HYDROGEN EMBRITTLEMENTDOE-HDBK-1017/1-93Properties of MetalsThe important information in this chapter is summarized below.Hydrogen embrittlementThe conditions required for hydrogen embrittlement in steel is the presenceof hydrogen dissolved in the water and the carbon in the steel. Thehydrogen dissolved in the water comes from:Making of steelProcessing partsWeldingStorage or containment of hydrogen gasRelated to hydrogen as a contaminant in the environment that isoften a by-product of general corrosion.Hydrogen embrittlement is the result of hydrogen that diffuses along thegrain boundaries and combines with the carbon to form methane gas. Themethane gas collects in small voids along the grain boundaries where itbuilds up enormous pressures that initiate cracks and decrease the ductilityof the steel. If the metal is under a high tensile stress, brittle fracture canoccur.Zircaloy-4 is less susceptible to hydrogen embrittlement than zircaloy-2 because:Zircaloy-4 contains less nickelThe introduction of niobium into zircaloy-4 reduces the amount ofhydrogen absorption in the metal.Rev. 0Page 39MS-02
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