Double End Stud Bolts
Technical Delivery Conditions (TDC) for DIN 939 stud bolts are governed by DIN 267-2 for general fastener acceptance and EN 10204 for mill-test certification. Standard delivery includes an EN 10204 Type 3.1 certificate (manufacturer's test report covering chemical composition, mechanical properties, dimensional inspection, and surface finish, signed by an independent quality department). For pressure-equipment, nuclear, and oil and gas service, an EN 10204 Type 3.2 certificate countersigned by an independent inspector authorised by the official regulation is required. TorqBolt's NORSOK M-650 qualified production route satisfies all six certificate types in a single inspection package.
The matrix below summarises the underlying material, thread, mechanical, geometrical, surface, and acceptance references that DIN 939 invokes by reference. Every row points at a primary standard (ISO, DIN, or DIN EN) that the TorqBolt inspection lot must conform to before the EN 10204 certificate can be issued. The two tables on this page carry the dimensional and acceptance basis; the prose around them explains how the certificate cascade is built on top of those references.
| Material | Steel | ||
|---|---|---|---|
| General requirements | As specified in ISO 8992 | ||
| Thread | Tolerance class | Screw-sided threadSk 6 | Nut-sided:6g |
| Standard | DIN 13-51 | DIN 13-12 and DIN 13-51 | |
| Mechanical properties | Property class | 5.6, 8.8, 10.9 | |
| Standard | DIN EN 20898-1 | ||
| Limit deviations and geometrical tolerances | Product grade | A | |
| Standard | DIN ISO 4759-1 | ||
| Surface | 5.6: prepared as 8.8, 10.9: blackened (thermal or chemical) For
the surface roughness DIN 267-2. For the limits of the surface error is considered to DIN EN 26157-3. For galvanized surface protection applies to DIN ISO 4042. The procedures established for the threaded ends of thread cross dimensions apply after applying a coating. |
||
| Acceptance inspection | As specified in ISO 3269 | ||
| Material | Steel | ||
|---|---|---|---|
| General requirements | As specified in ISO 8992 | ||
| Thread | Tolerance class | Screw-sided threadSk 6 | Nut-sided:6g |
| Standard | DIN 13-51 | DIN 13-12 and DIN 13-51 | |
| Mechanical properties | Property class | 5.6, 8.8, 10.9 | |
| Standard | DIN EN 20898-1 | ||
| Limit deviations and geometrical tolerances | Product grade | A | |
| Standard | DIN ISO 4759-1 | ||
| Surface | 5.6: prepared as 8.8, 10.9: blackened (thermal or chemical) For
the surface roughness DIN 267-2. For the limits of the surface error is considered to DIN EN 26157-3. For galvanized surface protection applies to DIN ISO 4042. The procedures established for the threaded ends of thread cross dimensions apply after applying a coating. |
||
| Acceptance inspection | As specified in ISO 3269 | ||
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Two certificate types cover essentially every DIN 939 commercial bolting order. Type 3.1 is the default: the manufacturer issues the test report, results come from specific tests on the delivered lot, and the QA signatory is independent of the production department. Type 3.2 is the same specific-test basis but countersigned by an independent third-party inspector authorised by the official regulation, typically Lloyd's Register, DNV, Bureau Veritas, TÜV, ABS, or Stoomwezen. Type 3.2 is mandatory for PED Category III and IV pressure vessels, NORSOK-scope offshore equipment, ASME Section III nuclear bolting, and any tender that names a third-party witness. Type 2.1 (manufacturer conformity statement) and Type 2.2 (generic non-specific test report) are not used for DIN 939 pressure work and TorqBolt will not ship DIN 939 against either grade unless the customer explicitly accepts low-criticality use.
For pressure vessels built or commissioned in Germany, DIN 939 bolting must comply with the relevant AD 2000 Merkblatt sheet. W2 covers austenitic stainless steel bolting. W7 covers low-alloy CrMo and CrNiMo bolting steels including A320 L7 and A193 B7 equivalents. W10 covers austenitic steel bolting at elevated temperature. Each Merkblatt sets material qualification, supplier approval, marking, and certificate requirements that are stricter than ISO 898-1 alone. TorqBolt holds an internal qualification register that documents conformance with W2, W7, and W10 for every applicable grade family and the register is updated on each new heat lot. The material grade selection page lists which TorqBolt grades fall under each Merkblatt.
Lot acceptance for DIN 939 stud bolts follows ISO 3269 when EN 10204 Type 3.1 is the certificate basis. The sampling plan is single-sampling normal inspection at AQL 1.5 for major characteristics (mechanical properties and surface defects affecting load capacity) and AQL 4.0 for minor characteristics (cosmetic surface and packaging). For Type 3.2 deliveries the plan changes: 100% witness on mechanical tests is typical, with statistical witness on dimensional checks. The exact sampling is agreed between TorqBolt, the customer, and the named third-party inspector before the lot enters final inspection.
For North Sea offshore service, DIN 939 studs must trace through NORSOK M-650 qualified manufacturing. The chain runs: heat number, melt analysis certificate, forging or rolling reduction ratio record, heat-treatment batch (austenitise plus quench plus temper cycle for CrMo grades, solution-anneal cycle for austenitic stainless), mechanical test report, Charpy V-notch curve for cryogenic and sour-service grades, dimensional inspection per DIN 962, surface coating record, and final dispatch certificate. TorqBolt's manufacturing record packet covers every step and is independently auditable by Lloyd's Register, DNV, Bureau Veritas, ABS, or TÜV. The specification compliance data is appended to the dispatch packet so the customer receives one consolidated document set.
DIN 939 studs supplied for vessels falling under the Pressure Equipment Directive 2014/68/EC require material conformity declarations that map the delivered grade onto a PED-recognised material specification, typically EN 10269 for bolting steels or EN 10088-3 for stainless. The manufacturer must hold a Particular Material Appraisal (PMA) or an equivalent AVCP approval. TorqBolt maintains this approval through its EN 10204 3.2 certificate cascade. Conformity assessment routes A, A2, B+C, B+D, B+E, B+F, G, and H1 are all serviceable depending on vessel category I, II, III, or IV. The exact route is set by the vessel designer and TorqBolt aligns its inspection plan to whichever module the customer nominates.
For nuclear safety-related DIN 939 deliveries, items are classified under the Item Technical Notice Sheet (ITNS) regime. Safety class 1, 2, or 3 sets the qualification depth: class 1 requires melt-source pedigree, full Charpy curve, dye-penetrant 100% surface check, and ultrasonic inspection on diameters above 38 mm. Counterfeit, fraudulent, or suspect (CFS) detection procedures apply throughout the supply chain — any CFS event must be reported to the customer without delay, even where it does not affect the delivered lot. TorqBolt maintains a CFS register that is reviewed every quarter. Records retention for nuclear-class DIN 939 deliveries is a minimum of 40 years from the dispatch date.
When EN 10204 Type 3.2 is invoked, the third-party inspector witnesses a defined set of activities rather than the entire production run. Typical witness scope is: heat-treatment chart review, tensile test on the delivered lot (proof load, ultimate tensile, elongation, reduction of area), Charpy V-notch impact for cryogenic and sour grades, hardness check, dimensional inspection per DIN 962 (head, thread, length, straightness), surface check per DIN EN 26157-3, and final marking verification. The inspector signs the EN 10204 certificate alongside the TorqBolt QA-QC head, and the original signed certificate is included in the dispatch packet sent with the goods. The stud dimensions page covers the dimensional basis the inspector measures against.
TorqBolt issues a single inspection packet per DIN 939 lot that satisfies DIN 267-2, EN 10204 (3.1 or 3.2 as ordered), AD 2000 W2/W7/W10 where applicable, ISO 3269 sampling evidence, NORSOK M-650 traceability chain, PED 2014/68/EC material conformity declaration, and ITNS classification for nuclear orders. Material grades that ship with this packet by default include A193 B7, A193 B16, A320 L7, A320 L43, A193 B8/B8M/B8T, duplex UNS S31803/S32750/S32760, super austenitic 6Mo UNS S31254, and the nickel-alloy bolting families (Inconel 718, 625, 825, Monel 400, K500, Hastelloy C276, Incoloy 925). The material selection page maps each grade to its native standard, and the DIN 939 overview covers the standard's family relationship to DIN 938, DIN 835, and DIN 940.
For tender-specific TDC clarifications, deviation requests, or supplier qualification audits, contact TorqBolt QA-QC at info@torqbolt.com or +91-22-66157017. PMA appraisal letters, NORSOK M-650 qualification certificates, and AD 2000 register extracts are available on signed-NDA request.
