Lifting Trunnion Design Calculator report

Passing example — 10 t vessel lift · Rev A

2026-07-21 09:49:33 UTC

SI (mm · kN · MPa)

ASME — BTH-1 member, weld, and fatigue; WRC 537 shell stresses; BPVC VIII-2 acceptance

Inputs summary

Assessment route

ASME — BTH-1 member, weld, and fatigue; WRC 537 shell stresses; BPVC VIII-2 acceptance

Analysis mode

Symmetric stationary lift (Mode B)

Gross lifted weight (characteristic)

100.00 kN

Hook height above trunnion axis

6000.0 mm

Vessel shell

OD 2400.0 mm × 20.0 mm (CA 3.0 mm, mill tol 0.3 mm)

WRC cylinder geometry

straight length 8000.0 mm · attachment to nearest end 2000.0 mm

Trunnion

Hollow, OD 273.0 mm × wall 25.0 mm

Projection / contact centroid / band

300.0 mm / 150.0 mm / 90.0 mm

Collar

OD 340.0 mm × 20.0 mm · no referenced resistance supplied

Shell-stress method

WRC Bulletin 537 — unreinforced round attachment

Sling-contact capacity

150.00 kN · Illustrative contact assessment CA-001 — replace for project use

Trunnion material

$F_{y}$ 355.0 MPa · $F_{u}$ 490.0 MPa

User allowables (normal / shear / weld)

213.0 MPa / 142.0 MPa / 140.0 MPa

Attachment weld

Fillet all-around, leg 12.0 mm

Planned lifts

Schematic

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

Governing summary

Governing check

ASME BPVC VIII-2 Part 5 — elastic shell acceptance

Utilisation

0.645 (64.5%)

Overall status

pass

FEA recommended

Checks

Check	Demand	Capacity	U	Status
Trunnion root — normal stress	9.8 MPa	213.0 MPa	0.046	Pass
$σ = ∣ F_{x} ∣/ A + M_{b} / Z$ with $M_{b} = M_{y}^{2} + M_{z}^{2}$ at the root plane. Governing state: symmetric stationary lift — worst trunnion — sling angle 12.7° from vertical, leg tension 68.1 kN.
Equations used $σ = \frac{∣ F _{x} ∣}{A} + \frac{M _{y}^{2} + M _{z}^{2}}{Z}$ (Elastic beam stress — public mechanics)
Trunnion root — shear stress	6.8 MPa	142.0 MPa	0.048	Pass
Maximum elastic transverse shear of the circular section, conservatively summed with the torsional shear $τ = T c / J$ .
Equations used $τ = τ_{V, m a x} + \frac{M _{x} c}{J}$ (Elastic shear identities — public mechanics)
Trunnion root — combined (von Mises)	15.3 MPa	213.0 MPa	0.072	Pass
Conservative diagnostic: the peak normal and peak shear stresses are superposed as if co-located on the circumference.
Equations used $σ_{v m} = σ^{2} + 3 τ^{2}$ (Distortion-energy identity — public mechanics)
Attachment weld — fillet throat demand	22.1 MPa	140.0 MPa	0.158	Pass
Governing weld point at 90.0° (from local $+ y$ toward $+ z$ ); resultant line force 187.6 N/mm over throat 8.49 mm. Demand kernel only — the selected route's separate weld rows apply strength, detailing, and fatigue provisions.
Equations used $f (φ) = n (φ)^{2} + t (φ)^{2}, τ_{w} = \frac{f _{m a x}}{a}$ (Elastic line-weld method — public mechanics)
Sling contact — average bearing (diagnostic)	2.7 MPa	—	—	Info
Average pressure over the projected contact area (band width × trunnion OD). This value is diagnostic only; the separate contact-capacity row must cover local wall bending, ovalization, and crippling for the actual geometry.
ASME BTH-1 §3-2.3 — trunnion bending	9.0 MPa	130.2 MPa	0.069	Pass
Section classified "compact" (BTH-1 Table 3-2.2-1); $F_{b}$ per eq. (3-6).
Equations used $F_{b} = \frac{1.10 F _{y}}{N _{d}}$ (ASME BTH-1–2020)
ASME BTH-1 §3-2.3.6 — trunnion shear	6.8 MPa	68.3 MPa	0.099	Pass
Equations used $F_{v} = \frac{F _{y}}{3 N _{d}}$ (eq. (3-28))
ASME BTH-1 §3-2.2 — trunnion axial (compression)	0.8 MPa	116.4 MPa	0.007	Pass
Inward (−x) root axial force — compression allowable, $K l / r = 6.8$ vs $C_{c} = 105.5$ (cantilever $K = 2.0$ , full projection unbraced).
Equations used $F_{a} = \frac{F _{y} [ 1 - \frac{( K l / r ) ^{2}}{2 C _{c}^{2}} ]}{N _{d} [ 1 + \frac{9 ( K l / r )}{40 C _{c}} - \frac{3 ( K l / r ) ^{3}}{40 C _{c}^{3}} ]}$ (eq. (3-3))
ASME BTH-1 §3-2.4 — combined axial + bending	—	—	0.076	Pass
Governing interaction: eq. (3-34).
ASME BTH-1 §3-2.5 — combined normal + shear	15.3 MPa	118.3 MPa	0.129	Pass
BTH-1 Chapter 3 has no dedicated torsional allowable; torsional shear is folded into this combined check per the shear allowable basis (§3-2.3.6) — see the assumption note.
Equations used $f_{cr} = f_{x}^{2} - f_{x} f_{y} + f_{y}^{2} + 3 f_{v}^{2} \leq \frac{F _{y}}{N _{d}}$ (eq. (3-37))
ASME BTH-1 §3-3.4.1(b) — fillet weld allowable	22.1 MPa	80.5 MPa	0.275	Pass
Governing weld point at 90.0° (from local $+ y$ toward $+ z$ ); base-metal adequacy is checked separately at the root plane.
Equations used $F_{v} = \frac{0.60 F _{E X X}}{1.20 N _{d}}$ (eq. (3-55))
ASME BTH-1 §3-4 — weld-throat fatigue (Category F)	22.1 MPa	—	—	Pass
Service Class 0 (10 planned lift(s) ≤ 20,000 cycles) — §3-1.4 exempts this from a fatigue check.
ASME BTH-1 §3-4 — base-metal fatigue	—	—	—	Pass
Service Class 0 (10 planned lift(s) ≤ 20,000 cycles); BTH-1 §3-1.4 does not require the Chapter 3 fatigue check.
Local shell stress — WRC 537	151.6 MPa	—	—	Pass
Governing total stress intensity occurs at Au; membrane intensity governs at Au. The automatic path uses the bulletin's Original round-attachment curves only; no extrapolated curve table is used. This row establishes shell stresses and method applicability. Route-specific acceptance is evaluated separately.
Equations used $Y = \frac{a + c β + e β ^{2} + g β ^{3} + i β ^{4}}{1 + b β + d β ^{2} + f β ^{3} + h β ^{4} + j β ^{5}}$ (WRC 537 curve-fit equation) $γ = R_{m} / T, β = 0.875 r_{0} / R_{m}$ (WRC 537 eqs. (25)-(26))
ASME BPVC VIII-2 Part 5 — elastic shell acceptance	151.6 MPa	235.0 MPa	0.645	Pass
WRC 537 supplies the local components; the entered general $P_{m}$ is conservatively added as a scalar envelope. Governing criterion: $P_L_plus_Pb$ ; $S_{P L} = 235.00$ MPa. Ratcheting is not evaluated here; the 2025 edition's eq. (5.95) definition must not be replaced by the older textbook expression.
Equations used $P_{m} \leq S, P_{L} \leq S_{P L}, P_{L} + P_{b} \leq S_{P L}$ (BPVC VIII-2 §5.2.2.4 eqs. (5.3)-(5.5))
Sling contact — local wall / ovalization capacity	66.41 kN	150.00 kN	0.443	Pass
External-capacity evidence: Illustrative contact assessment CA-001 — replace for project use. Xarpis calculates the factored demand only; it does not derive or certify the entered local contact capacity.
Collar / axial retention	0 N	—	—	Pass
No outward axial contact force drives the sling toward the free end in this load case; collar retention is not load-active.

Load path and factor ledger

Characteristic loads, the factor ledger (each factor applied exactly once), and the factored actions transferred from the sling-contact centroid to the root plane by rigid-body statics.

Load factor ledger
Factor	Value	Applied to	Origin	Applied?
Weight contingency	1.100	characteristic gross weight / input actions	user	yes
Dynamic amplification / impact	1.150	characteristic gross weight / input actions	user	yes
Load-share / skew factor	1.050	worst trunnion of the symmetric pair	user	yes
Project / marine-operation factor	1.000	characteristic gross weight / input actions	user	yes

Factored actions — Symmetric stationary lift — worst trunnion (local axes: $x$ outward, $y$ circumferential, $z$ parallel to vessel axis)
Location	$F_{x}$	$F_{y}$	$F_{z}$	$M_{x}$	$M_{y}$	$M_{z}$
Contact centroid	-14.94 kN	0 N	66.41 kN	0.00 kN·m	0.00 kN·m	0.00 kN·m
Root plane	-14.94 kN	0 N	66.41 kN	0.00 kN·m	-9.96 kN·m	0.00 kN·m

Demand factor (product of applied ledger rows)

1.328×

Sling angle from vertical

12.7°

Sling leg tension (factored)

68.07 kN

Vertical share, worst trunnion (factored)

66.41 kN

Weld governing point

90.0° from local +y · 187.6 kN/m on throat 8.5 mm

Average contact bearing (diagnostic only)

2.7 MPa

Trunnion section properties (effective, corroded)

$A$

19478 mm²

$I$

1.5127e+8 mm⁴

$Z$

1.1082e+6 mm³

$Z_{p}$

2.2164e+6 mm³

Scope limits and exclusions

Excluded: global vessel supports, tail lug, rigging hardware, crane capacity, upending, and marine-operation checks.

Assumptions

Right-handed local axes per trunnion: $x$ outward, $y$ circumferential, and $z$ parallel to the vessel axis. Moments follow the right-hand rule.
The two trunnions are identical, diametrically opposed, and coaxial at one shell station; the worst trunnion of the pair is assessed.
The trunnion corrosion allowance is deducted from the outside diameter (both surfaces of a solid section) and from the wall of a hollow section before section properties are computed.
The mechanics-only allowable-stress rows use user-supplied design-basis values. Code-route member, weld, fatigue, and shell-acceptance rows derive their resistances from their cited provisions and material inputs.
All demand kernels are linear-elastic; doubling every applied action doubles every reported demand.
Combined-stress diagnostics conservatively superpose the maximum normal stress and the maximum shear stress as if they occurred at the same point on the circumference.
The all-around weld is idealised as a thin circular line at the trunnion outside radius; effective throat $a = s / 2$ .
Contact bearing pressure is averaged over the projected contact area (contact width × trunnion OD). This is a diagnostic only — it does not establish the local capacity of a thin tube wall against ovalization or crippling.
BTH-1 §3-2.2/§3-2.4 treats the trunnion as a fixed-free cantilever with $K = 2.0$ and unbraced length $l$ equal to the full projection.
BTH-1 §3-2.4 coefficient $C_{m} = 1.0$ ; no end-moment reduction is taken.
BTH-1 §3-3.4.1(b) allowable $F_{v}$ is compared with the resultant weld-throat traction.
Each planned lift is treated as one fatigue stress cycle, ranging from zero load to the peak factored weld-throat stress and back to zero.
The Canadian hybrid route applies BPVC VIII-2 elastic shell acceptance to WRC 537 stresses within the CSA B51 framework.

Source traceability

Vector statics
Circular section properties
Elastic beam stresses
Distortion-energy (von Mises) identity
Elastic line-weld method
Average bearing pressure
ASME BTH-1 · 2020 · §3-1.3 (Nd), Table 2-3-1 (Service Class), §3-2.1 (3-1/3-2 tension), §3-2.2 (3-3/3-4/3-5 compression), §3-2.3 (3-6/3-9/3-25 bending), §3-2.3.6 (3-28 shear), §3-2.4 (3-32/3-33/3-34/3-36 combined), §3-2.5 (3-37 von Mises), §3-3.4.1(b) (3-55 fillet weld), §3-4 (Table 3-4.3-1/3-4.4-1 fatigue)
WRC Bulletin 537 · Consolidated bulletin with accumulated errata · §§4.4-4.5; eqs. (25)-(26), (47)-(49); Tables 4-5; Original Figures/Tables 1A-4C
ASME BPVC Section VIII, Division 2 · 2025 · §5.2.2.4 eqs. (5.2)-(5.5); §4.15.5.2; §5.5.5.2.1.1 eq. (5.95)
External sling-contact capacity

Preliminary calculation. PASS means every modelled check in the selected route passed; it is not approval or release for lifting. Independent review by a qualified engineer is required.