Analyze cathodic/anodic protection in buried slurry pipelines

Companies spend a large amount of money in constructing pipeline networks that must be protected against corrosion. It was estimated, in the USA alone, that the cost of corrosion is about {dollar}160 billion or 4.2% of the gross national product. Cathodic/Anodic protection strategies have proven to be effective against corrosion, but these strategies have not been applied to buried slurry pipelines such as used for the transport of phosphate in southern Idaho.; The objective of this research was to evaluate such strategies and develop costs and benefits. The procedure was to combine experimental cathodic/anodic protection strategies with new finite element modeling techniques. Laboratory potentiodynamic analysis gave necessary boundary conditions to three-dimensional models of pipeline corrosion. These models were compared to coupon immersion tests and pipe corrosion measurements.; The test solutions were made of 13%H₃PO₄, 13% H ₂SO₄, and different ratios of both. Immersion tests were carried out to understand the behavior of mild steel in these environments. The results of immersion tests indicated that mild steel is unsuitable to be in service under these environments without proper protection.; Potentiodynamic results of mild steel in these solutions did not show a passive region. This made anodic protection under stagnant solutions difficult at longer test times than 48-hours. In addition, corrosion rates increased with increasing sulfuric acid concentration. On the other hand, cathodic protection results were favorable.; The design of an anode placement provided the best protection possible internally under cathodic protection. The acidic solutions were allowed to flow at a low rate to simulate a pipeline. The corrosion rate of the pipe under cathodic protection was much better than without.; Finite element software packages used were Pdease 2-D and Marc/Mentat 3-D. The result was a low cost protection strategy that kept internal laboratory pipeline corrosion to 11 mils/year while pumping up to 13% H₃PO ₄. This low corrosion rate compared to a reported 30 mils/year under current practice in southern Idaho.; Today the pipeline is protected by severely limiting any choices on slurry feed from new flotation strategies or dump leaching practices.; The conclusion was that an electrochemical strategy will be cost effective because of an increase of phosphate production and throughput. This increase will come by allowing phosphate heap and dump acid leach solutions to be added to the slurry pipeline, without increasing corrosion or endangering lifetime. The results of this research are universally applicable to other buried pipeline systems containing slurries, water, and the gas and oil pipelines so crucial to the economy in many countries.