Plastic Water Pipe Failure

This consultant was contacted by an insurance company. A newly installed plastic water pipe had failed in the home of one of their policyholders. The resulting water damage was extensive, and expensive. This consultant wanted to determine: Did the pipe burst as a result of a manufacturing flaw or did it burst as a result of the expansion of freezing water? The event occurred in the winter while the homeowner was away for a few days. A frozen pipe meant that the insurance company was totally liable. If, however, the pipe was flawed, the insurance company could demand reimbursement from the pipe manufacturer.

This consultant sent the broken section of the pipe to a laboratory for microscopic analysis. They found four separate cracks and a piece of charred material. After reviewing their findings and overlaying them onto the pipe extrusion process, findings were submitted to the client.

If a screen pack was present on the extruder it either didn't do its job properly or material got trapped in the die (downstream of the screen pack), degraded there and then broke loose to enter the melt stream. One or both of these events seems to have occurred and as a result cold and/or degraded pellets were incorporated into the pipe.

Finally; if the die itself is not smooth the pipe will be extruded with internal or external imperfections which could lead to crack formation. This could be caused by gouges or scratches on the die itself or by degraded polymer becoming lodged in the die. This type of imperfection is sometimes referred to as a "die line". Die lines tend to become crack initiation sites. Given that four cracks were found in the pipe, it is possible that they initiated at these sites.

In summary this consultant felt that the water pipe failed as a result of poor manufacturing practices - allowing cold and/or burned material to be incorporated into the pipe. Also, the fact that there was more than one crack led this consultant to believe that the extrusion die was also chipped or had acquired a buildup of degraded material in the flow path which also led to cracking and failure.

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