Fracture parameters for buried cast iron pipes subjected to internal surface corrosions and cracks

Abstract

The cast-iron pipeline has been utilized as the water main since the last century and continuously contributes to the present community by supplying potable water. These pipes are subjected to corrosions on the internal and external surfaces, causing pipeline breakage or leakage. For economical maintenance decisions of water distribution networks, it requires assessing the remaining strength of the pipes. Fracture mechanics has been effectively applied for evaluating the remaining strength of deteriorating structures. However, the major challenges in applying the fracture mechanics are obtaining the parameters such as the stress intensity factor (SIF) and fracture toughness. This paper presents a method for calculating the SIFs for cast-iron pipe subjected to internal surface corrosion. Finite element analysis is employed to calculate the SIFs using the contour-integral method for buried cast iron pipes considering crack only and crack with corrosion defects under internal pressure and vertical surface loads. Various aspect ratios and crack depths of semi-elliptical defects at the springline and invert/crown of the pipe are considered. In general, the surface load decreased the SIF for the springline internal crack and increased the SIF for the invert/crown crack. For the crack geometries and the loading conditions considered, the maximum reduction of the SIF for the springline crack was 85.1%, and the maximum increase for the invert/crown crack was 72.8%. A crack depth increase from 0.2t to 0.8t increased the SIFs by 130% to 243% under the internal pressure and 95% to 141% under the combined load for the invert/crown cracks.

Keywords

• Cast iron pipe
• Internal crack
• Corrosion
• Fracture mechanics
• Shape parameter
• Stress intensity factors (SIF)