Reasons of stress corrosion failure of erection girth joint of main gas pipeline

Abstract

Considered are some issues of stress corrosion failure of metal of main gas pipeline under operation. It is shown that, except for conventional orientation of stress corrosion cracks in longitudinal direction, the defects of such a type can propagate in transverse direction relatively to axis of the gas pipeline. Found transverse stress corrosion cracks, including ones passing through the whole thickness of the pipe wall, were formed in a zone of girth weld, joining 1420 mm diameter pipes of K60 strength class. Defective zone of 800 mm length was located from both sides of the weld and propagated at approximately 60 mm width from fusion line. Failure surface in zone of defects has specific step nature as a result of coalescence of finer semi-elliptical cracks, nucleated in different planes being displaced relatively to each other. The cracks are mainly characterized by rounded tips, that is typical for stress corrosion defects, formed as a result of anode metal dissolution.