STRESSED AND DEFORMED STATE OF MIG-SOLDERED JOINTS OF GALVANIZED PIPES

Abstract

The main challenge in joining zinc-coated pipes using arc welding is to ensure the corrosion resistance of the welds and the preservation of the protective coating in the adjacent areas. This problem can be solved by using MIG brazing technology, which ensures sufficiently high joint strength - almost on a par with the base metal - and preserves the integrity of the protective zinc coating due to significantly lower thermal impact compared to arc welding. The stress-strain state of pipelines is determined by the characteristics of internal and external loads, the main one being internal pressure. This paper investigates the stress-strain state of MIG brazed joints of galvanised pipes by simulation modelling and experimentally. The MIG-butt welded joints of 150 mm diameter low-alloy steel pipes were studied, which were loaded with an internal pressure of 9 MPa. The stresses and strains on the pipe walls near the annular weld were determined by strain measurement using the SPIDER-8 strain measuring complex and a specially designed test bench. The research results showed that when using a V-shaped edge shape, the greatest localisation of annular stresses occurs on the outer wall of the pipes between the weld and the base metal. To reduce the ring stresses and change their localisation, the edge shape was optimised. It was found that the X-shaped edge shape is the most optimal for butt MIG-brazed pipe joints, and its dimensions were determined. It was found that the use of the proposed type of edge processing reduces the level of residual stresses by 21% compared to standard edges. The proposed shape of the edges made it possible to reduce the value of annular stresses and change their localisation from the outer to the inner wall of the pipe, which will increase the strength of MIG-welded joints and the service life.