Quick Answer
Quick Answer
JIS steel mill certificates use a four-type inspection certificate system (3.1A, 3.1B, 3.1C, 3.2) that maps closely to EN 10204 types. The key fields — heat number, grade, chemical composition, mechanical properties, and conformance stamp — follow consistent positions across Japanese mills. This guide translates each field and explains when a Japanese-only certificate is acceptable versus when an English translation or bilingual certificate is needed.
Japanese steel mills have issued mill test certificates (MTCs) for more than a century, long before EN 10204 was established. The JIS inspection certificate system is mature, legally recognized, and widely accepted by classification societies and engineering authorities worldwide. However, the documents are typically issued in Japanese (日本語), and even bilingual versions use Japanese as the authoritative language. Western engineers who encounter a JIS certificate for the first time — often when sourcing structural steel, plate, or pipe from Japanese mills — benefit from a systematic approach to reading and verifying these documents.
This guide covers certificates issued for JIS structural steel standards including JIS G3101 (SS grades), JIS G3106 (SM grades), JIS G3114 (SMA weathering grades), and JIS G3444 (STK tube grades). The field layout and vocabulary are consistent across these standards.
Scope and Applicability
This guide applies to:
- Hot-rolled structural steel plates (JIS G3101, G3106, G3114)
- Structural tubes (JIS G3444, G3466, G3475)
- Any steel product supplied against a JIS standard requiring a material certification
For pressure vessel or boiler steel (JIS G3115, G3118), the same field structure applies with the addition of pressure-vessel-specific supplementary tests. For stainless steel (JIS G4304, G4305), additional fields for nickel, chromium, and molybdenum chemistry are present.
JIS Inspection Certificate Types
The JIS inspection certificate type system predates EN 10204 and uses different terminology, but the functional levels map closely:
| JIS Type | JIS Description | Who Inspects | EN 10204 Functional Equivalent |
|---|---|---|---|
| 3.1A | Inspection by the manufacturer's own authorized technical representative | Mill's internal QA inspector | 2.2 (Works certificate — not witnessed independently) |
| 3.1B | Inspection by an independent inspector designated by the manufacturer | Third-party inspector selected and paid by the mill | 3.1 (Inspection certificate 3.1) |
| 3.1C | Inspection by a technical representative of the purchaser | Buyer's own representative present at mill | 3.1 (Inspection certificate 3.1 — buyer-side) |
| 3.2 | Inspection by both the manufacturer's representative and the purchaser's independent inspector | Dual witness: mill QA + buyer's independent surveyor (DNV, Bureau Veritas, SGS, etc.) | 3.2 (Inspection certificate 3.2) |
Practical guidance:
- JIS 3.1A is a works certificate with no independent witness. It confirms the mill's own test results but no external verification. Equivalent to EN 10204 type 2.2. Acceptable for low-criticality general fabrication; not suitable for structural engineering or classification-society certification.
- JIS 3.1B is the most common export certification for Japanese structural steel. Widely accepted by European, US, and Australian structural engineering authorities in place of EN 10204 3.1, though formal substitution should be confirmed with the project's structural engineer or approval authority.
- JIS 3.1C is used when the buyer's own QA representative (or their local agent) witnesses mill testing. Functionally similar to 3.1B but the inspector is accountable to the buyer rather than the mill.
- JIS 3.2 is required for the highest-criticality applications — major bridges, offshore structures, nuclear, and projects invoking ASME or EN classification-society rules. Must be specified at order stage since it requires advance notice to arrange the buyer's independent inspector.
How JIS Certificate Types Map to EN 10204
| EN 10204 Type | EN Description | JIS Equivalent |
|---|---|---|
| 2.1 | Declaration of compliance | No direct JIS equivalent (verbal declaration only) |
| 2.2 | Test report (works) | JIS 3.1A |
| 3.1 | Inspection certificate 3.1 (independent at mill) | JIS 3.1B or 3.1C |
| 3.2 | Inspection certificate 3.2 (dual witness) | JIS 3.2 |
When a European purchase order or project specification states "EN 10204 3.1 certificate required," a JIS 3.1B certificate from a reputable Japanese mill is generally accepted by most European structural engineers and classification societies (DNV, Lloyd's Register, Bureau Veritas) as functional equivalent. When "EN 10204 3.2 is required," only a JIS 3.2 certificate meets the requirement.
Common Japanese Terms on Mill Certificates
The following vocabulary covers the fields found on virtually all JIS structural steel certificates. Fields are grouped by location — header, body (chemistry), body (mechanical), and footer.
Header / Identification Fields
| Japanese | Romaji | English Translation | Notes |
|---|---|---|---|
| 試験成績書 | Shiken seiseki-sho | Test certificate / Inspection report | General title for a mill certificate |
| ミルシート | Miru shīto | Mill sheet | Common informal term for MTC |
| 規格 | Kikaku | Standard / Specification | e.g., JIS G3106 |
| 鋼種 | Kōshu | Steel grade | e.g., SM490B |
| 熱番号 | Netsu bangō | Heat number | Unique identifier for the cast (heat) |
| チャージ番号 | Chāji bangō | Charge number | Alternate term for heat number |
| 製造番号 | Seizō bangō | Manufacturing number | Internal mill production tracking number |
| 注文番号 | Chūmon bangō | Order number | Customer purchase order number |
| 製造年月日 | Seizō nengappi | Manufacturing date | Date of rolling/production |
| 製造工場 | Seizō kōjō | Manufacturing plant | Mill name and location |
Dimensional Fields
| Japanese | Romaji | English Translation | Notes |
|---|---|---|---|
| 寸法 | Sunpō | Dimensions | Overall heading for dimension section |
| 厚さ | Atsusa | Thickness | In mm |
| 幅 | Haba | Width | In mm |
| 長さ | Nagasa | Length | In mm |
| 外径 | Gaikei | Outer diameter | For tubes — OD in mm |
| 肉厚 | Nikuatsu | Wall thickness | For tubes — WT in mm |
| 質量 | Shitsuryo | Mass / Weight | Net weight in kg |
| 枚数 / 本数 | Maisū / Honsū | Number of pieces | Plates/sheets (maisū) or tubes/bars (honsū) |
Chemical Composition Fields
| Japanese | Romaji | English Translation | Notes |
|---|---|---|---|
| 化学成分 | Kagaku seibun | Chemical composition | Section heading |
| 炭素 / C | Tanso | Carbon | wt% |
| ケイ素 / Si | Keiso | Silicon | wt% |
| マンガン / Mn | Mangan | Manganese | wt% |
| リン / P | Rin | Phosphorus | wt% |
| 硫黄 / S | Iō | Sulfur | wt% |
| 銅 / Cu | Dō | Copper | wt%; important for weathering steel (G3114 W grades) |
| クロム / Cr | Kuromu | Chromium | wt%; for weathering and alloy steels |
| ニッケル / Ni | Nikkeru | Nickel | wt% |
| モリブデン / Mo | Moribuden | Molybdenum | wt% |
| 炭素当量 / CEV | Tanso tōryō | Carbon equivalent | Dimensionless; critical for weld assessment |
Mechanical Property Fields
| Japanese | Romaji | English Translation | Notes |
|---|---|---|---|
| 機械的性質 | Kikaiteki seishitsu | Mechanical properties | Section heading |
| 降伏点 | Kōfuku-ten | Yield point (upper yield) | MPa or N/mm² |
| 耐力 | Tairyoku | Proof strength (0.2% offset) | MPa; used where no distinct yield point |
| 引張強さ | Hippari kyōsa | Tensile strength | MPa or N/mm² |
| 伸び | Nobi | Elongation | % |
| 絞り | Shibori | Reduction of area | % (not always reported) |
| 硬さ | Katasa | Hardness | HB, HR, or HV |
Impact Test Fields
| Japanese | Romaji | English Translation | Notes |
|---|---|---|---|
| 衝撃試験 | Shōgeki shiken | Impact test | Section heading |
| シャルピー衝撃試験 | Sharuppī shōgeki shiken | Charpy impact test | Full name |
| 試験温度 | Shiken ondo | Test temperature | e.g., 0°C or −5°C |
| 吸収エネルギー | Kyūshū enerugī | Absorbed energy | Joules (J) |
| 3本平均 | 3-hon heikin | Average of 3 specimens | The required reported value |
| 最小値 | Saishō-chi | Minimum (single) value | Lowest of the three specimens |
Bend and Other Tests
| Japanese | Romaji | English Translation | Notes |
|---|---|---|---|
| 曲げ試験 | Mage shiken | Bend test | Common in G3101 |
| 曲げ角度 | Mage kakudo | Bend angle | e.g., 180° |
| 曲げ内半径 | Mage uchi hankei | Inside bend radius | e.g., 1.0 × t |
Conformance and Signature Fields
| Japanese | Romaji | English Translation | Notes |
|---|---|---|---|
| 合格 | Gōkaku | Conforming / Passed | Green stamp or written declaration indicating compliance |
| 検査員 | Kensain | Inspector | Signature or stamp of the authorized inspector |
| 検査機関 | Kensa kikan | Inspection body | Name of the inspection organization (for 3.1B/3.2) |
| 証明書番号 | Shōmei-sho bangō | Certificate number | Unique document ID |
| 発行年月日 | Hakkō nengappi | Issue date | Date certificate was issued |
The 合格 (Gōkaku) Stamp
The character combination 合格 (gōkaku) literally means "passing the standard" or "conforming." On a JIS mill certificate, it appears as:
- A red or green ink stamp (角印 — kakuin, square seal) impressed on the document
- A typed or handwritten declaration such as 上記の通り合格であることを証明します ("We certify that the above material conforms")
- A digital signature block on electronically issued certificates
The 合格 stamp is the Japanese equivalent of the "declaration of conformity" signature on an EN 10204 certificate. Its absence means the material has not been declared conforming — the certificate would be incomplete.
When to Request English Translation vs. When Japanese-Only Is Acceptable
Japanese-only certificate is generally acceptable when:
- The certificate is being verified internally by a procurement team with this guide and the relevant standard's numerical limits
- The project specification does not require an English-language document
- The receiving country's customs or engineering authority does not mandate English documentation
- The numbers and grade designations (which are often in Roman characters or Arabic numerals) can be cross-checked without language translation
Request bilingual or translated certificate when:
- The certificate will be submitted to a classification society (DNV GL, Lloyd's Register, Bureau Veritas, ABS) — most will accept Japanese-only originals but prefer bilingual for efficiency
- The project involves European engineering sign-off where the engineer needs to read the document directly
- The certificate will be used in legal proceedings or insurance claims
- The purchase order or project specification explicitly requires English-language certification
Practical tip: Most major Japanese mills (Nippon Steel, JFE Steel, Kobe Steel, Tokyo Steel) offer bilingual certificates for export orders at no additional cost when requested at the time of order. The request must be made before production; it cannot be retrofitted after the original certificate has been issued.
Verifying Heat Number Traceability
The heat number (熱番号 / Netsu bangō) on the certificate must be traceable to the physical material. Japanese mills mark material using:
- Stencil stamps on plate surfaces (熱番 marking in white or yellow paint)
- Color-coded tags on bundles and coils
- Laser or ink-jet marks on tube ends
- Embossed marks rolled into the section for structural shapes
When receiving material, verify that the heat number on every piece (or representative sample) matches the certificate. If multiple heats are present in a delivery, a separate certificate is required for each heat. Mixed-heat deliveries with a single certificate covering only one heat are a common discrepancy in incoming inspection.
MTC Verification Checklist
When receiving any JIS steel certificate:
- Identify the certificate type (3.1A, 3.1B, 3.1C, or 3.2) — confirm it meets project requirements
- Confirm the standard (規格) matches the purchase order specification
- Confirm the grade (鋼種) including sub-grade suffix exactly matches the purchase order
- Record the heat number (熱番号) and verify it matches physical markings
- Verify all chemical values against the applicable JIS standard limits
- For SM/SMA B, C, and W grades: confirm CEV is reported and within limit
- Verify yield strength, tensile strength, and elongation against thickness-appropriate limits
- For B, C, and W impact grades: confirm Charpy test temperature, average energy, and single-specimen minimum
- Confirm the 合格 stamp or conformance declaration is present
- Confirm the inspector name/signature and (for 3.1B/3.2) the inspection body name
- Record the certificate number (証明書番号) and issue date (発行年月日) for your records
Frequently Asked Questions
Is a JIS 3.1B certificate the same as an EN 10204 3.1 certificate?
Functionally equivalent, not formally identical. Both require testing by an independent inspector who is not the manufacturer's production department, and both require the inspector to certify that the material meets the specified standard. Major classification societies (DNV, Bureau Veritas, Lloyd's Register) and many European structural engineering authorities accept JIS 3.1B in lieu of EN 10204 3.1 for structural steel. However, if the purchase order or project specification explicitly states "EN 10204 3.1 required," strictly speaking an EN 10204 3.1 certificate from an EN-certified mill is required. Consult the project engineer before accepting substitution on critical structures.
What does 熱番号 (Netsu bangō) mean and why does it matter?
熱番号 is the heat number — the unique identifier for a single batch of steel melted together in the steelmaking furnace (heat). All material from the same heat has the same base chemistry because it was made from the same liquid steel. Heat traceability is the fundamental mechanism of material certification: it links the physical steel you receive to the chemical analysis and mechanical tests recorded in the certificate. Without confirmed heat number traceability from certificate to physical material, the certificate has no evidential value for that material.
The mill certificate I received is in Japanese only. Can I verify it without translation?
For most verification purposes, yes. Chemical composition values are reported as numbers in the standard elements (C, Si, Mn, P, S, and others where applicable) — these are universally recognizable. The grade designation (e.g., SM490B) uses Roman letters and Arabic numerals even in Japanese documents. Mechanical property values (MPa, %) are numbers. The key additional step is identifying the correct row and column for each value using the vocabulary table in this guide. For the conformance stamp (合格), the two characters are distinctive enough to recognize visually once you have seen them once.
Why do some JIS certificates report 降伏点 and others report 耐力?
降伏点 (kōfuku-ten) means yield point and is reported when the stress-strain curve shows a distinct upper and lower yield point — typical for mild structural steels (SS400, SM400, SM490). 耐力 (tairyoku) means proof strength (0.2% offset yield) and is reported when there is no distinct yield point — typical for high-strength steels, cold-worked material, or stainless steel. Both serve as the yield strength value for design purposes; the distinction reflects the measurement method.
What is the difference between a JIS 3.1B and a JIS 3.2 certificate in practice?
In a JIS 3.1B certificate, the independent inspector is selected and engaged by the manufacturer (mill). The inspector verifies the test procedures and results but is not present as the buyer's agent. In a JIS 3.2 certificate, both the mill's authorized representative and the buyer's independent inspector (or a classification-society surveyor engaged by the buyer) must sign the certificate. JIS 3.2 provides the highest level of assurance and is required for offshore, nuclear, and classification-society-approved structures. It must be planned at order stage because the buyer must arrange and pay for their independent inspector to visit the mill.
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