PSI - Issue 72

Nedeljko Vukojević et al. / Procedia Structural Integrity 72 (2025) 157 –163

161

The test specimens are made with a mechanical notch in the area of the heat affected zone (HAZ), as a critical area of the structure. The fracture toughness was determined on a total of 4 samples and the values are shown in Tab.1. 3.6. Residual stress determination Residual stress measurements were performed in the heat-affected zone (HAZ) or areas close to the HAZ, Fig. 5. Heat-affected zones are very narrow regions near the weld, so there is a possibility that some measurement points were only partially within the HAZ. Accurate definition of the HAZ can only be done by etching the samples, which was not possible under the factory conditions of the tests. It is also important to note that residual stress measurements on steel structures, especially welded joints, require many measurement points to obtain a proper distribution of stress fields. Residual stress was determined using standard procedure acc. ASTM 837(2020).

Fig.5. (a) strain gauge position - series I; (b) strain gauge position - series II.

Samples before plastic deformation (Series I) have the highest level of residual stresses in the initial samples. The residual stresses reach values close to the yield stress of the respective steel. Samples after plastic deformation (Series II) show a decrease in the level of residual stresses due to incremental deformation. The largest reduction was spotted in samples S235/#6, where the stress level was reduced by approximately 33-53%, and in P460/#14, where the stress level was reduced by approximately 63-72%. In the other samples this effect was not as pronounced. The weakest effect was observed in samples S235/#14. 4. Results of experimental research A summary of the experimental test results for all series of samples are presented in Table 1. 4.1. Comparison of wall thickness The estimation of the required wall thickness of the pressure vessel dish end was performed according to AD Merkblat 2000-B0 (2003). Taking into account all the influential parameters for this calculation and the adopted data (internal pressure p=20 bar, safety factor S=1,5 and weld coef.  =0,9) using equation (1), the necessary dish end thicknesses were obtained:

a eH D p R 

(1)

s

c

.





1,2

40

p





S

Table 2 gives values of thicknesses for different yield stress values and dish end diameters, and also gives comparative values for the base material (BM) of the sheets according to the material certificate and for the values of yield stress in HAZ obtained by experimental testing for Series I and Series II.