External surface protection

External surface protection is used on ductile iron pipes laid in soil, where the coating forms the barrier between the pipe and the surrounding ground. Several designs are available depending on the aggressiveness of the soil. An alloy coating of zinc-aluminium (ZnAl) is covered with bitumen paint or synthetic resin. External polyurethane coating (ELECTRO-PUC) is available for size 80–1200 mm and provides a thick, chemically tight barrier with high wear resistance. PE sleeve protects against direct currents and acts as a physically inert barrier, whilst PE tape with adhesive is applied over a bitumen-based primer with 25 mm overlap. In highly corrosive soil, a surface coating of at least 400 g/cm2 is recommended, applied and tested in accordance with EN 15189.