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Cathodic Protection Coupon Interpretation in Multi-Line Corridors

Published: 20210421 by Association for Materials Protection & Performance
Author(s): Daniel Fingas
Co-Author(s): Daniel Fingas - Corrosion Service, Len J. Krissa - Enbridge, Liquid Pipelines

Pipeline operators are becoming more dependent on coupons for demonstrating adequate cathodic protection as the use of multi-line corridors has increased. In such complex right-of-way configurations, the pipelines are often bonded together for cathodic protection purposes. The presence of widely varying coating qualities and current requirements means that protection levels measured during test post or close interval potential surveys are mixed potentials influenced by all the pipelines in the corridor. Targeted assessment of an individual pipeline therefore becomes much more complicated, particularly when a pipeline is newly constructed and is situated amongst legacy operating assets. To help account for this, coupons are heavily relied on to accurately assess protection levels on a specific pipeline.

Literature and the NACE standard SP0104 indicate that correct interpretation of coupon measurements may require the use of non-metallic soil-access tubes and/or a nearby stationary reference. In practice, it is not always possible to install soil-access tubes along with the coupons due to factors such as land use, coupon depth, etc. This paper considers the theoretical and experimental basis for the need for a soil-access tube or a close-coupled reference. The interpretation of coupon data for new pipelines is examined in light of coupon data recorded on a new transmission pipeline that shares a corridor with several older pipelines. Recommendations are provided.

This paper examines the existing approach to coupon interpretation and installation. Specifically considered is the requirement for a soil-access tube and/or a nearby stationary reference in NACE standard SP104. The data which initially supported this decision is discussed, and the applicability to modern pipelines, and especially multi-line corridors, is evaluated. The outcome is an updated approach for interpreting coupon measurements around new pipelines.