Investigation of the welded joints of siphon pipes of the underwater crossing of main oil pipeline

Abstract

The article investigates the welded joints of siphon pipes of the underwater crossing of the main oil pipeline manufactured from 09G2 steel. The diameter of the welded pipes is 1220 mm, the wall thickness is 29 mm. The manufacturing of steel pipes involves thermal strengthening during accelerated cooling. The studies were performed both in the field and in the laboratory. The following studies are described: hardness measurement, its distribution along the fusion line and heat affected zone, measuring the distribution of residual welding stresses, and tensile testing of samples at room temperature. Distributions of residual welded stresses are determined from both the outer and inner walls of the oil pipeline siphon. Destructive and non-destructive direct methods were used to determine the mechanical properties of the metal on standard samples of the welded joint and heat affected zone of the pipeline. Tensile strength, yield strength, and relative elongation are determined. The mechanical properties of the pipeline metal were calculated concerning the hardness. It has been established that the mechanical properties and structure of the welded joint of the pipeline metal comply with the regulatory documents, certificates, and specifications for pipelines. Analysis of the results shows that there is a tendency toward hardening of heat affected zone during multilayer welding and a decrease in ductility.