Issue 53

S. Kirin et alii, Frattura ed Integrità Strutturale, 53 (2020) 345-352; DOI: 10.3221/IGF-ESIS.53.27 347 R HPP BAJINA BASTA – PENSTOCK DESIGN AND TESTING aving in mind the importance of the penstock, special design procedure has been used, combined with extensive testing of the full-scale prototype, Fig. 2, including static, dynamic and fracture mechanics testing, based on the request to construct only one pipeline, made of steel with yield strength significantly higher than for the common structural steels. Therefore, SUMITEN HT80 was chosen, quenched and tempered weldable High Strength Low Alloyed (HSLA) steel, with nominal Yield Strength (YS) above 700 MPa, and Tensile Strength (TS) cca 800 MPa. Anyhow, welded joints made of such steels are well known for their susceptibility to cracking, making three stages hydrostatic proof testing of the model inevitable: 1. Loading from 0 to 3 MPa to check the measuring system. 2. Loading from 0 to 9.02 MPa, to reach the service stress. 3. Overloading (33.3%) from 0 to 12.05 MPa, as required by the regulation. Full-scale model strains were measured by Strain Gages (SG) and Moiré grids, as described in details in [1,2]. In the base metal (BM) response was dominantly elastic, whereas plastic strain (0,24%) was registered in welded joint LS1 (SG2, SG34), indicating non-uniform, even strange behavior due to stress concentration and weld mismatching, as shown in [4]. Potential consequences Event Frequency People Property Environment Reputation A B C D E Negligible Low Moderate Medium Large 0 No injuries No losses No damage No harm 1 Insigni ficant injuries Loss up to 10 K€ Minor damage to environment Insignificant consequences. Employees and population awareness. 2 Minor injuries Loss from 180 K€ to 540 K€ Minor consequ- ence and damage to environment. Small costs.. Mild consequences. There is a concern at the local level. 3 Serious injuries Loss from540 K€ to 1,8 M€ Moderate consequence. Short-term damage to environment.. Minor consequences. There is a concern at the regional level 4 Perma- nent incapabilit y Loss from 1,8 K€ to 50 M€ Major conse- quences. Big damage to en- vironment. Large costs. Moderate consequenes. There is a concern at the national level. 5 Death Loss over 50 M€ Dire consequ- ences. Long- term and big damage. Huge costs. Dire consequence. Concern and reaction at the international level. Table 1: Descriptive risk matrix, taken from [11]. H