Corrosion is a naturally occurring phenomenon with virtually all metallic structures, including steel pipelines. External corrosion (occurring on the outside surface of the pipe) and internal corrosion (occurring on the inside surface of the pipe) are both potential threats to the integrity of a steel pipeline. In order to protect the environment and public safety, Sunoco Pipeline L.P. employs a comprehensive corrosion control program.
External corrosion on aboveground piping is controlled with a coating and visual inspection program. Corrosion on below grade piping is controlled with a combination of pipeline coatings and cathodic protection (CP), a technique to control the corrosion of a metal surface by making it work as a cathode of an electrochemical cell. The CP systems are monitored periodically at permanent test points along the pipeline by our personnel. The Close Interval Survey (CIS) is an additional method used. This involves taking measurements along the pipeline right-of-way at approximate 3 foot intervals. The CIS is normally conducted by a contractor equipped with specialized equipment and field experience.
Internal corrosion is controlled with a combination of chemical inhibitors, periodic cleaning and process controls. Instrumentation inserted in the liquid flow of the pipelines provides a measureable local corrosion rate. If corrosion rates are above acceptable limits, changes are made to address them.
The testing and inspection techniques described above provide a way to measure the effectiveness of the corrosion control systems and provide an early warning when changing conditions may be causing a corrosion problem. These procedures combined with additional assessments contained in our Integrity Management Plan allow us to operate our system safely and in full compliance with state and federal regulations.