Polyvinylchloride (PVC) is one of the most widely produced plastics in the world and accounts for approximately 70% of new buried water distribution and sanitary sewer pipes being installed in the U.S. and Canada today. With so much more PVC in use today, there are more situations in which pipes can fail. Whether caused by improper installation or manufacturing defects, one of the most common failures – PVC cracking – is a response to stress. There are two types of typical crack formation: ductile and brittle fracture. Ductile fracture is a bulk response of the polymer coupled with yielding. Conversely, brittle fracture is a localized response without yielding. The type of failure and crack formation depends on multiple parameters including the material used and internal vs. external stresses. Proper pipe installation is also very important and minimizes unnecessary stress that can be due to bending or lack of support.
In a recent accident and pipe failure investigation, large diameter PVC pipe used in a water treatment system failed and resulted in significant worker injury. Numerous failure scenarios were proposed by others including water hammer and pressure surges in the PVC system. Our investigations included expert visual observations, microscopic analyses, polymer fractography and spectroscopic and thermal analysis in the inspection of the pipe service conditions, orientation, fracture surfaces, and solvent welds. After carefully piecing together the analytical data and the visual observations, the crack formation story unfolded. We determined that it would have been virtually impossible for water hammer or pressure surges to yield the observed fracture patterns and orientation. The pipe failure was a result of poor PVC installation practices which caused significant external stresses on the pipe by using it as a load bearing structural component in the water treatment system.