Under what circumstances are the HIC test and SSC test performed in MR0175?

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This post was last edited by SSC Test HIC Test on 2019-5-17 at 10:28. Hello everyone, I have been working with NACE materials recently. I have a question about the HIC and SSC tests. Usually, materials are selected in accordance with NACE MR0175; sometimes customers request HIC and SSC tests, while these may not be necessary in other cases. My question is. Under what circumstances are HIC and SSC tests required, and when is it sufficient to meet NACE standards alone? HIC is usually something that needs to be done ； The SSC test is required in the following situations: when the material is not among those pre-qualified, or when the operating conditions exceed the limits set by NACE for a particular material. Nevertheless, MR0175 is essentially based on experience; if the equipment user believes there is a possibility of failure, they can still request an SSC test to be conducted. It is up to the end user to decide whether to conduct tests when the material meets all other requirements. Or, in accordance with other applicable standards for common pipe and sheet materials made of low-strength steel, the mechanism of HIC (hydrogen-induced cracking) is such that hydrogen atoms diffuse into the internal defects and impurities within the material (porusions, sulfides, carbides), where they form gas molecules (H2, CH4, H2S). This generates internal pressure, and this pressure can cause bulging and failure without the need for any stress. This surface corrosion is caused by hydrogen entering the metal. The HIC vulnerability of the material decreases as the strength of the steel increases. The HIC test lasts for 96 hours without applying any load, and is conducted in accordance with NACE TM0284. High-strength steels are prone to hydrogen embrittlement (HE), which is damage caused by hydrogen atoms within the material’s interstices without the formation of gas molecules. Under load, the toughness of steel is greatly reduced. The martensite lattice structure is particularly fragile. The occurrence of pure hydrogen embrittlement does not require the presence of corrosion. Therefore, high-strength fasteners must be tested under load, in accordance with ASTM F519 or F1624. (i.e., interstitial atoms, which are theoretically classified as “point defects” in crystal structures. ) Sulfide stress corrosion cracking (SSCC) is a combination of hydrogen embrittlement (HE) and stress corrosion cracking (SCC). In a corrosive, wet environment, H2S is the source of hydrogen. The fragility of the material increases with the strength of the steel and the applied load (as it increases). Corrosion is also taken into account; the SSC test is conducted in accordance with NACE TM0177, and a load must be applied: the SSC test has a long duration. No, any type of material, as long as it can be processed into suitable specimens, can be used for (HIC testing). Generally, it is mainly \"rolled steel or its products\" that are subjected to HIC testing in accordance with NACE MR0175/ISO 15156-2 Table B.3; however, this also applies to seamless tubes. For forgings with a specified carbon content of no more than 0.025%, conducting HIC testing is already a required procedure. (See EFC 16). (Translator’s note: NACE has now merged with ISO. The following excerpt is taken from Clause 8 of MR0175/ISO15156-2, which states that carbon steel forgings are not sensitive to HIC when their sulfur content is ≤0.025%. It means that it’s not necessary to conduct the HIC test. ) 1. Generally, an SSC test is required when the service conditions under which the material is used exceed the specified limits, such as elevated H2S levels, lower test stresses, temperature limits that are exceeded, and lower pH values. 2. When the material is carbon steel, an HIC test is usually required. The following text is excerpted from Clause 8 of MR0175/ISO 15156-2, which states that for flat-rolled carbon steel materials, the issue of HIC must be taken into consideration even if they contain a \"trace amount of H2S\", that is, very small amounts of H2S. Finally, once again, material selection is a skill based on experience; whether to conduct tests or not, and communicating with end-users are important considerations ； Conducting tests on the material increases costs, and it is the users who have to bear these costs. Summary: 1. When designing containers, equipment operating in H2S-containing environments is usually quite sensitive; therefore, it is necessary to discuss material requirements with the customer ； MR0175 and MR0103 are the two most commonly used standards; therefore, understanding these specifications helps to have a better grasp of the material requirements specified by customers, preventing confusion. 2. By studying this standard, several key points can be noted: a. The SSC test takes a longer time to conduct, while the HIC test is easier to carry out ； As for the costs, they can be negotiated and shared by both parties; B. HIC cracks occur less frequently in CRA-type materials ； c. Laboratory testing methods are always more stringent than those in actual operating conditions. d. Currently, low-alloy steels achieve high success rates in such tests; so if you do need to conduct such tests, rest assured. Our laboratory also offers commissioned HIC and SSC testing services at reasonable prices – feel free to leave me a message. As for MR0175, it contains a lot of content; I hope to learn from everyone together*.