Integrity Evaluation of Duplex Stainless Steel Flanges
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Duplex stainless steel flanges are normally forged to form, as required by the ASTM A182/A182M standard, but may also potentially be machined directly from forged stainless steel bar. In order to evaluate the integrity of such flanges, axisymmetric elastic-plastic finite element models have been developed, considering static effects such as bolt load and internal pressure. Additionally, tensile testing of a sample forged bar (UNS S31803) has been conducted. The stress distribution in a flange during gasket seating and operating conditions has been determined, as well as the degree of plastic strain caused by the bolt loads. The maximum stresses have been found to be around the same values as the minimum yield strength requirement of the studied material (UNS S31803), and the location of the maximum stress concentrations have been identified as the gasket groove. The tensile tests of the forged bar (UNS S31803) have shown that the yield and tensile strength properties are considerably higher than the standardized minimum requirements. The elastic modulus of the forged bar has also been determined, and was found to be lower than anticipated in the axisymmetric models. Some specimens have also been found to exhibit highly non-linear elastic properties.