RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, NACE MR0175 compliance, DIN 25201 / VDI 2230 tested products, Third-Party Inspection available, and complete EPC export documentation packages.
Nord-Lock
Washers
A world-class technical reference for EPC contractors, mechanical and structural engineers, procurement heads, maintenance engineers, and global project buyers specifying wedge-locking washers, serrated flange solutions, and anti-loosening systems for vibrating machinery, structural connections, rotating equipment, rail, wind energy, offshore, and any application where bolt loosening under dynamic loading represents a safety, reliability, or maintenance cost risk.
Mechanism &
Why Bolts Loosen
Nord-Lock washers — and equivalent wedge-locking washers — work on a fundamentally different principle from conventional anti-loosening methods: instead of preventing the nut or bolt from rotating, they make rotation geometrically impossible without increasing the bolt preload. Understanding why standard bolted joints loosen under vibration is essential to selecting and applying the correct solution.
1.1 — Why Bolts Loosen — The Junker Test Principle
Bolt loosening under vibration is not caused by the nut spinning off due to inertia — it is caused by transverse (lateral) vibration loading that momentarily eliminates the friction force at the thread and bearing face contact zones. Gerhard Junker (1969) demonstrated in his landmark paper that transverse vibration — even at amplitudes far below the bolt elastic range — causes micro-slip at the thread flanks and bearing face, progressively rotating the nut in the loosening direction. Each micro-slip event contributes a small angular rotation; after thousands of vibration cycles the cumulative rotation is sufficient to significantly reduce bolt preload.
The Junker test (DIN 65151 / ISO 16130) quantifies anti-loosening performance by applying controlled transverse vibration to a bolted test assembly and measuring the residual clamp force after a defined number of cycles. Standard hex nuts on standard washers lose 50–100% of initial clamp force within 1000–5000 Junker cycles. Spring washers (split ring washers) provide negligible improvement — once the spring is compressed flat in a properly preloaded joint, they provide no locking function. Prevailing torque nuts (nylon-insert, all-metal prevailing) perform better but lose effectiveness after re-use. Wedge-locking washers are among the most effective anti-loosening solutions in comparative Junker testing — maintaining 60–95% of initial clamp force across 10,000+ vibration cycles.
1.2 — The Wedge-Locking Mechanism Explained
Cam-and-Wedge Geometry
A Nord-Lock type wedge-locking washer pair consists of two identical washers — each washer has radial teeth on one face (the mating faces between the pair) and a cam profile on the other face (the face that contacts the bolt head/nut and the structural surface). The cam angle β is greater than the thread pitch angle α of the bolt. When installed as a pair (teeth meshing together, cams facing outward), the washers rotate as a unit relative to the bolt head and structural surface as the joint is assembled.
Tightening — How It Loads
During tightening, the bolt head or nut rotates relative to the structural surface. The washer pair is dragged by friction — the outer (cam) faces slip against the bolt head and structural surface while the teeth mesh together, locking the two washers as a unit. As the nut is tightened, the cam profile lifts the nut or bolt head: the cam rise ΔR = D × tan(β) increases bolt elongation beyond the nominal elongation for the tightening torque — the bolt is pre-tensioned to a higher level than a joint without washers for the same tightening torque, because the cam rise adds bolt elongation.
Why It Cannot Self-Loosen
If vibration induces a loosening rotation tendency in the nut, the cam faces (between the nut bearing face and the washer) must traverse the cam ramp in the loosening direction. Traversing the cam ramp in the loosening direction requires lifting the nut — increasing the bolt elongation further — which means increasing the bolt tension beyond the installed preload. Since the bolt tension cannot spontaneously increase (no external force is applied), the geometry makes it mechanically impossible for the nut to rotate in the loosening direction without an applied external torque. This is the wedge-locking principle: loosening is geometrically locked, not friction-locked.
Cam Angle vs Thread Pitch — The Critical Relationship
The cam angle β must exceed the bolt thread pitch angle α for the wedge-locking principle to be effective. If β ≤ α, a loosening rotation can still occur because the cam geometry no longer creates a net resistance to loosening rotation. Standard Nord-Lock washer cam angles are designed to exceed the pitch angle of all standard metric (ISO 965) and inch (ASME B1.1) thread forms — the cam angle is proprietary and varies by washer size, but is typically 10–15° for M6–M64 metric threads where the thread pitch angle ranges from approximately 2–4°.
Serrated (Radial Teeth) Engagement
The radial serrations on the inner mating faces of the washer pair mesh together when the two washers are assembled — the serrations prevent relative rotation between the washer pair. The serration geometry is designed so that the teeth mesh at any rotational position of the two washers relative to each other (full 360° engagement in increments of one tooth pitch). The number of teeth determines the angular increment of engagement — typically 8–32 teeth depending on washer size, giving angular increments of 11.25°–45°. Serration depth must be adequate to withstand the shear load from the cam force without teeth shearing off.
Nord-Lock vs Other Anti-Loosening Methods
Comparative Junker test data (DIN 65151) consistently shows: Standard nut + flat washer: 100% preload loss within 1000–3000 cycles; Spring (split) washer: 90–100% preload loss within 1000–3000 cycles (minimal improvement); Prevailing torque nut (nylon): 60–80% preload maintained to 5000 cycles; Prevailing torque nut (all-metal): 70–85% to 5000 cycles; Thread-locking adhesive (Loctite): 85–95% to 5000 cycles (but difficult to disassemble); Wedge-locking washers: 70–95% to 10,000+ cycles with easy disassembly. Wedge-locking is the preferred solution where maintenance access requires repeated disassembly.
1.3 — Anti-Loosening Solution Comparison
| Method | Mechanism | Junker Residual Preload | Reusable | Disassembly | Cost | Preferred Application |
|---|---|---|---|---|---|---|
| Wedge-Lock Washer | Geometric cam lock | 70–95% | Multiple times | Standard tools | Medium | Vibrating machinery; structural; offshore |
| Split (Spring) Washer | Spring friction | 5–20% | Yes (single use) | Easy | Very low | Not recommended — negligible locking |
| Serrated Flange Nut/Bolt | Serration bite | 50–70% | Limited (2–3 uses) | Easy | Low | Light vibration; thin sheet metal |
| Prevailing Torque Nut (Nylon) | Friction (nylon) | 60–80% | Limited (3–5 uses) | Easy | Low | General machinery; max 100°C |
| Prevailing Torque Nut (All-Metal) | Friction (deformed thread) | 70–85% | 3–5 uses | Easy | Medium | High-temp vibration; above 100°C |
| Thread-Locking Adhesive | Chemical adhesive | 85–95% | Single use | Heat required | Low | Permanent or semi-permanent joints |
| Castle Nut + Cotter Pin | Mechanical positive lock | 100% (positive) | Yes | Remove pin | Medium | Safety-critical; aircraft; vehicle axles |
| Double Nut (Jam Nut) | Friction inter-lock | 50–70% | Yes | Two wrenches | Low | General machinery; pipe supports |
| Disc Spring (Belleville) | Spring preload reserve | 85–95% | Yes | Standard tools | Medium | Thermal cycling; flange preload |
1.4 — Wedge-Locking Geometry and Clamp Force Mechanics
D_cam = Mean diameter of the cam surface on the washer (mm) — approximately equal to washer OD
β = Cam angle of the wedge-locking washer (°) — typically 10–15° for standard metric thread sizes
k_bolt = Bolt stiffness (N/mm) = E × A_stress / L_bolt
F_additional = Additional bolt tension generated by cam rise (N)
Loosening resistance condition (cam angle must exceed thread pitch angle):
β > α_thread where α_thread = arctan(p / π × d₂)
p = Thread pitch (mm); d₂ = Thread pitch diameter (mm)
For M16 bolt: p = 2 mm; d₂ = 14.701 mm → α = arctan(2 / π × 14.701) = 2.48°
Nord-Lock M16 cam angle β ≈ 12° → β >> α → loosening geometrically locked
Because the cam rise adds bolt elongation during tightening, the effective bolt tension at a given installation torque is higher with wedge-lock washers than without. Tightening torque values published in VDI 2230 and ASME bolt torque tables assume flat hardened washers — when wedge-lock washers are used, the installation torque should be reduced by approximately 10–20% to achieve the same target bolt preload. Consult the washer manufacturer’s installation torque correction table for each bolt size and friction coefficient.
Submit your bolt size, application environment, material grade, and quantity for a documented RFQ within 24 hours.
Dimensional Reference
& Standards Compliance
Nord-Lock type wedge-locking washers are available in standard, large OD (SP), and bolt-specific variants across metric M5–M100+ and inch 3/16″–4″. Dimensional compliance per DIN 25201 and the manufacturer’s published dimensional tables. All applicable standards are supported at RR Hydraulic.
Submit bolt size, washer type (standard / SP / wide), material, coating, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — Nord-Lock Type Washer Product Variants
Standard Wedge-Lock Washer (NL Series)
Supplied as a pair — two identical washers that form the cam-and-serration locking system. Inner diameter slightly larger than the bolt nominal diameter (clearance fit for installation). OD sized to match the bearing face of the bolt head or nut. Standard washer OD is compatible with standard hex bolts (ASME B18.2.1 / ISO 4014) and hex nuts (ISO 4032/4033). Property class hardness ≥ 430 HV (to exceed the bolt property class hardness and prevent the washer teeth from being sheared by the bolt bearing force). Available in carbon steel (zinc-flake coated), stainless steel SS 316, and titanium Grade 5.
Large OD Washer (SP / Wide Washer Series)
Same cam-and-serration geometry as the standard washer but with a larger outside diameter — providing a larger bearing area on the connected material surface. Specified when: the connected material has low compressive strength (aluminium, FRP, timber, plastic) and a standard-OD washer would cause localised crushing under the bolt head bearing force; or when the bolt hole in the connected material is oversized (slotted hole, oversized clearance hole) and a larger washer is required to bridge the hole. SP washers are dimensionally compatible with the same bolt head/nut as standard washers — the inner diameter is the same; only the outer diameter increases.
Bolt-Specific (NLB / NSBL) Washers
Wedge-locking washers pre-installed on specially designed bolts — the washer pair is captive on the bolt shank before installation, preventing washer loss and ensuring correct installation orientation (cam faces outward). Used in: high-volume automated assembly lines where washer pre-assembly eliminates component handling; confined-space installations where separately handling washer pairs is impractical; overhead installations where dropped washers represent a safety risk. The captive washer design requires a corresponding groove or feature machined into the bolt shank — not compatible with standard bolts unless the bolt is modified.
Nord-Lock Expander System
A different product category from the standard Nord-Lock washer — the Expander System uses radial expansion (cam-and-wedge in the radial direction) to secure bolts in oversized or elongated holes. Suitable for retrofit applications where the original bolt hole has been enlarged by corrosion or wear, for slotted holes where standard fasteners would slide under load, and for pipe support connections where slot holes allow thermal expansion positioning. The Expander System is not a substitute for standard wedge-lock washers in vibration applications — it addresses a different problem (hole oversize), although it also provides some vibration resistance.
Twin Stud Plate (W-Series)
A flat plate with wedge-locking washers pre-integrated at each corner bolt hole position — provides a complete locking solution for equipment base plates, cover plates, and inspection hatch connections without requiring separate washer pairs at each bolt position. Used for: access panels on rotating equipment (compressor, turbine, gearbox covers); equipment inspection covers on offshore and industrial machinery; mounting plates for vibrating instrument connections. The pre-integrated design ensures every bolt position receives the washer pair — reduces installation errors from missed washers on multi-bolt plates.
Glued (Adhesive-Bonded) Variants
Wedge-locking washers with a thin adhesive layer on the inner-face serrations — the adhesive bonds the two washers together as a single pre-assembled unit before installation, preventing accidental separation during handling and ensuring correct mating face orientation at assembly. The adhesive bond breaks during installation tightening, allowing the serrations to engage properly. Available as an option for difficult installation environments (overhead work, confined spaces) and for automated assembly where single-unit handling reduces cycle time. The adhesive does not affect the cam-locking performance once the bond is broken by tightening.
2.2 — Wedge-Lock Washer Dimensional Reference
| Bolt Size | Washer ID (mm) | Standard OD (mm) | Large OD / SP (mm) | Pair Thickness (mm) | Min Hardness (HV) | Max Bolt Property Class |
|---|---|---|---|---|---|---|
| M5 | 5.5 | 9.6 | — | 2.0 | 430 | 12.9 |
| M6 | 6.6 | 11.5 | 14.5 | 2.2 | 430 | 12.9 |
| M8 | 8.6 | 15.2 | 19.6 | 3.2 | 430 | 12.9 |
| M10 | 10.8 | 18.0 | 24.0 | 3.6 | 430 | 12.9 |
| M12 | 13.0 | 21.8 | 28.0 | 4.2 | 430 | 12.9 |
| M14 | 15.0 | 25.6 | 33.0 | 4.6 | 430 | 12.9 |
| M16 | 17.0 | 29.4 | 38.0 | 5.2 | 430 | 12.9 |
| M20 | 22.0 | 36.8 | 47.0 | 6.0 | 430 | 12.9 |
| M24 | 26.0 | 44.0 | 56.0 | 7.2 | 430 | 12.9 |
| M30 | 32.0 | 55.0 | 70.0 | 8.8 | 430 | 10.9 |
| M36 | 38.0 | 66.0 | 85.0 | 10.8 | 430 | 10.9 |
| M48 | 50.0 | 87.0 | 110.0 | 13.0 | 430 | 10.9 |
| M64 | 67.0 | 115.0 | — | 17.0 | 430 | 10.9 |
2.3 — Applicable Standards and Compliance Framework
DIN 25201
Design Criteria for High-Strength Bolt Connections with Locking Elements — the German standard governing the design and testing of bolt locking systems, including wedge-locking washers. DIN 25201 defines the Junker test method (transverse vibration test) parameters, the acceptance criteria for locking systems (minimum residual clamp force after a defined number of cycles), and the load conditions for which locking systems must be qualified. All wedge-locking washer systems intended for structural, machinery, and EPC industrial applications should be tested per DIN 25201 / ISO 16130 as a qualification requirement — demand test certificates from the washer manufacturer confirming DIN 25201 compliance.
VDI 2230
Systematic Calculation of High Duty Bolted Joints — the comprehensive German engineering guideline for bolted joint design. VDI 2230 provides the calculation method for: required bolt preload; minimum bolt cross-section; fatigue load at thread root; tightening torque for a given bolt material and friction coefficient; and selection of anti-loosening method based on the loading type (static, vibrational, thermal cycling). For wedge-locking washer applications: VDI 2230 confirms that the required bolt preload can be achieved with the washer in the joint, and the tightening torque is calculated accounting for the washer friction coefficient and cam geometry.
ISO 16130
Aerospace series — Bolts and screws — Dynamic (vibrational) test method and acceptance criteria. The international standard for vibration testing of fastening systems — formally specifies the Junker test apparatus parameters (test frequency, lateral displacement amplitude, axial preload) and acceptance criteria for locking performance. ISO 16130 is the aerospace-sector equivalent of DIN 25201 and uses an equivalent test methodology. Wedge-locking washers claiming ISO 16130 compliance must have third-party test certificates demonstrating residual preload above the minimum acceptance threshold after the specified number of test cycles.
ISO 7089 / 7090 / 7091
Plain washers for bolted connections: ISO 7089 (normal series, product grade A), ISO 7090 (chamfered, product grade A), ISO 7091 (normal series, product grade C). These standards govern the OD, ID, and thickness of plain flat washers used alongside or instead of wedge-locking washers. In joint design: if wedge-locking washers are specified, plain flat washers are not additionally required under the same nut or bolt head — adding a plain washer between the wedge-lock washer and the bolt head/nut reduces the cam effect and must be avoided. Flat hardened washers (ISO 7090, product grade A) may be used under the structural surface side of the washer pair where the surface is soft or has a protective coating.
EN 14399 (High-Strength Structural)
High-strength structural bolting assemblies for preloading. EN 14399-1 through -10 cover the system requirements for high-strength structural bolting (property class 10.9 hex bolt + nut + washer assemblies for controlled pretensioning). Wedge-locking washers are not part of the standard EN 14399 structural bolting assembly, but may be specified as a supplementary locking measure on structural connections subject to vibration (crane runway connections, machinery mounting structures, offshore structural joints). When wedge-locking washers are added to an EN 14399 structural assembly, the installation procedure and torque values must be re-evaluated per VDI 2230 accounting for the washer cam geometry.
ASME B18.21.1 / B18.22.1
ASME B18.21.1: Lock Washers (Inch Series) — covers split-ring and tooth lock washers in inch sizes. ASME B18.22.1: Plain Washers (Inch Series) — covers flat washers. Wedge-locking washers are not covered by either standard — they are a proprietary product category. For US-coded EPC projects referencing ASME B18 for washer specification: specify wedge-locking washers by manufacturer designation or by describing the DIN 25201-tested cam-and-serration design explicitly in the project specification, referencing the bolt size, material, and locking performance requirement (minimum residual Junker clamp force). This ensures the EPC specification is unambiguous regardless of the washer supplier.
ISO 4042 — Coatings on Fasteners
Fasteners — Electroplated coatings. ISO 4042 governs electroplated coatings (zinc, nickel, chrome) on fasteners — including wedge-locking washers. Zinc electroplate on wedge-locking washers: minimum 5 µm (Fe/Zn5 class) per ISO 4042 for general indoor service; 8–12 µm for mild atmospheric outdoor service. Zinc-flake coating (Geomet, Dacromet) per ISO 10683 is preferred over zinc electroplate for wedge-locking washers in outdoor and industrial environments — provides better corrosion resistance without hydrogen embrittlement risk and without dimensional change that would affect the tight OD/ID tolerance of the washer.
ISO 10683 — Zinc-Flake Coatings
Non-electrolytically applied zinc flake coatings — the preferred coating system for wedge-locking washers in corrosive environments. Zinc-flake coatings (Geomet, Dacromet, Atotech Zintek) provide: corrosion protection equivalent to HDG (≥ 1000 hours neutral salt spray per ISO 9227); zero hydrogen embrittlement risk (no acid pickling, no cathodic current); thin and uniform coating (8–20 µm) that does not affect the precision cam geometry and serration engagement of the washer; and consistent friction coefficient (μ ≈ 0.10–0.16) essential for torque-tension calculation accuracy. Specification: ISO 10683 Class A-80 (480 hours neutral salt spray minimum) for standard EPC outdoor service; Class A-240 (720 hours) for marine atmospheric service.
Surface Treatment
& Installation Protocol
Wedge-locking washer material must be selected to match the bolt material, the service environment (corrosion class), and the temperature range. RR Hydraulic supplies wedge-locking washers in all standard grades — carbon steel with zinc-flake, SS 316, and titanium Grade 5 — with full EN 10204 3.1 material traceability.
3.1 — Material and Coating Options
| Material / Coating | Hardness | Temp Range | Seawater / Offshore | Industrial Atmosphere | H₂S Sour | Compatible Bolt Grade |
|---|---|---|---|---|---|---|
| Carbon Steel — Zinc-Flake (Geomet) | 440–500 HV | −40 to +150°C | Not suitable | Good | No (carbon steel) | 8.8 / 10.9 / 12.9 |
| Carbon Steel — HDG (ISO 1461) | 430–480 HV | −40 to +200°C | Fair (limited) | Very Good | No | 8.8 / 10.9 |
| Carbon Steel — Dacromet 500 | 440–500 HV | −40 to +300°C | Good | Excellent | No | 8.8 / 10.9 / 12.9 |
| SS 316 — Passivated | 430–450 HV | −196 to +400°C | Very Good | Excellent | Good (≤220 HV) | A4-70 / A4-80 |
| Duplex 2205 — Passivated | 290–320 HB | −50 to +315°C | Excellent | Excellent | Very Good (NACE) | Duplex stud bolts |
| Titanium Grade 5 | 300–380 HV | −200 to +300°C | Excellent | Excellent | Excellent | Ti Grade 5 bolts |
| Inconel 625 | 200–250 HB | −196 to +500°C | Excellent | Excellent | Excellent | Inconel stud bolts |
3.2 — Hardness Requirement for Washer Teeth Integrity
A critical but frequently overlooked requirement for wedge-locking washers: the washer hardness must exceed the bolt property class bearing hardness equivalent to prevent the radial serration teeth from being sheared or deformed under the combined axial bolt load and the cam shear force. If the washer hardness is below the bolt bearing face hardness, the serration teeth will plastically deform during tightening — reducing the cam rise, reducing the locking effectiveness, and generating metallic debris in the joint.
- For ISO 898-1 Grade 10.9 bolts (940 MPa yield): washer hardness ≥ 430 HV mandatory — carbon steel washers meet this requirement; SS 316 washers (≈430–450 HV) are at the limit for Grade 10.9 bolts; check manufacturer’s data for each specific SS 316 washer product
- For ISO 898-1 Grade 12.9 bolts (1100 MPa yield): washer hardness ≥ 440 HV — carbon steel washers are adequate; SS 316 washers may be marginal — consult manufacturer; titanium Grade 5 washers (≈300–380 HV) are NOT suitable for use with Grade 12.9 bolts
- For A4-70/A4-80 (SS 316) bolts (700–800 MPa UTS): SS 316 wedge-lock washers are compatible — the washer hardness (430–450 HV) exceeds the bearing hardness requirement for A4 bolts
- For Duplex 2205 stud bolts: Duplex 2205 washers are compatible; SS 316 washers may also be used if the PREN requirement for the environment is met by SS 316
3.3 — Correct Installation Protocol
1. Install as a Pair — Cams Facing Outward
Wedge-locking washers must always be installed as a matched pair. The correct orientation: both cam faces (smooth inclined ramp surfaces) must face outward — one cam face against the bolt head or nut bearing face; the other cam face against the structural surface or the connected component. The serrated (radial teeth) faces of the two washers must face each other (inward, mating together). If only one washer is installed, or if the washers are installed with the cams facing inward, the locking mechanism does not function. The most common installation error is orienting one or both washers incorrectly — the cam and serrated faces must be identified before installation.
2. Use Standard Tightening Method
Standard torque wrench or hydraulic bolt tensioner — no special tools required. The installation torque for wedge-locking washers is the same as for standard flat washers with the same bolt grade and friction coefficient. Some washer manufacturers recommend a 10–15% torque reduction vs standard flat-washer values to account for the cam rise additional preload — consult the manufacturer’s data sheet for the specific washer product and bolt size. Do NOT use impact wrench for final tightening — impact torque is poorly controlled and may exceed the bolt yield load when combined with the cam preload addition.
3. Surface Preparation — No Paint or Coating Between Washer and Structure
The cam face of the washer that contacts the structural surface must make direct metal-to-metal contact — do not install wedge-locking washers over painted, galvanised, or coated structural surfaces where the coating thickness will compress and relax under the washer bearing load. Any coating or non-metallic layer between the washer cam face and the structural surface will creep under sustained bolt preload, reducing the effective cam height and lowering the locking effectiveness. Where the structural surface is coated: either remove the coating at the washer contact zone before installation, or accept reduced locking performance.
4. Hardened Washer Under Structural Surface Side
If the structural surface material is softer than the washer cam face (aluminium, FRP, plastic, timber), install a hardened flat washer between the wedge-lock washer cam face and the soft structural surface — the hardened flat washer distributes the cam force over a larger area, preventing the cam profile from indenting the soft surface. The hard flat washer must be installed on the structural surface side only (not between the washer pair and the bolt head or nut) — a flat washer between the wedge-lock washer pair and the bolt head/nut will reduce the cam engagement and must be avoided.
5. Reuse and Replacement Criteria
Wedge-locking washers are reusable for multiple assembly and disassembly cycles — the locking function is mechanical (geometry), not chemical, so it is not consumed by the first use as with thread-locking adhesive. Replacement is required when: the serration teeth show visible plastic deformation or shearing; the cam surface shows wear grooves deeper than 0.2 mm; the washer shows corrosion pitting that breaks the cam profile continuity; or the washer OD or ID has been damaged preventing correct seating. Inspect visually at each disassembly — discard and replace any washer with visible serration damage, cam wear, or corrosion pitting. Never re-use a washer pair that was torqued past the bolt yield load.
6. Identification — Distinguishing Cam from Serrated Face
On a standard wedge-locking washer pair: the cam face (smooth inclined ramp surface) appears as a smooth annular surface with a visible slope when viewed at an angle — looking across the washer face you can see the flat ramp segments. The serrated face appears as a pattern of radial ridges (teeth) across the inner mating zone. In practice: the cam face is smoother to the touch; the serrated face is textured. Most quality manufacturers stamp or mark the washer to identify the cam face direction — look for a directional arrow, “IN” / “OUT” markings, or a surface texture difference. When in doubt: place the two washers face-to-face (teeth meshing) — the remaining faces (cams) face outward, which is the correct installation orientation.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from raw material to packed washer shipment on all wedge-locking washer orders. Dimensional inspection of cam geometry, hardness testing, coating inspection, and EN 10204 3.1 / 3.2 material traceability are standard on all project-grade wedge-locking washer supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Minimal — general hardware | Not acceptable for EPC structural or offshore applications |
| 3.1 | Material heat-traceable mech + chem | Minimum for all EPC structural washers | All wedge-lock washers for structural, machinery, offshore use |
| 3.2 | 3.1 + TPI countersign | Offshore critical; NACE; subsea | Safety-critical structural joints; NACE sour+offshore combined |
4.3 — Applications by Industry
Rotating Machinery — Compressors, Turbines, Pumps
The primary EPC wedge-locking washer application. Reciprocating and rotating machinery generates continuous transverse vibration at the bolted connection between the machine body, baseplate, and foundation. Standard nuts on flat washers loosen progressively — requiring periodic re-torquing that interrupts operations. Carbon steel zinc-flake wedge-lock washers (M20–M52) on holding-down bolts and on machine casing cover bolts. SS 316 or Duplex 2205 washers where the machine handles corrosive process fluids and SS bolts are already specified. DIN 25201 Junker test certification mandatory for machinery foundation bolt washer supply to major rotating equipment OEMs.
Wind Turbine Tower Flange Connections
Wind turbine tower flange bolted connections (M36–M80, property class 10.9) are subject to continuous fatigue loading from wind-induced tower bending — one of the most demanding cyclic loading environments for structural fasteners. Wedge-locking washers are specified by several wind turbine OEMs (Vestas, Siemens Gamesa, GE) for tower flange connections where conventional flat washers and prevailing torque nuts have shown bolt loosening in service. Carbon steel Dacromet-coated wedge-lock washers for tower flange service (Dacromet withstands the wet atmospheric marine environment at wind farm locations). SP (large OD) variants for joints with oversized or slotted tower flange bolt holes.
Offshore Platform Structural and Topside Connections
SS 316 or Duplex 2205 wedge-locking washers for offshore topside structural connections subject to dynamic wave loading — module support frame connections, crane pedestal bolting, helideck structural connections, and firewater pump foundation bolts. Dynamic wave loading imposes transverse and bending loads on structural bolt assemblies similar to machinery vibration — conventional flat washers lose preload under sustained wave loading. EN 10204 3.1 minimum; 3.2 with DNV/Lloyds TPI for safety-critical structural connections. Passivation per ASTM A967 for all SS washer lots for offshore supply.
Rail and Railway Track Fastening Systems
Railway rail fastening systems experience high-frequency, high-amplitude transverse vibration from train wheel-rail interaction — one of the earliest industries to adopt wedge-locking washers. Carbon steel zinc-flake washers for rail joint fishplate connections (M20–M24); Duplex 2205 for coastal and tunnel rail joints in high-humidity or chloride environments. Railway bolt-loosening creates a safety risk — loose joint bolts lead to rail displacement and potential derailment. European railway standards (EN 13481) require Junker test qualification for all rail joint fastening components. Nord-Lock washers are tested and approved per the relevant UIC (Union Internationale des Chemins de fer) specifications for rail applications.
Pressure Vessel and Flanged Joint Applications
Wedge-locking washers on pressure vessel manway closures and flanged connections subject to vibration (reciprocating compressor discharge flanges, pulsating flow piping). The combination of internal pressure fluctuation and external machine vibration creates cyclic loading that progressively loosens standard bolted flange joints. Carbon steel Dacromet or Geomet-coated wedge-lock washers on A193 B7 stud bolt assemblies for compressor discharge flanges. SS 316 wedge-lock washers on A193 B8M SS stud bolt assemblies for corrosive fluid flanges. Note: verify that the washer pair thickness does not increase the effective stud bolt grip length to the point where the stud bolt must be specified longer — recalculate required stud bolt length per ASME B16.5 adding washer pair thickness to the standard formula.
Mining, Heavy Machinery, and Quarrying Equipment
Heavy mining machinery — crushers, screens, vibrating feeders, conveyor drive units, mill liner bolts — operates in the highest vibration loading environment of any industrial equipment category. Vibrating screen and crusher deck liner bolts are a classic wedge-locking application: bolt loosening on a crusher liner causes liner plate movement, accelerated wear, and crusher damage within hours of operation. Heavy-duty carbon steel zinc-flake wedge-lock washers (M20–M36, SP large OD for soft liner material) are the standard solution. Mill liner bolts (M48–M64) use large-OD SP washers to spread the bolt bearing load over the softer rubber or composite liner material without crushing it.
4.4 — Export Packaging Specification
- Wedge-locking washers packed in matched pairs — each pair (two washers, teeth facing each other) in a single polybag; pre-assembled pairs labelled with bolt size, OD variant (standard or SP), material grade, coating type, and lot number; never loose washers in bulk where the mating pair could become separated
- For large volume supply (100+ pairs per size): pairs polybag-packed, then inner carton-packed per size and variant with clear external labelling; inner cartons inside outer ISPM-15 crate; size-mixed shipments with individual size/grade compartments in the shipping crate
- SS and Duplex washer pairs in dedicated SS-labelled polybags, segregated from carbon steel hardware — iron contamination from CS packaging clips or other hardware deposits iron particles on SS surfaces causing marine corrosion pitting after installation in offshore service
- Carbon steel zinc-flake washers: VCI poly inner packaging to protect the zinc-flake coating from moisture during ocean freight; zinc-flake coatings are hydrophobic but prolonged moisture exposure in unsealed packaging can cause white rust on the zinc surface during transit
- Titanium washer pairs: packed as for titanium fasteners — grade identification by anodise colour or label; segregated from all other metals; individual pair serialisation for aerospace or safety-critical applications
- Junker test certificate, EN 10204 3.1/3.2 MTC, dimensional inspection report, hardness certificate, cam geometry report, coating inspection certificate, PMI report (SS/exotic grades), and FAI report in waterproof document pocket per shipment lot
- ISPM-15 heat-treated timber crates or strong cardboard export cartons for international shipping; desiccant sachets in sealed inner bags for high-humidity destination countries
4.5 — Complete Project Documentation Package
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 3.1 / 3.2 | Mandatory — all structural washer supply | Material heat-traceable; one MTC per heat lot |
| 02 | Chemical Composition Report | Certified lab analysis | Mandatory | Per material grade (carbon steel / SS 316 / Duplex) |
| 03 | Hardness Test Report | ISO 6507 Vickers | Mandatory — all lots | Minimum 430 HV confirmed; SS 316 cold-worked to 430 HV |
| 04 | Dimensional Inspection Report | Per manufacturer table / DIN 25201 | Mandatory | OD, ID, pair thickness, cam rise verified |
| 05 | Cam Geometry Profile Report | CMM / profilometry | Mandatory — EPC structural; offshore | Cam angle β; cam rise height at 4 positions per washer |
| 06 | Coating Inspection Certificate | ISO 10683 / ISO 2178 / ASTM A967 | Mandatory — all coated washers | Zinc-flake thickness; salt spray hours; passivation (SS) |
| 07 | PMI Report (XRF) | Per lot — SS / Duplex / Ti / Inconel | Mandatory — non-CS grades | SS 316 vs SS 304; Duplex 2205 vs 2507; Ti Gr.5 vs Gr.2 |
| 08 | Junker Test Certificate (DIN 25201) | Accredited test lab — DIN 65151/ISO 16130 | Conditional — machinery OEM; rail; wind; offshore critical | Product qualification certificate; residual preload ≥ 60% at 10,000 cycles |
| 09 | Pair Assembly Verification Report | In-house inspection per procedure | Mandatory — all lots | Teeth mesh; cam faces parallel; pair thickness uniformity |
| 10 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new configurations | All parameters; released before batch production |
| 11 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2 | Co-witness at manufacturer; hardness + dimensional |
| 12 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers wedge-lock washer manufacture |
| 13 | Country of Origin + Packing List | Chamber of Commerce / item-level | Mandatory | HS tariff code; paired lot count per line item |
| 14 | Commercial Invoice + Bill of Lading | Per INCOTERMS 2020 | Mandatory | Freight forwarder issued; HS tariff code |
4.6 — ISO and Quality System Compliance
ISO 9001:2015
Quality Management System covering raw material procurement and heat traceability, pressing and forming process qualification for the cam and serration geometry, cold-working process control for SS 316 washers to achieve ≥430 HV hardness, zinc-flake and Dacromet coating process control (temperature, time, coating thickness per batch), Vickers hardness testing protocol, dimensional inspection programme, cam geometry profilometry procedure, pair assembly verification, and full material traceability. Mandatory for all EPC, structural, and machinery project procurement qualification of wedge-locking washers.
DIN 25201 / VDI 2230
DIN 25201 is the governing design and test standard for wedge-locking washer qualification — all EPC project specifications requiring wedge-lock washers should reference DIN 25201 as the performance standard and require a Junker test qualification certificate from the washer supplier. VDI 2230 provides the bolted joint calculation framework within which the wedge-locking washer is specified — confirming that the required preload can be achieved, the washer hardness is adequate, and the installation torque is correctly calculated accounting for the washer friction coefficient and cam geometry. These two standards together constitute the complete specification and verification framework for industrial wedge-lock washer applications.
EN 14399 / AISC J3
EN 14399 (High-strength structural bolting for preloading) and AISC Specification Chapter J3 (Bolts and Threaded Parts) govern structural bolted connections. Wedge-locking washers supplement the EN 14399 / AISC J3 assembly system for structural connections subject to vibration or fatigue loading. When specifying wedge-lock washers in structural connections: verify that the additional washer pair thickness is included in the bolt grip length calculation; verify the net slip coefficient between the washer cam surface and the structural steel meets the EN 1993 / AISC slip-critical connection friction requirements; and confirm that the washer does not violate the maximum permitted washer stack height under the bolt head or nut per the applicable structural connection standard.
ISO 16130 / EN 3535
ISO 16130 (aerospace vibration test for fastening systems) and EN 3535 (aerospace SS fasteners) are the aerospace sector standards governing wedge-lock washer qualification for aircraft and aerospace applications. For EPC projects involving aerospace ground support equipment (GSE), launch structures, or defence applications requiring DIN 25201 / ISO 16130 equivalency: demand a combined test certificate covering both the DIN 25201 residual preload criteria and the ISO 16130 acceptance parameters. The test frequency, displacement amplitude, and acceptance criteria differ slightly between the two standards — a combined certificate ensures both aerospace and industrial structural qualification requirements are simultaneously satisfied.
Submit your bolt size, washer OD variant, material, coating, and quantity to RR Hydraulic for a complete, certified commercial offer.