB410, STB510) and all five manufacturing routes (S-H, S-C, E-G, E-H, E-C), with mill-direct heat-treatment control and MTC EN 10204 3.1 as the default, 3.2 on request. The pressure tubes programme covers JIS G 3461, G 3462, G 3463 and adjacent ASTM / EN / GB standards on the same production line, so a JIS-spec RFQ that needs an ASTM-spec cross-stock can be filled from one heat.

A JIS G 3461 order through EZ Steel Industrial typically ships with the tube, the matching pipe fittings and pipe flanges, and the gasket / stud-bolt & nut set under one combined MTC. For a multi-standard project, the same supplier can also quote the heat efficiency tubes (finned and U-bend) for the air-side and boiler-economizer sections, so inspection and logistics stay with one team.