Remote Monitoring of Pitting Corrosion Using a Next Generation Electric Field Mapping (EFM) System

Abstract

Pitting corrosion is one of the most serious problems in sour gas / oil pipelines and in crude oil refineries. Unlike generalized wall loss, pitting corrosion can grow at non-uniform rates and can rapidly proceed to full depth penetration. Such a loss of integrity can lead to leaks that cause production shutdowns, environmental damage, or in the worst case, loss of life. In practice, pitting corrosion is generally detected during pipeline inline inspection or during routine ultrasound scans undertaken as part of a maintenance program. Locations identified to exhibit pitting corrosion are then often risk ranked, and then either repaired or monitored depending on a variety of factors. Unfortunately, the sites where this type of corrosion frequently occurs are often inaccessible for frequent follow-up wall thickness inspections due to geographical remoteness or the need to the use of scaffolding to reach the site. This difficulty creates a need for an advanced internal corrosion monitoring system capable of remotely monitoring the progression of pitting corrosion. This paper describes a new pitting corrosion monitoring system based on the principal of Electric Field Mapping (EFM) and proceeds to describe recent results from an operational field installation of this technology. Using this technique, remaining wall thickness is carefully mapped out within a pre-defined area of interest. The system indicates the presence of any generalized corrosion in addition to the location, width, and depth of individual pitting corrosion defects. Innovations of this new EFM system include the use of a robust pre-fabricated fiberglass shell that significantly reduces the installation time compared to earlier technologies; non-welded contacts that have minimal metallurgical impact; permanent, self-powered on-site data acquisition system equipped with cellular or satellite data communication. Design principles of this technique are discussed, and installation procedures are outlined. Results are presented from a field site where pitting corrosion is being monitored on an ongoing basis. Background information on the installation, in addition to project goals and observations are reported. Daily wall thickness data obtained remotely from the site is used to report individual corrosion rates for pitting defects within the pipeline. These corrosion rates are then plotted over time and correlated to events such as process upsets, chemical inhibitor application, cleaning pig runs, and other actions intended to mitigate for internal corrosion. This correlation provides data which is then subsequently used to improve the corrosion mitigation program in place, and better schedule maintenance activities.