INFLUENCE OF REPAIR ON THE BASIS OF THERMAL TREATMENT ON CORROSION RESISTANCE OF WELDED CONNECTIONS SECTIONS OF LONG-TERM MAIN PIPELINES

Abstract

Background The main cause of accidents of long-term operation main pipelines operating in the Republic of Belarus is the failure of ring welded joints due to the development of existing ones and the generation of new defects that lead to pipeline rupture or the formation of a corrosion fistula. The restoration of the visco-plastic properties of the welded metal is possible due to the repair work using the heat treatment method. At the same time, there are no studies on the effect of this method on the corrosion resistance of welded joints. Aims and Objectives To determine the effect of heat treatment on the corrosion resistance of sections of the ring welded joint of long-term operation main pipelines. Methods Corrosion studies were carried in accordance with the recommendations of State Standard 9.908 «Unified system of corrosion and ageing protection. Metals and alloys. Methods for determination of corrosion and corrosion resistance indices», State Standard 9.907-83 «Unified system of corrosion and ageing protection. Metals, alloys, metallic coatings. Methods for removal of corrosion products after corrosion tests», State Standard 9.905-82 «Unified system of corrosion and ageing protection. Corrosion test methods. General requirements». Results The use of heat treatment for repair work leads not only to the restoration of the visco-plastic properties of the welded joints of the long-term operation main pipelines, but also to a decrease in the corrosion rate by an average of 4 %. An increase in corrosion resistance is observed in all areas of the welded joint, which can be explained by the relative homogenization of the microstructure and the removal of residual stresses.