Lift arrangement — end elevation

Section 01

What the calculator assesses

A lifting-trunnion result is a chain, not a single stress comparison. The engine carries one declared load basis through factors, equilibrium, attachment mechanics, shell stress, route acceptance, external evidence, fatigue, and finally the report.

The complete assessment chainFigure 1

Read left to right, then down. A required contact, retention, shell, or fatigue row has the same status weight as a member or weld row; PASS requires all of them.

01Start with gross lifted weight or six entered per-trunnion actions.
02Resolve the factor ledger once.
03Derive sling geometry and the worst-trunnion share when stationary mode is selected.
04Establish the six-component action state at the contact centroid.
05Transfer actions rigidly to the root / shell-face plane.
06Check member resistance and active stability provisions.
07Distribute demand around the circular attachment weld.
08Compare transverse contact demand with referenced local capacity.
09Check outward axial escape against collar retention when active.
10Calculate WRC 537 local shell stress inside its envelope.
11Apply the selected route’s shell-acceptance criteria.
12Assess fatigue from the planned lift count.
13Select the governing decisive utilization and assemble the report.

Section 02

Supported scope and firm boundaries

The calculator is deliberately narrow enough to produce a defensible result. Boundaries stop unsupported configurations from inheriting a misleading PASS; they are part of the engineering model, not hidden defects.

Supported automatically	Requires referenced external evidence	Outside this calculator’s scope
Symmetric pair of identical, diametrically opposed radial trunnions. Straight cylindrical steel shell and unreinforced round set-on attachment. Solid round or circular hollow trunnion, subject to route restrictions. All-around fillet attachment weld. Symmetric stationary lift or direct actions per trunnion. WRC 537 within the implemented geometry envelope. ASME, EN, Canadian hybrid, and Australian hybrid routes. SI and US customary display units.	Sling-contact wall bending, ovalization, and crippling capacity. Collar and collar-attachment retention resistance when outward escape demand exists. Higher-Service-Class base-metal fatigue utilization where the BTH-1 basis requires it. Any additional assessment required by the owner, lift plan, vessel code, jurisdiction, or reviewing engineer.	Global vessel, saddle, skirt, or complete support-system design. Crane, sling, shackle, spreader, and other rigging-hardware capacity. Tail-lug design, planar upending, or marine-operation assessment. Reinforcement pads in the supported interface and CJP groove-weld assessment. Heads, cones, or other non-cylindrical attachment locations. Fabrication, welding qualification, inspection, proof testing, and regulatory registration.

Section 03

Load path, local axes, and reference planes

Start by locating the actions. A correct force at the wrong reference plane gives the wrong root moment even when every number and unit looks plausible.

Local axes, positive actions, and reference planesFigure 2

Local x points outward along the trunnion; local y is circumferential/tangential; local z is parallel to the vessel axis. Positive moments follow the right-hand rule. The contact band is centred on the contact reference plane.

Local x

Outward from the shell along the trunnion axis. Positive axial force is an outward pull; negative is inward compression.

Local y

Circumferential, tangent to the shell at the trunnion. It is out of the axial-section plane in the figure.

Local z

Parallel to the vessel axis. In stationary mode the vessel axis is vertical, so positive z is upward.

The root is the shell-face plane at the attachment. The contact plane passes through the sling-contact centroid, a distance $a$ outward along local x. The calculator transfers a force/moment system with $M_{r oo t} = M_{co n t a c t} + r \times F$ , where $r = (a, 0, 0)$ runs from the root reference point to the contact point.

Rigid action transfer to the rootFigure 3

For the implemented geometry, a positive vertical force at the contact centroid creates negative root bending about y. A tangential force creates root bending about z. The transfer does not create torsion about x; direct mode can still contain an entered torsional moment.

M_{x, r} = M_{x, c}, M_{y, r} = M_{y, c} - a F_{z}, M_{z, r} = M_{z, c} + a F_{y}

Forces do not change with the reference plane, but the entered moments must describe that same plane. If a lift-analysis result is reported at the shell face, select the root plane. If it is reported at the band centroid, select the contact centroid and let the engine transfer it. An outward contact component $F_{x} > 0$ drives the sling toward the free end and activates the retention path.

Section 04

Two ways to establish the per-trunnion load

Choose the mode that matches the provenance of the load—not the mode that produces the more convenient answer. Stationary mode solves one defined geometry; direct mode accepts a documented six-component envelope from elsewhere.

Symmetric stationary lift

Use this mode when the vessel axis is vertical, the hook lies on that axis above the trunnion elevation, one sling leg connects to each trunnion, the pair is identical and diametrically opposed, and the centre of gravity lies on the vessel axis. Real imbalance must be bounded by the entered skew factor because CG eccentricity is not solved.

Implemented sling geometryFigure 4

The horizontal offset is the vessel outside radius plus the contact-centroid distance—not the trunnion projection and not the sling-band edge. For fixed weight and factors, lowering the hook increases the angle from vertical, leg tension, and inward axial component.

L = \frac{D _{v}}{2} + a, θ = atan2 (L, h), V = \frac{W}{2} k_{d}, T = \frac{V}{cos θ}

F_{co n t a c t} = (- V tan θ, 0, + V), M_{co n t a c t} = 0

Here $W$ is the entered characteristic gross lifted weight, $k_{d}$ is the product of non-suppressed ledger factors, $h$ is hook height above the trunnion-axis elevation, and $V$ is the factored vertical share of the worst trunnion. A flatter leg means a larger $θ$ ; it raises $T$ and the magnitude of the inward axial force. In this symmetric stationary model, the root bending caused by vertical share is $M_{y} = - aV$ .

Direct load per trunnion

Use direct mode when a lift analysis already supplies actions for one trunnion—for example from a global vessel/rigging model, or after asymmetric, transient, transport, or operation-specific effects have been enveloped externally. The direct set may be entered at the contact centroid or root plane.

Action	Physical meaning in the implemented local system	Typical consequence
$F_{x}$	Axial force; positive outward, negative inward.	Member axial demand; positive outward contact force activates retention.
$F_{y}$	Circumferential/tangential force.	Transverse shear, contact demand, and—at the contact plane—root bending about z.
$F_{z}$	Force parallel to the vessel axis.	Transverse shear, contact demand, and—at the contact plane—root bending about y.
$M_{x}$	Torsional moment about the trunnion axis.	Torsional section and weld traction; it may exist in a direct action envelope.
$M_{y}$	Bending moment about local y.	One component of resultant member and weld bending.
$M_{z}$	Bending moment about local z.	The other component of resultant member and weld bending.

Section 05

The demand-factor ledger

The factor ledger records what turns a characteristic load into factored per-trunnion actions. It is separate from the design factors, partial factors, and capacity factors used by the selected resistance route.

Factor-ledger flowFigure 5

Every enabled demand factor multiplies the characteristic weight or direct action set once. Route-specific resistance factors act later inside their own checks.

Control	What it represents	Where the value should come from	Common error
Weight contingency	Allowance for uncertainty in the lifted gross weight.	Approved weight report, mass-control procedure, or lift basis.	Applying contingency here and again in the entered gross weight.
Dynamic amplification	Impact or motion amplification in the declared lift condition.	Project lift procedure, governing lifting standard, or qualified dynamic assessment.	Treating a default seed as a universal code value.
Skew / load share	Bounds the worst trunnion when the real pair will not share perfectly.	Rigging tolerance, CG uncertainty, geometry, or external load-share analysis.	Using 1.0 despite unbounded imbalance, or applying skew in both the global model and ledger.
Project factor	Any additional explicitly required project action factor.	Owner specification or documented project design basis.	Using it as an undocumented blanket safety factor; a value here does not perform a marine-operation assessment.
Loads already factored	Declares that the entered weight/actions are already design actions.	The load-case provenance and calculation record.	Turning it on before every required factor is actually present—or leaving it off and double-applying factors.

The applied product is visible in the result and report. Values below 1.0 generate a warning because they reduce demand. Do not add a generic safety factor merely because the route also contains $N_{d}$ , $γ_{M}$ , or $ϕ$ ; those are resistance/design provisions with a different role.

Section 06

A defensible step-by-step workflow

Work from basis to result. The sequence makes load provenance and external evidence visible before the final status is interpreted.

Confirm applicability
Confirm a symmetric pair of fixed radial trunnions on a straight cylindrical shell, with a supported circular section and all-around fillet weld.
Choose the assessment route
Select ASME, EN, Canadian hybrid, or Australian hybrid from the project design basis and jurisdictional requirements.
Choose the load mode
Use symmetric stationary lift for the built-in two-leg geometry, or direct per-trunnion actions from a documented external lift analysis.
Declare demand factors
Enter contingency, dynamic, skew, and project factors once, or mark the entered actions as already factored.
Enter vessel and trunnion data
Enter nominal geometry, corrosion and tolerance deductions, material properties, contact position, contact width, weld, and route-specific values.
Supply required external evidence
Reference contact capacity and, when outward axial demand exists, collar-plus-attachment resistance; provide higher-class base-metal fatigue evidence when required.
Review every active row
Check WRC applicability, route acceptance, member, weld, contact, retention, fatigue, warnings, and the governing supported utilization.
Review and issue the report
Reconcile the calculation with the lift basis, drawings, fabrication, inspection, regulatory obligations, and independent project review.

Section 07

Assessment-route guide

The route selector changes the member, weld, fatigue, and shell-acceptance basis. Choose it from the governing project framework; a route label describes the calculation path and never claims certification or jurisdictional approval.

Route	Normally selected when	Implemented check chain	Active route inputs	Still project-specific
ASME	The lifting attachment and vessel assessment are governed by the stated ASME basis.	BTH-1 member, weld, and fatigue; WRC 537 local shell stress; BPVC VIII-2 elastic shell acceptance.	BTH design category; planned lifts; trunnion and weld strengths; BPVC allowable, yield, SMYS, and UTS values.	Design-category justification, load factors, material applicability, contact/collar evidence, fabrication, inspection, and lift approval.
EN	The project adopts EN structural and pressure-vessel provisions.	EN 1993 member, fillet weld, and fatigue; WRC 537 local shell stress; EN 13445-3 elastic acceptance.	Buckling curve, weld correlation and partial factors, fatigue detail category and factor, shell yield and tensile strengths.	Applicable National Annex, adopted editions, detail-category selection, loads, evidence, conformity, and project review.
Canadian hybrid	A Canadian project adopts CSA S16 for the CHS attachment while using the documented BPVC shell path within the CSA B51 framework.	CSA S16 CHS member, weld, and fatigue; WRC 537 stresses; BPVC VIII-2 shell acceptance.	CSA fatigue category and weld-metal strength; BPVC shell material values; CHS geometry.	Provincial adoption, CRN responsibility, owner requirements, evidence, fabrication, inspection, and registration. This is not “CSA-certified.”
Australian hybrid	The project requires AS 4100 attachment and AS 1210 vessel provisions with the stated complementary lifting basis.	AS 4100 CHS member/weld; AS 1210 shell acceptance; WRC 537 stress; BTH-1 complementary buckling, torsion interaction, weld, and fatigue checks.	CHS residual-stress category, SP/GP weld category, AS 1210 room/design-temperature strengths and evaluation location, plus BTH design category.	The adopted hybrid basis, load factors, materials, contact/collar evidence, fabrication, inspection, and Australian regulatory/project obligations.

Section 08

Geometry, material, and service inputs

After project, route, load mode, and factor ledger, the input panel proceeds through vessel shell, shell assessment, trunnion geometry, contact and collar, materials, weld, and service. Enter nominal values from controlled project records—not measurements or catalogue values with an unclear basis.

Input	Meaning and normal source	Units / effect	Common mistake
Vessel outside diameter	Outside diameter at the attachment from the approved vessel drawing or model.	Length. Sets the stationary sling offset and WRC mean radius.	Entering inside or mean diameter.
Shell nominal thickness	Nominal shell-course thickness at the attachment from the vessel design/drawing.	Length. The automatic shell thickness is nominal minus corrosion allowance and negative mill tolerance.	Entering an already-corroded thickness and deducting allowances again.
Shell corrosion allowance	Project vessel corrosion allowance applicable at the lift condition.	Length. Deducted from nominal shell thickness.	Using remaining measured loss in place of the design allowance without documenting the basis.
Negative mill tolerance	Absolute thickness deduction required by the material/product basis.	Length. Kept separate and deducted with corrosion.	Entering a percentage instead of the corresponding length.
Straight cylinder length	Length of the applicable straight cylindrical shell region.	Length. Used in the WRC condition on cylinder length divided by mean radius.	Including a head or cone as straight cylinder.
Distance to nearest end	Attachment centreline to the nearest cylinder end or relevant discontinuity.	Length. External moment requires at least half the mean radius in the automatic method.	Measuring from the weld toe, band edge, or far end.
Trunnion section	Solid round or circular hollow section from the controlled attachment drawing.	Selection. Changes effective section properties and route applicability.	Selecting solid on the CHS-only Canadian or Australian route.
Trunnion outside diameter	Nominal OD of the welded member.	Length. Controls section properties, contact area, weld-line radius, and WRC attachment radius.	Entering collar or repad diameter.
Wall thickness	Nominal CHS wall from material certification/drawing; used only for hollow sections.	Length. Corrosion is deducted before properties and classification.	Entering a wall at or above half the OD, leaving no valid bore.
Projection	Root/shell-face plane to free end.	Length. Supplies the unbraced cantilever length in active stability checks.	Using contact-centroid distance instead of full projection.
Contact centroid from root	Root plane to the centroid of the actual sling/shackle/bail contact band.	Length. Sets stationary sling offset and contact-to-root moment transfer.	Locating it beyond the projection or using the band edge.
Contact-band width	Effective axial width of the actual contact region.	Length. Used only in average projected bearing pressure.	Assuming a larger width automatically proves local wall capacity.
Trunnion corrosion allowance	Allowance applicable to the trunnion at the assessed lift condition.	Length. Deducted before circular section properties are calculated.	Consuming the wall or reducing a solid diameter to impossible geometry.
Trunnion yield and tensile strength	Applicable values for grade, thickness, temperature, and route.	Stress. Feed member, weld correlation, and route resistance rules.	Using a catalogue nominal that does not apply to the actual product/thickness.
Elastic modulus	Project material basis for steel at the assessed condition.	Stress. Used in BTH and route-specific stability/classification calculations.	Changing it as a tuning parameter.
Route-specific shell values	BPVC allowable/yield/SMYS/UTS; EN shell yield/tensile; or AS 1210 room/design-temperature strengths and location.	Stress and selection. Supply the shell acceptance limits.	Using trunnion material values for the vessel shell.
Fillet-weld leg size	Specified all-around weld leg from the attachment drawing.	Length. Effective throat is the leg divided by the square root of two.	Entering throat as leg size, or assuming the calculator checks a CJP weld.
Electrode / weld-metal strength	Applicable consumable classification and route-specific weld basis.	Stress. Supplies the active route’s weld resistance.	Using base-metal yield strength as weld-metal ultimate strength.
User mechanics allowables	Documented project normal, shear, and weld allowables for the mechanics cross-check rows.	Stress. They do not replace route-derived resistance rows.	Inventing them from an undocumented blanket factor.
Planned number of lifts	Total expected lift cycles over the attachment life, including repeated handling/turnarounds where applicable.	Integer count. Drives BTH Service Class and EN/CSA fatigue cycles.	Entering only the immediate campaign when the trunnion remains in service.

Section 09

How the member and weld checks work

The member and weld share the same factored root action set, but use different mechanical models. The report keeps demand, resistance, utilization, equation reference, intermediate values, and assumptions together for each active row.

Effective circular section

Area, second moment, elastic section modulus, polar inertia, and polar modulus are calculated from the effective solid or annular geometry.
Axial stress uses the root axial-force magnitude divided by area.
Resultant bending combines the y- and z-moment components and divides by elastic section modulus in the mechanics row.

Shear, torsion, and interaction

Transverse shear uses the exact elastic maximum for the solid or hollow circular section.
Torsional shear uses the root torsion and polar section modulus.
Mechanics and route rows combine actions conservatively; active compression stability uses the full projection as a fixed-free cantilever length.

Circular all-around weld demandFigure 6

The line-weld kernel sweeps the full circumference. Axial force and biaxial bending create normal traction; transverse shear and torsion create tangential traction. Their resultant identifies the governing angular point from local +y toward +z.

The fillet weld is idealized as a thin circular line at the trunnion outside radius. Its effective throat is $a_{w} = s / 2$ , where $s$ is the entered leg. The demand kernel reports maximum line force, resultant throat stress, and governing angle. The selected route then supplies its weld resistance: BTH-1 on the ASME route, the EN 1993 simplified fillet method, CSA S16, or AS 4100 plus the stated complementary BTH row on the Australian hybrid.

Classification, buckling/stability, route interaction, weld category/factor, and weld-fatigue rows appear only where their route activates them. Minimum/detailing obligations reported by an active row must be reconciled with the fabrication drawing and governing standard; increasing the entered weld leg is not a substitute for checking weld length, access, base metal, qualified procedure, or inspection.

Section 10

WRC 537 stress and route-specific shell acceptance

WRC 537 calculates local shell stress caused by the attachment actions. It does not decide whether those stresses meet the selected vessel-code criteria; that decision is made by a separate route acceptance row.

WRC round-attachment geometry and stress conceptFigure 7

The automatic method uses the corroded shell thickness, shell mean radius, and unreinforced round attachment radius. It evaluates representative inner/outer surface states; the diagram is conceptual and is not a finite-element contour plot.

T = t_{n o m} - c_{a} - t_{mi l l}, R_{m} = \frac{D _{v}}{2} - \frac{T}{2}

γ = \frac{R _{m}}{T}, β = \frac{0.875 r _{0}}{R _{m}}, r_{0} = \frac{D _{t r}}{2}

Automatic applicability condition	Implemented limit	What happens outside it
$β$	$0.05 \leq β \leq 0.20$	The WRC applicability row fails; no extrapolated curve is used.
$γ$	$5 \leq γ \leq 100$	The automatic shell method stops rather than extending the coefficient tables.
Straight-cylinder length	$L / R_{m} > 3$	The automatic WRC cylindrical-shell result is unavailable.
Nearest end with any external root moment	$e / R_{m} \geq 0.5$	The attachment is too close to the cylinder end for the implemented automatic path.
Attachment form	Unreinforced round set-on attachment on a straight cylinder	A repad, head, cone, or other footprint requires a separate accepted assessment.

Inside that envelope the engine consumes all six factored root actions, evaluates the implemented eight-point stress states, and reports governing membrane and total stress intensities. The WRC row passing means the stress method ran within its bounds. It is not the code PASS.

Route	Acceptance applied after WRC	Treatment of entered general primary membrane intensity
ASME	BPVC VIII-2 elastic checks for general primary membrane, local primary membrane, and local membrane plus primary bending.	The entered general intensity remains the general membrane demand and is conservatively added to local WRC membrane and total intensities for the local categories.
EN	EN 13445-3 design-by-analysis limits for primary membrane and primary membrane plus bending.	The entered general intensity is conservatively added to the WRC membrane and total intensities.
Canadian hybrid	The same documented BPVC VIII-2 shell-acceptance adapter used within the stated Canadian framework.	Combined in the same implemented scalar envelope as the ASME route.
Australian hybrid	AS 1210 Appendix N membrane, shear, compressive membrane, and location-dependent local membrane-plus-bending limits.	Added to the applicable membrane/local/compression envelopes; WRC shear is evaluated separately.

Section 11

Sling contact, collar retention, and fatigue

These checks protect load paths that a strong trunnion member and weld do not prove. Their evidence must describe the real geometry, attachment, and service—not merely repeat the entered capacity.

Contact and retention are separate load pathsFigure 8

Transverse force through the band drives local tube-wall behavior. Positive outward axial force drives sling escape toward the free end. One capacity cannot be assumed to cover both mechanisms.

Sling-contact evidence

The required demand is the resultant of contact-plane y and z forces.
Average projected bearing pressure uses contact width times trunnion OD and is diagnostic only.
Referenced capacity must cover local wall bending, ovalization, and crippling for the actual trunnion and contact band.
The reference should identify the calculation, nonlinear analysis, qualification, or test that established the entered resistance.

Collar / retainer evidence

Only positive outward contact-plane axial force creates the implemented sling-escape demand.
Collar diameter and thickness describe geometry; they do not establish capacity.
The referenced resistance must cover the collar plate, its attachment, and the actual escape geometry.
No collar can be acceptable in the calculation only when no outward escape demand exists; otherwise missing evidence fails the row.

Fatigue and planned lifts

Every planned lift is one zero-to-peak-to-zero stress cycle. Static utilization may be low while repeated turnaround or maintenance use moves the attachment into a fatigue regime, so the lifetime count—not merely the current lift campaign—belongs in the input.

BTH-1 Service Class	Planned cycles in the implementation	Effect
0	Up to and including 20,000	The mapped Chapter 3 weld-throat and base-metal fatigue checks are exempt.
1	20,001 to 100,000	Category F weld-throat fatigue is checked; referenced base-metal detail utilization is required.
2	100,001 to 500,000	Lower Category F allowable; referenced base-metal detail utilization remains required.
3	500,001 to 2,000,000	Further reduced Category F allowable and required base-metal evidence.
4	More than 2,000,000	Highest implemented service class; weld and referenced base-metal fatigue can govern.

The ASME route and the Australian hybrid’s complementary BTH basis distinguish weld-throat fatigue from base-metal attachment-detail fatigue. Above Service Class 0, the latter requires a referenced external utilization. The EN route uses the entered nominal-stress detail category and fatigue factor; the Canadian hybrid uses the selected CSA fatigue category and the planned cycle count. Category selection remains a project engineering responsibility.

Section 12

How to read the result

Start with the overall state, then read the governing row, warnings, load path, and every active calculation. The report is strongest when the reviewer can trace each number back to an input or evidence reference.

Overall-status logicFigure 9

Utilization above 1.0 fails. Missing required evidence is also a failed active row. A temporarily incomplete or undecidable required path remains INDETERMINATE; only all required active passes produce PASS within scope.

Visible result area	How to interpret it
Overall status	PASS, FAIL, or INDETERMINATE from all required active route rows—not from the governing utilization alone.
Governing utilization	The largest decisive supported demand-to-resistance ratio. A value above 1.0 fails.
Governing check	The decisive row with the largest supported utilization; it is not necessarily the project’s most important unmodelled risk.
PASS	Every required implemented row passes within scope. It is not approval, certification, registration, or release for lifting.
FAIL	At least one implemented row fails resistance, applicability, or required-evidence logic.
INDETERMINATE	A required calculation cannot be decided, commonly while inputs are incomplete or geometrically invalid.
Information-only row	A useful computed diagnostic with no capacity—such as average contact bearing. It is neither a pass nor a hidden failure.
FEA recommendation	Triggered by stated scope heuristics or governing utilization above 0.85. It is a review signal, not an automatic acceptance method.
Warnings	Factor, geometry, scope, or high-utilization messages that should be resolved even when they do not numerically govern.
Load-path summary	Applied factor product, sling geometry, vertical share, leg tension, root axial force, resultant shear/bending, and torsion.
Active calculations	All route and mechanics rows evaluated for the selected route. Every required one must explicitly pass.
Intermediate values	Section class, WRC parameters, component stresses, weld throat, resistance factors, and other traceability data.
Equations and clauses	Compact mathematical basis and standard title/edition/clause or equation references for review.
Assumptions	The coordinate system, symmetry, corrosion treatment, cantilever idealization, fatigue-cycle model, and route-specific assumptions actually used.

Section 13

Worked example calculated by the live engine

The page calculates this example on the server from the calculator’s current default inputs, then passes the same results through the real report-model builder. Values below are not copied into the guide.

Passing example — 10 t vessel lift · engine v0.2.0

ASME BPVC VIII-2 Part 5 — elastic shell acceptance

ASME · Symmetric stationary lift · SI

Overall status

PASS

U = 0.645 (64.5%)

Live default schematic

Live calculation schematic — dimensions govern; some details may be exaggerated for clarity. Not for fabrication.

Project / geometry input	Current default
Project description	Passing example — 10 t vessel lift
Vessel shell	OD 2400.0 mm · nominal 20.0 mm · shell CA 3.0 mm · mill tolerance 0.3 mm
Straight cylinder / nearest end	8000.0 mm / 2000.0 mm
Trunnion	Circular hollow · OD 273.0 mm · wall 25.0 mm
Projection / contact centroid / band	300.0 mm / 150.0 mm / 90.0 mm
Characteristic gross weight	100.00 kN
Hook height above trunnion axis	6000.0 mm

Factor ledger	Value	Applied?
Weight contingency	1.100×	Yes
Dynamic amplification / impact	1.150×	Yes
Load-share / skew factor	1.050×	Yes
Project / marine-operation factor	1.000×	Yes

Applied demand-factor product: 1.32825×.

Calculated load-path value	Live result
Sling angle from vertical	12.68°
Factored vertical share, worst trunnion	66.41 kN
Factored sling-leg tension	68.07 kN
$F_{x}$ at root	-14.94 kN
Resultant root shear	66.41 kN
Resultant root bending	9.96 kN·m
$M_{x}$ at root	0.00 kN·m
Average contact bearing—diagnostic	2.7 MPa
WRC beta / gamma	0.1002 / 71.36
WRC total stress intensity	151.6 MPa

Why this example passes

The live overall state is PASS and the governing utilization is 0.645.
The default geometry lies inside the implemented WRC envelope and satisfies its length/end-distance conditions.
The referenced illustrative contact capacity row is passing for the current transverse demand.
No outward axial contact force drives the sling toward the free end in this load case; collar retention is not load-active.
Service Class 0 (10 planned lift(s) ≤ 20,000 cycles); BTH-1 §3-1.4 does not require the Chapter 3 fatigue check.

What it does not prove

The illustrative contact reference is not evidence for another trunnion, band, material, or vessel.
No crane, sling, shackle, tail lug, global vessel, fabrication, inspection, proof-test, or registration assessment is included.
A different vessel diameter, shell thickness, contact position, material, factor basis, route, or lift count requires its own complete calculation.

View the complete unblurred example report Open this example in the calculator

Section 14

Sensitivity and engineering judgment

These are directional intuitions within a fixed valid geometry, load mode, route, classification, and evidence basis. A change can cross a section-class, Service-Class, WRC, stability, or scope boundary and alter the governing method.

Change	Typical effect with other inputs fixed	Important qualification
Increase hook height	Reduces stationary sling angle, leg tension, and inward axial component for fixed weight/factors.	The vertical share and its root moment from a fixed contact distance remain unchanged.
Increase full projection	Increases effective fixed-free length in active stability checks.	If contact-centroid distance is unchanged, the rigid root transfer itself does not use the extra unused projection.
Move contact centroid outward	Increases the stationary horizontal offset and inward axial component, and increases root moment from transverse force.	It also changes direct-mode moment transfer when the actions are entered at the contact plane.
Increase trunnion OD	Raises circular section and weld-line dimensions; average projected bearing falls for fixed band width and force.	It also increases WRC attachment radius and beta, so shell effect is not a one-direction optimization.
Increase CHS wall thickness	Generally increases area and section moduli and can improve wall classification.	The referenced sling-contact capacity does not update automatically.
Increase effective shell thickness	Generally reduces direct stress scales in a fixed WRC regime.	It also changes mean radius, gamma, curve ordinates, and applicability; always rerun the complete shell chain.
Increase contact-band width	Reduces the reported average projected bearing pressure at fixed transverse force.	It does not create automatic local wall resistance; the external capacity and evidence must be revised for the real band.
Increase fillet leg	Increases effective throat and route weld resistance; the elastic line force around the weld is unchanged.	It does not prove base metal, detailing, access, heat input, or weld procedure.
Increase an applied demand factor	Scales the contact and root actions linearly, so linear-elastic demands rise proportionally.	Classification and capacity normally stay fixed until another regime or scope boundary is crossed.
Increase planned lifts	Leaves static action demand unchanged but can reduce fatigue resistance or enter a higher BTH Service Class.	Crossing 20,000 cycles activates required external base-metal fatigue evidence on the BTH basis.

Section 15

Why can’t I get PASS?

Treat each message as a model or evidence question. The correct response is to verify the real design basis, repair an input error, revise the physical design, or provide an accepted external assessment—not to manipulate inputs until the badge changes.

Message or symptom	What it means / what to verify	Correct engineering response
Invalid or temporarily incomplete geometry	A required positive value is blank, zero, non-finite, or otherwise fails the input schema.	Complete the controlled input set; do not interpret paused results.
Wall thickness is too large for the diameter	A hollow section would have no positive bore because twice the wall is at least the OD.	Check OD/wall units and section schedule against the drawing.
Corrosion consumes the effective section	Trunnion CA consumes the hollow wall/solid diameter, or shell CA plus mill tolerance consumes nominal shell thickness.	Reconcile nominal, allowance, and measured-condition bases; redesign if the remaining geometry is not physical.
Contact centroid beyond projection	The load point lies beyond the modeled free end.	Correct the root datum/contact location or revise the physical projection.
Contact band wider than projection	The entered effective bearing band cannot fit on the modeled projection.	Confirm the actual hardware footprint and available straight contact length.
Trunnion diameter incompatible with vessel	Trunnion OD is at least the vessel OD, outside the radial set-on geometry.	Correct the selected diameters or use a different project-specific attachment model.
WRC geometry outside beta or gamma	The automatic round-attachment curves are outside the implemented common envelope.	Use a genuinely applicable geometry or a separate accepted shell analysis; do not extrapolate.
Attachment too close to a shell end	With external root moment, end distance is less than half the shell mean radius.	Reposition/detail the attachment or use a project-specific shell method that addresses the discontinuity.
Missing contact evidence	Transverse band force exists but no referenced wall/ovalization/crippling capacity was entered.	Provide an assessment covering the real tube, band, material, and failure modes.
Outward axial force without retention	Positive contact-plane axial force can drive sling escape and no collar is selected.	Provide a suitable retainer and verify its full load path, or revise the real rigging/load direction through the lift analysis.
Missing collar evidence	A collar is present but its geometry alone does not prove resistance.	Reference a capacity covering the collar plate and attachment at the actual escape demand.
Missing higher-class fatigue evidence	BTH Service Class is above 0 and no detail-specific base-metal utilization/reference is supplied.	Complete and reference the external fatigue-detail assessment.
Member or weld utilization above 1.0	An implemented demand exceeds its route resistance.	Check load provenance and inputs, then redesign the real section/weld/load path and repeat the full assessment.
Wrong direct-mode reference plane	Actions and selected plane describe different points, producing incorrect moments.	Return to the source free body, identify its datum, and enter a consistent six-component action set.
Factors applied twice	Imported design actions were multiplied again by the ledger.	Document the imported load basis and use the already-factored control only when every required demand factor is already included.
Wrong unit interpretation	A value was entered as kN versus N, mm versus inches, or MPa versus ksi in the wrong display mode.	Set the intended unit system first and verify every value against the unit shown beside its field and in the report.

Section 16

Report, entitlement, and pre-issue review

The report is the calculation record, not the final engineering decision. Use it to make the load basis, active checks, evidence, assumptions, warnings, and boundaries reviewable against the project documents.

Project preview

The normal free project-report preview is locked/blurred in accordance with the site entitlement. The calculator and overall state remain usable.

Unlocked project PDF

A subscription unlocks the clean professional PDF with report values, checks, sources, assumptions, warnings, and scope statements.

Example report

The built-in report at /report/demo/lifting-trunnion is complete and unblurred so the deliverable can be reviewed before subscription.

The generated report includes the project header and unit system; route and mode; input summary; factor ledger; contact/root actions; effective section properties; governing summary; every active check with demand, resistance, utilization, equations and notes; warnings; assumptions; source titles/editions/clauses; exclusions; and the live schematic.

Pre-issue checklist

Load basis, gross weight, inclusions, and action provenance are approved and revision-matched.
Every demand factor has a documented source and is applied exactly once.
Sling geometry, hook height, contact centroid, and load-share assumptions match the lift plan.
Assessment route, standard editions, adoption, and National Annex/jurisdictional basis are confirmed.
Trunnion, weld, and shell material values apply to grade, thickness, and temperature.
Corrosion allowances and negative mill tolerance are neither omitted nor double-deducted.
Contact capacity and evidence cover the actual band, tube, and local failure modes.
Collar evidence covers the collar and its attachment whenever outward demand is active.
Planned lifts and any required base-metal fatigue evidence cover the full intended life.
WRC beta, gamma, cylinder-length, end-distance, and unreinforced-attachment conditions are satisfied.
The governing result and all other required rows are understood—not merely passed over.
Warnings, assumptions, and exclusions are closed or assigned in the project record.
Fabrication drawing geometry and weld detail match the calculation inputs.
A qualified engineer has completed independent project review before issue or lift release.

Section 17

Frequently asked questions

Short answers to the scope, evidence, route, shell, fatigue, units, and report questions that most often change how the calculation should be used.

What does PASS mean?

PASS means every required active row implemented for the selected route explicitly passes within the calculator’s stated scope. It is not project approval, certification, a lift release, or an engineer’s stamp.

Which assessment route should I select?

Select the route required by the vessel design basis, lifting-device basis, jurisdiction, owner specification, and reviewing engineer. The route changes member, weld, fatigue, and shell-acceptance rules; its name does not establish regulatory adoption for the project.

Can I use a solid trunnion?

Yes on the ASME and EN routes. The current Canadian hybrid and Australian hybrid member adapters are CHS-only, so a solid round cannot obtain PASS on those routes.

Can I use a pipe or CHS trunnion?

Yes. Enter the actual outside diameter, nominal wall thickness, corrosion allowance, material values, and contact geometry. The calculator forms the effective corroded annular section and checks route-specific wall classification where applicable.

Why is external sling-contact capacity required?

The engine can calculate transverse demand and average projected bearing pressure, but average pressure does not establish resistance to local wall bending, ovalization, or crippling. A referenced calculation, analysis, qualification, or test must cover the actual tube and contact band.

Why does WRC 537 not by itself produce code acceptance?

WRC 537 supplies local cylindrical-shell stress components and intensities. The selected ASME, EN, Canadian hybrid, or Australian hybrid route supplies the acceptance criteria and applicable material values in a separate check.

What should I enter for general primary membrane stress?

Enter the applicable non-negative general primary membrane stress intensity from the pressure and global vessel analysis at the assessed condition. The calculator combines that scalar with local WRC demand only in the manner implemented for the selected route.

What happens if the attachment is outside the WRC range?

The automatic WRC applicability row fails and the calculator does not extrapolate or claim shell acceptance. The geometry must be revised on an engineering basis or assessed separately by an accepted project-specific shell method.

When is a collar required?

The implemented retention path activates when the contact-plane axial force is positive outward, toward the trunnion free end. A collar is then required together with referenced resistance for the collar and its attachment. With no outward escape demand, the row is not load-active.

How are planned lifts used?

Each planned lift is treated as one zero-to-peak-to-zero stress cycle. The count selects the BTH-1 Service Class where that basis applies and supplies the cycle count to the EN and CSA fatigue checks.

What changes when I switch SI and US units?

Only entered and displayed units change. The same calculation runs on the canonical N, mm, and MPa basis, and the report identifies the chosen display system.

Can I assess a reinforcement pad or a CJP groove weld?

No in the supported calculator interface. Automatic WRC 537 is limited to an unreinforced round attachment, and the implemented attachment is an all-around fillet weld. Repads and CJP welds require separate project-specific methods.

Can the calculator assess planar upending?

No. Symmetric stationary lifting and direct per-trunnion actions are supported. A tail lug, changing support shares, rotation through an upending sequence, and operation-specific dynamics remain in the external lift analysis.

Does the report replace engineering review?

No. It records the inputs, factor ledger, actions, checks, sources, assumptions, warnings, and exclusions. A qualified engineer must still reconcile it with the lift plan, vessel design, drawings, fabrication requirements, inspection, and jurisdiction.

What is available without a subscription?

Free users can run the calculator, see its overall state and diagrams, and inspect a locked project-report preview. A subscription unlocks the clean project PDF. The built-in example report linked from this guide is intentionally complete and unblurred.

Continue with the calculation

Use the guide, calculation, and report as one reviewable engineering record.

Start from the built-in example, replace every project-dependent value and evidence reference, then review the complete chain before issuing the report.

Open calculator View example report Read methodology & sources