NACE – General
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Sulphide stress cracking generally occurs in environments that have a high concentration
of H²S and which are acidic. Hydrogen is absorbed into the steel where it expands
causing cracks that can damage or reduce the integrity of the steel structure.
A number of factors affect the likelihood of a steel grade being affected by SSC. These include: the grade, hardness, form and heat treatment of the steel being used, the H²S partial pressure, the acidity and the presence of sulphur and chloride ions. Also important is the temperature, the tensile stress applied and the length of time of exposure.
The normal option for improving SSC resistance (as opposed to HIC, SOHIC or SZC resistance) is to select plates with a maximum hardness.
Carbon steel plates with a maximum 22 HRC (according to NACE MR0175:2) are qualified for use in SSC environments. They must however have a maximum of 1% nickel content and require heat treatment (hot–rolled; annealed; normalised, normalised and tempered; normalised, austentised, quenched and tempered; and, austentised, quenched and tempered) for the hardness requirement to be valid.
Welds are also susceptible to SSC and need to be hardness tested – meeting similar requirements and potentially requiring PWHT if the hardness is too high.
This page is a summary of the requirements of NACE MR075 and is not a substitute for use of the standard by a suitably qualified engineer for decision making purposes.
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SSC Characteristics | SSC Test Certs | SSC Sizes & Dimensions
