Observed Effects of the May 2024 Gannon Storm on the New Zealand Gas Pipeline Network—Toward Predicting the Effects of an Extreme Storm

Abstract We present cathodic protection (CP) monitoring data from the New Zealand gas pipeline network during the Gannon Storm of May 2024. At some locations potentials between the pipe and a Cu/CuSO 4 reference cell and between an installed metal coupon and the reference cell both underwent large variations ‐ changes which took the pipeline outside the desired potential range for CP. At these locations both potentials became positive for significant lengths of time, which, in the event of defects in the pipe coating, can lead to corrosion of the pipe. Highly negative pipe to reference cell potentials, which can lead to detachment of the coating from the pipe, were also observed. Pipe to reference cell potentials and coupon to reference cell potentials are both indicators of the level of CP. The observed relationship between them when the rectifier is turned off is seen to have a complex form. Whilst the relationship is linear over a reasonably wide range of pipe to reference cell potentials, coupon‐off potentials at some sites approach an asymptotic limit at highly negative pipe potentials, but rise sharply and become scattered at larger, including positive, pipe potentials. At locations where pipe to reference cell potentials are not routinely monitored, measurements of the potential between the anode bed and the pipe may be used to assess the level of CP. Assessment of the effects of the Gannon Storm allow the development of methods of predicting the effect of extreme storms on the network, which we put forward here.