A Closer Look at the Role of Corrosive Soils in Water Main Breaks

The report by Utah State University's (USU) Buried Structures Laboratory on failure rates of the most commonly used water pipe materials titled, "Water Main Break Rates In the USA and Canada: A Comprehensive Study," has received a lot of attention since it was released in March 2018. The report has been reviewed in more than 155 countries and cites corrosive soils as a leading contributor in water main breaks. Click here for report.

NACE's Materials Performance Magazine Reviews Utah State Study

An article by Ben DuBose in Materials Performance titled, "Study Examines Corrosive Soil Conditions Behind Water Main Breaks," has a closer look at USU's findings. Materials Performance is the world's largest circulation journal dedicated exclusively to corrosion prevention and control. It is published by the National Association of Corrosion Engineers (NACE International).

Below are excerpts from the article:

Direct Correlation Between Soil Corrosiveness and Break Rates of Metallic Pipes

Of utilities surveyed, 75% reported operating pipes in one or more soil areas with moderate or highly corrosive conditions. "Utilities with a higher percentage of iron pipe may experience a higher percentage of corrosion-related breaks…This would especially apply to pipe installed without an increased investment in condition assessment, pipe monitoring, and corrosion control measures. The study found a direct correlation between soil corrosiveness and the break rates of metallic pipes."

According to lead researcher Dr. Steven Folkman, a cast iron pipe located in highly corrosive soil is expected to have over 20 times the break rate of a similar pipe in low corrosive soil. "Traditionally, the thickness of the iron pipe wall provided the additional corrosion protection," he writes. "[Cast iron] pipes manufactured after World War II have significantly higher failure rates due to thinner walls."

Meanwhile, ductile iron (DI) pipe in highly corrosive soil has over 10 times the break rate compared to DI pipe installed in mildly corrosive soils. "Because the wall thickness of [ductile iron] pipe has decreased over time, internal and external corrosion are a bigger concern for this pipe product," Folkman says.

Corrosion Prevention Methods Used by Utilities Often Ineffective

The survey found that 80% of respondents reported using at least some form of corrosion protection. In order, the top five most common preventive methods used by water main operators are polywrap; anodes or cathodic protection; V-bio polywrap; impressed current; and dielectric coatings.

However, Folkman cautions that many water utilities often do not know the specific cause of external corrosion observed on their water mains. Consequently, the chosen preventive measure may not work effectively. "For example, it is not effective to install an anode on a main that has a bacteriological corrosion problem," he says. "Similarly, an anode bag installed to reduce corrosion caused by a stray impressed current would be quickly used up and would provide only short-term protection. Also, polywrap does not protect a pipe from all corrosion types and may get damaged during installation.”

Municipalities Urged to Consider Using More PVC Pipe Which Has Lowest Failure Rate

Dr. Folkman urges water main operators to consider using PVC pipe, which had the lowest overall failure rates in both the 2012 and 2018 USU surveys. "PVC is not subject to corrosion, unlike ferrous and concrete steel cylinder pipes," he explains. Folkman says water main operators are gradually moving in the direction of PVC, with 74% of utilities allowing its use in 2018 - up from 60% in 2012. "A lower failure rate contributes to a lower total cost of ownership," he says, in addressing cost concerns.

Regards,
	Bruce Hollands Executive Director | Uni-Bell PVC Pipe Association 201 E. John Carpenter Freeway, Suite 750 | Irving, TX 75062 T. 972.243.3902 ext. 1019 | F. 972.243.3907 www.uni-bell.org