As we are about to cross two decades into the 21st century, it may sound regressive talking about coal tar-based coating technologies for protection of underground pipelines. However, looking around, it is apparent that in the Indian (as well as African) subcontinent there is a maze of water transportation pipelines being laid that faithfully relies on the proven track record of coal tar products (commonly referred as wrapping coating) for underground installations. Thus, let us look upon various coal tar-based anti-corrosive systems used for UG piping and their relevance in today’s industry, especially the widely used torch-applied coal tar tapes.
An underground pipeline can be conceptualized as one integrated structure that passes through a variety of phases – across its length and in the changing surroundings in the same location over time. In India, all UG pipelines have to pass through different types of soil. It can be sandy, clay or a mix of both in varied proportions. A clay-type soil is more expansive and exerts higher stress on the buried pipeline than a sandier soil. This happens when the soil is subjected to top-down water ingress during the rainy season or due to bottom-up capillary rise of moisture while in a geography having a higher water table.