Method for measuring residual stresses in metal at pipe welds

摘要

The present invention is in the field of non-destructive testing of construction materials, and it is possible to check the residual voltage at the longitudinal and girth welding sites. Alternatively, it is possible to evaluate the pipe welding quality based on the residual voltage level, and to check the input parameters to calculate the pipe strength. The technical result of the present invention provides the possibility of separately checking horizontal and vertical residual stresses. In that case, the stress is measured in the area where the maximum value is reached at the weld. According to the first option, the technical result of the present invention is provided as a method for determining residual stress in the metal pipe weld area. According to this method, the transverse and longitudinal polarized transverse and longitudinal wave propagation times of the pipe axis are measured by the ultrasonic echo method in the pipe research area, and the stress state characteristics of the welded area are found according to the results. According to this solution for a particular pipe type, the balancing section is pre-determined through computational modeling so that the balancing ring stress in the main area metal in the balancing section is minimized. Alternatively, the value of the balance factor is equal to the relationship between the maximum elongated membrane ring residual stress at the weld site and the minimum compressive membrane ring residual stress at the main region metal surface. At the same time, before welding, the initial value of the transverse transmission time of the transverse wave polarization of the pipe axis is measured in the balancing section. Measure the actual times of transverse and longitudinal transmission of the same transverse and longitudinal waves using the negative elastic equation for biaxial stresses at the same measurement point after welding: where t 01 , t 02 , and t 03 are the basic values and t 1 , t 2 , and t 3 are the actual values of transverse and longitudinally polarized transverse and longitudinal transmission times along the generating pipe. Thus, К 1 and К 2 are elastic acoustic couplings. Determine the membrane longitudinal and ring stress values and deflection sections for each measurement section. Using the bending part, determine the longitudinal and ring local residual stress values of the weld site, taking into account the membrane stress equilibrium principle and the equilibrium coefficient. The technical result according to the second option is to measure the volume wave transmission time through the ultrasonic echo method of the residual stress in the pipe welding area made of acoustic isotropic metal in the research area. or to characterize the residual stress state of the weld area according to the result. For the pipe type defined by the present invention, computational modeling is used to determine the balance section position. In the balance section, the equilibrium ring stress achieves a minimum value and a value of individual acoustic anisotropy, and the equilibrium coefficient value is equal to the relationship between the maximum ring membrane tensile stress and the minimum compressive membrane stress of the weld site metal. Measure the actual value of the transverse and longitudinally polarized transverse wave transmission time along the pipe axis in the balanced section after welding. According to the result, find the indicated difference value of each measurement point for the difference of longitudinal and ring membrane stress using the negative elastic equation below. where a 0 is the individual acoustic anisotropy of the main metal, and D is the elastic acoustic coupling. Use the longitudinal stress results in a further section to separate longitudinal and ring membrane stresses and warpages. Determine the longitudinal and ring local residual stress values of the weld area by the membrane stress equilibrium principle using the flexure part or by taking the equilibrium coefficient into account.