PSI - Issue 13

Evy De Bruycker et al. / Procedia Structural Integrity 13 (2018) 226–231 Evy De Bruycker/ Structural Integrity Procedia 00 (2018) 000 – 000

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For all three materials, two subsequently executed permeation tests on the same sample showed the same breakthrough times. This means that no irreversible trapping occurred in these materials at room temperature. The higher apparent diffusion coefficient at room temperature of the T12 material compared to those of the T24 material is an indication that T12 is less sensitive to hydrogen embrittlement than T24. In order to draw more precise conclusions relevant to the failure cases, however, permeation tests at higher temperature need to be carried out, which was not possible with the used equipment.

Table 3. Breakthrough times and calculated apparent hydrogen diffusion coefficients at room temperature. Material condition Breakthrough time ( s ) Thickness L ( mm )

Apparent diffusion coefficient D b ( m²/s )

T12 BM T24 BM T24 HAZ

252

0.689 0.757 0.689

1.2E-10 1.7E-11 3.1E-11

2220 1016

4. Summary and conclusions

Based on the principle that the larger the hardness and the diffusible hydrogen pick-up capacity of a material, the more susceptible it is to hydrogen embrittlement, the following conclusions can be drawn:  T12 is less susceptible to hydrogen embrittlement than T24, both as base material and as in the HAZ condition.  The HAZ of T24 is more susceptible to hydrogen embrittlement than the base material, both in as-welded and in PWHT condition.  Based on the results of this investigation it cannot be determined if the T24 HAZ is less susceptible to hydrogen embrittlement after PWHT, since hardness decreases, but diffusible hydrogen pick-up capacity increases. Bendick, W, Gabrel, J., Hahn, B., Vandenberghe , B., 2007. ‘ New low alloy heat resistant ferritic steels T/P23 and T/P24 for power plant application’. Int. Journal of Pressure Vessels and Piping 84, 13-20. Devanathan, M.A., Stachurski, Z., 1962. Proc. Royal Soc., London, England, A270, 90. Husemann, U., Bendick, W, Haarmann , K.,1999. ‘ The new 7CrMoVTiB10-10 (T24) material for boiler waterwalls’. PWR 34, 633-640. Louthan Jr., M.R., 2008. ‘ Hydrogen embrittlement of metals: a primer for the failure analyst'. Journal of Failure Analysis and Prevention 8, 289. Lüdenbach, G., 2012. ‘ S tress corrosion cracking of T24’. VGB Kongress, Mannheim. Pérez Escobar, D., Verbeken, K.,Duprez, L., Verhaege, M., 2012. 'Evaluation of hydrogen trapping in high strength steels by thermal desorption spectroscopy'. Materials Science and Engineering A 551, 50. Spencer, G.L., Duquette, D.J., 1998. 'The role of V carbide traps in reducing the HE susceptibility of high strength alloy steels'. Benet Laboratories, Watervliet, NY: US Army Armamaent Research Development and Engineering Center, ARCCB-TR-98016. Vaillant, J.C., Vandenberghe, B., Hahn, B., Heuser, H., Jochum , C., 2005. ‘ T/P23, 24, 911 and 92: new grades for advanced coal-fired power plants – properties and experience’. ECCC creep Conference, London, 87-98. Wei, F.G., Hara, T., Tsuzaki, K., 2004. 'Precise determination of the activation energy for desorption of hydrogen in two Ti-added steels by a single thermal-desorption spectrum'. Metallurgical and Materials Transactions B 35, 587. References