PSI - Issue 37

R.J. Mostert et al. / Procedia Structural Integrity 37 (2022) 763–770 Author name / Structural Integrity Procedia 00 (2021) 000 – 000

767

5

Table 2: Parameters of the sigmoidal equation for the curves shown in Figure 3.

x o

dx

R

2

Carbon Steel (Munsterman, Seijas, and Williams 2010)

13.5 195 213 366

1.97 34.6 52.8 55.8

1.00 0.992 1.00 0.996

C 0.5 Mo Weld metal C 0.5 Mo Base metal

C 0.5 Mo Heat affected zone

Figure 3: HTHA damage fraction development curves of a C-0.5 Mo WM, BM, HAZ welded joint zones at a hydrogen pressure of 200 bar at 500 °C, as well as that of a carbon steel (Munsterman, Seijas, and Williams 2010) at a hydrogen partial pressure of 98 bar at 545 °C The HTHA damage rates are presented in Figure 4. For the HAZ zone, it was found that the damage rate was initially constant and that the sigmoidal behaviour was observed after ~ 200 hours. The comparison of the damage rates of the various zones provides insights which are important for both quantitative and qualitative management of the HTHA damage process. This comparison shows that the damage processes start slowly for all cases and later accelerates towards a peak damage rate. For all zones, the damage rate decelerates beyond the peak time. The peak in damage rate probably coincides with a peak in decarburization rate, so that the HTHA rate diminishes beyond this point due to diminishing availability of carbon.