CRACKING SUSCEPTIBILITY OF WELDED JOINTS IN REPAIR STRUCTURES ON MAIN GAS PIPELINES

摘要

Repair of main pipelines under pressure involves application of various reinforcing welded structures. Operation periods of trunk lines in many cases are longer than 30 years, and pipe material can have an unfavourable structure, hence the need to broaden the concepts of ensuring the technological strength of welded joints under repair conditions. The work gives the results of studying the susceptibility of low-alloyed steel welded joints to cold and lamellar cracking. For this purpose, experiments were conducted on technological samples, simulating the real welded joints of repair structures. Positive impact of preheating, postweld heating and thermal annealing effect on cold cracking resistance is shown, as well as significant influence of sulphur on lamellar cracking susceptibility of steels. Possibility of prediction of lamellar cracking probability by the indices of reduction in area, impact toughness and critical crack opening displacement, as well as by delayed fracture critical stresses and fractographs of base metal fracture surface, is shown.