Investigation of welded joints of long-term operated gas pipeline controllable rolled X70 steel

Abstract

The complex properties (mechanical, microstructure, and electrochemical) of controllable rolling X70 steel pipes of the main gas pipeline with a diameter of 1420 mm after an operation for 20 years and emergency reserve pipe after a similar period of storage were studied. Taking into account specified heterogeneity caused by the technological effect on X70 steel of controllable rolling, it is difficult to draw unequivocal conclusions about the effect of operational work on changes in the condition of welded joints of investigated pipes. It was established that operating loads did not significantly affect the characteristics of base metal and welded joints. Electrochemical properties (corrosion potential, hydrogen recovery potential, anodic curves slopes) of long-term operated pipes of different manufacturers (Ukraine, France) and stock pipes in NS4 solution are similar. Due to the high reserve of impact viscosity at standard temperature conditions, investigated pipes are characterized by satisfactory resistance against breaking.

Keywords

• x70 pipeline steel
• microstructure
• yield strength
• tensile strength
• elongation
• impact toughness
• corrosion potential
• cathodic polarization
• hydrogen reduction