Mechanical Behavior Study of Steam Turbine Casing Bolts Under In-Service Conditions

Abstract

In order to avoid the failure of bolted joints used on ultra-super critical steam turbine inner casing, their mechanical behavior should be strictly assessed, especially under the in-service conditions with steam temperature and pressure fluctuations. In this study, a 3D bolted inner casing is modeled using the commercial finite element software ABAQUS. The Norton-Bailey constitutive model and strain-life–based Manson-Coffin equation are applied to study the mechanical behavior of the bolted inner casing under in-service conditions. The results demonstrate that the inner casing could exert significant influence on the bolts by conduction, structure restriction and thermal expansion difference of the materials. The temperature and von Mises stress of the bolts experience continuous fluctuations during the steady state operation phase due to the constant variation in the steam temperature and pressure, and the alternative stresses give rise to fatigue damage of the material. The steam temperature and pressure fluctuations decline the fatigue lifetime of these high-temperature bolts in long-term operation, which should be taken into account in the design.

Development of a technological approach to the control of turbine casings resource for supercritical steam parameters

“…Depending on pressure of steam medium, the level of these forces can reach very high values [8]. As a result, there is a significant influence of clamping forces of pins on stressed-strained state of casing elements during operation in the elastic range of loads [9]. Similarly, the influence of high-temperature casing elements on stressed-strained state in the plastic statement of the problem was studied in paper [10].…”