Historically, sanitary waste and vent pipe systems have offered the longest service life of most building systems due to the installation of extra heavy (XH) bell and socket cast iron pipe.  An average service life exceeding 85 years is common, with many systems lasting 100 years or longer.  Orientation has a significant bearing upon the level of corrosion occurring; the degree of pitch or grade for horizontal lines a major factor in their deterioration.  Since each joint is made using rubber, cement, poured lead or oakum for older properties, or some other material, there is always the potential for leaks.

Like many piping systems, the movement toward thinner pipe materials has had its expected result, and new buildings constructed using hubless or “no-hub” pipe are now experiencing far lesser service life primarily due to its significantly thinner pipe wall.  For 5 in. HX cast iron soil pipe previously the standard for sanitary waste service, wall thickness was 0.370 in. or greater.  Yet today, the same 5 in. waste line will have a specified wall thickness of just 0.190 in., with a manufacturing tolerance allowing its production and installation down to 0.150 in. – a 60% loss of wall thickness!  With the corrosivity of the waste similar to what it always has been, and seemingly less corrosion resistance of current pipe products, service life has been reduced proportionately – with the failure of new hubless pipe within 20 years not uncommon.

Vent stack pipe offers significantly greater service life, but is still vulnerable at longer horizontal runs where corrosive gases can condense.  Unlike steel, copper, or brass pipe, cast iron and ductile iron pipe have hidden stresses which produce much larger splits and fractures once wall thickness weakens.  The result is often the loss of a large section of pipe wall as opposed to a pinhole type failure with steel or copper pipe.

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