Failure of pipeline expander segments due to undesirable EDM

Abstract

The premature failure of pipeline expander segments made of AISI D2 tool steel has been studied. After collecting the historical data of the segments, three possibilities were taken into account regarding the failures. Namely, the undesirable electrical discharge machining (EDM) performed on the segments, environmentally assisted cracking (EAC), and fatigue. Analysis of the cleaning water used in the pipe milling process was also performed which indicated high concentrations of sulphate and chloride ions which invigorated this assumption that corrosion played a role in the failure. However, relatively good corrosion resistance of the alloy and microscopic observations hinted to the more decisive role of the sharp cracks formed due to poor EDM on the sides of the failed segments. These cracks were held responsible for the premature failure of the segments.