The aim of the present study is to develop a procedure for residual life evaluation of welded joints of supercritical structures. To measure changes in service characteristics of pipe steels a magnetic method was used for controlling stress-strain state and residual life of the material in monitoring of welded metal structures. Investigations were performed on samples from pipe steel 09G2S using a special coercimeter with an attached magnetic device (AMD). The principle of the investigation was as follows: a local region ot the test sample was magnetized using AMD with mono-polar current pulses. Then, a demagnetizing current (of inverse polarity) was delivered to the AMD coil and its actual value l(0) was documented at the moment when the magnetic induction, was equal to zero. The 1(0)-value is then proportional to the local coercivity of the pipeline steel. To obtain the value Hf in absolute units the instrument was previously calibrated on reference samples with known reference values. Then, mono-axial static loading of pipe steel samples of standard sizes (700 x 60 x 28) was realized in a standard tensile testing machine according to the given standards. The use of the AMD device allowed quick measurement of the coercivity value H(0) in different directions (stepwise loading in the directions 0-90 degree). The analysis of the results obtained from the investigations showed that the method by which the coercive force is measured in the 90 degree direction is most sensitive to tensile stresses in the region of elastic deformations. The process of damage accumulation by plastic deformation of the pipeline steel under cyclic loading was made on similar 09G2S steel samples under low-cycle fatigue condition at zero cycle of loading, 5 Hz frequency and 280 MPa load amplitude. The typical dependence of the coercivity values H (0) on the number of cycles N are given. Thus, threshold values of H(C) were determined for the weld zone, and also the parent metal regions in which irreversible changes are accumulated on reaching these values. This should, in combination with the examination data of other non-destructive techniques, improves significantly the quality and validity of the evaluation of the residual life condition of pipelines
Residual life evaluation of welded joints using a magnetic method for monitoring of welded structures
Welding in the World ; 47 , 1/2 ; 7-11
2003
5 Seiten, 8 Bilder, 10 Quellen
Article (Journal)
English
Residual stresses in welded structures
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