01
The reference padeye
A perfectly ordinary 300 kN lift point that passes everything with room. Every section below changes exactly one thing about it.
30 mm plate in S355, 260 mm wide, a 60 mm hole on a 56 mm pin, 90 mm from the hole centre to the top edge, welded all round with a 12 mm fillet 240 mm long, pin 190 mm above the weld. The sling arrives 10 degrees off the plate's axis.
Lifting Lug Calculator · computed at page render
The reference: everything passing, shear-out governing
A 300 kN lift point at 10 degrees off axis, checked on public-domain mechanics against declared allowables.
| Design load | 300.0kN |
|---|---|
| Net-section tension | 23.5% |
| Double-plane shear-outgoverns | 67.8% |
| Pin bearing on the lug | 55.8% |
| Pin double shear | 27.7% |
| Fillet weld throat resultant | 52.8% |
Sound, and with enough margin that most of the changes below would not look alarming on a drawing.
Open this example in the calculator02
Details 1 to 3: the three dimensions at the hole
Hole diameter, edge distance and plate thickness. Trimming the edge distance multiplies the governing check by 2.4, thinning the plate by 1.5, and opening the hole by 1.15 - and the edge distance is the one least often specified with a tolerance.
Detail 1: the hole opened out to clear a bigger shackle pin.
The commonest site modification there is, and it is usually done for a good reason: the shackle that arrived is bigger than the one on the drawing. It looks like a bearing question, and it is not.
Lifting Lug Calculator · computed at page render
Detail 1: hole opened from 60 mm to 76 mm
Everything else identical. The pin is unchanged, so the bearing check is unchanged.
| Net-section tensionagainst 23.5% | 25.5% |
|---|---|
| Double-plane shear-outagainst 67.8% | 78.2% |
| Pin bearing on the lugunchanged: the pin did not change | 55.8% |
Shear-out moved and bearing did not, which is the opposite way round from the intuition that a bigger hole is a bearing problem. The shear-out planes run from the hole to the free edge, so opening the hole shortens them.
Open this example in the calculatorThere is a second cost the numbers here do not show. A hole substantially larger than the pin lets the pin bed into one part of the bore and produces a local contact stress that a uniform bearing calculation does not represent. That is a real limit on how loose a hole may be, and it is the reason the clearance is specified rather than left to the fitter.
Detail 2: edge distance trimmed to fit.
This is the one to watch on every drawing.
Lifting Lug Calculator · computed at page render
Detail 2: edge distance cut from 90 mm to 55 mm
A 35 mm trim, to clear a bracket. Nothing else changes.
| Double-plane shear-outagainst 67.8% - failed | 162.6% |
|---|---|
| Net-section tensionunchanged | 23.5% |
| Pin bearing on the lugunchanged | 55.8% |
| Fillet weld throat resultantunchanged | 52.8% |
A 39 percent reduction in one dimension took the governing check from 68 percent to 163. Nothing else on the drawing moved, and on a general arrangement the change would look like a small radius adjustment.
Open this example in the calculatorDetail 3: the plate thinned to save weight.
Lifting Lug Calculator · computed at page render
Detail 3: plate thinned from 30 mm to 20 mm
A third off the thickness. Thickness appears in three checks at once, which is what makes this change deceptive.
| Net-section tensionagainst 23.5% | 35.2% |
|---|---|
| Double-plane shear-outfailed | 101.6% |
| Pin bearing on the lugagainst 55.8% | 83.7% |
| Fillet weld throat resultant | 56.1% |
Three checks moved together, which is why thickness is a poor place to look for weight saving on a lift point. Everything that resists load at the hole is proportional to it.
Open this example in the calculator03
Details 4 to 6: the three that only touch the weld
A taller lug, unreturned ends, a smaller leg. None of them reads as a structural change on a drawing, and together they move the weld from 53 percent to 79.
Detail 4: the lug made 90 mm taller for shackle clearance.
Lifting Lug Calculator · computed at page render
Detail 4: pin raised from 190 mm to 280 mm above the weld
A change made for fit, not for strength, and one that a general arrangement revision would not flag.
| Fillet weld throat resultantagainst 52.8% | 62.9% |
|---|---|
| Every plate checkthe plate does not know how tall it is | unchanged |
The lever arm from pin to weld is the input the drawing never labels. Forty-seven percent more of it bought 19 percent more weld utilisation - not proportional, because only the bending part of the demand moves with the arm. Here the direct term stays at 64.5 MPa while the bending term goes from 44.2 to 65.1.
Open this example in the calculatorDetail 5: the weld ends not returned.
Lifting Lug Calculator · computed at page render
Detail 5: two parallel runs instead of welding all round
The same leg size and the same length, with the returns across the ends omitted.
| Fillet weld throat resultantagainst 52.8% all round | 64.7% |
|---|
Worth about a fifth in utilisation, and worth more than that for a reason the number does not show. The bending stress in a weld group peaks at the ends of the runs, so an unreturned end puts a geometric stress raiser exactly where the stress is highest. On a lug used repeatedly, that is where the crack starts.
Open this example in the calculatorDetail 6: the weld leg reduced from 12 mm to 8 mm.
Lifting Lug Calculator · computed at page render
Detail 6: fillet leg reduced from 12 mm to 8 mm
A third off the leg size, which is a common substitution when a fabricator standardises on one weld size across a job.
| Fillet weld throat resultantagainst 52.8% - now governing | 79.2% |
|---|---|
| Double-plane shear-outunchanged, and no longer the governing check | 67.8% |
Note what happened to the governing check. On the reference lug the plate governed; here the weld does. A design whose governing check moves when a fabricator standardises a weld size is a design whose margin nobody is tracking.
Open this example in the calculator04
Details 7 to 9: the ones that are not on the drawing
An angle nobody specified, a corrosion allowance nobody declared, and a parent plate nobody checked. The first two have numbers; the third is the most expensive.
Detail 7: the sling arriving 30 degrees off axis rather than 10.
Lifting Lug Calculator · computed at page render
Detail 7: the sling 30 degrees off the plate axis
Nothing about the padeye changed. The rigging did.
| Fillet weld throat resultantagainst 52.8% at 10 degrees | 90.3% |
|---|---|
| Every plate checkthe shear-out length is taken along the primary load path | unchanged |
Seventy percent more weld utilisation from a decision made by whoever hired the slings. Unless the drawing carries an angle limit somebody can fail on site, nothing connects the calculation to what happens.
Open this example in the calculatorDetail 8: a corrosion allowance, declared.
Lifting Lug Calculator · computed at page render
Detail 8: 3 mm of corrosion allowance declared
An outdoor or marine lug that will be in service for years. The steel that will not be there at the end of its life is removed from the checks.
| Net-section tensionagainst 23.5% | 26.1% |
|---|---|
| Double-plane shear-outagainst 67.8% | 75.3% |
| Pin bearing on the lugagainst 55.8% | 62.0% |
Eleven percent, for a declaration that changes nothing on the drawing. A permanent lift point with no corrosion allowance is a lift point designed for the day it was fabricated.
Open this example in the calculatorDetail 9: the parent plate, unchecked.
This one has no number here because it is not a padeye check at all, and that is exactly why it goes missing. A padeye delivers a concentrated force and a moment into whatever it is welded to. That structure needs its own check: local plate bending under the lug, shear in the parent material, and on a shell or a thin plate, a local stress assessment.
The failure is organisational rather than technical. The padeye is designed by the lifting engineer, the parent structure by somebody else, and the interface belongs to neither. Two habits fix it:
- State the reactions the padeye delivers on the padeye's own calculation, as an output. Force along the plate, force across it, and moment at the weld line.
- Name who receives them. A calculation that ends with "delivered to the parent structure" and no name is a calculation with a loose end.
05
All nine, on one axis
Ranked by what each change did to the governing check. The two mistakes that failed the lug outright were both single dimensions on a drawing, which is why a padeye design review is mostly a dimensional review.
Reviewing a padeye drawing in five minutes
- 01Measure the edge distanceHole centre to free edge, against the calculation's value. This is the single most consequential dimension and the easiest to lose in a revision.
- 02Check the hole against the pinThe clearance is specified, not left to the fitter, and the calculation used the hole on the drawing rather than the pin.
- 03Find the lever armPin centre to the weld line, and it matches what the weld check used. It is usually not dimensioned, which is why it has to be looked for.
- 04Read the weld symbol against the calculationLeg size, length, and whether the ends are returned. All three are in the check.
- 05Look for an angle limitA note a rigger can fail on site, in the form 'sling to arrive within N degrees of the plate axis'.
- 06Look for a corrosion allowanceDeclared for anything permanent or outdoor, and the checks were run with it.
- 07Find where the reactions goThe calculation states the force and moment delivered into the parent structure, and names who checks it.
Common questions
- What is the most common padeye design mistake?
- Losing edge distance. It is one dimension on a drawing, it gets trimmed to clear brackets and pipework, and it is the input the shear-out check is most sensitive to. On this article's reference padeye, cutting the edge distance from 90 mm to 55 mm took the governing check from 68 percent to 163 percent while every other check on the drawing stayed exactly where it was.
- Can I open out a padeye hole to fit a bigger shackle?
- Not without rechecking, and the check that moves is not the one people expect. Opening the hole shortens the shear-out planes, which run from the hole to the free edge, so shear-out rises while bearing is unchanged because the pin did not change. On the worked lug, going from a 60 mm hole to 76 mm took shear-out from 68 percent to 78. There is a second limit too: a hole substantially larger than the pin produces a local contact stress that a uniform bearing calculation does not represent.
- Does making a lug taller matter?
- Yes, and it is the change least likely to be recorded as structural. The height of the pin above the weld is the lever arm that turns the transverse component of the sling force into a moment on the weld group. Raising it from 190 mm to 280 mm on the worked lug took the weld from 53 percent to 63, with every plate check unchanged. It is usually done for shackle clearance by someone who is not looking at the weld calculation.
- Do lifting lugs need a corrosion allowance?
- Any permanently attached lug, and anything outdoors or offshore, yes. Declaring 3 mm on this article's reference padeye moved shear-out from 68 percent to 75 and bearing from 56 to 62 with no change to the drawing at all, because the checks are run on the steel that will still be there at the end of the lug's life rather than on the day it was fabricated.
- Who checks the structure a padeye is welded to?
- Somebody has to be named, and this is the detail that most often belongs to nobody. A padeye delivers a concentrated force and a moment into its parent structure, which needs its own check for local plate bending, shear in the parent material, and on a shell or thin plate a local stress assessment. The fix is procedural: state the reactions the padeye delivers as an output of the padeye calculation, and name who receives them.
Sources
Every document below is linked at its publisher or regulator. Xarpis reproduces no standard text; where a clause is named, the identifier is given so you can find it in your own copy.
ASME BTH-1Design of Below-the-Hook Lifting Devices
ASME · paid document
Structural, mechanical and electrical design criteria for below-the-hook lifting devices, used alongside ASME B30.20 which carries the safety requirements. The current edition is BTH-1-2023; Xarpis implements the 2020 edition and says so on every result.
EN EurocodesEurocodes: Building the future
European Commission, Joint Research Centre · free portal
The Commission's own Eurocodes portal: the structure of EN 1990 to EN 1999, the database of Nationally Determined Parameters, and the second-generation timetable. The standards themselves are sold by the national bodies, but the NDP database is free and is what decides which partial factors apply in your country.
ASME B30.26Rigging Hardware
ASME · paid document
Shackles, links, rings, swivels, turnbuckles, eye bolts, hoist rings and load-indicating devices: identification, effect of environment, inspection and removal criteria. The volume that governs the pin your padeye is designed around.
29 CFR 1926.251Rigging equipment for material handling
US Occupational Safety and Health Administration · free to read
Inspection and safe-use requirements for chain, wire rope, fibre rope, synthetic webbing, shackles and hooks on US construction sites, including the requirement that rigging be inspected before each shift.
Run the check properly
Reading about a calculation is not the same as being able to hand one over. These tools produce the traceable record.
Something here wrong, or thinner than it should be? Tell us which paragraph and it gets rewritten. Articles carry the date they were last revised for exactly this reason.