Water Hammer Causes Water Main Breaks

Abstract

Most underground water main breaks can be stopped, since the technology is now available to evaluate water system piping failures and determine corrective actions. The problem is defined in terms of several variables: (1) Water hammer is the initiator of nearly all underground water main breaks. (2) In nonacidic soils, fatigue directly causes piping cracks. (3) In acidic soils, water hammer cracks the pipes, and crevice corrosion is accelerated at those crack sites. Additionally, those cracks serve as moisture sources to induce piping surface corrosion due to galvanic corrosion between the soil and the metallic pipe wall. Even so, some failures are solely due to corrosion. (4) Dynamic pipe stresses are significantly larger than stresses caused by static loading, i.e., hoop stresses and strains may be as much as four times the calculated static stress due to water hammer. (5) If dynamic stresses are not considered, calculations incorrectly conclude that water mains will not be damaged. (6) That is, water hammer calculations determine pressure surge magnitudes that are multiples of the operating pressures, where dynamic effects cause fatigue cracks due to the applied pressures and the number of cycles for those pressures to break water mains.

Our Water Mains Contaminate Us with E. Coli, Lead and Copper – Preventable Illness and Death Follow

“…Additionally, this author disagrees with other proposed causes of water main breaks [15]. Although the cited causes of soil stresses and corrosion are contributing causes to water main breaks, water hammer is the common cause as proven in publications [3,4,7], which in turn were based on hundreds of other references and many years of research. For example, ground shift due to winter temperatures was cited as a cause of piping cracks due to soil stresses, but this author contends that the possibility approaches zero to crack an underground metal pipe when concrete roads above that pipe do no crack.…”

“…That is, this simplified approach provides more go-no go conditions to determine if further modeling is recommended. where t 1 =the rise time=0.0021 seconds; ω=the hoop stress frequency of the pipe=7622 Hz (Earlier work showed that this frequency approximation underestimates the frequency for a thick wall pipe, but this error does not significantly influence the maximum DLF for this example); k=the bulk modulus of water=140,000 psi; r=the pipe radius=3.45 inches; T=the ductile iron pipe wall thickness=0.25 inches; g=the gravitational constant=32.174 feet/second 2 ; ν=Poisson's ratio=0.211; ρ pipe =pipe density=0.26 pounds per inch 3 ; ρ water =water density=0.03611 inch 3 ; E=modulus of elasticity=13,400,000 psi; σ static =the thin wall approximation for a hoop stress based on the measured pressure; and σ dynamic =the dynamic stress which is the estimated stress to cause a fatigue failure in the pipe. Since the soil frequency is much lower than the pipe wall frequency, the soil frequency predicts a bounding maximum stress response, and the soil frequency was used for this single degree of freedom approximation to a two degree of freedom system.…”

“…Since corrosion has been incorrectly believed to be the cause of water main breaks for more than a century, plastic piping has become popular as a replacement for metal pipes. As noted in other work [3,4,7], plastic water mains break due to water hammer, just like metallic pipes, which permits seepage of ground chemicals into drinking water systems through leaks as well. In other words, plastic pipes do not solve the problem of cracked water mains, but introduce new contamination problems as well.…”

“…Available theories discuss the mechanics of water main breaks [3,4], but a new relationship to E. coli emerged through an innovative insight that power outages, and power plant restarts, implement a common cause for temporary E. coli contamination of water systems.…”

“…All of these high values for DLFs are applicable to systems with suddenly closed valves. As the valve closure rate decreases, the DLFs approach one in all cases [3,4,7]. There are different methods to control water hammers, but slowing down the valve closure rates and pump startups and shutdowns are quite effective in reducing piping cracks.…”