The role of welded structures, used widely in construction, power engineering, transportation, shipbuilding, and other branches of industry, is growing continuously. They operate on the earth, under water, in space, at normal, high, and cryogenic temperatures, in aggressive media, and under the conditions of intensive radiation. Therefore, the requirements for their quality, reliability, and long life are increased. These cause the need to develop new design-technological solutions by updating the methods of computation, performing comprehensive studies on the strength of welded joints, and by optimizing the manufacturing technologies of the structures. Most in-service, heavy-duty welded structures in many countries are approaching their critical age. At present, the service life of about half of the main gas-and oil-pipelines exceeds the design service lifetime or is close to it. This leads to a decrease in their load-carrying ability due to strain ageing and accumulation of damage in the pipe metal and also in welded joints and, as a consequence, to an increase in risk for failure. When estimating the residual life in order to extend the service life of gas- and oil-pipelines, it is necessary to concentrate on definite sections of main pipeline, which have already passed the design service lifetime and operate in a regime of high risk for failure. Their condition should be verified by using technical monitoring with analysis of existing damage and their causes. The contribution reports on an NDT-technology based on magnetic coercivity measurements and its calibration in standard tensile tests in order to characterize strain ageing of welds, recently introduced in the Ukraine.
