Lifting Trunnion Design Calculator — methodology & sources

This calculator addresses a symmetric pair of fixed, radial lifting trunnions welded to a straight cylindrical steel vessel shell — solid-round or circular-hollow sections, an all-around fillet weld, a defined sling-contact band, and an optional end collar.

Status: available. All four assessment routes have complete, implemented required-check sets: ASME (BTH-1–2020, WRC 537, BPVC VIII-2:2025), EN (EN 1993-1-1/-1-8/-1-9 and EN 13445-3 Annex C), Canadian hybrid (CSA S16 with the BPVC VIII-2 acceptance adopted under CSA B51), and Australian (AS 4100:2020 / AS 1210-2010 with the adopted BTH-1 basis). Each route produces a computational Pass only when every required row explicitly passes. Applicability limits and required project-specific external evidence remain enforced in every route.

Analysis modes

Mode A — direct load per trunnion. You supply the six local action components ( $F_{x}, F_{y}, F_{z}, M_{x}, M_{y}, M_{z}$ ) at the sling-contact centroid or the root plane, and declare whether they are characteristic or already-factored design actions.
Mode B — symmetric stationary lift. Vessel axis vertical, hook on the vessel axis, one sling leg per trunnion, centre of gravity on the axis. The solver derives the sling angle from the hook height and contact radius, resolves each leg by vector equilibrium, and transfers the contact action to the root by rigid-body moment transfer. CG eccentricity is not modelled in this version — the skew factor must bound real imbalance.

Coordinate and sign convention

Each trunnion carries a right-handed local system: $x$ along the trunnion axis, positive outward from the shell; $y$ circumferential (tangent to the shell); $z$ parallel to the vessel axis. Moments follow the right-hand rule. Actions are transferred from the contact centroid to the root with $M_{r oo t} = M + r \times F$ .

Factor ledger

Weight contingency, dynamic amplification, skew/load-share, and a project/marine factor are each represented once, with their application target shown in the report. Declaring the input loads as already factored suppresses the ledger so factors can never be applied twice. Defaults are editable seeds tagged as user values — they carry no code authority.

Result states

Pass — every required modeled check for the selected route (ASME, EN, Canadian hybrid, or Australian) explicitly passes. This is not engineering approval or a release for lifting.
Fail — an implemented check exceeds its resistance, lies outside its applicability, or lacks required referenced external evidence.
Indeterminate — a required modeled check cannot be evaluated, including while an input is incomplete or geometrically invalid.
Scope exclusions — genuinely separate design systems (global vessel/saddle/skirt stress, crane/rigging/tail-lug capacity, head/cone mounting, planar-upending mode, marine-operation overlay) are stated in the report and this methodology page rather than shown as always-pending result rows.
Info — a computed diagnostic with no pass criterion, e.g. the average contact bearing pressure, which cannot clear a thin tube wall on its own.

Implemented mechanics

Solid/annular circular section properties $A, I, Z, J, Z_{p}$ , computed on the corroded section.
Root normal stress $σ = ∣ F_{x} ∣/ A + M_{y}^{2} + M_{z}^{2} / Z$ , exact elastic transverse-shear maxima, torsional shear $T c / J$ , and a conservative co-located von Mises combination — compared against user-supplied allowables.
Six-component elastic line-weld demand around the circular fillet, with the governing point angle reported.
Stationary-lift vector equilibrium and contact-to-root moment transfer, hand-verified in the validation suite.

Implemented ASME BTH-1–2020 clauses

The implemented BTH-1 checks use the following clauses:

Bending, §3-2.3: compact-pipe (eq 3-6), noncompact-pipe (eq 3-9), and solid-round (eq 3-25) allowables, classified by $D / t$ against Table 3-2.2-1.
Shear, §3-2.3.6, eq (3-28): $F_{v} = F_{y} / (3 N_{d})$ .
Axial, §3-2.1/§3-2.2: tension eq (3-1) or compression eqs (3-3)/(3-4)/(3-5), by the sign of the root axial force (cantilever K = 2.0, unbraced length = full projection).
Combined axial + bending, §3-2.4: eqs (3-32)/(3-33)/(3-34) compression, or eq (3-36) tension.
Combined normal + shear, §3-2.5, eq (3-37) — also carries the torsional shear, since Chapter 3 has no dedicated torsion allowable.
Fillet weld allowable, §3-3.4.1(b), eq (3-55): $F_{v} = 0.60 F_{E X X} / (1.20 N_{d})$ on the resultant throat traction.
Weld-throat fatigue, §3-4, Table 3-4.3-1 Category F: allowable stress range by Service Class, derived from the planned-lift count per Table 2-3-1.

Base-metal attachment fatigue is a separate required row. Service Class 0 is treated as exempt under the mapped BTH-1 basis; higher Service Classes require a referenced external detail assessment and entered utilization rather than a guessed Table 3-4.4-1 category.

WRC 537 local shell stresses

The automatic unreinforced round-attachment path implements the bulletin's rational Original curve fits, interpolation of the evaluated ordinate between $γ$ rows, the Table 4/5 eight-point sign and computation mapping, equations (25)–(26) and (47)–(49), and plane-stress intensity. Extrapolated tables are not used. The conservative automatic envelope is $0.05 \leq β \leq 0.20$ and $5 \leq γ \leq 100$ , with $L / R_{m} > 3$ and the cited end-distance condition. Geometry outside that range is outside the calculator scope.

BPVC VIII-2:2025 shell-acceptance limits

The pure acceptance helper implements §5.2.2.4 equations (5.2)– (5.5): $P_{m} \leq S$ , $P_{L} \leq S_{P L}$ , and the already-combined $P_{L} + P_{b} \leq S_{P L}$ . When $S M Y S / U T S \leq 0.7$ , $S_{P L} = max (1.5 S, S_{y})$ ; otherwise it is $1.5 S$ . This helper does not invent or reclassify shell stresses. Section 4.15.5.2 identifies WRC 537 as an accepted local-stress input. The engine consumes the automatic WRC result; general primary membrane intensity is conservatively enveloped with the local WRC components.

Ratcheting is not implemented. In the 2025 edition, equation (5.95) uses $S_{P S, k} = S_{y, co l d, k} + S_{y, h o t, k}$ ; the older $max (3 S, 2 S_{y})$ expression is deliberately not used.

Implemented Australian clauses

AS 4100:2020 CHS bending: $M_{s} = f_{y} Z_{e}$ with compact, noncompact, and slender $Z_{e}$ from §§5.2.1–5.2.5 and Table 5.2.
CHS shear $V_{w} = 0.36 f_{y} A_{e}$ (§5.11.4), axial section capacity $N_{s} = k_{f} A_{n} f_{y}$ (§§6.2.1–6.2.4 and Table 6.2.4), and the CHS-specific linear combined-actions rule in §§8.3.2/8.3.4. The I-section and RHS/SHS power-law alternatives are not used.
Fillet-weld resistance per unit length, $v_{w} = 0.6 f_{u w} t_{t} k_{r}$ (§9.6.3.10), with the selected SP/GP capacity factor from Table 3.4 and kr = 1.0 for the non-lap perimeter weld.
AS 1210-2010 Appendix A design strength and Appendix N membrane, shear, compressive-membrane, and location-dependent local membrane-plus-bending acceptance limits, consuming automatic WRC stresses.

AS 4991-2004 Clause 1.1 covers detachable below-the-hook devices, not a trunnion welded to the vessel, so it cannot provide this route's lifting basis. The calculator therefore labels this an Australian hybrid route and supplements AS 4100/AS 1210 with BTH-1 member buckling, torsion interaction, weld, and fatigue provisions. Project load factors remain explicit in the factor ledger.

Contact, collar, and advanced evidence

The calculator does not infer sling-contact ovalization/crippling or collar-retention resistance from average pressure alone. Transverse contact demand is checked against a referenced capacity from a calculation, nonlinear analysis, vendor qualification, or test covering the actual band and tube geometry. Outward axial contact force similarly requires a collar and referenced collar-plus-attachment resistance. Missing required evidence is an explicit Fail, while zero demand is reported as not applicable.

Source status

The report lists only the active standard edition and clause or table reference. It does not expose storage paths, internal identifiers, or document filenames. Public mechanics and user-supplied project evidence are labelled separately; no standard text ships with the product.

Limitations

Xarpis does not approve the lift plan, crane, rigging, tail lug, proof test, fabrication, NDE, pressure-vessel registration, PED/CRN compliance, or any regulatory submission. A computational Pass confirms only that the modeled scope and supplied evidence passed; independent review by a qualified engineer remains mandatory.