Drain corrosion

Drain corrosion describes the gradual breakdown of metal pipework, most often cast iron soil stacks and waste pipes, by acidic condensate, hydrogen sulphide gas, household chemicals and biological action over time. The internal surface becomes pitted, scaled and eventually perforated, reducing effective bore and allowing leaks. In London, many Edwardian and inter-war properties still have their original cast iron stacks, and corrosion is a common reason for unexplained smells, weeping joints and slow drainage. Engineers usually identify the issue through a CCTV inspection of the bore and visual assessment of external surfaces. Repair options include partial or full replacement with PVC-U or HDPE under BS EN 12056, application of internal coatings where structurally appropriate, and improved ventilation to reduce condensate formation. Maintenance and routine inspection help extend remaining service life.