Tuesday, April 14, 2015

Understanding Environmental Stress Cracking

This guest blog post was provided by Jim Rancourt, Ph.D. of Polymer Solutions.

If you have ever had a water pipe burst in your home you know how disastrous it can be. The leak results in property damage, extensive restoration work, and economic losses.  When it comes to the material used for pipes within commercial and residential settings, chlorinated poly vinyl chloride (CPVC) is one common material of choice. CPVC is often used because the material can handle corrosive water at higher temperatures and is more ductile than PVC. This type of pipe is also selected because it typically performs well. However, when CPVC is subjected to stress in conjunction with incompatible chemicals failure can occur—this mode of failure is known as Environmental Stress Cracking (ESC).

ESC occurs when CPVC plastic pipe is subjected to stress in conjunction with incompatible chemicals. Essentially, the chemicals weaken the CPVC pipe and as a result, the pipe cannot bear physical stress, resulting in failure. Within buildings and construction a common place that ESC induced failure occurs is inside Fire sprinkler systems because these systems are inherently stressed by internal water pressure which creates a propensity for failure if incompatible chemicals are induced. In actual fire sprinkler systems the stress level and chemical concentration of the ESC agent can delay the failure for several years.  This timescale is particularly troublesome because the facilities are normally fully occupied at that point.  The failure of the fire sprinkler system can trigger lawsuits. 

Surfactants, amines, and glycol-based anti-freeze solutions are all potential sources of ESC failure within CPVC pipes. An additional source, that we routinely provide testing for, is phthalates. Phthalates are small, non-polymer, organic molecules that are often used as plasticizers in order to make polymers more flexible than they would otherwise be.  Common sources of phthalates within building and construction systems include caulks, adhesives, and cable insulation.

ESC can happen from the inside-out or vice versa—the direction of failure can be determined. If it is outside-in there is no point analyzing the water within the pipe. If it is inside-out in there is no point in harvesting materials from the installation environment.
It takes analysis, expertise, and experience to determine if ESC has occurred and to identify the source of the incompatible chemicals that caused the ESC. Optical microscopy is a great analytical starting point when investigating ESC; it allows the scientist to understand the propagation direction of the facture. Determining the direction of failure shapes the direction of future tests used. If the pipe failed from the outside than it would not make sense to analyze the water within the pipe in search of incompatible chemicals. If the cause of failure is determined to be from within the pipe it would not make sense to examine exterior environmental characteristics for incompatibility.

Once the direction of failure is determined additional follow up testing can verify the presence of chemicals that caused the ESC. Two techniques that are commonly used for this type of analysis are Gas Chromatography-Mass Spectrometry (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR). Both techniques are used to indentify compounds within a sample, which can prove difficult if the ESC occurs from within the pipe. The ESC chemical causes a crack, the crack causes a leak, and the leak can potentially wash away the problematic chemical.

This begs the question: why even use CPVC pipes if they are prone to ESC? This type of pipe is less expensive, low weight, and more flexible when compared to steel pipes. CPVC pipe also have lower installation costs. Protecting pipes from ESC can be done by using phthalate free seals, fittings, o-rings, rubber sleeves, and ancillary components. It is also as simple as following all manufacturer instructions when installing pipes. 

Should you find yourself in a situation where you suspect ESC has occurred make sure to partner with an accredited  independent testing lab as soon as possible, to quickly assess the situation, provide the correct analytical approach, and arrive at data-supported conclusions.

About the Author:

About Jim Rancourt, Ph.D.
Jim Rancourt is the Founder and CEO of Polymer Solutions Incorporated (PSI), an independent testing lab that serves a global client base with chemical analysis and physical testing services. Jim, in conjunction with his staff of scientists at Polymer Solutions, frequently test pipes and fittings used by the building and construction industries. Jim is recognized as an authority in the field of materials science and is often called on to provide independent testing for expert testimony for a myriad of litigated matters. He has given over 65 presentations, has been published over 60 times, and holds 7 United States patents.

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