Study On The Steady-state Creep Deformation Rate For High-temperature Weld Structures

Many components and pipes at high temperature conditions are used in petrochemical plants, energy sources and metallurgical plants. Creep failure is one of the main failures of the high temperature components and pipes, and is the main factor to affect in a long cycle operation. Therefore, the researches in creep for high temperature welded components are an important foundation for the design of high temperature components and life prediction, and it has important value both in theoretical research and in engineering. In this paper, the creep deformations rates for the mismatch weld joints were studied. The general formulations of steady-state creep deformation rates for statically determinate structures and statically indeterminate structures had been derived based on the formulations of various simple components under creep deformation. A lot of finite element analysis on compact tension(CT)specimen and thick-walled main steam pipe was used to confirm the applicability for the general formulation. The study in this paper gives a theoretical based on calculations of creep fracture parameter C~* for heterogeneous material welded structure and the achievements are as follows:(1) The properties of weld joints under high temperature and the basic types of failure for weld joints were discussed. The mechanism and the three stages of creep were briefly introduced, and the constitutive equation in high-temperature creep and the fracture mechanics control parameter C~* which indicates the properties for creep crack growth under the steady-state creep condition were emphatically described.(2) The analytical solutions of creep deformation rate for typical statically determinate structures under steady-state creep condition were discussed, such as the load line displacement rate (?) of rod-shaped structures in a simple tensile load, the deflection rate (?) and the slope angle rateθof cantilever beam in pure bending and the rotation angle rate (?) of a circular rod-shaped structure in pure torsion were calculated. Based on the calculation formula of creep deformation for a single material or multi-material statically determinate structures under the steady-state creep, a general formulation to calculate the for creep deformation rate for multi-material components was presented in the first time.(3) The analytical solutions of creep deformation rate for typical statically indeterminate structures under the steady-state creep condition were discussed, such as the formula of the creep deformation rate (?)_i of two-bar structure in a simple axial tensile, the curvature rate (?) of multi-layer beam in pure bending, the radial deformation rate (?)_i of the thick-walled cylinder under internal pressure were analyzed. Based on the expressions of creep deformation rate for two and three materials of statically indeterminate structure, a general formulation for the steady-state creep deformation rate of multi-material components can be obtained.(4) Compact Tension(CT)Specimen with two-material widely used in practical engineering and the typical weld joint with three-material in an ax-symmetrical thick-walled main steam pipe were analyzed by ABAQUS finite element(FE)under steady-state creep deformation condition. It was shown that the creep deformation rates gained by finite element method were well agreed with the one by general formulations, therefore the general formulations proposed in this paper was proved to be accurate and can be used in calculation for creep deformation rates.