The problem with PEX Pipe
July 21, 2012 4 Comments
Cross-linked polyethylene or PEX pipe has been on the plumbing market for a several years and has been accepted by most plumbers as an acceptable substitute for copper piping in potable water systems. There are at least two methods by which PEX pipe is manufactured and depending on the manufacturer, theirs is the best way. However, regardless of the method of manufacture, PEX pipe has a couple of drawbacks. PEX pipe is subject to degradation by exposure to chlorine, ultraviolate radiation, and rough handling. I bring this up because I am presently working on a case involving extensive water damage due to a leaky PEX pipe. It seems that the pipe cracked longitudinally and released a great deal of water into the crawl space causing damage to the subflooring and consequently, the interior flooring as well. This scenario isn’t unusual. But, after the hot water line was repaired, a second crack developed in the same line, only days after the first crack was replaced. To make matters worse, a short time later, a third crack occurred, again, in the same hot water line. It almost seems that the fact that a hot waterline is involved has something to do with the failures and there are accounts on-line of people having similar problems. However, according to the manufacturer, as long as the conditions of the water do not exceed 80 psi and 140 deg, the piping shouldn’t be affected. In addition, as long as the chlorine level is below 3500 parts per million, again, the piping should not be affected. I’m not sure how accurate that information is since it tends to conflict with the pressure and temperature information written on the exterior pipe wall. As for the chlorine level, I have found reports stating that chlorine will continually degrade PEX piping, the greater the concentration, the shorter the service life. I have also found that the failures affecting PEX pipe currently are similar to the type of failures that were affecting polybutylene pipe, for which there was a massive recall. As far as I can tell, there are currently no recalls for PEX pipe.
About R.J. Hill, P.E.
R.J. Hill Consulting's Blog 
Our water supply is treated with chloramine salts rather than chlorine. Significant leaks can occur where PEX piping is used with brass fittings with this kind of sanitation chemical. The chemical interaction produced between the PEX, brass and chloramine salts eats away at the brass with corrosion occurring, small leaks turn into big problems over a short period of time. Caution should be taken to find out how your water supply is made safe. Within 6 months from finishing our new home, you could easily see the corrosion inside the brass. This fix was an additional pre-treatment filtration system at $6K. All copper would have been far less expensive.
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PEX (or crosslinked polyethylene) is part of a water supply piping system that has several advantages over metal pipe (copper, iron, lead) or rigid plastic pipe (PVC, CPVC, ABS) systems. It is flexible, resistant to scale and chlorine, doesn’t corrode or develop pinholes, is faster to install than metal or rigid plastic, and has fewer connections and fittings.
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I have had a similar case with PEX as you identified above with my hot water line … longitudal split inside a wall. Do you recommend testing chlorine levels in water? Is there a setting on the water heater to lower the hot temps?
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Good Morning Mr. Cohen,
Testing chlorine levels is somewhat impractical for most people unless you have the time and access to testing materials or a lab. In addition, it is difficult to say what chlorine level would be acceptable as it depends on several factors. Those factors are out of everyone’s control since the chlorine is added by the local water treatment plant. If you are having problems with PEX pipe failure, it would be easier to replace the pipe with PVC, polyethylene, or copper. As far as temperature is concerned, yes you should be able to turn down the temperature setting on your water heater. If you have a gas unit, the control valve is usually mounted in front, in plain sight, and has a knob that is marked with “Lo” and “HI” or ‘Hot” and “cold”. If you have an electric water heater, you will have to remove the two covers on the front side. There might be some insulation covering the thermostats at the top and bottom that will have to be moved out of the way. ***CAUTION*** Both thermostats are electrically live and operate at 230 volts. DO NOT TOUCH ANY OF THE ELECTRICAL TERMINALS!!! You will see temperature dials on both thermostats that can be adjusted using a small screwdriver. Turn the dial screw until the desired temperature is opposite the arrow indicator. Don’t go below 120 F as this is the minimum required temperature for washing dishes and doing laundry. If you don’t feel comfortable adjusting your water heater thermostats, don’t do it! I would recommend finding someone who can make the adjustments for you.
Thanks for you comments.
R.j.
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