Abstract
A major pipeline Company has an inventory of approximately 2300 cased crossings throughout the various regions of Canada and the USA. Emphasis for managing and controlling corrosion within cased pipeline crossings is increasing from both operator and regulatory perspectives. Understanding the causes and characteristics of carrier pipe corrosion is an important stride towards improved integrity management of cased crossings. An excavation at a cased highway location is a complicated and intrusive process considering the impact to traffic and the numerous permits required prior to initiating any repair activity. Execution of repair activities under these circumstances is also very expensive and time constrained.
The pipeline industry has recognized these challenges and responded with a proactive solution to prevent situations of this nature. A vapor phase corrosion inhibitor gel solution is being applied to control the corrosiveness of the environment within the annular space of the casing and its effectiveness is continually monitored using remote telecommunication technologies. The technique is very effective on a case by case basis; however due to the number of casings within the system, it becomes impractical to qualify the entire inventory. Subsequently, a prioritization method has been developed to select cased crossings that require immediate mitigation and also schedule long range planning for repairs. The innovative and systematic process evaluates critical information and attributes within an expert environment using established decision making techniques. Priority for all locations is determined by structuring a hierarchy of criteria and eliciting technical judgment of company’s Subject Mat ter Exper ts (SMEs), stakeholders, and unbiased industry specialists. Experts’ opinions are supported by combining Cathodic Protection (CP) and Inline Inspections ( ILI) results within a structured, multi-criteria decision making matrix to create an enterprise listing for the casing management program.
Introduction
The liquid pipeline system is large and complex, comprised by several regions and lines with pipe diameters ranging from 6 to 48 inches (168mm to 1219mm). These pipelines cross creeks, farm lands, highways, railroads and rivers. In order to alleviate the mechanical loads induced on these terrains due to traffic flow or other activities, concentric casings are installed around the carrier pipe. While casings effectively minimize mechanical damage; the environment within the casing annulus can promote corrosion of the carrier pipe through ingress of water, oxygen, microbial activity and metallic shorts or electrolytic coupling conditions that affect Cathodic Protection (CP). The presence of a casing substantially increases the complexity and expense when the carrier pipe requires repair from such circumstances. Permitting and interruption of road/rail traffic can increase the duration of the repair planning cycle from the normal 2-3 months to several years. Therefore, the Operator has introduced vapor phase corrosion inhibitor (VCI) gel solution within the casing annular space to control the corrosiveness of the environment and continually monitor inhibitor effectiveness through remote telecommunication technologies. The technique is proving to be very effective at controlling external corrosion on a case by case basis; however impractical to apply to the numerous locations where casings occur.
