1. What is a padeye and why does it matter?

A padeye (also written "pad eye") is a structural attachment point welded to a component to enable lifting, rigging, or securing with a shackle and sling. Padeyes are found on virtually every offshore structure: topsides modules, subsea manifolds, jacket nodes, transport frames, flare towers, and even individual equipment skids. If something needs to be lifted by crane, it almost certainly has padeyes.

The term "padeye" comes from the eye-shaped hole in the lug through which a shackle pin passes. Despite their simple appearance, padeyes are safety-critical components. A failure during a lift can drop loads weighing tens or hundreds of tonnes, with consequences ranging from equipment destruction to fatalities. This is why padeye design is governed by rigorous standards and every offshore lifting lug must be formally verified before use.

The primary standard for padeye design in the offshore industry is DNV-ST-0378 (Standard for Offshore and Platform Lifting Appliances), specifically Appendix E, which prescribes the geometry checks, load factors, and utilisation limits. Other relevant standards include NORSOK R-002 (Lifting Equipment), EN 13155 (Cranes — Safety — Non-fixed load lifting attachments), and AS 4991 (Lifting Devices) used in Australia.

A padeye design calculator automates the checks required by these standards: net section stress, bearing stress, shear-out (tear-out), combined loading from sling angles, and weld capacity. Done manually, these calculations involve multiple cross-references, interpolations, and iteration — particularly when optimising plate thickness or cheek plate sizing. A calculator reduces a multi-hour spreadsheet exercise to minutes, and eliminates the transcription errors that plague manual work.

Scope of this guide This article covers the engineering theory behind padeye design — the geometry, the stress checks, the material considerations, and the practical pitfalls. At the end, we show how Leide's Padeye Calculator handles all of these checks in a single tool, with DXF export and scenario comparison built in.

2. Anatomy of a padeye: tombstone geometry

The standard padeye shape is often described as a tombstone: a rectangular base (the deck plate connection) that transitions through a tapered neck into a semicircular head with a central pin hole. This geometry efficiently transfers the concentrated shackle load into the base structure through a combination of tension, bearing, and shear.

Key dimensions

Every padeye is defined by a small set of critical dimensions. Understanding these is essential before any stress check can be performed:

  • W — Width of the main plate at the neck (the narrowest section above the deck plate connection)
  • H — Total height from the base weld line to the top of the semicircular head
  • t — Main plate thickness
  • tc — Cheek plate thickness (if fitted, one on each side)
  • R — Radius of the semicircular head
  • d — Pin hole diameter
  • e — Edge distance from the pin hole centre to the nearest edge of the head
  • hshear — Shear-out distance: from the pin hole centre to the top of the head, measured along the load direction

The relationship between these dimensions is not arbitrary. The edge distance e must be large enough to prevent tear-out, while the neck width W must provide sufficient net section area. The pin hole diameter d is determined by the shackle size, which is in turn determined by the safe working load.

Deck plate / base structure cheek plate W H d R e t t_c F_d

Tombstone padeye geometry with key dimensions. Dashed orange outline shows cheek plate extent.

Geometric proportions

Good padeye proportions follow well-established rules of thumb derived from decades of offshore practice:

  • Edge distance e should be at least 0.75 × d (pin hole diameter), and ideally closer to 1.0 × d. This ensures adequate material for shear-out resistance.
  • Head radius R is typically sized so that the minimum ligament (distance from pin hole edge to plate edge) is at least 0.5 × d.
  • Pin-to-hole clearance should be between 1 mm and 3 mm diametrically for standard offshore shackles. Too tight and the shackle cannot be inserted; too loose and load is transferred over a reduced contact arc, increasing bearing stress.
  • Neck width W must be wide enough that the net section stress (subtracting the pin hole) remains within allowable limits.
Practical tip Always check the shackle catalogue before finalising the pin hole diameter. The pin diameter, jaw width, and inside width of the shackle must all be compatible with the padeye geometry. Green Pin, Van Beest, and Crosby catalogues provide the dimensional data. The padeye plate thickness plus both cheek plates must fit within the shackle jaw width.

3. Design methodology: DNV-ST-0378 Appendix E

DNV-ST-0378 is the governing standard for offshore and platform lifting appliances. Appendix E provides a prescriptive method for padeye design using the Load and Resistance Factor Design (LRFD) framework. The philosophy is straightforward: multiply the working load by a consequence factor to obtain the design load, then verify that stresses in the padeye remain below factored material capacities.

Step 1: Determine the design load

The design load $F_d$ is the safe working load (SWL) multiplied by a consequence factor that accounts for the criticality of the lift:

$$F_d = \gamma_{f1} \times \text{SWL}$$
where:
$\gamma_{f1}$ = 1.30 for Consequence Class 1 (personnel not at risk, redundant rigging)
$\gamma_{f1}$ = 1.50 for Consequence Class 2 (personnel at risk, non-redundant, or single-line lifts)

Most offshore lifts are classified as Consequence Class 2, so the factor of 1.50 is the default in practice. Some operators apply additional factors for dynamic effects (DAF) during marine lifts, in which case:

$$F_d = \gamma_{f1} \times \text{DAF} \times \text{SWL}$$
DAF typically ranges from 1.10 to 2.00 depending on sea state, vessel motions, and lift type (per DNV-ST-0378 Section 5)

Step 2: Effective thickness

If cheek plates are fitted, the effective thickness for stress calculations is the combined thickness of the main plate and both cheek plates:

$$t_{\text{eff}} = t + 2 \times t_c$$
where $t$ = main plate thickness, $t_c$ = cheek plate thickness (each side)

This assumes that the cheek plates are properly welded and cover the full stressed region around the pin hole. If the cheek plates do not extend below the neck, only the main plate thickness is used for the net section check at the neck.

Step 3: Net section check (tension through the pin hole)

The net section check verifies that the material on either side of the pin hole can carry the design load in tension. The net section area is calculated by subtracting the pin hole from the total width at the critical section:

$$A_{\text{net}} = (W - d) \times t_{\text{eff}}$$
where $W$ = width at the critical section through the pin hole centre, $d$ = pin hole diameter

The net section stress is then:

$$\sigma_{\text{net}} = \frac{F_d}{A_{\text{net}}}$$

This stress must not exceed the allowable tensile stress:

$$\sigma_{\text{net}} \leq \frac{f_y}{\gamma_{M0}}$$
where $f_y$ = material yield strength, $\gamma_{M0}$ = 1.10 (material factor per DNV-ST-0378)

The utilisation ratio for net section is therefore:

$$\text{UR}_{\text{net}} = \frac{\sigma_{\text{net}}}{f_y / \gamma_{M0}}$$

Step 4: Bearing check (pin contact pressure)

The bearing check ensures that the contact pressure between the shackle pin and the pin hole wall does not cause local yielding or ovalling of the hole. The bearing area is the projected area of the pin on the plate:

$$\sigma_{\text{bearing}} = \frac{F_d}{d \times t_{\text{eff}}}$$

The allowable bearing stress is higher than the yield strength because the confined state of stress around the pin hole permits local yielding without failure:

$$\sigma_{\text{bearing}} \leq \frac{1.5 \times f_y}{\gamma_{M1}}$$
where $\gamma_{M1}$ = 1.25 (material factor for bearing per DNV-ST-0378)

The utilisation ratio for bearing is:

$$\text{UR}_{\text{bearing}} = \frac{\sigma_{\text{bearing}}}{1.5 \times f_y / \gamma_{M1}}$$
Pin-to-hole clearance matters The bearing check assumes load is distributed over the full projected area $d \times t_{\text{eff}}$. Excessive clearance between pin and hole (more than 3 mm diametral) reduces the effective contact arc and increases the peak bearing stress. Some standards require a Hertzian contact correction when clearance exceeds specified limits. Keep the clearance within 1–3 mm for standard offshore shackles.

Step 5: Shear-out (tear-out) check

The shear-out check prevents the pin from tearing through the top of the padeye head. The failure mode is a shear plane on each side of the pin hole, extending from the pin hole edge to the outer surface of the head. The shear area depends on the distance from the pin centre to the top of the head:

$$\tau_{\text{shear}} = \frac{F_d}{2 \times h_{\text{shear}} \times t_{\text{eff}}}$$
where $h_{\text{shear}}$ = distance from pin hole centre to top of head, minus $d/2$ (the effective shear length along each shear plane)

More precisely, the shear-out length on each side of the pin is:

$$l_{\text{shear}} = e - \frac{d}{2}$$
where $e$ = edge distance from pin centre to nearest head edge

The allowable shear stress is:

$$\tau_{\text{shear}} \leq \frac{f_y}{\sqrt{3} \times \gamma_{M0}}$$
The $\sqrt{3}$ factor converts shear yield from tensile yield (von Mises criterion)

The utilisation ratio for shear-out is:

$$\text{UR}_{\text{shear}} = \frac{\tau_{\text{shear}}}{f_y / (\sqrt{3} \times \gamma_{M0})}$$

Step 6: Overall utilisation

The governing utilisation ratio is the maximum of all individual checks:

$$\text{UR} = \max\left(\text{UR}_{\text{net}},\; \text{UR}_{\text{bearing}},\; \text{UR}_{\text{shear}}\right)$$

The padeye passes if $\text{UR} \leq 1.0$. In practice, engineers aim for $\text{UR} \leq 0.90$ to provide margin for fabrication tolerances and minor load path uncertainties. A utilisation ratio above 0.95 typically triggers a review, and anything above 1.0 is a hard fail requiring redesign.

Additional checks Beyond the three primary checks above, a complete padeye assessment also considers: weld capacity (the fillet or full-penetration weld connecting the padeye to the base structure), local stress in the base structure (punching shear, stiffener requirements), fatigue (if the padeye is used for repeated lifts), and out-of-plane bending (from sling angles not aligned with the padeye plane). These are addressed in DNV-ST-0378 Sections 5 and 7.

4. Sling angle effect on design load

In most lifting arrangements, slings are not vertical. They run at an angle from the crane hook down to the padeyes, and this angle increases the force in each sling — and therefore the force on each padeye — relative to the total lifted weight.

For a symmetrical lift with $n$ slings, the force in each sling is:

$$F_{\text{sling}} = \frac{\text{SWL}}{n \times \cos\theta}$$
where $\theta$ = sling angle from vertical, $n$ = number of slings

As $\theta$ increases, $\cos\theta$ decreases, and the sling force increases. At $\theta = 60°$, the sling force is double the vertical share — this is why most standards prohibit sling angles greater than 60 degrees from vertical.

Sling angle load factor table

The following table shows the load multiplication factor $1/\cos\theta$ for common sling angles. This factor is applied to the per-sling share of the SWL to obtain the force on each padeye:

Sling Angle from Vertical cos(theta) Load Factor 1/cos(theta) Sling Force Increase
0° (vertical) 1.000 1.000 Baseline
15° 0.966 1.035 +3.5%
30° 0.866 1.155 +15.5%
45° 0.707 1.414 +41.4%
60° 0.500 2.000 +100%

In addition to the axial increase, a non-vertical sling also introduces a horizontal component that creates out-of-plane bending in the padeye if the sling direction does not lie in the plane of the padeye plate. This is particularly important for asymmetric lifts or when padeyes are positioned at the edges of a module where sling geometry is constrained.

Design for the actual rigging It is common practice to design the padeye for the worst-case sling angle that could occur during the lift, not just the nominal geometry. Rigging arrangements on installation vessels may differ from engineering assumptions due to deck space, crane boom position, or operational constraints. A 5–10 degree margin on the assumed sling angle is prudent.

Horizontal force component

The horizontal force on the padeye from an angled sling is:

$$F_{\text{horizontal}} = F_{\text{sling}} \times \sin\theta = \frac{\text{SWL}}{n} \times \tan\theta$$

This horizontal force must be resisted by the padeye-to-structure weld and the local structure. For large sling angles, the horizontal force can be substantial: at 45 degrees, it equals the vertical share; at 60 degrees, it is 1.73 times the vertical share. The base structure must be checked for this lateral load, which may require additional stiffening.

5. Material selection for offshore padeyes

The choice of steel grade for a padeye depends on the design load (which determines required plate thickness), the operating environment (corrosion, temperature), and the weldability requirements. Most offshore padeyes are fabricated from structural steel plate, flame-cut to shape, and welded to the base structure.

Common padeye steels

Steel Grade Yield Strength (MPa) Charpy Temp Typical Application
S355J2 355 -20°C General offshore padeyes, moderate loads
S355N / S355NL 355 -40°C / -50°C North Sea, Arctic operations
S420ML 420 -50°C Heavy lifts requiring reduced plate thickness
S460ML / S460QL 460 -40°C / -60°C High-load padeyes, thickness-limited applications
S690QL 690 -40°C Very high loads, specialist lifting equipment
Duplex 2205 450 -46°C Subsea padeyes, splash zone, corrosive environments

Impact toughness requirements

Offshore lifting equipment must satisfy Charpy impact toughness requirements at a specified test temperature. The test temperature depends on the minimum design temperature of the installation:

  • DNV-ST-0378 requires Charpy testing at the design temperature or -20°C, whichever is lower, with a minimum absorbed energy of 27 J (longitudinal) or 20 J (transverse) for most structural steels.
  • NORSOK R-002 specifies -20°C for the North Sea and -40°C for Arctic operations.
  • For thick plates (above 40 mm), through-thickness (Z-quality) testing per EN 10164 may be required to prevent lamellar tearing at welded joints.

Weldability considerations

Higher-strength steels (S460 and above) require more stringent welding procedures: controlled heat input, preheating, and post-weld heat treatment (PWHT) in some cases. S690QL in particular demands qualified WPS (Welding Procedure Specifications) with narrow parameter windows and is typically limited to specialist fabricators. For most offshore padeyes, S355J2 or S355NL provides the best balance of strength, weldability, and availability.

Practical tip When specifying padeye material, always include the EN 10204 Type 3.1 inspection certificate requirement in the purchase order. This ensures that the actual yield strength and Charpy values of the specific plate are documented — not just the minimum values from the standard. For critical lifts, actual material properties may be used in the design calculation (with appropriate factors) to demonstrate additional margin.

Corrosion protection

Padeyes in the splash zone or on subsea structures require corrosion protection. Options include:

  • Protective coating — epoxy or polyurethane paint systems, typically 250–500 μm DFT. Standard for topsides padeyes.
  • Hot-dip galvanizing — effective for transport frames and temporary lifting points. Not suitable for high-strength steels above S460.
  • Corrosion allowance — adding 1–3 mm to the plate thickness. Simple but adds weight. Used when coating maintenance is not feasible.
  • Duplex stainless steel — eliminates the need for coating in seawater environments. Higher material cost but zero maintenance. Refer to DNV-RP-F112 for HISC (Hydrogen-Induced Stress Cracking) considerations for subsea duplex applications.

6. Cheek plate design and welding

Cheek plates (also called reinforcement plates or doubler plates) are plates welded to both sides of the main padeye plate around the pin hole area. They increase the effective bearing and shear-out area without requiring a thicker main plate — which may be constrained by the base structure thickness, shackle jaw width, or material availability.

When to use cheek plates

  • When the required effective thickness $t_{\text{eff}}$ exceeds the available main plate thickness $t$
  • When the main plate must match the base structure thickness for full-penetration butt weld compatibility
  • When a thicker single plate would exceed the shackle jaw width
  • When upgrading an existing padeye for a higher SWL without cutting a new main plate

Effective thickness with cheek plates

The effective thickness used in stress calculations depends on which check is being performed:

$$t_{\text{eff}} = t + 2 \times t_c$$
Used for bearing and shear-out checks at the pin hole, where the cheek plates directly contribute to the resisting area

For the net section check at the neck (below the cheek plate extent), only the main plate thickness applies unless the cheek plates extend fully through the neck region and are continuously welded along their edges.

Cheek plate extent The cheek plates must extend far enough below the pin hole to cover the full stressed region. As a minimum, they should extend to at least 1.5 × d below the pin hole centre. If the cheek plates terminate too close to the pin hole, the shear-out check must be performed with the main plate thickness alone, which may govern the design.

Weld details for cheek plates

The connection between cheek plates and the main plate is critical. Two approaches are common:

Full-penetration groove weld: The cheek plate is welded with a full-penetration weld around its entire perimeter. This provides 100% load transfer and allows the full cheek plate thickness to be counted in $t_{\text{eff}}$. Required for high-utilisation designs and typically specified for SWL above 50 tonnes. Requires volumetric NDT (ultrasonic or radiographic testing) per DNV-ST-0378.

Fillet weld: The cheek plate is fillet-welded around its perimeter. The fillet weld throat must be sized to transfer the proportion of design load carried by the cheek plates. The weld throat a is typically sized as:

$$a \geq 0.7 \times t_c$$
This ensures the weld can transfer the full cheek plate capacity. For circular cheek plates, the weld length is the full circumference minus the pin hole opening.

NDT requirements for cheek plate welds

  • Full-penetration welds: 100% UT (ultrasonic testing) or RT (radiographic testing), plus MT (magnetic particle testing) or PT (penetrant testing) on the root and cap passes.
  • Fillet welds: 100% MT or PT on the finished weld. No volumetric testing required for standard fillet welds, but many operators specify UT for fillet welds on critical lifting points.
  • Acceptance criteria: Quality Level B per EN ISO 5817 for all padeye welds (the most stringent level for arc welding).
Practical tip Ensure adequate weld access when designing cheek plates. The cheek plate must be set back from the padeye-to-deck-plate weld by at least 10 mm (preferably 15–20 mm) to allow the welder to complete both the cheek plate perimeter weld and the main padeye base weld without interference. Insufficient weld access is one of the most common fabrication issues with padeyes.

Cheek plate hole alignment

The pin holes in the cheek plates must be precisely aligned with the main plate pin hole. Typical practice is to tack-weld the cheek plates in position, then bore all three holes simultaneously on a horizontal boring mill. This guarantees concentricity and a consistent hole diameter through the full effective thickness. Misalignment greater than 0.5 mm is generally unacceptable as it creates stress concentrations and uneven bearing.

7. Practical design tips and common mistakes

Padeye design is conceptually simple but has numerous practical pitfalls. The following guidance is drawn from common findings in lifting engineering reviews and third-party verification (DNV, Lloyd's, Bureau Veritas):

Minimum edge distance

The most common padeye failure mode is shear-out (tear-out), where the pin rips through the top of the head due to insufficient material above the hole. DNV-ST-0378 Appendix E does not prescribe a fixed minimum edge distance ratio, but industry practice converges on:

  • Minimum edge distance $e \geq 0.75 \times d$ for low-utilisation padeyes (UR < 0.70)
  • Recommended edge distance $e \geq 1.0 \times d$ for general design
  • For high-strength steels (S460+), increase to $e \geq 1.1 \times d$ due to reduced ductility

Weld access and fit-up

A padeye that looks good on a drawing may be difficult to fabricate if:

  • The padeye is positioned too close to a stiffener or bracket, preventing welding torch access on one side
  • The base structure is a curved shell (e.g., a tubular member), requiring a profiled base edge on the padeye plate
  • The padeye plate is very thick (above 60 mm), requiring multi-pass welding with preheating and controlled interpass temperatures
  • Cheek plates are too close to the base weld, as discussed above

Out-of-plane loading

Padeyes are designed primarily for in-plane loading. When the sling direction has a component perpendicular to the padeye plate, the resulting bending moment can significantly increase stresses at the base weld. Common solutions include:

  • Gusset plates (stiffeners perpendicular to the padeye plate) to resist lateral bending
  • Trunnion-type padeyes that allow the shackle to rotate and self-align with the sling direction
  • Limiting the out-of-plane angle to 5 degrees in the lift plan

Base structure verification

The padeye itself may pass all checks, but the base structure must also be verified. A common oversight is designing a strong padeye welded to a base plate or shell that cannot resist the concentrated load. Check for:

  • Punching shear in the base plate if the padeye is welded to a flat plate
  • Local shell buckling if welded to a tubular member
  • Stiffener loads and web crippling if welded near a beam web

Fatigue for repeated-use padeyes

Most offshore padeyes are designed for a limited number of lifts (typically 1–20 over the structure's lifetime) and fatigue is not a concern. However, padeyes used for routine crane operations (e.g., hatch covers lifted daily, pipe-handling padeyes on a lay vessel) require a fatigue assessment per DNV-RP-C203. The critical detail is typically the weld toe at the padeye-to-base-plate connection, which falls into fatigue category D or E depending on weld geometry.

Documentation requirements Every offshore padeye must be documented with: (1) a design calculation report referencing the applicable standard, (2) a fabrication drawing with material grade, weld details, and NDT requirements, (3) material certificates (EN 10204 Type 3.1), (4) welding procedure qualifications (WPQR), and (5) NDT reports. Third-party verification by a classification society (DNV, Lloyd's, BV, ABS) is required for most offshore lifts above 1 tonne.

8. Leide vs spreadsheets vs other tools

Engineers have several options for performing padeye design calculations. The following table compares the three most common approaches:

Feature Manual / Spreadsheet Other Online Tools Leide
DNV-ST-0378 Appendix E compliance Depends on author Partial or unverified Full implementation
Net section check Yes (manual entry) Usually included Automatic
Bearing stress check Yes (manual entry) Usually included Automatic
Shear-out check Often missing or incorrect Sometimes missing Automatic
Sling angle correction Manual calculation Rarely included Built-in angle input
Cheek plate support Depends on spreadsheet Usually not supported Full cheek plate sizing
DXF drawing export No No One-click DXF export
Scenario comparison Copy-paste worksheets Single calculation Side-by-side scenarios
Sensitivity analysis Manual parameter sweep Not available Built-in sensitivity
Save and share via URL File sharing required No persistent state Shareable URL with all inputs
Material database Manual lookup Limited S235 to S690, Duplex
Audit trail Spreadsheet version control Not available Timestamped calculations

Why spreadsheets fall short

Excel spreadsheets remain the most common tool for padeye calculations in the offshore industry. While flexible, they suffer from well-documented problems:

  • Formula errors: A European Spreadsheet Risks Interest Group study found that over 90% of audited engineering spreadsheets contain at least one error. In padeye calculations, the most common errors are incorrect area formulas, missing checks, and wrong material factors.
  • Version control: Multiple copies of a spreadsheet circulate during a project, and it is difficult to ensure everyone uses the latest version with the correct material factors and load cases.
  • No drawing output: A spreadsheet produces numbers but not a drawing. The geometry must be separately drawn in CAD, introducing another opportunity for transcription errors between the calculation and the fabrication drawing.
  • No sensitivity analysis: Exploring "what if" scenarios (thicker plate, larger hole, different steel grade) requires manually changing inputs and recording each result. This discourages optimisation.

What Leide adds

Leide's padeye calculator addresses these limitations by combining the calculation engine, code compliance checks, and drawing generation in a single tool. Key capabilities:

  • All three DNV-ST-0378 checks (net section, bearing, shear-out) computed automatically with correct material factors
  • Sling angle input with automatic load correction and horizontal force calculation
  • Cheek plate sizing with effective thickness calculation and weld throat guidance
  • DXF export producing a dimensioned padeye outline ready for fabrication drawing integration
  • Scenario comparison to evaluate multiple design options side by side
  • Sensitivity analysis showing how utilisation varies with key parameters
  • Shareable URL encoding all inputs, so a colleague or verifier can instantly reproduce the calculation

Design Your Padeye Now

Leide's Padeye Calculator handles DNV-ST-0378 Appendix E stress checks, sling angle correction, cheek plate sizing, sensitivity analysis, and DXF export — all in one tool, with no spreadsheet required.

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