PSI - Issue 48

Evgeniia Georgievskaia / Procedia Structural Integrity 48 (2023) 310–317 Georgievskaia / Structural Integrity Procedia 00 (2019) 000 – 000

314

5

 for effective testing the LSS welds the width of 70-100 mm immediate space around weld zones needs cleaning restoring the protective coating afterwards; practically it is difficult and time consuming;  selective ultrasonic testing on the surveyed LSS turned out to have low information value and found no new dangerous defects. The MCF found that the maximum level of metal damage occurs in LSS reinforcing elements, specifically – on the rectangular stiffeners, welded to the butt beams on the LSS central part side (Area A in Fig. 2) and on triangular patches, welded to the butt beams on the spoke side (Area B in Fig. 2). Local coercive force values Нс in areas A and B significantly exceed the corresponding values in the remaining LSS elements. Figure 3b shows the distribution of coercive force in areas A and B over the LSS spokes (see Georgievskaia et al. (2023)). Measurements were made at the right and left side in equal points of each spoke. The presented data leads to the following conclusions:  the damage level of the base metal and LSS welds does not exceed the permissible value, because the coercive force Hc is below the permissible value typical for present metal grade ( Ht =5.2 A/cm);  significant uneven distribution of coercive force in LSS spokes was revealed, which reflects different degrees of physical wear and therefore different residual lifetime of the different spokes of the spider;  different coercive force levels on the left and right sides of the same LSS spoke indicate (during actual operation) a bending load element, usually not considered during design stage. a b

Fig. 3. (a) LSS weld crack ; (b) Coercive force Нс distribution ( 1÷12 – LSS spokes numbers; Amax – maximum value in area A, Bmax – maximum value in area B)

LSS spokes base metal thickness measurements’ results show that the actual thicknesses of the main LSS elements correspond to the design documentation, there is no corrosive wear. The measured actual thicknesses were used in the creation of LSS computational models to assess the strength and estimate the residual lifetime of the structure. The testing of the fasteners did not reveal unacceptable defects. However, there were numerous damage cases in the form of jamming, stud end surface dents, nut edge damage, initial screw- threads’ jamming (probably obtained during the assembly and installation work). Such damage is acceptable but may further contribute to premature or accelerated crack growth in fasteners. 5. Computational studies The computational studies were conducted to optimize the scope and timing of non-destructive testing during the inter-repair period and were aimed at identifying the most heavily loaded LSS areas as well as assessment of the residual lifetime of the structure. LSS structural strength and durability calculation was carried out based on the results of the instrumental inspection and actual load data.