The use of thermal-spray coatings for preventing wet H_2S cracking in HSLA steel plates

摘要

COATING IS one of the most effective methods of preventing sulphide stress-corrosion cracking (SSCC) and hydrogen-induced cracking (HIC) in the high-strength low-alloy steels (HSLA) used for liquid-petroleum gas (LPG) tanks. Several thermal-spray materials (Al_3O_3 centre dot 3TiO_2, Al, Ni, and 50Ni centre dot 50Cr) were applied on the surface of tensile specimens. To evaluate the corrosion resistance of the sprayed specimens, constant-load tests were performed in an H_2S-saturated NACE solution (0.5 percent acetic acid +5 percent NaCl) and monitored by potential-drop. The results showed that the SSCC and HIC resistance of HSLA steels was improved by plasma-sprayed coatings. The effect of H_2S on the cracking resistance of HSLA decreases in the sequence: Ni>50Ni centre dot 50Cr >Al_2O_3 centre dot 3TiO_2>Al. One may conclude that the SSCC and HIC susceptibility of the sprayed specimens in an H_2S environment can be well evaluated by the combination of the potential-drop technique and constant-load tests. On the other hand, the slow-strain-rate test is not adequate for this evaluation.