PSI - Issue 37

R.J. Mostert et al. / Procedia Structural Integrity 37 (2022) 763–770

768 6

Mostert et al/ Struc u al Integrity Procedia 00 (2021) 000 – 000

Figure 4: Instantaneous HTHA damage rates of the C-0.5 Mo WM, BM, HAZ welded joint zones at a hydrogen partial pressure of 200 bar at 500 °C and carbon steel (Munsterman, Seijas, and Williams 2010) at a hydrogen partial pressure of 98 bar at 545 °C, as a function of time.

Higher order derivatives of the strain-life curves offer a way in which HTHA damage monitoring can be executed. Figure 5 shows the first, second and third order derivatives of the published carbon steel curve [8]. The third derivative plot can be split into four quarters regarding the HTHA process. Accordingly, if a strain gauge is attached to a certain zone of a structural component which is in HTHA service, monitoring the third derivative strain versus time plot will indicate in which quarter of the HTHA life the component is operating. Further work regarding the extent of degradation of structural integrity in each quarter and the limit of allowable degradation is required.