Corrosion in a buried pressurised water pipeline

Premature and frequent failures by rapid corrosion in a pressurised underground bitumen coated mild steel ERW water pipeline were investigated. Metallurgical and chemical characterisation of the corroded region as well as the corrosion products did not show any unusual behaviour. The soil adjacent to the pipe was also found to be only mildly aggressive in terms of the redox potential, pH, water-soluble chloride and sulphate ion concentrations and concentration of sulphate-reducing bacteria and acid-producing bacteria over the entire length of the pipe. However, soil surface potential gradient survey and pipe-to-soil potential measurements at various locations along the pipeline as a function of time indicated the presence of stray currents. The rapid and frequent failures observed are promoted by stray current corrosion.