Different Vintage Pipeline Coating Failure Mechanisms and External Corrosion Conditions Between Liquids and Gas Transmission Pipelines

Abstract Within North America, vintage pipeline coatings, such as Polyethylene (PE) tape and Coal Tar Enamel (CTE) were widely used in transmission pipelines that transported both liquid and gas commodities during the 1950s–1980s. At the time, these coatings were believed to be the most reliable method of preventing damage to a pipeline from external corrosion. After more than half a century of operations, it is observed that some of these pipeline coatings have more failures and defects than others, which leads to more severe corrosion conditions. This paper outlines the vintage pipeline coating failure mechanism (i.e., PE tape, CTE) and root causes of variable corrosion conditions, on liquids and gas transmission pipelines of similar age. These potential root causes include operation temperatures, pressure cycling, and pipe diameter size. A detailed analysis of corrosion feature population and density from In-line Inspections (ILI) is conducted to provide evidence of potential root causes. The review of field verification reports was also completed to confirm the coating failure mechanism. The data is gathered from the operator’s active liquids and gas transmission pipelines with similar conditions so that the coating correlation can be understood. Any data skew will also be highlighted to prevent biases in this assessment. The corrosion growth rates (CGR) shall also be considered to compare the effect of coating and justify the increase in the frequency of inspection on certain vintage assets. The outcome of this study is to recommend the “best operating practices” to prevent or reduce failures of vintage coating systems. The suggestions of recoat types on different pipeline systems will also be discussed based on pipe size, original coating types, and products being transported.