PSI - Issue 38

B. Depale et al. / Procedia Structural Integrity 38 (2022) 317–330 "B. Depale-M. Bennebach" / Structural Integrity Procedia 00 (2021) 000 – 000

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Corrosion due to neglected maintenance,

- Fabrication shortcomings (e.g. full penetration welds executed with partial penetration, remaining welds of temporary supports, scars…), - Unauthorized interventions: welds or drilled holes located in stress sensitive areas, without a record, - Missing bolts or lower quality of bolts, - …. For any major equipment, a preliminary inspection is de facto mandatory and a comparison with the original drawings if they are available, for future modelling. The owner of equipment has also to ensure that the equipment is available for a sufficient time to allow a rigorous inspection. In many cases, the loads and cycles applied to the equipment under consideration have not been reported/counted. If the equipment is very old, operators and technical staff from the initial period of service may have retired and it may be necessary to call them for a meeting. This Phase is activated only if Phase 1 does not result in reliable input data for load cases and they can be determined by monitoring, visual observation during a relevant period, use of standards/rules giving standardized loadings/spectra… Load cases resulting from Phase 2 should be agreed by owner of equipment, before using them in Phase 3.1 . In order to establish the load spectra of the equipment, it is sometimes necessary to train the crane owner staff to the basis of fatigue design (Wöhler curve, Miner’s rule): this will facilitate the dialogue with engineers leading the assessment. An ISO standard such as ISO 9374- 1 “Information to be provided” [11] can be useful during that phase. - Phase 3 : Special Evaluation 3.1: Global calculations It usually consists of a FEA with a refined model. Load cases and combinations, as well as configurations, are based on input data from previous phases. Critical points and main stress concentrations shall be identified, regarding the fatigue behavior, and eventually buckling/static proof if needed. 3.2: Detailed inspection of structure/equipment This phase completes Phase 1 Inspection, it is more detailed and focused on identified concentration stress areas. It is usually visual, but it can be completed using NDT methods. The main purpose is identifying fatigue phenomena related to the past duty. Consequently, control methods are more often surface methods such as: - Magnetic particle testing, - Alternating Current Field Measurement, - Eddy Current, - Ultrasonic Testing (UT) method (for specific points), - Investigative methods for bolted connections (for checking tightening torque), - … - Phase 4: Complementary local investigations (optional) Phase 4 is activated only if Phase 3 results are not globally reliable, e.g., when the local loadings of constructional details classified as critical require a more accurate evaluation, or when a numerical zoom is necessary, or more generally when conclusions are difficult to give. When the design fatigue life of equipment has expired or when cracks have been detected, it is necessary to calculate the remaining life using the fracture mechanics methods, which is not yet routinely mastered by many engineers in industry. Only this technique will result in reliable inspection intervals. - Phase 2: Assessment of load cases (optional)