RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, ASTM F436 / F844 compliance, hot-dip galvanising inspection per ISO 1461, Third-Party Inspection available, and complete EPC and structural export documentation packages.
Dock & Square
Washers
A world-class technical reference for EPC contractors, structural and civil engineers, procurement heads, TPI inspection agencies, and global project buyers specifying dock washers, square washers, large-OD plate washers, and heavy structural washers for marine timber connections, structural steel base plates, anchor bolt assemblies, pipe support bearing plates, equipment foundations, heavy civil construction, and any application requiring maximum load distribution area under a bolt head or nut bearing face.
Type Classification
& Load Distribution Principles
Dock washers and square washers are large-format bearing washers — significantly larger in outer dimension than standard plain washers for the same bolt size — specifically designed to distribute the bolt bearing load over a larger contact area, preventing localised bearing failure in soft, low-strength, or wide-clearance connected materials.
1.1 — Technical Definition and Scope
Standard plain washers per ISO 7089 (normal series) and ASME B18.22.1 are designed to distribute the bolt bearing load over an area approximately 2–3× the bolt shank cross-section — adequate for connecting steel-to-steel or steel-to-concrete where the connected material bearing strength exceeds the bolt preload. However, in applications involving timber, softwood, engineered wood products (LVL, glulam, plywood), fibre reinforced polymer (FRP), aluminium, thin plate, or concrete with oversized holes, the bearing stress under a standard washer OD exceeds the material compressive strength — causing localised crushing, plastic deformation, and loss of bolt preload.
Dock washers and square washers address this problem by providing an outer bearing dimension 4–8× the bolt diameter rather than the 2–3× of a standard washer, reducing the bearing stress under the washer to below the allowable compressive stress of the connected material. The square profile of a square washer additionally provides an anti-rotation function — the corners of a square washer engage with the timber grain or the anchor bolt hole formation, preventing washer rotation during tightening without requiring a wrench on the washer. The term “dock washer” derives from their historical use in timber marine dock and wharf construction, where large-OD washers on through-bolts prevented pull-through of the bolt head into the soft timber pile or decking.
RR Hydraulic supplies dock washers and square washers under all applicable standards with full EN 10204 3.1 / 3.2 material traceability and complete project documentation.
1.2 — Washer Type Classification
Dock Washer (Round, Large OD)
A circular washer with an outside diameter significantly larger than the standard plain washer series for the same bolt hole — typically 75–150 mm OD for M16–M36 bolt holes, compared to 30–66 mm OD for ISO 7089 standard washers. The large bearing area distributes the bolt clamp force over soft timber, softwood decking, timber piles, laminated veneer lumber (LVL), and glulam beam faces without causing localised crushing. Standard dock washer thickness: 4–8 mm for timber applications (sufficient to bridge any surface irregularity and provide a flat bearing surface for the nut). ASTM A36 carbon steel, hot-dip galvanised per ISO 1461 for all marine and exterior applications.
Square Washer (Square Profile, Anti-Rotation)
A square flat washer with a central bolt hole — the square geometry provides: (1) anti-rotation during bolt tightening without requiring a separate tool (the square corners engage with the timber grain or bolt hole formation); (2) maximum bearing area in a compact footprint (a square washer provides 27% more bearing area than a round washer of equal outer dimension because the corners contribute area that a circle does not); and (3) alignment reference for bolt hole positioning in timber or composite construction. Standard square washer sizes: 50×50 to 150×150 mm for M12–M48 bolt sizes. ASTM A36 / A572 Grade 50 structural steel. Per ASME B18.21.1 and DIN 436.
Plate Washer (Heavy / Oversized Round)
A heavy flat washer with a round OD but substantially greater thickness than a standard or dock washer — used where both large bearing area AND rigidity are required to bridge irregularly shaped surfaces, oversized anchor bolt holes, and slotted holes in base plates. Plate washers are typically cut from flat plate stock (ASTM A36 or A572 Grade 50) rather than stamped from coil — this allows custom OD, ID, and thickness combinations not available in catalogue washers. Common in: column base plate anchor bolt assemblies (plate washer over slotted or oversized bolt hole); equipment base plate connections; bridge beam bearing plates; heavy equipment foundation packs.
Bevelled / Taper Washer (Slope Compensation)
A washer with one flat face and one tapered face — designed to compensate for a sloping connected surface so that the bolt head or nut bearing face is parallel to the washer face. Per BS 3410 (taper washers for I-sections) and ASME B18.21.1. Used on structural I-beam and channel flange connections where the flange is tapered — the taper washer compensates the slope so the bolt preload is applied perpendicular to the washer face rather than at an angle. Without a taper washer on a sloped flange, the bolt bends as it is tightened and the bolt tension is significantly lower than the target preload. Standard taper: 1:14 for I-beam flanges; 1:6 for channel flanges.
Hardened Structural Washer (ASTM F436)
A round, flat, hardened washer per ASTM F436 — the standard washer for high-strength structural bolting assemblies (ASTM A325 and A490 / ISO 898-1 Grade 8.8 and 10.9) where the washer must resist the bolt bearing force without yielding. ASTM F436 washers are through-hardened (min 38 HRC) and have a controlled OD and ID — not oversized like dock or square washers, but dimensionally precise to fit standard structural bolt heads and nuts. Required on all ASTM A490 / ISO 898-1 Grade 10.9 high-strength structural bolting assemblies per AISC Specification. The combination of large OD dock/square washer geometry with F436 hardness is a custom product for special structural applications.
Fender Washer (Thin, Large OD)
A thin flat washer (1.5–3 mm thick) with a large OD relative to the bolt hole — designed for fastening thin, fragile, or soft sheet materials (rubber sheeting, neoprene pads, fibreglass panels, polycarbonate sheeting) where a standard washer would either pull through or crush the material. The fender washer distributes the bolt bearing load over the maximum area possible within the thin profile. Per ASME B18.22.1 (Type A extra-large series). Used in: rubber dock fender bolt connections, GRP (glass reinforced plastic) panel fixings, polycarbonate rooflight fastening, rubber-to-steel isolation mount connections, and neoprene bearing pad bolt assemblies.
1.3 — Load Distribution Principles and Bearing Stress
F_bolt = Bolt clamping force (N) — from bolt preload at installation torque
A_bearing = Washer net bearing area (mm²) — annular area between ID and OD
OD = Washer outside diameter (mm)
ID = Washer inside diameter (mm) — hole diameter ≈ bolt nominal + clearance
Allowable bearing stress for common connected materials:
Structural steel (A36, Fy = 250 MPa): σ_allow = 0.9 × Fy = 225 MPa → standard washers adequate
Concrete (f’c = 25 MPa): σ_allow = 0.85 × f’c = 21 MPa → large OD washer often required
Softwood timber: σ_allow perpendicular to grain = 2.5–5 MPa → dock washer essential
Hardwood timber: σ_allow perpendicular to grain = 5–10 MPa → dock washer often required
GRP / FRP composite: σ_allow = 60–120 MPa → plate/fender washer typically required
M20 bolt preload at installation (ISO 898-1 Cl.8.8, torque method): F_bolt ≈ 90 kN = 90,000 N
Standard ISO 7089 M20 washer OD = 37 mm, ID = 22 mm:
A_bearing = π/4 × (37² − 22²) = π/4 × (1369 − 484) = 694 mm²
σ_bearing = 90,000 / 694 = 130 MPa → far exceeds 4 MPa allowable → timber crushing
With 100 mm dock washer OD, same M20 bolt hole:
A_bearing = π/4 × (100² − 22²) = π/4 × (10000 − 484) = 7,464 mm²
σ_bearing = 90,000 / 7,464 = 12 MPa → still exceeds 4 MPa → use 130 mm OD dock washer or reduce preload
130 mm OD: A = π/4 × (130² − 22²) = 12,900 mm² → σ = 90,000/12,900 = 7 MPa → near limit; use 150 mm OD
1.4 — Standard vs Dock / Square Washer Bearing Area Comparison
| Bolt Size | Standard OD (ISO 7089) | Bearing Area Std (mm²) | Dock Washer OD | Bearing Area Dock (mm²) | Bearing Area Ratio | Typical Application |
|---|---|---|---|---|---|---|
| M12 | 24 mm | 310 | 50 mm | 1,790 | 5.8× | Timber joist hangers; softwood decking |
| M16 | 30 mm | 568 | 75 mm | 4,140 | 7.3× | Timber pile through-bolts; dock connections |
| M20 | 37 mm | 923 | 100 mm | 7,464 | 8.1× | Wharf decking; structural timber connections |
| M24 | 44 mm | 1,330 | 100 mm | 6,850 | 5.2× | Heavy timber; glulam; LVL connections |
| M30 | 56 mm | 2,225 | 125 mm | 11,600 | 5.2× | Column base plates; anchor bolt assemblies |
| M36 | 66 mm | 3,100 | 150 mm | 16,600 | 5.4× | Heavy equipment base plates; bridge bearings |
| M48 | 92 mm | 6,250 | 200 mm | 29,500 | 4.7× | Major structure anchors; machinery foundations |
Submit your bolt size, outer dimension, thickness, material, coating, and quantity for a documented RFQ within 24 hours.
Size Reference Tables
& Compliance Framework
Dock washer, square washer, and large-OD plate washer dimensions are governed by ASTM F436, F844, ASME B18.21.1, ASME B18.22.1, DIN 125, DIN 436, DIN 9021, and ISO 7089/7093. All applicable standards are supported at RR Hydraulic with full certification.
Submit bolt size, outer dimension, thickness, material, coating, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — Square Washer Dimensional Reference (DIN 436)
| Bolt Size | Hole Dia (mm) | Side Length (mm) | Thickness (mm) | Bearing Area (mm²) | Material | Typical Application |
|---|---|---|---|---|---|---|
| M10 | 11 | 30×30 | 3 | 805 | A36 / HDG | Timber framing; light structural |
| M12 | 13 | 37×37 | 4 | 1,236 | A36 / HDG | Timber joists; softwood decking |
| M16 | 17 | 50×50 | 4 | 2,211 | A36 / HDG | Structural timber; dock bolting |
| M20 | 22 | 60×60 | 5 | 3,116 | A36 / HDG | Heavy timber; pile through-bolts |
| M24 | 26 | 72×72 | 6 | 4,508 | A36 / A572 Gr.50 / HDG | Glulam; LVL; heavy timber connections |
| M30 | 33 | 92×92 | 8 | 7,387 | A36 / A572 Gr.50 / HDG | Column base plates; anchor bolts |
| M36 | 39 | 110×110 | 10 | 10,579 | A36 / A572 Gr.50 / HDG | Heavy structural; equipment bases |
| M42 | 45 | 125×125 | 10 | 13,589 | A572 Gr.50 / HDG | Large anchor bolt assemblies |
| M48 | 52 | 140×140 | 12 | 17,296 | A572 Gr.50 / HDG | Machinery foundations; heavy civil |
2.2 — Dock Washer (Round Large OD) Dimensional Reference
| Bolt Size | Hole Dia (mm) | OD (mm) | Thickness (mm) | Net Bearing Area (mm²) | σ_bearing at 90 kN (MPa) | Material / Coating |
|---|---|---|---|---|---|---|
| M12 | 14 | 50 | 4 | 1,810 | 49.7 | A36 HDG; SS 316 |
| M16 | 18 | 75 | 5 | 4,164 | — | A36 HDG; SS 316 |
| M20 | 22 | 100 | 6 | 7,464 | 12.1 @ 90 kN | A36 HDG; SS 316 |
| M24 | 26 | 100 | 6 | 6,850 | — | A36 HDG; SS 316 |
| M24 | 26 | 125 | 8 | 11,726 | — | A36 HDG; SS 316 |
| M30 | 33 | 125 | 8 | 11,474 | — | A36 / A572 HDG |
| M30 | 33 | 150 | 10 | 16,727 | — | A36 / A572 HDG |
| M36 | 39 | 150 | 10 | 16,490 | — | A572 Gr.50 HDG |
| M48 | 52 | 200 | 12 | 29,300 | — | A572 Gr.50 HDG |
2.3 — Applicable Standards and Compliance Framework
ASTM F436
Standard Specification for Hardened Steel Washers Inch and Metric Dimensions. F436 Type 1 (inch series) and Type 3 (weathering steel): through-hardened (38–45 HRC), controlled OD and ID tolerances, flat bearing face, chamfered hole. The structural standard washer used with ASTM A325 and A490 high-strength structural bolts. Dock washers and square washers are NOT covered by F436 — they are a separate product category. However, for applications combining high-strength bolting (A325/A490) with soft connected materials, a custom washer combining F436 through-hardening with dock/square OD geometry may be specified.
ASTM F844
Standard Specification for Washers, Steel, Plain (Flat), Unhardened, for General Use. Covers plain (unhardened) washers for general bolting applications — these are the basis for dock washers in larger OD configurations. ASTM F844 washers are not hardened (no minimum hardness requirement) — they are used where the bolt grade and application do not require a hardened bearing surface. Dock washers are typically supplied to F844 material grade (ASTM A36 carbon steel) with hot-dip galvanising per ISO 1461 for marine and outdoor service. Custom dock washers may reference F844 as the base material specification with an additional OD/ID/thickness callout on the project drawing.
DIN 436 / DIN 125 / DIN 9021
DIN 436: Square washers for timber construction — the definitive European standard for square washers. Covers OD (side length), hole diameter, and thickness for M5–M48 metric bolt sizes. DIN 125: Plain washers — normal series (equivalent to ISO 7089). DIN 9021: Plain washers — large OD series (approximately 3× bolt diameter OD — the European large-series plain washer, wider than DIN 125 but narrower than a dock washer). For EPC projects using European material designations, dock and large OD washers may be specified as DIN 9021 (large series) for the standard large-OD form, or referenced to the project drawing for custom dock washer ODs beyond the DIN 9021 range.
ASME B18.21.1 / B18.22.1
ASME B18.21.1: Lock Washers (inch series). ASME B18.22.1: Plain Washers (inch series) — covers Type A (narrow), Type B (regular), and Type A extra-large (wide) series. The Type A extra-large series provides OD approximately 3–4× the bolt diameter, approaching dock washer territory. For US-coded EPC projects where oversized dock-type washers are required: specify by ASME B18.22.1 Type A extra-large series (if within catalogue range) or specify by the project drawing defining OD, ID, and thickness. Custom dock washers for US-coded projects are commonly referenced as “plate washer per project drawing, ASTM A36 material, HDG per ASTM A153.”
ISO 7089 / ISO 7090 / ISO 7093
ISO 7089: Plain washers — normal series (OD ≈ 2× bolt diameter, product grade A). ISO 7090: Chamfered plain washers (bearing face chamfered for use with socket cap screws). ISO 7093: Plain washers — large series (OD ≈ 3× bolt diameter, product grade A). The ISO 7093 large-series washer is the international equivalent of ASME B18.22.1 Type A extra-large. For dock washer ODs exceeding ISO 7093 dimensions, specify by the project drawing with material and coating per applicable standards. All RR Hydraulic dock and square washers are manufactured to project drawing dimensions with material certification per EN 10204 3.1.
ASTM A36 / A572 Grade 50
ASTM A36: Structural Steel — Fy = 250 MPa, Fu = 400–550 MPa. The standard material for dock washers and square washers in general structural and marine timber applications. For higher strength applications (heavy equipment base plates, large machinery foundations): ASTM A572 Grade 50 (Fy = 345 MPa) provides higher yield and allows a thinner washer for the same bearing capacity. Both A36 and A572 Grade 50 are weldable per AWS D1.1 — important for dock washers that may be tack-welded to base plates to prevent repositioning during concrete pour.
ASTM A153 / ISO 1461 (HDG)
ASTM A153: Zinc Coating (Hot-Dip) on Iron and Steel Hardware — the US standard for HDG hardware including washers. Minimum zinc coating: 1.0 oz/ft² (305 g/m²) average, equivalent to approximately 43 µm. ISO 1461: Hot-dip galvanised coatings on fabricated iron and steel — European/international equivalent. For dock washers in marine service: specify HDG per ASTM A153 Class A (for material above 1.6 mm thick) or ISO 1461 with minimum 45 µm average coating thickness. HDG dock washers provide 15–25 years corrosion protection in marine atmospheric environments before maintenance recoating is required.
NDS (National Design Specification for Wood)
NDS: National Design Specification for Wood Construction — the governing design standard for timber bolted connections in the US. NDS Table 11.5.1 provides reference design values for bolts in wood with standard washers; NDS Section 11.5.4 requires that washers be used under bolt heads and nuts in wood connections, with minimum washer dimensions per bolt diameter. When dock or square washers are used in NDS-governed timber connections, the washer bearing area must be checked against NDS Table 3.3A perpendicular-to-grain compression design values (Fc⊥) to verify that the bearing stress does not exceed the allowable. The dock washer bearing area and the NDS Fc⊥ allowable for the specific timber species determine the maximum bolt preload.
Corrosion Protection
& Manufacturing Process
Dock washer and square washer material is selected by the structural engineer to match the design load, service environment, and corrosion protection requirements of the connection. RR Hydraulic supplies dock and square washers in all standard grades and coatings with full EN 10204 3.1 material traceability.
3.1 — Material and Coating Options
| Material / Coating | Yield Strength | Marine Atmospheric | Seawater Immersion | Buried | High Temp | Typical Application |
|---|---|---|---|---|---|---|
| A36 Plain (uncoated) | 250 MPa | Poor — rust | Not suitable | Not suitable | Good to 300°C | Indoor structural; dry interior only |
| A36 Hot-Dip Galvanised | 250 MPa | Very Good | Fair (limited) | Good | Limited (Zn melts at 420°C) | Marine timber; outdoor structural; dock construction |
| A572 Gr.50 Hot-Dip Galvanised | 345 MPa | Very Good | Fair | Good | Limited | Heavy structural; equipment bases; column pads |
| A36 Epoxy-Coated | 250 MPa | Good | Good (FBE 300 µm) | Very Good | Limited | Embedded and buried dock washer over anchor bolts |
| SS 316 (A4-70) Passivated | 450 MPa | Excellent | Good | Very Good | Good to 400°C | Offshore; marine splash zone; coastal bridge |
| Duplex 2205 Passivated | 620 MPa | Excellent | Excellent | Excellent | Good to 315°C | Offshore subsea; hot seawater; aggressive marine |
| A36 Zinc-Flake (Geomet) | 250 MPa | Very Good | Fair | Good | Good to 300°C | Industrial; machinery base plates; EPC equipment |
3.2 — Manufacturing Process
3.2.1 — Stamping and Punching (Standard Sizes)
Standard dock washers (round) and square washers in the M12–M36 range are manufactured by press-punching from flat plate or coil stock. A punch-and-die set sized for the washer OD (or side dimensions for square) and the bolt hole ID punches the washer profile in a single or two-stage press operation. Tolerances achievable by punching: OD/side ±1 mm; hole diameter ±0.5 mm; thickness per the plate stock tolerance. The punched edge (OD and ID) will show a shear face and a rollover — no further edge finishing is required for structural and timber applications. Burrs on the hole edge are acceptable per most structural standards but must not prevent the washer from seating flat against the connected surface.
3.2.2 — Flame Cutting and Plasma Cutting (Custom and Large Sizes)
- Flame cut / oxy-fuel cut: For OD above 200 mm or non-standard OD/shapes (rectangular, octagonal, offset-hole plate washers) where press tooling is not available — flame cutting from plate stock per project drawing; post-cut edge quality cleaned by grinding to remove dross and scale; tolerances: OD/side ±2 mm, hole ±1 mm
- Plasma cut: Faster and cleaner edge quality than flame cutting — preferred for SS 316 and Duplex plate washers where the flame-cut heat input would degrade the corrosion resistance at the cut edge; plasma cut edge is passivated after cutting to restore the SS passive film; tolerance: OD/side ±1 mm, hole ±0.5 mm
- Laser cut: Highest dimensional accuracy for custom plate washers — ±0.2 mm on OD and hole; smooth square edges requiring no post-processing; preferred for precision applications (instrument stand base plates, equipment-mounting shim washers); limited to plate thickness ≤ 25 mm for standard laser cutting equipment
- Post-cutting operations: Hole edges chamfered 1×45° for all dock washers where the washer OD ≥ 100 mm (prevents edge-of-hole stress concentration at high preload); faces ground flat if flame cut or plasma cut introduces distortion (flatness ≤ 1 mm per 100 mm of width is the typical structural acceptance criterion)
3.2.3 — Hot-Dip Galvanising Sequence
- All fabrication before galvanising: All cutting, punching, chamfering, and edge grinding completed before galvanising — no post-galvanising cutting or welding
- Pre-treatment: Degreasing, acid pickling, fluxing; any mill scale from the plate face removed by shot blasting before pickling if required for uniform zinc adhesion
- Bath immersion: Full immersion in molten zinc at 445–455°C; large dock washers may require jigging to prevent overlap (flat washers stacked in the bath receive no zinc at the contact faces — jig or basket them individually or in spread stacks)
- Draining and quenching: Withdraw slowly to allow uniform zinc drainage; quench in water to arrest zinc-iron alloy layer growth; inspect for drips, runs, and bare spots before dispatch
- Coating thickness inspection: Magnetic gauge per ISO 2178 on both faces of each washer for large structural dock washer lots; 5 measurements per side minimum; minimum average coating per ISO 1461 table for the material thickness
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified plate stock to final coated and packed dock and square washer shipment. Dimensional inspection, flatness verification, coating thickness inspection, material certification, and complete EPC and structural export documentation packages are standard on all project-grade dock and square washer supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | EPC / Structural Requirement | When Mandatory |
|---|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Manufacturer | Not acceptable for structural EPC | Never for structural, offshore, or marine dock washers |
| 3.1 | Plate heat-traceable mech + chem | Manufacturer’s authorised QC | Minimum for all EPC structural washers | All dock and square washers for structural and marine service |
| 3.2 | 3.1 + TPI countersign | Manufacturer + SGS / BV / DNV / Lloyds | Offshore critical; NACE; subsea; safety structure | Offshore primary structural; subsea; nuclear; seismic critical |
4.3 — Applications by Industry
Marine Timber Dock, Wharf, and Jetty Construction
The original and highest-volume dock washer application. Round A36 HDG dock washers (M20–M36, 100–150 mm OD) on through-bolts connecting timber deck planks, stringers, and wales to timber or concrete piles in marine wharf and jetty construction. The large bearing area prevents the bolt head from pulling through the timber decking under wave loading and impact from vessels. HDG per ISO 1461 is the standard coating — marine timber structures require 15–25 year maintenance intervals and the 55–70 µm HDG zinc coating is essential for this service life. SS 316 dock washers for premium marine structures where long-term maintenance-free performance justifies the cost premium over HDG carbon steel.
Structural Column Base Plate and Anchor Bolt Assemblies
A572 Grade 50 square washers (M24–M52, 72×72 to 140×140 mm) or custom flame-cut plate washers over anchor bolt holes in structural steel column base plates — the square washer bridges the oversized or slotted bolt hole in the base plate and distributes the anchor bolt load over a larger bearing area on the base plate face. For slotted base plate holes (allowing thermal expansion adjustment during erection): the plate washer must cover the full slot length plus the washer engagement margin on each side. Plate washers for column base plates are typically tack-welded to the base plate after final column alignment, before grout pour — verify that the plate washer material is weldable (A36 or A572 Grade 50) before specifying tack welding.
Timber Pile and Heavy Timber Connections
Square washers per DIN 436 or project drawing (M16–M36, 50×50 to 110×110 mm) on marine fender pile through-bolt connections, timber retaining wall tie-back anchors, log crib retaining walls, and heavy timber framing connections in jetties and boathouses. The square washer anti-rotation feature prevents washer rotation during bolt tightening without a second wrench, which is practically important in confined or elevated work positions in marine construction. Hot-dip galvanised per ISO 1461; oversized holes punched to allow field adjustment of bolt position within the timber grain during on-site assembly.
Glulam, LVL, and Engineered Wood Structural Connections
Round or square dock washers (M16–M30, 75–125 mm OD) on through-bolt connections in glulam portal frames, LVL (laminated veneer lumber) primary beams, and CLT (cross-laminated timber) floor panel connections. Engineered wood products have documented bearing strength per Eurocode 5 / NDS table values — the dock washer bearing area must be verified against the perpendicular-to-grain compression strength of the specific engineered wood product. LVL compressive strength perpendicular to face grain ≈ 4–6 MPa; glulam ≈ 3–5 MPa. Bearing stress calculation per the formula box in Part 1 determines the minimum dock washer OD for each bolt size and preload level.
Pipe Support and Equipment Base Plate Bearing Plates
Custom flame-cut or punched plate washers (A36 or A572 Grade 50, HDG) used as bearing plates under pipe support U-bolt saddle connections, equipment skid base plate anchor bolt connections, and pump / compressor base plate anchor bolt bearing plates. A plate washer here serves the same load-spreading function as a dock washer but is cut to a non-standard size matching the base plate configuration from the structural drawing. Common dimensions: 100×100 to 200×200 mm custom square, or 100–200 mm round, 10–20 mm thick. Tack-welded to the base plate in the fabrication shop to prevent misalignment during installation.
Offshore Topside and Floating Structure Hardware
SS 316 (A4-70) or Duplex 2205 dock washers for offshore platform equipment skid base plate connections, jacket launch cradle timber blocking connection bolts, helideck panel connections, and temporary construction fixings on offshore topsides. The combination of large bearing area and marine-grade corrosion resistance makes SS 316 dock washers preferred over HDG carbon steel for offshore service above the splash zone — HDG zinc coating corrodes at 10–15 µm/year in severe offshore atmospheric environments, giving 3–7 years service before the bare steel is exposed. SS 316 dock washers require no coating maintenance for the platform life.
4.4 — Export Packaging Specification
- Dock and square washers bulk-packed by size (OD/side × hole × thickness) in polybag or hessian sack per project bolt schedule — washers for different bolt sizes in separate bags; mixing washer sizes in one bag is the most common site sorting error in anchor bolt installation
- HDG carbon steel washers in plain polybags — the zinc surface requires no additional VCI protection; do not seal in airtight plastic packaging (condensation under sealed packaging on hot galvanised surfaces promotes white rust); allow air circulation
- SS 316 and Duplex dock washers in dedicated SS-labelled polybags, separated from carbon steel; stainless-only packaging hardware; passivation certificates in documentation pocket
- Large structural plate washers (OD ≥ 150 mm or custom flame-cut) individually wrapped in VCI poly for EPC projects — these are typically high-value custom items where surface damage during transit would require replacement; face-to-face stacking with VCI poly interleaved between faces
- For anchor bolt template packages: custom plate washers with multiple hole patterns shipped as a matched set with the anchor bolt bundle — every plate washer tagged with the anchor bolt position reference (e.g., “Column C-101, Position 1 of 4”) to prevent mismatching on site
- Coordinate measurement report for custom multi-hole plate washers included in documentation pocket — confirms hole pattern geometry before concrete pour
- ISPM-15 heat-treated timber crates or strong cardboard export cartons for all international export; heavy large-format plate washers individually crated or palletised with steel banding; documentation in waterproof pocket: EN 10204 3.1 MTC, mechanical test certificate, dimensional inspection report, flatness report, HDG inspection certificate, PMI report (SS/Duplex), passivation certificate (SS), FAI report
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 dock/square washers | Plate heat-traceable; one MTC per heat lot |
| 02 | Chemical Composition Report | Plate mill certificate / certified lab | Mandatory | Per ASTM A36 / A572 Gr.50 / A276 SS 316 limits |
| 03 | Mechanical Properties Report | UTS, yield, elongation per plate spec | Mandatory | One tensile test per plate heat lot |
| 04 | Dimensional Inspection Report | Per DIN 436 / project drawing / ISO 7093 | Mandatory | OD/side, hole diameter, thickness, flatness verified |
| 05 | Flatness Inspection Report | Straight-edge measurement per face | Mandatory — structural base plate washers | ≤ 1 mm flatness for precision base plate; ≤ 2 mm general |
| 06 | HDG Inspection Certificate | ISO 1461 / ASTM A153 thickness per washer | Mandatory — all HDG dock and square washers | Min 5 measurements per face; adhesion test on sampled lot |
| 07 | PMI Report (XRF) | Per lot — SS 316 / Duplex / non-CS grades | Mandatory — SS and Duplex lots | SS 316 vs SS 304; Duplex 2205 vs 2507 differentiation |
| 08 | Passivation Certificate | ASTM A967 | Mandatory — all SS and Duplex washers | Method confirmed; water immersion or Cu-sulphate test |
| 09 | Coordinate Inspection Report | CMM / coordinate measurement vs drawing | Conditional — multi-hole custom plate washers | Hole positions verified vs template drawing before dispatch |
| 10 | Weld Inspection Report | AWS D1.1 visual / weld gauge | Conditional — tack-welded base plate washers | Weld size per drawing; pre-heat if A572 Gr.50 material |
| 11 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new configurations | All parameters; released before batch production |
| 12 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2; offshore critical | Co-witness at manufacturer; dimensional + coating |
| 13 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers structural washer manufacture |
| 14 | Country of Origin + Packing List | Chamber of Commerce / item-level | Mandatory | HS tariff code; per-size lot quantities |
| 15 | 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 plate stock procurement and heat traceability, press punching and cutting process qualification, flatness verification procedure, HDG process control (pre-treatment records, zinc bath temperature, coating thickness inspection), SS plasma/laser cutting process qualification (heat input control for corrosion resistance preservation), passivation process control, coordinate hole measurement procedure for custom plate washers, and full material traceability from plate heat certificate to dispatched washer lot. Mandatory for all EPC, structural, and marine project dock and square washer procurement qualification.
AISC Specification / Eurocode 3
AISC Specification for Structural Steel Buildings (Chapter J: Bolts, Welds, and Connected Parts) and EN 1993-1-8 (Eurocode 3: Design of Steel Structures — Connections) govern the design of structural bolt connections including washer requirements. Both standards require hardened washers under bolt heads and nuts for high-strength structural bolting (A490 / ISO 898-1 Grade 10.9) to prevent bearing failure in the base plate or flange. For column base plate connections: AISC Design Guide 1 (Base Plate and Anchor Rod Design) specifies the minimum plate washer size and thickness for anchor bolt hole bridging — a direct reference standard for EPC structural dock/plate washer specification.
Eurocode 5 / NDS
Eurocode 5 (EN 1995-1-1: Design of Timber Structures) and NDS (National Design Specification for Wood Construction) are the governing structural design codes for timber bolted connections incorporating dock and square washers. EC5 Section 8.5 covers bolted connections in timber — minimum washer dimensions for bolt connections in timber are given in EC5 Table 8.4 (minimum washer diameter = 3× bolt diameter for end grain connections; 2.4× for side grain). NDS Section 11.5.4 has equivalent requirements. These minimum washer dimensions are significantly smaller than standard dock washers — the bearing stress check per the formula in Part 1 typically governs and requires larger washers than the EC5/NDS minimum.
ACI 318 / EN 1992-4
ACI 318 (Building Code Requirements for Structural Concrete) Appendix D and EN 1992-4 (Design of Fastenings in Concrete) govern anchor bolt design including the bearing area requirements at the concrete surface. For anchor bolts through steel base plates to concrete: the base plate acts as the primary bearing element on the concrete surface — but where a dock washer or plate washer is installed over the anchor bolt hole in the base plate (to bridge an oversized hole or slot), the washer bearing area is part of the load transfer path from the bolt to the base plate to the concrete. ACI 318 Appendix D requires that any bearing element (base plate, washer, or anchor plate) have adequate area to transfer the design load to the concrete without exceeding the concrete bearing strength.
Submit your bolt size, outer dimension, thickness, material, coating, and quantity to RR Hydraulic for a complete, certified commercial offer.