Failure Reasons of Stainless Steel Flange of Flare Gas Liquid Separation Tank
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Abstract
Fracture failure occurred at a stainless steel flange of a flare gas liquid seperation tank in a chemical enterprise. The failure causes of the flange were studied by chemical composition analysis, hardness measurement, metallographic examination, fracture morphology and composition analysis. The results showed that the sulfur content and hardness of the base metal of the failed flange exceeded their standards. The fracture was located in the heat affected zone (HAZ) of the weld with the characteristics of brittle fracture. The cracks on the inner and outer walls near the fracture extended from surface to inside, showing dendritic bifurcation and extending along grain boundaries, which accorded with the characteristics of sensitization-intergranular corrosion failure. Welding caused the sensitization of the HAZ. Cracks propagated along the grain boundaries under the combined action of stress and corrosion environment, which eventually leaded to intergranular corrosion fracture of stainless steel flange in HAZ.
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