ISO 24038:2020 Crane Fatigue Life Assessment Guide

Fatigue Assessment Procedure

The load spectrum is determined either from field measurements or estimated from the crane's work duty classification. Stress analysis is performed using finite element analysis (FEA) or strain gauge measurements. The S-N curve reference values are 160 MPa for parent metal with ground welds, 125 MPa for as-welded butt joints, 112 MPa for as-welded fillet welds, 100 MPa for cruciform joints, and 80 MPa for transverse load-carrying joints. The fatigue limit corresponds to 2×10⁶ cycles. Miner's cumulative damage is calculated as D = Σni/Ni, where D ≤ 1.0 indicates a safe condition. Safety factors of 1.25 apply to inspectable joints, 1.5 for non-inspectable joints, and 2.0 for joints supporting personnel. Kelude Heavy Industry offers fatigue assessment services for steel structures.

Hot Spot Stress Method

For complex welded joints, stress extrapolation is performed at distances of 0.4t and 1.0t from the weld toe. The FAT class is 100 MPa. When D > 0.7, enhanced inspection is required; when D > 0.9, a comprehensive reassessment is mandatory. Kelude Heavy Industry provides fatigue assessment services including load spectrum measurement, S-N analysis, and hot spot stress evaluation, with a detailed report issued upon completion.

The fatigue assessment method specified in ISO 24038:2020 is applicable to the lifecycle safety assessment and management of crane steel structures. The evaluation process begins with load spectrum collection. For cranes in service, on-site measurement is recommended, using strain gauges placed at critical locations to capture load-time history data over at least one complete duty cycle. Measurement points should cover fatigue-sensitive areas such as the mid-span region of the main girder, end connections, and stiffener ends. Each measurement point should be monitored for no less than 30 minutes, covering no-load, full-load, and combined operating conditions. For newly designed cranes, the characteristic load spectrum factor corresponding to the work duty classification per ISO 4301 may be used for estimation. Stress analysis employs the finite element method to build a refined structural model, with mesh size refined to plate thickness dimensions in weld regions to ensure accurate stress gradient capture.

The selection of S-N curves directly affects the accuracy of fatigue life assessment. The standard provides recommended FAT class values for five welded joint detail categories, ranging from 160 MPa for base material to 80 MPa for cruciform joints — a full factor of two. In practical assessments, reductions should be applied based on weld quality level: FAT class may be raised by one level for welds passing UT flaw detection Grade I, while Grade II welds retain the characteristic value. Engineering experience with Miner cumulative damage rule indicates that when the D value reaches 0.7–0.8, monitoring frequency should be increased and more detailed flaw detection inspections conducted. When D approaches 1.0, repair or replacement should be scheduled before structural failure occurs. Kelude Heavy Industry offers steel structure fatigue assessment and life management services, including on-site load spectrum measurement, S-N curve selection analysis, and hot spot stress evaluation, delivering complete fatigue life assessment reports.

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