RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, ISO 3506 SS grades, NACE MR0175 compliance, Third-Party Inspection, DIN / ISO / ASME standards, and complete EPC export documentation packages.
Spring Washers
A world-class technical reference for EPC contractors, mechanical and structural engineers, procurement heads, TPI inspection agencies, and global project buyers specifying spring washers in bolted joint assemblies across Oil & Gas, Power Generation, Petrochemical, Offshore, Instrumentation, Rotating Equipment, and Industrial Construction sectors worldwide.
Type Classification
& Locking Mechanics
Spring washers are resilient, non-flat washers that store elastic energy when compressed under a bolt or nut, providing a sustained spring force that compensates for joint relaxation, thermal cycling, vibration-induced loosening, and embedment creep — maintaining bolt preload and joint integrity over the service life of the assembly. They are fundamental components in bolted assemblies throughout EPC, Oil & Gas, rotating equipment, instrumentation, and structural applications.
1.1 — Technical Definition and Functional Role
A spring washer is a mechanically formed washer that derives its anti-loosening, load-maintaining, or vibration-damping function from its non-flat geometry — which stores elastic strain energy when flattened under bolt preload. Unlike a plain flat washer (which distributes load but provides no spring function), a spring washer acts as a calibrated spring element in series with the bolted joint, maintaining residual clamp force when the joint experiences settlement, thermal expansion or contraction, embedment relaxation, or dynamic vibration loads that would otherwise cause a plain bolt to loosen progressively.
In EPC and industrial environments, spring washers appear in: valve bonnet bolting, pump and compressor flange connections, instrument and transmitter mounting, rotating equipment panel fastening, pipe support bracket bolting in vibrating pipe systems, HVAC fan and blower assembly, motor terminal cover fastening, control valve actuator and positioner connections, cable tray structural joints, modular building cladding screws in vibrating structures, and any bolted joint subject to cyclic loads, thermal cycling, or vibration that would cause progressive loss of preload in a plain bolted joint.
RR Hydraulic manufactures and supplies spring washers under all applicable international standards with full EN 10204 3.1 / 3.2 traceability and project documentation capability.
1.2 — Spring Washer Type Classification
Split (Helical) Spring Washer — DIN 127
The most widely used spring washer type globally. A single-coil helical washer cut and offset axially — the cut ends bite into both the bolt/nut bearing face and the mating surface when fully loaded, providing both a spring force and a mechanical bite resistance against rotation. Per DIN 127 (metric, Type A standard / Type B heavy) and ASME B18.21.1 (inch). Standard for general EPC assembly, panel fastening, and instrument mounting across all industries.
Disc Spring (Belleville Washer) — DIN 2093
Conical disc washer with a defined load-deflection characteristic. Provides far higher spring force than a split washer for the same bolt size — load capacity 5–50× higher than split washers. Per DIN 2093 Series A, B, C. Used in high-load preload-retention applications: valve bonnet bolting, high-pressure flange connections, bearing preload systems, and spring packs where precise deflection-force relationship is required. Often stacked in series (lower force, more deflection) or parallel (higher force, same deflection).
Conical Spring Washer (DIN 6796)
Truncated cone geometry — shallower angle than Belleville; designed specifically for bolted joint preload retention under vibration and thermal cycling. Per DIN 6796. Works by maintaining a calibrated spring force across the full bolt relaxation range — superior to split washers for sustained preload retention in dynamically loaded joints. Used in machinery, rotating equipment covers, and automotive-type assemblies imported into EPC equipment. Load capacity intermediate between split and Belleville washers.
Wave Washer — DIN 137 / DIN 6905
Corrugated washer with multiple sinusoidal waves around the circumference. Provides a lower, more uniform spring force than split or disc washers — used where a gentle, distributed spring preload is required without the point-contact bite of a split washer. Per DIN 137 (single-wave) and DIN 6905 (multi-wave). Applications: instrument panel assembly, electronics mounting, bearing pre-loading in small assemblies, and thin-gauge sheet metal enclosures where split washer bite would damage the mating surface.
Toothed Lock Washer (Serrated) — DIN 6798
Flat washer with internal, external, or both-sided radial teeth that bite into the mating surface and nut face under load, providing positive mechanical locking. Per DIN 6798 Type A (external teeth), Type I (internal teeth), Type J (both sides). Higher bite resistance than split washers — better vibration loosening resistance. Used in electrical earthing connections (excellent galvanic contact through paint layers), motor terminal blocks, and high-vibration panel assembly. Not recommended where surface damage is unacceptable.
Tab / Locking Washer
Flat washer with one or more tabs that are bent up against a bolt head flat or into a slot after tightening, providing a positive mechanical lock. Per DIN 93 (single-tab), DIN 432 (multi-tab). Used in applications where vibrational loosening is catastrophic and a self-locking nut or thread-lock compound is not acceptable — rotating shaft locking nuts, bearing lock nuts, and gear retention systems. Must be renewed (replaced, not re-bent) on every removal — tab metal fatigues after one or two bends.
1.3 — Spring Washer Type vs Application: Engineering Selection
| Washer Type | Spring Force | Vibration Resistance | Preload Retention | Surface Damage Risk | Reuse | Primary EPC Application |
|---|---|---|---|---|---|---|
| Split (Helical) DIN 127 | Low–Moderate | Good | Moderate | Low–Moderate (bite marks) | Good | General assembly, panels, instruments |
| Disc / Belleville DIN 2093 | Very High | Excellent | Excellent | Low (flat bearing) | Excellent (if not overloaded) | Valve bonnets, flanges, bearing preload |
| Conical DIN 6796 | High | Very Good | Very Good | Low | Very Good | Machinery covers, rotating equipment |
| Wave DIN 137 | Low | Moderate | Moderate | Very Low | Good | Instrument panels, electronics, thin sheet |
| Toothed DIN 6798 | Low (bite only) | Very Good | Good | High (tooth bite) | Limited (teeth deform) | Earthing, motor terminals, high-vibration |
| Tab / Locking | None (positive lock) | Excellent (mechanical) | Excellent (mechanical) | Moderate (tab slot) | Single-use only | Shaft lock nuts, bearing retention |
1.4 — Locking Mechanics and Anti-Vibration Function
Spring Washer Anti-Loosening Mechanism
Spring washers resist loosening through two mechanisms: (1) elastic spring force — the compressed washer continuously pushes against the nut face, maintaining friction between nut and bolt thread even as the joint relaxes; (2) mechanical bite — the cut ends or teeth of the washer engage the mating surface and nut bearing face, providing a mechanical pawl-like resistance to backward rotation. Both mechanisms are load-dependent: once the spring is fully compressed (washer flattened), both mechanisms are lost.
Junker Vibration Test Performance
The Junker transverse vibration test (DIN 65151) is the industry standard for quantifying bolt loosening resistance under lateral vibration loads. Split (DIN 127) spring washers provide limited improvement vs a plain washer on the Junker test — they lose effectiveness once the washer flattens under preload. Nord-Lock, Belleville disc springs at correct loading, and prevailing-torque nuts significantly outperform split washers on the Junker test. For high-vibration critical applications, specify Belleville disc springs or Nord-Lock in preference to split washers.
Thermal Cycling Preload Retention
In assemblies subject to thermal cycling (flanged piping, valve bonnets, high-temperature equipment covers), bolt preload loss occurs through differential thermal expansion and creep/relaxation of joint members. Disc (Belleville) spring washers, correctly sized to remain within their elastic working range at operating temperature, maintain residual spring force throughout the thermal cycle — preventing flange leakage and cover loosening that would occur with plain bolted joints in cyclic thermal service.
Washer Flatness and the “Fully Flat” Limit
All spring washer types have a maximum compression limit — the point at which the washer becomes fully flat and all spring function is lost. For split washers (DIN 127): the washer must not be compressed fully flat under installation torque, or no spring force remains in service. The installation torque must be calibrated so the washer remains partially sprung at full tightening. Disc and conical washers are designed with a defined working deflection range — operating at the correct point on the load-deflection curve is essential for correct function.
Embedment Relaxation Compensation
All bolted joints experience embedment relaxation — a loss of bolt preload in the first hours to days after installation due to asperity smoothing at joint interfaces (typically 5–15% preload loss). Spring washers compensate for this loss by maintaining spring force while the joint settles. For Grade 8.8 and 12.9 high-preload joints where embedment loss must be minimised, Belleville disc spring stacks sized to accommodate the expected relaxation deflection are specified to maintain design preload within the required tolerance band.
Stacking Configuration (Disc Springs)
Belleville / disc springs can be stacked in parallel (same orientation — forces add, deflection same as single washer) or in series (alternating orientation — deflection adds, force same as single washer). Mixed stacks combine both. The correct stack configuration for a specific bolted joint depends on the required spring force at the working deflection point — a mechanical spring design calculation per DIN 2093 or equivalent is required for critical Belleville spring washer stack specifications.
1.5 — Spring Washer Load-Deflection Relationship
E = Young’s modulus of material (210,000 MPa for steel)
ν = Poisson’s ratio (0.3 for steel)
s = Axial deflection (compression) of washer (mm)
h₀ = Free height minus thickness: h₀ = H − t (mm)
H = Free (unloaded) height of washer (mm)
t = Washer material thickness (mm)
D = Outside diameter (mm)
K₁ = Factor depending on D/d ratio (tabulated in DIN 2093 Annex A)
Maximum elastic working deflection: s_max = 0.75 × h₀ (DIN 2093 recommendation)
Force at flat (s = h₀): F_flat = approx. 1.5 × F at s = 0.75 × h₀
Installation torque must leave the washer partially sprung — i.e., washer gap must NOT be fully closed after tightening. If gap is fully closed: the assembly has no spring reserve and vibration loosening will occur. Verify by checking for a residual gap (0.2–0.5 mm) under the washer after torquing. If no gap: reduce torque or specify a heavier section DIN 127B washer.
Submit your BOM, washer type, bore, material, coating, and quantity for a documented RFQ within 24 hours.
Load Ratings &
Standards Compliance
Spring washer dimensions — inside diameter, outside diameter, thickness, free height, and spring force — are governed by DIN 127 (split), DIN 2093 (Belleville), DIN 6796 (conical), DIN 137 (wave), DIN 6798 (toothed), and ASME B18.21.1 (inch). All applicable standards are supported with full certification at RR Hydraulic.
Submit washer type, bore size, material, coating, standard, and quantity to sales@rrhydraulics.com for a fully certified offer.
2.1 — DIN 127 Split (Helical) Spring Washer Dimensional Table
| Bolt Size | ID d₁ (mm) | OD d₂ — 127A (mm) | Thickness s — 127A (mm) | OD d₂ — 127B (mm) | Thickness s — 127B (mm) | Free Height H (mm) | Min Spring Load (N) — 127B |
|---|---|---|---|---|---|---|---|
| M3 | 3.1 | 6.0 | 0.8 | 6.2 | 1.0 | 1.6 | 55 |
| M4 | 4.1 | 7.6 | 1.0 | 7.9 | 1.2 | 2.0 | 110 |
| M5 | 5.1 | 9.3 | 1.2 | 9.7 | 1.5 | 2.4 | 165 |
| M6 | 6.1 | 11.8 | 1.6 | 12.3 | 2.0 | 3.2 | 310 |
| M8 | 8.2 | 14.8 | 2.0 | 15.5 | 2.5 | 4.0 | 540 |
| M10 | 10.2 | 18.1 | 2.5 | 18.9 | 3.0 | 5.0 | 825 |
| M12 | 12.2 | 21.1 | 3.0 | 22.0 | 3.5 | 6.0 | 1200 |
| M16 | 16.2 | 27.4 | 4.0 | 28.6 | 4.5 | 8.0 | 2100 |
| M20 | 20.2 | 33.6 | 5.0 | 35.0 | 5.5 | 10.0 | 3300 |
| M24 | 24.5 | 40.2 | 6.0 | 41.9 | 6.5 | 12.0 | 4750 |
| M30 | 30.5 | 50.2 | 7.5 | 52.4 | 8.0 | 15.0 | 7400 |
| M36 | 36.5 | 59.2 | 9.0 | 61.8 | 10.0 | 18.0 | 10500 |
2.2 — DIN 6796 Conical Spring Washer Dimensional Table
| Bolt Size | ID d₁ (mm) | OD d₂ (mm) | Free Height H (mm) | Thickness t (mm) | Spring Load at 0.75H (N) | Bolt Grade Compatibility | Typical Bolt Torque Range (Nm) |
|---|---|---|---|---|---|---|---|
| M4 | 4.3 | 9.0 | 1.3 | 0.7 | 360 | 5.8 / 8.8 | 2.5–4.5 |
| M5 | 5.3 | 11.0 | 1.6 | 0.9 | 610 | 5.8 / 8.8 | 4.5–8.0 |
| M6 | 6.4 | 13.0 | 1.9 | 1.0 | 1000 | 5.8 / 8.8 | 8.0–14.0 |
| M8 | 8.4 | 17.0 | 2.5 | 1.3 | 2100 | 8.8 / 10.9 | 18.0–32.0 |
| M10 | 10.5 | 21.0 | 3.0 | 1.6 | 3500 | 8.8 / 10.9 | 36.0–65.0 |
| M12 | 13.0 | 25.0 | 3.5 | 1.9 | 5200 | 8.8 / 10.9 | 60.0–110.0 |
| M16 | 17.0 | 34.0 | 4.8 | 2.5 | 9500 | 8.8 / 10.9 | 140.0–260.0 |
| M20 | 21.0 | 42.0 | 6.0 | 3.2 | 15000 | 8.8 / 10.9 | 280.0–500.0 |
| M24 | 25.0 | 50.0 | 7.0 | 3.8 | 21000 | 8.8 / 10.9 | 480.0–860.0 |
2.3 — Applicable Standards and Compliance Framework
DIN 127 (A & B)
Split (helical) spring washers — metric series. DIN 127A: standard section; DIN 127B: heavier section with higher spring load capacity. The most widely used spring washer globally. Hardened carbon spring steel (65 Mn or equivalent); Vickers hardness 420–500 HV; surface finish: electroplated zinc or passivated SS. Nominal bore matches metric bolt sizes M3 through M72. Companion to DIN 934 hex nuts and ISO 4762 SHCS.
DIN 2093
Disc springs (Belleville washers) — dimensions, force-deflection characteristics, and series classifications A, B, C (varying h₀/t ratio). Series A: h₀/t ≤ 0.4 (approximately linear load-deflection); Series B: 0.4 < h₀/t ≤ 0.75; Series C: 0.75 < h₀/t ≤ 1.3 (nonlinear, snap-through possible). DIN 2093 provides full design data tables and stacking guidance for engineering spring pack design in precision load-retention applications.
DIN 6796
Conical spring washers for bolted connections — specifically designed to compensate for bolt relaxation and maintain preload under vibration and thermal cycling. Load-deflection data provided in DIN 6796 for each size and bolt grade compatibility. Used with Grade 5.8, 8.8, and 10.9 bolts; each washer size is matched to a specific bolt size and grade combination. Widely used in automotive-derived machinery exported to EPC projects.
DIN 137 / DIN 6905
Wave washers — single corrugation (DIN 137) and multi-wave corrugated (DIN 6905). Provide gentle, uniform spring force without the bite marks of split or toothed washers. Used in instrument panel assembly, electronics housing, and thin-gauge enclosure fastening where split washer tooth bite would damage anodised or powder-coated surfaces. Spring force lower than split or conical washers — verify adequacy for the specific application load and vibration severity.
DIN 6798 (A / I / J)
Serrated (toothed) lock washers — external teeth (Type A), internal teeth (Type I), double-sided teeth (Type J). Teeth bite through paint, anodising, and oxide layers to create direct metal-to-metal contact — critical for low-resistance electrical earthing connections in electrical panels and equipment enclosures. Type J (double-sided) provides highest bite and locking resistance. Per DIN 6798; also referenced in BS 4320 and equivalent standards.
ASME B18.21.1
Helical spring (split) lock washers — inch series. Regular, heavy, and extra-duty sections for inch bolt sizes #2 through 3″. The governing standard for inch-series split spring washers in North American EPC projects and ASME-coded equipment. Material: medium-carbon steel hardened; minimum hardness 38–45 HRC. Used with inch UNC/UNF bolts and screws in US EPC specifications.
ISO 3506
Mechanical properties of corrosion-resistant stainless steel fasteners — applicable to SS spring washers as a material specification reference. Property classes A2-70 (SS 304) and A4-70 / A4-80 (SS 316) define the strength requirements for SS spring washer material. SS spring washers must be manufactured from the correct grade to meet the mechanical property requirements — particularly important for split and conical spring washers where hardness (work-hardening of SS) is the primary strength mechanism.
NACE MR0175 / ISO 15156
For spring washers used in H₂S sour service environments (O&G production, amine plants, sour crude handling): carbon steel spring washers with hardness above 22 HRC are NOT acceptable. Standard hardened carbon steel spring washers (DIN 127) typically exceed this limit. Specify SS A4-70 (SS 316) spring washers for all sour service bolted joint assemblies. SS spring washers are inherently NACE-compliant within the hardness limits of ISO 3506.
2.4 — Spring Washer vs Alternative Anti-Loosening Methods
| Method | Standard | Vibration Resistance | Thermal Cycling | Removability | Complexity | EPC Application |
|---|---|---|---|---|---|---|
| Split Spring Washer (DIN 127) | DIN 127 | Good | Moderate | Excellent | None — drop in | General assembly; instruments; panels |
| Belleville Disc Spring (DIN 2093) | DIN 2093 | Excellent | Excellent | Good | Design calculation required | Valve bonnets; flanges; bearing preload |
| Nord-Lock Wedge Washer | Nord-Lock proprietary | Excellent (Junker tested) | Good | Excellent | None — pair required | Critical rotating equipment; structural |
| Prevailing-Torque Nut (Nyloc) | ISO 7042 / DIN 985 | Very Good | Limited (>100°C nylon) | Good (multiple uses) | None | General assembly; enclosures; panels |
| Thread Lock Adhesive | Loctite 243 / 270 | Excellent (243) / Permanent (270) | Good | Moderate (heat to remove) | Application process | Hydraulic; precision machinery; OEM |
| Castellated Nut + Cotter Pin | ISO 7035 / DIN 937 | Excellent (positive lock) | Excellent | Good | Requires drilled bolt | Safety-critical; pressure vessel; piping |
| Tab / Locking Washer | DIN 93 / DIN 432 | Excellent (mechanical) | Excellent | Single-use (replace each time) | Tab bending after tightening | Shaft lock nuts; bearing retention |
| Double Nutting | Engineering practice | Good | Good | Good | None — extra nut | Rod ends; turnbuckles; hanger rods |
2.5 — Bore and Outside Diameter Reference
| Bolt Size | DIN 127A ID/OD (mm) | DIN 127B ID/OD (mm) | DIN 6796 ID/OD (mm) | DIN 6798A ID/OD (mm) | DIN 6905 Wave ID/OD (mm) | ASME B18.21.1 Regular ID/OD (in) |
|---|---|---|---|---|---|---|
| M4 / #8 | 4.1 / 7.6 | 4.1 / 7.9 | 4.3 / 9.0 | 4.1 / 9.0 | 4.3 / 10.0 | 0.168 / 0.337 |
| M5 / #10 | 5.1 / 9.3 | 5.1 / 9.7 | 5.3 / 11.0 | 5.1 / 11.0 | 5.3 / 12.0 | 0.194 / 0.380 |
| M6 / ¼” | 6.1 / 11.8 | 6.1 / 12.3 | 6.4 / 13.0 | 6.1 / 13.0 | 6.4 / 14.5 | 0.260 / 0.489 |
| M8 / 5/16″ | 8.2 / 14.8 | 8.2 / 15.5 | 8.4 / 17.0 | 8.2 / 17.2 | 8.4 / 19.0 | 0.323 / 0.586 |
| M10 / ⅜” | 10.2 / 18.1 | 10.2 / 18.9 | 10.5 / 21.0 | 10.2 / 20.8 | 10.5 / 23.0 | 0.390 / 0.683 |
| M12 / ½” | 12.2 / 21.1 | 12.2 / 22.0 | 13.0 / 25.0 | 12.2 / 24.9 | 13.0 / 27.0 | 0.511 / 0.867 |
| M16 / ⅝” | 16.2 / 27.4 | 16.2 / 28.6 | 17.0 / 34.0 | 16.2 / 32.5 | 17.0 / 36.0 | 0.635 / 1.040 |
| M20 / ¾” | 20.2 / 33.6 | 20.2 / 35.0 | 21.0 / 42.0 | 20.2 / 40.6 | 21.0 / 44.0 | 0.760 / 1.209 |
| M24 / 1″ | 24.5 / 40.2 | 24.5 / 41.9 | 25.0 / 50.0 | 24.5 / 48.9 | 25.0 / 53.0 | 1.011 / 1.493 |
Coatings &
Manufacturing Process
Spring washer material must provide both adequate spring properties (hardness, elastic range, fatigue life) and corrosion resistance for the service environment. RR Hydraulic manufactures spring washers in all standard grades — hardened carbon steel, stainless, phosphor bronze, and beryllium copper — with full EN 10204 material traceability.
3.1 — Material Grade Overview and Properties
| Material | Spec / Standard | Hardness (HV) | Tensile Strength (MPa) | Temp Range (°C) | Corrosion Resistance | NACE MR0175 | Primary Application |
|---|---|---|---|---|---|---|---|
| Medium-Carbon Spring Steel | DIN 127 / DIN 2093 | 420–500 | 1300–1600 | −20 to +200 | Low — must be coated | No (exceeds 22 HRC) | General EPC; standard industrial assembly |
| 65Mn Spring Steel | DIN 17221 | 420–490 | 1300–1500 | −20 to +200 | Low — must be coated | No | Standard split washers; DIN 127B |
| 51CrV4 Alloy Spring Steel | EN 10089 | 430–520 | 1400–1700 | −40 to +250 | Low — must be coated | No | Belleville disc springs; high-load packs |
| A2-70 (SS 304) | ISO 3506 / DIN 127 | Max 250 | 700 | −196 to +300 | Good | Yes | Food, pharma, mild chemical, indoor |
| A4-70 (SS 316) | ISO 3506 | Max 250 | 700 | −196 to +300 | Very Good | Yes | Marine, offshore, chemical, NACE service |
| A4-80 (SS 316 SH) | ISO 3506 | Max 320 | 800 | −196 to +300 | Very Good | Yes | High-load marine / offshore spring washers |
| Phosphor Bronze (CuSn8) | CW453K / DIN 17662 | 150–280 | 500–900 | −200 to +150 | Very Good | Yes | Non-magnetic; marine electrics; brass |
| Beryllium Copper (CuBe2) | CW101C / ASTM B197 | 340–400 | 1100–1300 | −200 to +150 | Excellent | Yes | Non-sparking; explosive atmospheres; ATEX |
| Inconel 718 | AMS 5663 | 370–444 | 1241 | −196 to +650 | Excellent | Yes | Very high-temp; extreme sour; critical |
3.2 — Corrosion Resistance Matrix
| Material | Indoor Dry | Outdoor Inland | Coastal / Marine | H₂S / Sour* | Chemical Process | High Temp (>200°C) | Non-Sparking |
|---|---|---|---|---|---|---|---|
| Carbon Steel (zinc plated) | Good | Fair | Poor | No | Poor | Poor >200°C | No |
| Carbon Steel (HDG) | Very Good | Good | Fair | No | Poor | Poor >200°C | No |
| A2-70 (SS 304) | Excellent | Excellent | Good | Fair | Fair | Good to 300°C | No |
| A4-70 (SS 316) | Excellent | Excellent | Excellent | Good | Good | Good to 300°C | No |
| A4-80 (SS 316 SH) | Excellent | Excellent | Excellent | Good | Good | Good to 300°C | No |
| Phosphor Bronze | Excellent | Very Good | Very Good | Good | Good | Limited >150°C | Yes |
| Beryllium Copper | Excellent | Very Good | Very Good | Good | Excellent | Limited >150°C | Yes — ATEX |
| Inconel 718 | Excellent | Excellent | Excellent | Excellent | Excellent | Excellent to 650°C | No |
3.3 — Surface Finish and Coating Options
| Finish | Spec | Thickness (µm) | Salt Spray (h) | Hydrogen Embrittlement Risk | Effect on Spring Function | Application |
|---|---|---|---|---|---|---|
| Plain / Self-Colour | As-formed + quench | — | <24 | None | None | Indoor dry; immediate assembly |
| Black Oxide | MIL-DTL-13924 | 1–2 | 24–72 | Low | None | Indoor assembly; standard engineering supply |
| Zinc Electroplate | ASTM B633 / ISO 4042 | 5–12 | 96–300 | HIGH — spring steel | Minimal | General EPC; panels; enclosures — bake mandatory |
| Yellow Zinc Chromate | ASTM B633 Type III | 5–12 + chromate | 200–500 | HIGH | Minimal | Enhanced corrosion; standard outdoor EPC |
| Geomet | ISO 10683 | 8–10 | 1000 | None | None | Coastal; aggressive atmosphere; preferred over zinc plate |
| Phosphate | ISO 9717 | 5–10 | 48–72 | Low | None | Short-term protection; oil-retaining surface |
| Passivation (SS) | ASTM A967 | Passive layer | 2000+ | None | None | All SS spring washers — standard finish |
| PTFE / Xylan | Proprietary | 15–25 | 1000+ | None | Reduces bite — not for split washers | Anti-galling SS; wave washers; disc springs |
3.4 — Manufacturing Process
3.4.1 — Split Spring Washer Manufacture (DIN 127)
- Blanking: Spring steel strip (65Mn or 51CrV4) blanked to washer ring; ID punched simultaneously to produce the blank ring
- Slitting and twisting: A single radial cut is made through the ring; the two cut ends are offset axially by the material thickness — creating the helical spring geometry. The offset angle is controlled to produce the correct free height (H) per DIN 127 table
- Heat treatment: Hardening (austenising at 810–850°C, oil or water quench) + tempering at 350–450°C to achieve 420–500 HV target hardness — balanced for maximum spring energy without brittleness
- Shot blasting: Remove scale, improve surface condition, and introduce compressive residual stress on surface — enhances fatigue life of the washer under cyclic load
- Surface finishing: Zinc plate, Geomet, or black oxide as specified — with mandatory hydrogen bake-out after any electroplating process
3.4.2 — Belleville Disc Spring Manufacture (DIN 2093)
- Blanking: Precision-blanked from spring steel strip or plate (51CrV4, 50CrV4) to OD and ID dimensions; blanking die accuracy critical for dimensional consistency of load-deflection characteristic
- Pressing (coining): Blank pressed in a precision die to form the conical geometry — cone angle defines h₀ (free height) and therefore the load-deflection characteristic per DIN 2093
- Heat treatment: Q&T to 420–500 HV; controlled hardness critical — soft material reduces spring force; brittle material causes fracture under deflection
- Grinding of bearing faces: Precision grinding of both flat bearing surfaces on Series A disc springs — contact must be uniform across the full bearing ring area for repeatable load-deflection performance in precision spring packs
- Load-deflection testing: Sampled units load-tested on calibrated press to verify F at s = 0.75 × h₀ against DIN 2093 characteristic value ± 15% tolerance
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from raw strip stock to final packed shipment on all spring washer orders. Dimensional inspection, hardness certificates, load test reports, coating certificates, EN 10204 MTRs, and complete EPC export documentation packages are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | EPC Requirement | When Mandatory |
|---|---|---|---|---|
| 2.1 | Conformity declaration only | Manufacturer | Non-critical general assembly | General commercial hardware only |
| 2.2 | Non-specific test results | Manufacturer | Standard EPC panel / instrument assembly | General EPC spring washer supply |
| 3.1 | Heat/lot traceable mech + chem | Manufacturer’s authorised QC | Disc springs, NACE, SS marine, offshore | DIN 2093 disc springs; SS A4-70/A4-80; offshore |
| 3.2 | 3.1 + countersigned by TPI | Manufacturer + SGS / BV / Lloyds | Critical offshore, nuclear, ATEX | Offshore structural; nuclear Class 2/3; ATEX BeCu |
4.3 — Applications by Industry
Valve Bonnet & High-Pressure Flange Bolting
Belleville disc spring packs (DIN 2093 Series B or C, 51CrV4 spring steel) are specified for valve bonnet bolting and high-pressure flanged connections where gasket relaxation and thermal cycling cause preload loss in plain bolted joints. Stack design per DIN 2093 to maintain gasket seating load across the full service temperature cycle. Material: 51CrV4 for standard service; Inconel 718 for high-temperature (>450°C) or extreme sour service valve bonnets. EN 10204 3.1 with load test certificate.
Rotating Equipment — Compressors & Pump Covers
DIN 127B heavy-section split washers or DIN 6796 conical spring washers for compressor casing covers, pump bearing covers, and rotating equipment inspection access panels subject to sustained vibration loads. Belleville disc springs for critical high-pressure compressor end-plate bolting. Grade 8.8 bolt + DIN 127B split washer standard combination for moderate vibration; Grade 10.9 + DIN 6796 conical for severe vibration zones. All carbon steel washers: Geomet or black oxide coating to avoid H₂E risk from electroplating.
Offshore Topside & Marine Equipment
All spring washers on offshore topsides: SS A4-70 (316) minimum — hardened carbon steel spring washers with zinc coating corrode rapidly in marine chloride atmosphere. Wave washers (DIN 6905) and split washers (DIN 127) in SS A4-70 for instrument panels, junction boxes, and enclosure fastening. Belleville disc springs in SS A4-80 or Inconel 718 for critical high-load offshore valve and flange applications. EN 10204 3.1 with PMI on all SS lots.
Electrical Earthing Connections
Serrated lock washers (DIN 6798 Type A — external teeth) are the standard component for low-resistance electrical earthing connections in EPC electrical panels, equipment enclosures, and motor terminal boxes. The external teeth penetrate through paint, anodising, and oxide layers to create direct bare-metal contact required for earth continuity per IEC 60364 / BS 7671. Material: zinc-plated carbon steel for standard service; SS A4-70 for marine and offshore earthing systems. One washer under the earthing bolt head, one under the nut.
ATEX / Ex Enclosures — Non-Sparking
In Zone 1 and Zone 2 explosive atmospheres where non-sparking fasteners are required: specify beryllium copper (CuBe2) spring washers — the only spring washer material that combines high spring force (hardness 340–400 HV), corrosion resistance, and non-sparking properties. Per IEC 60079-0 / EN 60079-0 ATEX equipment standard requirements for non-sparking hardware in hazardous areas. Phosphor bronze spring washers provide non-sparking function with lower spring force for lighter assembly applications in ATEX zones.
Bearing Preload Systems
Belleville disc spring stacks (DIN 2093 Series A — linear characteristic) for precision bearing preload in machine tool spindles, gearbox output shaft bearing assemblies, and conveyor/fan bearing housings exported to EPC process equipment. The DIN 2093 load-deflection data sheet is used to select the correct series, size, and stacking configuration to achieve the bearing manufacturer’s specified preload at the installed deflection. Critical: operating temperature effect on steel Young’s modulus must be accounted for in high-temperature bearing preload disc spring calculations.
4.4 — Export Packaging Specification
- Spring washers bulk-packed per type, bore size, material grade, and coating in polybags — prevents mixing with flat washers or different spring washer types of similar OD appearance
- VCI (Volatile Corrosion Inhibitor) poly bag packaging for all plain, black oxide, and phosphate-coated carbon steel spring washers — prevents surface oxidation on the precision spring surfaces during ocean freight and extended site storage
- Belleville disc springs: individually interleaved with VCI tissue or packed in single-layer trays to prevent nesting (stacked disc springs are difficult to separate and may be damaged by forced separation); each tray labelled with DIN 2093 size, series, material, and lot number
- SS spring washers: packed separately from carbon steel hardware in dedicated polybags — segregation prevents SS surface contamination from iron particles and prevents incorrect grade mixing
- Lot tagging: each polybag labelled with washer type, bore size, OD, standard reference (DIN 127A/B, DIN 2093, etc.), material grade, coating, heat/lot number, quantity, and PO item reference
- ISPM-15 heat-treated timber crates for all international export; disc spring lots in nested cardboard inner packs to prevent shock damage to precision-ground bearing faces during transit
- Documentation: packing list, EN 10204 MTC, hardness certificate, load test certificate (disc springs), coating / bake-out certificate, and FAI report enclosed with each lot — cross-referenced to polybag lot number
4.5 — Complete EPC Project Documentation Package
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 2.2 / 3.1 / 3.2 | Mandatory — grade per project spec | Strip stock lot heat-traceable |
| 02 | Chemical Composition Report | Strip stock lot lab analysis | Mandatory — 3.1 / 3.2 orders | Per DIN 17221 / EN 10089 / ISO 3506 |
| 03 | Mechanical Properties Report | Hardness + tensile (strip) | Mandatory — 3.1 / 3.2 orders | Washer finished hardness + strip UTS |
| 04 | Hardness Test Report | ISO 6507 Vickers | Mandatory — all spring steel grades | 420–500 HV for carbon steel; per ISO 3506 for SS |
| 05 | Spring Load Test Certificate | DIN 2093 / DIN 6796 load tables | Mandatory — disc springs; conical washers | Force at 0.75 × h₀ ± 15% DIN value |
| 06 | Dimensional Inspection Report | Per DIN 127 / DIN 2093 / DIN 6796 | Mandatory | ID, OD, thickness, free height per standard |
| 07 | Surface Finish / Coating Certificate | ISO 4042 / ISO 10683 / ASTM B633 | Mandatory — all coated supply | Coating thickness + salt spray per lot |
| 08 | Hydrogen Bake-Out Certificate | ASTM F1941 | Mandatory — electroplated spring steel | 190°C × 4h; dated; batch-specific |
| 09 | Post-Bake Hardness Check | ISO 6507 Vickers | Mandatory — after bake-out | Confirms bake did not reduce hardness below 420 HV |
| 10 | PMI Report (XRF) | Per lot — SS / bronze / exotic grades | Mandatory — non-CS grades | A4-70 vs A2-70 differentiation |
| 11 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new configs / first lots | Released before batch production |
| 12 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2 / offshore | Co-witness at manufacturer works |
| 13 | NACE Compliance Statement | Material + hardness declaration | Conditional — sour service supply | SS A4-70 only; carbon steel excluded |
| 14 | ATEX Non-Sparking Certificate | IEC 60079-0 / manufacturer cert | Conditional — BeCu / PBr ATEX supply | Material composition + non-sparking test record |
| 15 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers spring washer manufacture |
| 16 | Country of Origin Certificate | Chamber of Commerce | Mandatory — all export | HS tariff code for customs classification |
| 17 | Packing List | Item-level per shipment | Mandatory | Cross-references lot numbers and MTC |
| 18 | Commercial Invoice | Per INCOTERMS 2020 | Mandatory | Includes HS tariff code |
| 19 | Bill of Lading / Air Waybill | Per freight mode | Mandatory | Issued by freight forwarder |
4.6 — ISO and Quality System Compliance
ISO 9001:2015
Quality Management System covering strip stock procurement, blanking die maintenance and calibration, heat treatment Q&T process control, hardness testing, dimensional inspection, load testing for disc springs, coating process QC, bake-out verification, and full lot traceability from strip stock to finished washer. Mandatory for all EPC, rotating equipment, and O&G project procurement qualification. RR Hydraulic holds current ISO 9001:2015 certification.
ISO 10474
Steel and steel products — inspection documents. Source framework for EN 10204 certificate types. Some EPC project specifications reference ISO 10474 Type 3.1.B (= EN 10204 3.1) for spring washer material certification. RR Hydraulic provides documentation in either format and cross-maps for legacy specification compliance on request.
ISO 4413
Safety requirements for hydraulic fluid power systems. Spring washers used in hydraulic manifold, valve body, and HPU cover bolted assemblies must be specified to match the assembly bolt grade and retain adequate preload under hydraulic pressure cycling. For ISO 4413 hydraulic system assemblies, Belleville disc springs or DIN 6796 conical spring washers provide superior preload retention under cyclic hydraulic loads compared to standard DIN 127 split washers.
IEC 60079 (ATEX)
Explosive atmospheres — equipment protection. Spring washers in Ex d (flameproof) and Ex e (increased safety) enclosures must not create ignition sources. Beryllium copper (CuBe2) spring washers are the specified non-sparking, high-spring-force option for ATEX zone service. The specific spring washer material and size is defined in the Ex enclosure certificate where it differs from standard carbon steel. Non-sparking material certificates (composition + test) required for ATEX supply.
Submit your BOM, washer type, bore, material, coating, and quantity to RR Hydraulic for a complete, certified commercial offer.