Importance

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Abstract

An austenitic rounding fixture is inserted into the horizontal joint of a turbine casing. The casing is then assembled and stress relief cycle is carried out, resulting in rerounding of the casing and relief of residual stresses. Since an austenitic material has a higher thermal expansion coefficient than the metallic materials of conventional turbine casings, the rounding fixtures expand more than the casing during a stress relief cycle. The length of the fixtures are designed in such a way that at stress relief temperature the casing is slightly over-rounded. After the stress relief, the casing is rerounded and the austenitic rounding Fixtures is disengaged. The rounding fixture is installed in a cold condition (or with minimal heat for heavily collapsed casings). The removal of the rounding fixtures is easy since a clearance exists between the casing and the fixtures; the spring back of the casing is far less then the contraction of the fixtures. The stresses in the casing are far less than if rounding plates would have been used since the maximum deformation occurs at stress relief temperature.

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First Claim