This paper reviews the mechanisms of initiation and the prevention of top-of-the-line corrosion (TLC). Practical, multifaceted techniques based on the most recent research and developments will be described and then illustrated with documented sources to arrive at the best practices for control of this significant corrosion manifestation.
The rapid expansion of the production of oil and gas from unconventional sources requires the annual construction of thousands of miles of new pipelines, which will experience a bewildering and changing range of conditions that will require the use of new and innovative internal-pipeline-corrosion-protection methods that have been tested in field applications. These new corrosion-protection methods will be needed because of the complex corrosive environment of multiphase- and stratified-flow pipelines (including gathering lines), which is frequently observed in new shale-play production.
Conventional corrosion-inhibition methods (continuous or intermittent injection) may not be effective for inhibiting the pipelines because physical contact of the inhibitors is difficult to achieve in multiphase flowing systems at the top of the line (TOL). In addition, the pipelines must be piggable to be cleaned and treated properly, and traditional slug- or continuous-treatment methods have been found to be less than adequate where conditions exist for TLC to occur.
Several innovative methods are being developed to provide effective and long-lasting protection to the entire pipeline surface, including the use of pig trains with inhibitor slugs, improved inhibitor chemistries, inhibitors added to gels and foams, and special pigs that provide a 360° spray of inhibitor chemicals. The newer methods will be compared with the older technologies.