Abstract
Cased pipeline crossings are segments typically situated at road and railway crossings where the pipeline (carrier pipe) is surrounded by a larger diameter pipe (casing) for protection from mechanical damage. Although these locations face a similar threat of external corrosion as those which are conventionally buried; the management approach is considerably different. With time, spacers and end seals deteriorate and an environment conducive to external corrosion is created inside the casing leaving the pipeline vulnerable to damage if the coating system has also become compromised at any point. Execution of repair activities under these circumstances is very expensive and logistically challenging. Recently, a major North American pipeline operator has implemented gel-based vapor corrosion inhibitors (VCIs), in conjunction with cathodic protection to contend with such situations and control external corrosion of the carrier pipe at cased crossings. A VCI fluid mixture is initially injected into the casing’s annular space at a water equivalent viscosity and within a designed period of time it sets to a gel-like consistency. Since the gel is electrically conductive, it enables the carrier pipe to also receive cathodic current. Although the technique is proving to be very effective based from pipe-to-soil potential and ER probe measurement perspectives; some debate exists within industry regarding the simultaneous application of the two mitigation practices. This paper presents compatibility testing of VCI gel and CP and discusses the influences, effects or interactions between the two corrosion control methodologies. The overall objective of the project is to comprehensively identify and understand any offsetting effects between the concurrent use of VCI gel and cathodic protection inside a casing. The paper details results of laboratory experiments on VCIs for mitigating corrosion of casings.
