PSI - Issue 77

Enrique Gómez et al. / Procedia Structural Integrity 77 (2026) 49–55 Enrique Gómez et al. / Structural Integrity Procedia 00 (2026) 000–000

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The fracture toughness of the material (K mat ), also shown in Table 1, is the minimum value obtained from two different estimations: BS79190 Annex J proposal, which estimates K mat from Charpy results, and ASME Code Section XI, Appendix A (2023), which estimates K mat from the material reference temperature RT NDT and, for the case analyzed here, is the approach that provides the minimum value shown in Table 1: = 29.4 + 13.675 0 . 0261 ( − ) (1) T is the LST, which as mentioned above is -40 °C, and RT NDT is -85 °C following the specification of the material provided by the forge manufacturer. This last value is, approximately, 20 °C higher than the requirement established by ASME Code Section III, Div.3, for the thickness of the forge being analyzed, which is the main reason for the analysis described in this work. Additionally, it is important to note that equation (1) refers to dynamic loading conditions, in agreement with section 2.2 of this document. 2.2. Applied loads and defect geometry The stresses in the cask are calculated in accordance with the requirements of the ASME Code and the applicable regulations to the transport of this kind of components. The maximum tensile stresses are determined for each load case. The secondary stresses considered are the residual stresses in the welds of the forging. Thus, the stresses in the cask have been calculated taking into account the dynamic conditions to which the component is subjected, using FE analyses. The calculation considers the highest tensile stresses produced during all NOC (Normal Operating Conditions) and AC (Accidental Conditions) at a temperature of -40°C. For this purpose, post-processing was performed to determine the highest tensile stresses and to obtain their distribution throughout the thickness. As an example, the maximum tensile stresses in the inner shell are shown in tables 2 and 3. Absolute maximum values are underlined. The stress linearization was performed according to Section 6.4 (Figure 6.1) of BS7910 (2019). The welds between the lower and upper shells are full penetration welds subjected to a final heat treatment. The secondary (residual) stresses have been estimated according to section 7.1.10.3 of BS7910 (2019). For a heat treatment such as the one performed in the welds of the shells, between 580°C and 620°C, the residual stress values are 20% of the yield strength in the axial direction and 30% of the yield strength in the circumferential direction for carbon steels. This value is considered the average along the thickness and is therefore categorized as a secondary stress (Q m ). Concerning the size of the cracks considered in the analyses, the size of the maximum allowed defect by the ASME Code, Section III, Division 3 (2023) is included in the requirements of article WB-2540, for the examinations to be performed on forgings, and article WB-5300 for welds. Considering the inspections performed on the casks (ultrasonic testing for the inner part of both the forging and the welds, liquid penetrant/magnetic particles for the inner and outer surfaces of the forging and the welds, and X-rays for the welds of the forgings), and assuming a conservative aspect ratio (crack depth/crack length) of 1/6, the defects considered in the present work are as follows: • Surface cracks in the forgings: 6 mm deep and 36 mm long. • Internal (embedded) cracks in the forgings: 6 mm deep and 36 mm long. • Surface cracks in welds: 1.6 mm deep and 9.6 mm long. The defects are considered to be located at the point of greatest tensile stress for each load case, and oriented perpendicular to such a maximum stress. 2.3. Structural integrity approach The structural integrity assessment of the cask is performed using BS7910 Option 1. The component being evaluated is represented by an assessment point of coordinates (K r , L r ), defined by: