Corrosion is the first cause of pipeline incidents, and one of the most important responsibilities of a pipeline engineer is to choose the right strategy to protect the pipes from it. In trenchless installations, this aspect is even more important as interventions are not possible during the design life of the pipeline and usually such crossings are located in environmentally sensitive areas.
Currently, pipeline operators and designers choose between very robust versions of three-layer polyolefin (PE/PP) coatings, hoping the additional thickness will compensate material losses due to abrasion during installation, and relatively thin coatings with very high adhesion properties. In such situation, they expect the coating to perform better in combination with a cathodic protection system in the areas where the steel was exposed due to damages to the coating.
In both cases, practical experience has shown that damages cannot be avoided. Currently, specifically on pipes that are installed by trenchless processes, the available methods for identifying where the coating was damaged cannot provide absolute or accurate information on the location, size and geometry of the damages. Moreover, even though cathodic protection verification at HDD locations can be validated close to the starting and final points of the crossings; the region between can only be assumed and thus is a questionable strategy.
This paper gives evidence on why these strategies are not valid and provides a technical comparison of properties between pipeline coatings used in trenchless installations. It also introduces an engineered mechanical protection system that has been successfully used by German companies for the past 20 years with an impeccable track record. Such a solution is of particular importance to allow the trenchless industry to achieve longer and safer crossings.
According to a research aimed to check coating quality of pipelines installed by Horizontal Directional Drilling, during the period between 2005 and 2016 in Northern Continental Europe, over 10% of long (above 500 m) trenchless crossings required further investigation of anticorrosion coating condition after its installation creating delays and cost overruns. In all these cases, the factory applied anticorrosion coating and/or the field joint coating system was not specifically designed to withstand the stresses of a trenchless installation. The situation is similar on other parts of the world due to lack of engineering standards addressing the problem on how to protect steel pipelines during trenchless installations.
