PSI - Issue 48

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

312

3

Fig. 1. Lower supporting spider

Until recently, cracks in LSS elements were not detected on any of the seven HPP units. However, in 2019, numerous cracks were found in LSS corner welds on one of the HPP units. This happened five years after the unit modernization through runner replacement. Later, similar cracks were found on five of the six remaining HPP units, although in smaller numbers. When detected, the cracks have been welded up during the nearest scheduled repair period, after which the HU continued operation again. The total number of cracks detected on the unit studied reached 60, while as of 2022 it reached 72 (table 1).

Table 1 – Summarized crack formation data hydraulic unit number HU1

HU2

HU3

HU4

HU5

HU6

HU7

number of cracks ( p с . )

0

7

8

3

24

72

4

It is worth noting, that even the long cracks on LSS elements visible to the naked eye are in most cases not a signal to stop HU immediately. It is important to note, that the longer the length and depth of the crack, the more likely are the negative side effects of dealing with it, such as structural deformation, repeated crack formation of the same localization, the new cracks forming in the repair welds’ heat -affected zones, etc. In Fig. 2 red lines mark the zones in LSS corner welds prone to crack formation:  welding of the butt beams at the connection areas of the spider spokes to the central part of the LSS;  welding of reinforcing patches to butt beams on LSS spokes;  welding of spokes to the base plate;  welding of stiffeners to the LSS central part’s upper and lower disks;  welding of the band to the central part of the LSS.

Fig. 2. The zones in LSS welds prone to crack formation