Assessment of the integrity of welded pipes

Abstract

The subject of the paper is analysis of the integrity of welded pipes made of API J55 steel by high frequency contact welding (HF). Experimental research on the mechanical properties of the base material was conducted on pipes withdrawn from exploatation after 70 000 hours at service. Defect influence of the surface crack on the integrity of pipes was tested using hydrostatic pressure of pipes with axial surface crack in the base material. Fracture behaviour was tested using modified compact specimen (CT), with the initial crack in the base material, welded joint and heat affected zone (HAZ). Critical value of the tensile strength factors KIc was determined based on the critical value J of the integral JIc. Apart from the experimental research, based on the derived values of Kr and Sr and by applying fracture analysis diagram (FAD) an assessment of the integrity of welded pipes with axial surface crack on the outer surface area was conducted.

Keywords

• seam casing pipes
• axial surface crack
• high frequency contact welding
• fracture analysis diagram (fad)