Behaviour of longitudinally aligned corrosion pits

Corrosion normally results in pits or groups of pits being formed locally or over an area of the pipe wall. To assess the severity of such corrosion, the analytical techniques of the American Gas Association, Report NG-18, have been used as the basis of existing American and Canadian pipeline design codes. (1,2) (Ref. 1-ANSI/ASME, Guide for Gas Transmission and Distribution Piping Systems, AGA, Virginia, 1986; Ref. 2-CAN/CSA-Z184-M86, Gas Pipeline Systems, CSA, Ontario, 1986). These codes address isolated corrosion pits and do not provide guidance for dealing with adjacent pits. As the distance between two corrosion pits decreases, they will begin to interact reducing the burst strength of the pipe. The effect of this interaction is a function of the pit dimensions, their separation and the loading conditions. This paper summarizes the results of a series of burst tests on pipe-containing corrosion pits lying on a longitudinal axis. The finite element method is used to analyze the test data and to investigate geometric parameters not considered experimentally.