HIC resistance to hydrogen-induced cracking and SSC resistance to hydrogen sulfide stress corrosion testing

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Test standards for HIC resistance and their comparison with NACE TM 0284-2016: Method for evaluating hydrogen-induced cracking resistance in pipeline steels and pressure vessel steels, and GB/T 8650-2015: Method for evaluating hydrogen-induced cracking resistance in pipeline steels and pressure vessel steels. Test results: The test standards require only CSR, CTR, and CLR (value for a single test surface, average value for three test surfaces, and average value for a set of specimens)； Technical documents provided by the customer: hydrogen bubbling, corrosion rate ； Result evaluation: NACE MR0175, customer requirements, etc ； (2) Stress corrosion cracking (SCC) and sulfide stress corrosion cracking (SSC) – test standards and their comparison. GB/T 4157-2006: Laboratory methods for assessing a metal’s resistance to certain types of cracking in hydrogen sulfide-containing environments. GB/T 4157-2017: Laboratory methods for evaluating a metal’s resistance to sulfide stress corrosion cracking and stress corrosion cracking in hydrogen sulfide environments. NACET TM0177-2016: Tests for assessing a metal’s resistance to stress corrosion cracking in hydrogen sulfide environments. Several important factors that affect the results of HIC and SSC tests. A. Chemical composition: The higher the carbon content, the greater the susceptibility to HIC ； Mn: It tends to cause hard and brittle banding segregation, increasing susceptibility to HIC, especially in CLR ； S: Harmful elements that form inclusions such as MnS, increasing the material’s susceptibility to HIC ； P: Prone to segregation; the ferrite-porphyrite banded structure promotes P segregation, increasing susceptibility to HIC. Cu: Reduces susceptibility to HIC effectively in environments with a pH greater than 4.5 ； Mo: Inhibits the formation of bulk ferrite and reduces HIC sensitivity ； Cr: It can refine austenite grains. Being a medium-to-strong carbide-forming element, the dispersed carbides reduce the accumulation of hydrogen in the steel; meanwhile, the passivation film formed by chromium on the steel surface also prevents hydrogen from penetrating, both of which contribute to reducing the steel’s susceptibility to HIC. Elements such as V, Nb, and Ti are strong carbon/nitride-forming elements; the dispersed carbon/nitrides reduce hydrogen enrichment. B. Inclusions: The shape and distribution of inclusions affect the resistance to HIC. It is primarily Type A inclusions, such as MnS inclusions; the higher their concentration, the greater the susceptibility to HIC. C. Refining the grain size can significantly reduce susceptibility to HIC; for example, the grain size of 16MnHIC is grade 9, while that of 16Mn is grade 7.5. D. Microstructure. For low-alloy pipeline steel/plate: banded pearlite-ferrite structure > acicular ferrite (AF) structure; for alloy steel: tempered pearlite structure (quenching + tempering)