RFQ Today
Certifications: EN 10204 3.1 / 3.2 material test certificates, K-class preload testing per EN 14399-2, CE marking / DoP under EN 15048 or EN 1090, and complete export documentation packages.
EN 14399
High-Strength
Structural Bolting
A world-class technical reference for EPC contractors, structural steelwork fabricators, procurement heads, and TPI inspection agencies specifying EN 14399 preloadable structural bolt, nut, and washer assemblies — covering System HR vs. HV selection logic, K-class preload testing, slip-resistant connection design, tightening methods, and the certification discipline required for critical structural steel connections under Eurocode design.
System Architecture
& Design Logic
EN 14399 is the European standard series governing high-strength structural bolting assemblies for preloading — bolt, nut, and washer sets engineered as a matched system to deliver a guaranteed, testable clamping force for slip-resistant and bearing-type structural steel connections under Eurocode 3 (EN 1993-1-8) design.
1.1 — What EN 14399 Covers and Why It Exists as a Separate Standard
EN 14399 (“High-strength structural bolting assemblies for preloading”) is a ten-part European standard published by CEN specifically for structural steel connections where the bolt assembly must deliver a controlled, verified, reproducible clamping (preload) force between the connected steel plies — distinct from general-purpose mechanical fasteners covered by ISO 898-1 and EN ISO 4014/4032, which are not qualified or tested for preload consistency. The critical distinction is that an EN 14399 bolt, nut, and washer are always supplied and used as a matched set (identified by a common lot or batch marking) — the bolt, nut, and washer(s) are tested together as an assembly for their combined torque-tension (K-class) performance, because the achievable preload for a given applied torque depends on the friction characteristics of the specific bolt/nut/washer combination as manufactured and coated, not on the bolt alone. Substituting an EN 14399 nut or washer from a different manufacturer or lot invalidates the assembly’s K-class certification and is not permitted under the standard or under EN 1090-2 structural execution requirements.
This preload-testing discipline is what distinguishes EN 14399 assemblies from ordinary high-tensile bolts of the same nominal property class (8.8 or 10.9): an EN 14399 assembly carries a guarantee, verified by production-lot testing in a calibrated tension-testing device, that a specified installation torque (or turn-of-nut rotation, or direct tension indicator compression) will achieve the minimum preload force required by the structural design — a guarantee that a generic property-class-8.8 bolt/nut pairing, sourced independently and not lot-tested as an assembly, cannot provide. For slip-resistant (friction-grip) structural connections in particular — where the entire load transfer mechanism relies on friction generated by bolt clamping force rather than bolt shear — this preload guarantee is not a quality preference but a structural design prerequisite.
1.2 — System HR vs. System HV: The Two Assembly Types
System HR (EN 14399-3) — Hexagon Bolt/Nut/Washer Sets
The general-purpose EN 14399 assembly type — hexagon head bolts (EN 14399-4 geometry for HV, or the HR-specific geometry for HR) paired with hexagon nuts and, typically, one or two washers depending on the connection detail. System HR is the more widely specified system across European structural steelwork, offering property classes 8.8 and 10.9, a broad diameter range (M12–M36), and compatibility with all three standard tightening methods (torque control, combined method, turn-of-nut). System HR is the default choice absent a specific project requirement for System HV.
System HV (EN 14399-4) — Hexagon Bolt/Nut/Washer Sets, Fine Pitch
A structurally similar but dimensionally and metallurgically distinct assembly system, historically derived from the German DIN 6914/6915/6916 “HV” bolt series that predates EN 14399 harmonisation. System HV typically uses a fine-pitch thread and a specific bolt head/nut geometry that differs from System HR at the same nominal diameter — HR and HV components are NOT interchangeable even at the same diameter and property class, because the thread pitch, head bearing geometry, and washer dimensions differ between the two systems. Project specifications, particularly on European infrastructure and rail projects with a DIN-standard heritage, may specifically call out System HV; verify system compatibility explicitly before substituting HR for HV or vice versa on any connection.
1.3 — Property Classes and Mechanical Performance
| Property Class | Min. Tensile Strength (MPa) | Min. Yield / 0.2% Proof (MPa) | Min. Elongation (%) | Typical Use |
|---|---|---|---|---|
| 8.8 | 800 | 640 | 12 | Standard structural connections; System HR and HV both available |
| 10.9 | 1000 | 900 | 9 | High-load connections; reduced ductility margin — verify design accommodates lower elongation at ultimate connection capacity |
Property class 10.9 delivers approximately 25% higher tensile and 40% higher yield strength than property class 8.8, permitting smaller bolt diameters or fewer bolts for a given connection load — but with a corresponding reduction in ductility (minimum elongation 9% vs. 12%) and a documented increased sensitivity to hydrogen embrittlement during hot-dip galvanizing if the galvanizing process is not tightly controlled (baking/de-embrittlement heat treatment after pickling and before or immediately after galvanizing). Many structural specifications restrict property class 10.9 hot-dip galvanized bolts or require specific de-embrittlement heat treatment controls — verify the project corrosion protection specification’s position on 10.9 galvanized bolting before finalising the coating route for high-strength assemblies.
1.4 — K-Class Preload Testing System (EN 14399-2)
EN 14399-2 defines the test method used to determine the “K-class” (torque coefficient class) of a bolt/nut/washer assembly lot — a calibrated tension-testing device applies a controlled torque to the assembly while directly measuring the resulting bolt tension (preload), from which the mean torque coefficient (k-value) and its scatter (coefficient of variation) across the test sample are calculated. Every production lot of EN 14399 assemblies is tested and classified into one of three K-classes before release, and the K-class governs the installation torque required to achieve the specified preload for that specific lot.
| K-Class | Mean k-Value Range | Coating / Lubrication Typical | Engineering Significance |
|---|---|---|---|
| K0 | 0.10 – 0.16 | Special low-friction coating (e.g. wax-based, PTFE-enhanced) | Lowest, most consistent torque-to-preload relationship; used where tight preload control at lower installation torque is required |
| K1 | 0.10 – 0.16 (tighter tolerance band) | Standard delivery condition (typically wax/lubricant coated) | Most commonly supplied class — the default “as-delivered” condition for most EN 14399 assemblies |
| K2 | 0.12 – 0.20 | Hot-dip galvanized (as galvanized, without supplementary lubrication) | Wider torque coefficient scatter due to zinc coating surface friction variability — requires correspondingly wider torque tolerance in the tightening procedure |
1.5 — Preload, Slip Resistance, and Joint Categories per Eurocode 3
EN 1993-1-8 (Eurocode 3, Part 1-8: Design of Joints) classifies bolted connections into categories (A, B, C for shear connections; D, E for tension connections) based on the load transfer mechanism and whether preload is structurally relied upon. Category A (bearing type) connections use ordinary or preloaded bolts in shear/bearing without relying on friction — slip of the connection under service load is acceptable. Category B (slip-resistant at serviceability) and Category C (slip-resistant at ultimate limit state) connections rely entirely on the friction generated between the connected plies by the bolt preload force, requiring EN 14399 preloaded assemblies (never ordinary non-preloaded bolts) combined with a specified faying surface treatment (slip factor class per EN 1090-2, e.g., Class A blasted surface with slip factor μ = 0.5) to achieve the certified slip resistance the connection design relies upon.
1.6 — Bolt Preload Behaviour: Embedment, Relaxation, and Vibration
After initial tightening, an EN 14399 preloaded assembly experiences a predictable loss of preload over the first hours to days after installation due to embedment relaxation — localized plastic deformation at the thread flanks, under the bolt head, and under the nut bearing face as the high initial contact stresses redistribute. EN 1090-2 and the associated national annexes typically require either an allowance in the specified installation preload to compensate for anticipated embedment loss, or a re-tightening/verification step after an initial settling period on critical connections. Long-term relaxation from creep in the connected steel plies is generally negligible at ambient temperature but becomes a design consideration for elevated-temperature structural connections (e.g., adjacent to process equipment or in fire-engineering scenarios). Vibration loosening is not a significant risk for correctly torqued EN 14399 preloaded assemblies at the specified minimum preload — the preload level required by Eurocode 3 slip-resistant design is well in excess of the threshold at which vibration-induced bolt back-off becomes a practical concern, provided the assembly has been tightened to the specified method and preload.
Submit your system, diameter, length, property class, coating, and quantity for a documented RFQ within 24 hours.
Dimensions &
Tightening Methods
EN 14399 dimensions, mechanical properties, and testing methods are defined across ten interlocking parts. All applicable parts of the standard are supported at RR Hydraulic with matched-lot bolt, nut, and washer assemblies.
Submit system, diameter, length, property class, K-class, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — The Ten Parts of EN 14399
EN 14399-1 — General Requirements
The scope and general requirements document for the full EN 14399 series — defines the overall system architecture, marking requirements, and the relationship between the subsequent parts. Establishes that all EN 14399 assemblies must be supplied and identified as matched bolt/nut/washer sets from a common test lot.
EN 14399-2 — Suitability Test for Preloading
Defines the K-class torque-tension test method described in Section 1.4 above — the calibrated test procedure used to classify every production lot into K0, K1, or K2 before release, and to verify the assembly achieves the required preload at the specified installation torque.
EN 14399-3 — System HR
Dimensional and mechanical specification for System HR hexagon bolt, nut, and washer sets — the general-purpose EN 14399 assembly type covering property classes 8.8 and 10.9 across the full standard diameter range.
EN 14399-4 — System HV
Dimensional and mechanical specification for System HV hexagon bolt, nut, and washer sets — the fine-pitch, DIN-heritage assembly type, dimensionally distinct from System HR at the same nominal diameter.
EN 14399-5 / 14399-6 — Washers
EN 14399-5 covers plain (flat) washers for System HR assemblies; EN 14399-6 covers plain chamfered washers for System HV assemblies. Washer hardness, flatness, and dimensional tolerance are controlled because washer performance directly affects the achieved preload and the assembly’s K-class behaviour — a substituted, non-EN 14399 washer invalidates the assembly’s preload certification even if the bolt and nut are correctly matched.
EN 14399-7 — System HR Countersunk Head Bolts
Countersunk head bolt/nut/washer sets for System HR flush-surface structural connections — used where a protruding bolt head is not permitted by the connection detail (e.g., certain architectural exposed steelwork or sliding/bearing surface applications).
EN 14399-8 — System HV Fit Bolts
Close-tolerance (“fit”) bolt assemblies for System HV where the bolt shank must closely fit the clearance hole to transfer shear load in bearing without slip — used in bearing-type connections designed to Category A/C of EN 1993-1-8 where bolt-hole clearance must be minimised.
EN 14399-9 — System HR/HV Direct Tension Indicators (Washers)
Specifies direct tension indicator (DTI) washers — load-indicating washers with small protrusions that compress under bolt preload, providing a visual/gap-gauge verification of achieved preload independent of applied torque. DTI washers are compatible with both System HR and System HV bolt/nut combinations and provide an alternative, torque-independent method of preload verification.
EN 14399-10 — System HRC
Defines System HRC — a complete bolt/nut/washer assembly incorporating a splined bolt end (spline tip) that shears off at the specified preload torque, providing built-in, self-verifying preload control without a separate torque wrench or DTI washer. Widely specified where installation speed and inherent preload verification are priorities, particularly on high-volume structural steel fabrication and erection projects.
2.2 — Dimensional Reference: Diameter, Property Class, and Proof Load
| Size | Pitch (mm) | Tensile Stress Area (mm²) | Proof Load Class 8.8 (kN) | Proof Load Class 10.9 (kN) | Typical Standard Length Range (mm) |
|---|---|---|---|---|---|
| M12 | 1.75 | 84.3 | 54.0 | 75.9 | 30 – 100 |
| M16 | 2.0 | 157.0 | 100.5 | 141.3 | 40 – 140 |
| M20 | 2.5 | 245.0 | 156.8 | 220.5 | 50 – 180 |
| M22 | 2.5 | 303.0 | 194.0 | 272.7 | 55 – 200 |
| M24 | 3.0 | 353.0 | 226.0 | 317.7 | 60 – 220 |
| M27 | 3.0 | 459.0 | 293.8 | 413.1 | 70 – 260 |
| M30 | 3.5 | 561.0 | 359.0 | 504.9 | 80 – 300 |
| M36 | 4.0 | 817.0 | 522.9 | 735.3 | 100 – 360 |
2.3 — Tightening Methods per EN 1090-2
Torque Control Method
A calibrated torque wrench applies a specified torque, calculated from the assembly’s K-class and the target preload, directly to the nut or bolt head. Simplest method conceptually, but preload accuracy is sensitive to friction variation between individual assemblies within the K-class tolerance band — the least precise of the three standard methods, though fully compliant when using correctly K-class-certified assemblies and calibrated tools.
Combined Method
An initial “snug-tight” torque is applied (typically 50–70% of the full torque value), followed by a further specified partial nut rotation (e.g., 60°–90° depending on grip length and diameter) rather than a further torque value — combines the practicality of torque control for initial seating with the improved preload consistency of a controlled rotation for final tightening, reducing sensitivity to friction variation compared to torque control alone.
Turn-of-Nut (Rotational) Method
Snug-tight condition established, then the nut is rotated a specified fraction of a turn (typically 1/3 to 1 full turn depending on bolt length/diameter ratio and grip length) — preload is generated primarily by controlled elastic bolt stretch corresponding to the specified rotation, largely independent of friction/torque coefficient variation. Provides the most consistent preload of the torque-based methods but requires careful control of the snug-tight starting point and correct rotation value for the specific grip length.
HRC / DTI Direct Verification
System HRC (spline-shear) or DTI washer methods provide direct, built-in preload verification independent of torque or rotation calculation — the spline shears off, or the DTI washer gap closes to the specified value, at the target preload regardless of the actual friction coefficient of the specific assembly. Increasingly preferred on projects prioritising installation speed, inspection simplicity, and elimination of torque-wrench calibration dependency.
2.4 — Standards Compliance and Related Framework
EN 1090-2
Execution of Steel Structures and Aluminium Structures — Part 2: Technical Requirements for Steel Structures. Governs the site/shop execution class (EXC1–EXC4), permitted tightening methods, preload verification procedure, faying surface preparation for slip-resistant connections, and the CE marking / Declaration of Performance requirements for structural bolt assemblies used in EN 1090-certified fabrication.
EN 1993-1-8 (Eurocode 3)
Design of Steel Structures — Part 1-8: Design of Joints. The design code governing bolted connection categories (A–E), slip factor requirements for friction-grip connections, bolt group design resistance calculations, and the interface between the structural engineer’s connection design and the EN 14399 bolt assembly specification.
EN 15048
Non-Preloaded Structural Bolting Assemblies — the companion standard to EN 14399 covering ordinary (non-preloaded) structural bolt assemblies for bearing-type Category A connections where preload testing and K-class certification are not required. Used where the connection design does not rely on friction-grip slip resistance.
EN ISO 4014 / 4032 / 4017
General-purpose hexagon bolt, nut, and screw dimensional standards — referenced for the base thread and head geometry conventions but NOT sufficient on their own to qualify a fastener as an EN 14399 preloadable assembly, since these standards do not incorporate the K-class preload testing requirement.
ISO 898-1 / ISO 898-2
Mechanical Properties of Fasteners — Part 1 (bolts, screws, studs) and Part 2 (nuts) define the property class (8.8, 10.9) mechanical property requirements referenced by EN 14399 for the base material performance, tested per the standard tensile, hardness, and proof load methodology.
CE Marking / Construction Products Regulation (CPR)
EN 14399 assemblies for use in EU/UK construction works require CE marking (or UKCA for the UK market) with a Declaration of Performance (DoP) under the Construction Products Regulation, issued by the manufacturer against the harmonised parts of the EN 14399 series — verify current DoP validity and the specific harmonised standard clause referenced before accepting delivery for a CE-marked structural steelwork project.
Heat Treatment &
Coating Systems
EN 14399 bolts, nuts, and washers are manufactured from quenched-and-tempered alloy steel with tightly controlled heat treatment and coating processes that determine both mechanical performance and K-class preload behaviour. See our complete materials reference for grade and coating guidance.
3.1 — Material Grades
Property Class 8.8 — Medium Carbon / Low-Alloy Steel
Manufactured from medium-carbon steel (e.g., C35, C40) or low-alloy boron steel, quenched and tempered to achieve the property class 8.8 mechanical properties. The standard property class for the majority of EN 14399 structural connections, offering a good balance of strength, ductility, and cost, with generally lower sensitivity to hydrogen embrittlement during hot-dip galvanizing than property class 10.9.
Property Class 10.9 — Alloy Steel
Manufactured from alloy steel (e.g., 34CrMo4, 41Cr4, or equivalent boron-alloyed grades) quenched and tempered to the higher property class 10.9 strength level. Specified where higher connection capacity per bolt is required to reduce bolt count or connection size — but requires careful hydrogen embrittlement management if hot-dip galvanized, and generally exhibits reduced ductility margin at connection ultimate limit state compared to 8.8.
Nut Material — Matched Strength Grade
EN 14399 nuts are manufactured in a strength grade matched to the mating bolt property class (typically grade 8 nuts for 8.8 bolts; grade 10 nuts for 10.9 bolts) per ISO 898-2 proof load requirements — ensuring the nut does not become the weak link in the assembly and strips or fails before the bolt reaches its design preload or ultimate tensile capacity.
Washer Material — Hardened Steel
EN 14399-5/6 washers are manufactured from hardened steel (typically through-hardened or case-hardened to a specified hardness range) to prevent washer deformation or “dishing” under the high bearing stress generated at full bolt preload — an under-hardened washer that deforms during tightening absorbs part of the intended preload as plastic washer deformation rather than useful bolt tension, invalidating the assembly’s tested K-class preload relationship.
3.2 — Heat Treatment: Quenching and Tempering
All EN 14399 bolts and nuts undergo quenching (rapid cooling from austenitizing temperature, typically 850–900°C, in oil or polymer quenchant) followed by tempering (reheating to a controlled temperature, typically 400–650°C depending on the target property class) to develop the specified combination of tensile strength, yield strength, and ductility. Precise, consistent quench-and-temper process control — verified by production-lot hardness testing (typically Vickers or Rockwell C) and periodic mechanical testing (tensile, proof load, impact where specified) — is essential not only for meeting the nominal property class but for achieving the consistent, low-scatter mechanical behaviour that underpins reliable K-class preload testing results. Excessive hardness (over-tempering deficiency) increases hydrogen embrittlement susceptibility, particularly relevant for property class 10.9 assemblies destined for hot-dip galvanizing.
3.3 — Hydrogen Embrittlement Control
3.4 — Coating Systems
Plain / Uncoated (Oiled)
Bare quenched-and-tempered steel with a light rust-preventive oil film — used for indoor, dry, non-corrosive structural applications, or where a subsequent site-applied paint/coating system will provide the corrosion protection for the whole connection including the bolt heads.
Hot-Dip Galvanized (EN ISO 1461)
Zinc coating applied by immersion in molten zinc, providing robust, long-term corrosion protection for outdoor and exposed structural steelwork. Typically results in K2-class torque coefficient behaviour due to the zinc surface friction characteristics; requires hydrogen de-embrittlement process control for high-strength grades as noted above; nut thread over-tapping (to accommodate coating thickness in the internal thread) is a standard, code-permitted practice that must be correctly executed to preserve thread engagement and strength.
Zinc Flake Coating (e.g., Geomet, Dacromet-type)
Non-electrolytic zinc-aluminium flake coating, cured at relatively low temperature — avoids the hydrogen embrittlement risk associated with electroplating and the dimensional/thread-fit changes associated with hot-dip galvanizing, while providing corrosion resistance comparable to or exceeding hot-dip galvanizing in salt spray testing. Increasingly specified for high-strength (property class 10.9) EN 14399 assemblies in corrosive environments where hydrogen embrittlement risk must be minimised.
Special Low-Friction (K0) Coatings
Proprietary wax-based or PTFE-enhanced coatings engineered specifically to achieve K0-class torque coefficient performance — low, highly consistent friction that allows tighter preload control at a given installation torque. Specified for critical connections where the tightest possible preload accuracy is a design requirement, or where installation torque must be minimised for a given target preload (e.g., to reduce the required torque tool capacity on large-diameter high-class bolts).
3.5 — Manufacturing Process and Dimensional Control
- Cold heading: The standard manufacturing route for EN 14399 bolts up to approximately M36 — wire rod is cold-formed into the bolt blank (head and shank) in progressive die stations, producing a continuous, favourable grain flow through the head-to-shank transition that improves fatigue strength compared to a machined-from-bar alternative
- Thread rolling: Performed after heat treatment (quench and temper) for EN 14399 high-strength bolts — rolling the thread after heat treatment (rather than before) work-hardens the thread surface and produces superior fatigue and stress-corrosion performance compared to rolling before heat treatment or cutting the thread
- Nut tapping and washer machining: Nuts are hot-forged or cold-formed to shape, heat treated, and internally tapped to the matched thread tolerance class; washers are stamped or machined and through-hardened, with flatness and parallelism controlled to the tolerance required for consistent preload behaviour under the assembly’s certified K-class
- Lot traceability: Every EN 14399 production lot is assigned a unique lot/batch identifier that links the specific bolts, nuts, and washers in that delivery to the K-class test certificate, material certificate, and dimensional inspection records — this lot traceability is the practical mechanism that enforces the “matched assembly” requirement described in Section 1.1
Industry Applications
& Documentation
RR Hydraulic maintains full lot traceability from certified bar/wire rod to finished, K-class-tested EN 14399 assembly shipment. Dimensional verification, mechanical testing, K-class preload testing, and complete export/CE documentation are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 / Material Certification Requirements
| Certificate | Content | EPC / Structural Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Not acceptable for structural preloaded bolting | Never for EN 14399 structural connections |
| 3.1 (EN 10204) | Lot-traceable mech + chem + K-class test report | Mandatory — all EN 14399 supply | All structural steelwork connections, EXC1–EXC4 |
| 3.2 (EN 10204) | 3.1 + TPI countersign | Critical infrastructure; EXC3/EXC4 execution class; owner-specified critical connections | Bridges, high-rise, offshore steelwork, rail infrastructure |
4.3 — Applications by Industry
Slip-Resistant (Friction-Grip) Structural Connections
EN 14399 System HR or HV preloaded assemblies in Category B (serviceability slip-resistant) or Category C (ultimate limit state slip-resistant) connections per EN 1993-1-8, where the entire connection load path relies on friction generated by bolt preload rather than bolt shear — specified on bridge steelwork, crane runway beams, and any structure subject to load reversal or vibration where connection slip would be structurally unacceptable. Requires certified faying surface preparation (typically blast-cleaned to a specified slip factor class) in addition to correctly installed EN 14399 preloaded bolts.
Wind Turbine Tower Flange Connections
Large-diameter (M36–M48, often beyond standard EN 14399 range requiring project-specific qualification) high-strength preloaded bolt assemblies for tower section flange connections, subject to extremely high cyclic fatigue loading from wind and rotor dynamic loads over a 20–25 year design life. Preload consistency and long-term retention are critical — many wind turbine specifications require enhanced K-class testing, specific coating systems, and periodic re-torque inspection programmes beyond standard EN 14399/EN 1090-2 minimums.
Bridge and Infrastructure Steelwork
EN 14399 System HR or HV assemblies (frequently System HV on projects with a DIN-standard design heritage) for bridge girder splice connections, cross-frame connections, and bearing assemblies — subject to stringent execution class (typically EXC3 or EXC4 per EN 1090-2) requiring enhanced inspection, documentation, and often third-party witnessed installation and preload verification given the safety-critical, high-consequence-of-failure nature of bridge structural connections.
Industrial Plant and Petrochemical Pipe Rack Structures
Standard property class 8.8 System HR assemblies for the majority of industrial structural steelwork connections (pipe racks, equipment support structures, platform steelwork) where bearing-type (Category A) or standard slip-resistant (Category B) connections are specified — the most volume-significant EN 14399 application in EPC industrial project structural steel packages, typically procured in bulk against the project structural steel bolt schedule.
Modular and Prefabricated Steel Construction
System HRC (spline-shear, EN 14399-10) assemblies increasingly specified for modular and prefabricated steel building connections where installation speed and built-in preload verification (without requiring calibrated torque wrenches or DTI washer gap-gauging at every connection) support the fast-track erection schedules typical of modular construction methodology.
Offshore and Marine Structural Steelwork
Hot-dip galvanized or zinc-flake coated EN 14399 assemblies (property class 8.8, with careful hydrogen embrittlement control if 10.9 is required) for offshore platform topside structural steel, marine terminal structures, and coastal infrastructure steelwork — corrosion protection and long-term preload retention in a chloride-exposed, high-humidity marine environment are the dominant specification drivers, often combined with a supplementary paint system over the galvanized coating for extended maintenance-free service life.
4.4 — Installation Torque Reference
| Size | Target Preload — Class 8.8 (kN) | Torque — Class 8.8 (N·m) | Target Preload — Class 10.9 (kN) | Torque — Class 10.9 (N·m) |
|---|---|---|---|---|
| M16 | 70.3 | 225 | 98.9 | 316 |
| M20 | 109.8 | 440 | 154.4 | 618 |
| M22 | 135.8 | 595 | 190.9 | 836 |
| M24 | 158.2 | 760 | 222.4 | 1068 |
| M27 | 205.7 | 1115 | 289.2 | 1567 |
| M30 | 251.3 | 1510 | 353.4 | 2123 |
Indicative values for engineering reference only — final installation torque must be calculated from the specific lot’s certified K-value per its EN 14399-2 test report, and applied using a calibrated torque tool per the site tightening procedure required by EN 1090-2 for the applicable execution class.
k = Torque coefficient (mean k-value from the lot’s EN 14399-2 K-class test certificate)
d = Nominal bolt diameter (m)
F_p = Target preload force (N) — typically 70% of the bolt’s specified minimum tensile load (proof load) per EN 1090-2 default preload requirement, unless the project design specifies otherwise
Design note: Always use the specific lot’s certified k-value from its EN 14399-2 test report — the K0/K1/K2 class bands in Table 1.B are ranges, and the most accurate installation torque calculation uses the actual mean k-value stated on that lot’s certificate, not the class midpoint or an assumed generic value.
F_p (70% proof load) = 0.70 × 156,800 N = 109,760 N
T = 0.13 × 0.020 × 109,760 = 285 N·m
This calculated torque, using the lot’s specific certified k-value, is the value to programme into the calibrated torque tool for that installation — consistent with, though not identical to, the generic K1-class reference torque shown in Table 4.B, which uses a representative mid-range k-value.
4.5 — Export Packaging Specification
- Bolts, nuts, and washers packed together as complete matched assemblies per lot — never mixed across lots or split into separate bolt/nut/washer cartons, since the K-class certification applies only to the specific matched combination tested
- Each carton/box labelled with system (HR/HV/HRC), diameter, length, property class, coating, K-class, and lot/batch number, cross-referenced to the accompanying EN 14399-2 K-class test certificate and EN 10204 material certificate
- Hot-dip galvanized and zinc-flake coated assemblies packed with adequate separation/dunnage to prevent coating damage from bolt-to-bolt contact during transit — coating damage at the thread or bearing face can alter the assembly’s tested torque-tension behaviour
- Moisture-protective packaging (VCI paper or sealed poly bags within cartons) for uncoated/oiled bolts to prevent surface corrosion during ocean freight transit, particularly for shipments to humid or tropical destination climates
- ISPM-15 timber or export cartons; documentation in a waterproof pocket: EN 10204 3.1/3.2 MTC, EN 14399-2 K-class test certificate (per lot), dimensional inspection report, mechanical test report, hydrogen embrittlement test report (galvanized/plated 10.9), coating thickness report, CE Declaration of Performance, and packing list with system/diameter/length/class/K-class breakdown per item
4.6 — Complete Documentation Package for EPC / Structural Steelwork Supply
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate | EN 10204 3.1 / 3.2 | Mandatory — all supply | Lot-traceable; chemical + mechanical results, bolt/nut/washer |
| 02 | K-Class Preload Test Report | EN 14399-2 | Mandatory — every lot | Certified K0/K1/K2 class and mean k-value for the specific lot |
| 03 | Dimensional Inspection Report | EN 14399-3/4/5/6/9/10 tables | Mandatory | Diameter, length, thread, head/nut/washer dimensions |
| 04 | Mechanical Properties Report | ISO 898-1 (bolts) / ISO 898-2 (nuts) | Mandatory | Tensile, proof load, hardness per property class |
| 05 | Hydrogen Embrittlement Test Report | EN ISO 4042 | Mandatory — galvanized/plated Class 10.9 | Sustained-load or wedge test confirming de-embrittlement effectiveness |
| 06 | Coating Thickness Report | EN ISO 1461 (HDG) or coating-specific spec | Mandatory — coated assemblies | Local and mean coating mass/thickness by diameter |
| 07 | CE Declaration of Performance | EN 14399 harmonised parts / CPR | Mandatory — EU/UK construction works | Current, lot-applicable DoP reference |
| 08 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new project specifications | All parameters; before batch production |
| 09 | TPI Witness Certificate | SGS / BV / DNV / Lloyd’s / TÜV | Conditional — EXC3/EXC4; critical infrastructure | Co-witness K-class test, dimensional, mechanical |
| 10 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC / structural projects | Scope covers EN 14399 assembly manufacture |
| 11 | Country of Origin + Packing List | Chamber of Commerce / item-level | Mandatory | HS tariff code; system/class/K-class per item |
| 12 | Commercial Invoice + Bill of Lading | Per INCOTERMS 2020 | Mandatory | Freight forwarder issued |
Submit your system, diameter, length, property class, coating, and quantity to RR Hydraulic for a complete, certified commercial offer.