Photo Gallery G3:  Ductile & Cast Iron Pipe Failure

Every possible problem exists in the fitness for service assessment of cast iron and ductile iron pipe.  The material itself is the most difficult to ultrasonically test.  Both internal and external surfaces begin rough and deteriorate over time to interfere with the sound signal.  Corrosion characteristics vary widely.  Unlike other piping materials which require the almost complete penetration through the pipe wall for a failure to occur, cast iron and ductile iron pipe fractures and splits once sufficient wall thickness is lost to allow its bound stresses to release – an event which cannot be reliably predicted.  Nevertheless, most older cast iron pipe can provide near 85 years or reliable service.

Eventual failures are typically in the form of either longitudinal fractures or multiple pinholes.  Cross-sectional separations are also a threat, as some of our photographs show.  Horizontally oriented pipe is always more vulnerable although “channeling” can produce the same fracturing at vertical lines.  Although unpressurized and without the greater water damage threat that exists for most HVAC systems, entire sections of the pipe wall can fracture away.  Because such piping systems are unpressurized, early leaks are typically addressed with repair clamps and forgotten; only finally addressed after leaks become too frequent.

Similar to all other changes in the piping industry, thinner materials have taken over the industry.  This has resulted in the advanced failure of some sanitary waste systems in under 18 years; forcing their replacement with epoxy lined ductile iron pipe.  From the installation of extra heavy bell and socket cast iron decades ago for most sanitary waste, vent, and rain leader pipe, the same systems today are generally fabricated from standard or SV weight “no-hub” coupled pipe offering far less service.

Lesser wall thickness, undersized manufactured pipe, lower quality, and a greater vulnerability to corrosion – just do the math.  For one client, our testing at new 6 month old 4 in. no-hub sanitary waste pipe identified such low wall thickness, that it prompted them to contact the pipe manufacture with our report.  Their response was that their produce was not corroding at a high rate, but rather that they just manufactured it that thin.  Problem solved.