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A Trillion Dollar Waterhammer Problem? Oh My!

An article published this month in the AWWA Opflow trade magazine relates that America has a trillion dollar problem with our municipal water distribution system due to pipe failures. This information is old news to the water industry. What is novel about this article is that it suggests the issue is largely caused by waterhammer (see Stop Costly Water Main Breaks Before They Happen).

At last month's Turbomachinery and Pump Symposia in Houston I heard Robert Leishear present a tutorial session on waterhammer and pipe stresses. This was one of the more heavily attended sessions I have ever observed at TPS.

At that session he made this same assertion. This month he followed it up with a magazine article. Is it possible waterhammer could play this strong of a role in such an expensive problem?

I have witnessed first hand the sometimes negative impacts of fire hydrant testing in my home state of Colorado. One happened to a former neighbor where his basement was flooded immediately after a hydrant test. Another is a project we got involved in as a consultant at a housing development where multiple basements in homes were flooded – on more than one occasion.

Dr. Leishear posits that the way that we test our fire hydrants causes waterhammer transients. To me this fact is obvious. But he goes on to suggest that the waterhammer causes fatigue in pipes which ultimately causes microcracks to form. The cracks become a site for corrosion to begin ultimately leading to pipe failure after enough cycles have happened. If he is right, then we can avoid future such failures by testing fire hydrants in a different manner that cause lower levels of waterhammer. Unfortunately, the corrosion already happening due to past hydrant testing is too late to stop. We can only impact the future.

As he related at the TPS show, what is especially insidious about this problem is that the impact of the waterhammer does not show up until many years later. This is true of many types of fatigue problems. It is only after many cycles over many years where the failure occurs. Unfortunately, in some cases the failure is disconnected from the cause and no one ever makes the connection because of the time delay. The failure is just chalked up to "corrosion".

Hopefully someone who works in the water industry can get their arms around this issue and look into it with more direct attention. 




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Wednesday, 20 March 2019