Deterioration of Two Critical Force Mains

When Clean Water Services discovered inoperable valves and deteriorated connections along a critical sewer force main, evaluation and remediation ensued. The force mains consist of two 24-inch diameter lines, 46,000 feet long. Made of polyvinyl chloride (PVC), the mains transition to ductile iron (DI) at creek crossings. Twenty eight air release vaults are located along the alignment. Murray, Smith & Associates, Inc. inspected the vaults and force mains and measured soil resistivity. The metallic components within the air release vaults were experiencing corrosion. The corrosion was occurring at threaded connections, on the galvanized steel door hardware and on the vault lids. Microbiologically induced corrosion (MIC) was occurring inside pipes. Galvanic protection and impressed current systems were recommended. This presentation discusses the causes and potential cures for a problem that will become increasingly frequent as older ductile iron pipe with metallic fittings and appurtenances begin to show deterioration due to corrosion.