Determination of the stressed state of main pipelines in the zones of circular welds
- PDF / 206,924 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 265 Views
DETERMINATION OF THE STRESSED STATE OF MAIN PIPELINES IN THE ZONES OF CIRCULAR WELDS V. A. Osadchuk,1 Yu. V. Banakhevych,2 and O. O. Ivanchuk3
UDC 622.692.4
By using the numerical–experimental method based on the solution of inverse problems of the theory of shells with residual strains and the experimental data obtained by nondestructive methods, we determine the distribution of residual stresses near a circular weld in the main pipeline. The nonuniformity of the distribution of residual stresses under gauges of the measuring instruments is taken into account. The average characteristics of stresses with regard for the structural changes in the zone of thermal influence are found experimentally (by using measuring instruments).
Numerous inspections of main pipelines show that the period of their safe operation strongly depends on the corrosion resistance of the base metal and the reliability of welded joints [1, 2], To evaluate the serviceability of pipelines and their limiting state, it is necessary to use a complex approach including the analysis of stresses formed in the pipes, especially in the zones of welded joints, as an important component. In this case, the welding stresses are alternating and nonuniformly distributed over the thickness of the pipe. They can strongly affect the level and the character of distribution of total working stresses. There exist different numerical and nondestructive testing methods for the evaluation of residual stresses [3–5]. To apply the numerical methods, one must know the conditions of welding and the procedures used to decrease the level of technological stresses in the welded joints. This complicates or even makes impossible the application of these methods for the determination of stresses in pipelines operating for long periods of time. The nondestructive methods are also not always applicable for the diagnostics of welded joint due to the incompleteness of the data on the distribution of stresses in elements of the pipe. Thus, in [6], it is shown that none of the currently existing methods for nondestructive determination of stresses used separately (about ten different devices were tested) is capable of giving reliable data on the stress–strain state under the actual operating conditions of gas pipelines. In what follows, for the analysis of the stressed state formed near multilayer circular welded joints, we develop a special numerical–experimental approach based on the experimental data given by nondestructive methods and the solution of inverse problems of the mechanics of deformable bodies with inherent stresses [7]. To deduce key equations of the stress–strain state of the welded joint of a pipe, we consider a model of the pipe in the form of a circular cylindrical shell of thickness of 2h subjected to the action of localized residual welding strains. The shell is referred to a triorthogonal coordinate system α, β, γ, where α = z / R is a dimensionless coordinate along the axis of the pipe, z is the distance from the origin of coordinates (chosen in the plane
Data Loading...
