Photo Gallery F8: Sanitary Waste / Vent
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. Galvanized steel and galvanized wrought iron can be also found at many older properties; threaded in place from standard and even extra heavy 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 bell and socket joint is made using rubber, cement, poured lead, oakum for older building properties, or some other material, there is always the potential for leaks.
Although typically unpressurized, waste piping systems have the potential to fail catastrophically. Cast iron pipe is centrifugally formed; retaining significant internal stresses as it cools that are held in place by the strength of its wall thickness. Once one side of the pipe deteriorates more than the other, to a degree impossible to predict, the pipe can fracture or split longitudinally down its entire length, as this photo gallery shows. Failures can be in the form of small pinholes, a small fracture, or with the side wall shattered into pieces.
Like many piping systems, the movement toward thinner pipe materials has had its expected result. This is why 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 which was 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. if installed with extra heavy material, with a manufacturing tolerance allowing its production and installation down to 0.150 in. – a 60% loss of wall thickness! Add to that realization the fact that new cast iron pipe is typically undersized, and the beginning wall thickness may actually be loser to 0.120 in., as we have documented in our UT investigations. The very common use of standard or “SV” weight cast iron at substantially less wall thickness only increases the threat. With the corosivity 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 no-hub pipe within 20 years not uncommon.
Copper pipe also sees some utilization, but with very thinwall “DWV” for Drain Waste and Vent service typically installed. This much thinner than Type M copper pipe generally provides acceptable service, but is far more vulnerable when serving a waste carrying function. Galvanized steel and galvanized wrought iron are also found at many older building properties. Constructed of threaded schedule 40 or sometimes extra heavy pipe, their service life closely approximates extra heavy cast iron pipe, but is entirely dependent upon the quality of the galvanized zinc finish.
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.
