PSI - Issue 48

Mersida Manjgo et al. / Procedia Structural Integrity 48 (2023) 155–160 Manjgo et al/ Structural Integrity Procedia 00 (2023) 000–000

157 3

problem by numerical integration is imposed. This kind of integration is most easily solved with the use of a computer, but even without it, the procedure is not unacceptably long. If in the first approximation it is assumed that Y does not depend on the length of the crack, then the expression can be written in the form:

d a 

m

1



(4)

N  

2 a da

m

C Y a  

   

a

0

so, after integration, the solution is obtained in a closed form:

m

m

0   

  

  

  

1

1





a

a

1

2

2



  N



(5)

d

m

m

 

 

 C Y a 

1



2

This approximation leads to a non-conservative solution compared to solutions that consider the fact that Y=Y(a) and which must be determined by numerical methods. 3. Experiment The assessment of the integrity and the assessment of the remaining life of the pressure vessel was made with the previously performed qualification of the welding technology of the new BM - exploited BM sheets with a thickness of 50 mm, in accordance with the standard EN ISO 15614-1. Tests that this standard does not foresee, and which are necessary for the assessment of integrity and remaining life, are tests at working temperature, as well as additional tests of the exploitation properties of new and exploited BM and components of the welded joint at room and working temperature. Additional tests included determination of critical stress intensity factor K IC , critical crack length a c , and fatigue crack growth parameters ( da/dN and ΔK th ) BM, WM and HAZ. The results of these tests are given in the report for 2016 and 2018 of the EUREKA project BiH – Serbia [8]. The initial test parameters are:  Place of possible crack, i.e., whether it occurs in BM or WM or HAZ,  An initial crack a0 is a crack that can be detected by non-destructive testing from the outside, and which for the container in question must not exceed an average length of 5 mm,  Change in the load in the vessel, from the worst case, i.e., that the working stress σ is close to the yield stress σ0.2 of the tested material (211 MPa), up to the real working regime, i.e., to the level of the maximum working stress for the given vessel, measured by tensometric measurements in exploitation (46 MPa),  The length of the critical or permitted crack, which was changed from the size of 2 mm to the size of the critical length of the crack ac obtained by examining the fracture mechanics parameters at the calculated temperature of 5400C,  Paris equation constants C and m, determined in the fatigue crack growth parameters test at the calculated temperature of 5400C,  Coefficient Y-geometric term, which depends on the ratio of the length of the crack and the thickness of the BM vessel and is given in the literature for the case of a surface crack for different a/W ratios. The results of the assessment of the remaining working life of the vessel, i.e., the number of cycles ΔN , knowing that it is constantly exposed to the effect of variable load in operation are given in Table 1, Table 2. for new and exploited BM, Table 3 for WM, Table 4 for HAZ on the side of new BM and Table 5 for HAZ on the side of exploited BM.