Across the United States, there are thousands of miles of water and wastewater pipes buried beneath communities. These pipes come in a variety of materials and sizes, but all provide necessary services to customers across the country.
In recent years, several industry studies have warned that a large majority of these assets are aging and reaching the end of their designed lifespan. Although this is true, it is often prudent for municipalities to manage their assets – especially their large-diameter pipelines – in favor of replacement.
Replacement is expensive – industry experts estimate that the costs could reach $1 trillion over the next three decades. But beyond this massive expense are the unassailable logistical challenges of replacing thousands of miles of pipe.
Fortunately for municipalities, some pipe materials that make up the nation’s infrastructure have well-developed assessment methods that allow operators to determine the location of deterioration so that pipes can be renewed. Pipe deterioration is often due to localized problems – such as soil, loading and operating conditions – meaning pipelines do not fail systematically across their entire length and can often be effectively managed.
Unfortunately for some municipalities that own large-diameter metallic pipe, like Padre Dam Municipal Water District (PDMWD), the technologies available for assessing its condition have only recently been developed.
In November 2012, PDMWD wanted to assess the condition of a 1.2-mile (2-kilometer) stretch of 20-inch (500-mm) mortar-lined steel pipeline that was thought to be in poor condition and may need replacement. Before committing to the large capital project, PDMWD completed a non-destructive inline assessment using Mini PipeDiver®, a free flowing tool that can determine the baseline condition of metallic pipes.
The tool is equipped with PureEM™ technology and can detect broad areas of corrosion on metallic pipelines. While its resolution is not as high as other metallic inspection platforms, such as Magnetic Flux Leakage which can identify very small defects, PureEM is capable of detecting areas of corrosion that could lead to near-term pipe failure. It is also able to assess long distances in a single deployment, making it ideal for pipelines that cannot be removed from service.
In total, the inspection identified six pipes with signals consistent with localized circumferential anomalies and 15 pipe sections showed signal shifts indicative of a pipe class change.
Starting in February 2013, PDMWD began validating the results of the inspection by excavating the six pipes with circumferential anomaly signals. All six anomalies were confirmed to have some level of defect including:
- Unknown concrete encasement covering a 2-foot longitudinal weld at a pipe joint; this pipe was damaged and repaired during the installation phase without proper documentation
- Damaged mortar lining and steel cylinder after the pipe was installed on a rock
- Localized cylinder and wire mesh corrosion
- Excessive wire wraps caused by a manufacturing defect
While the six anomalies represented different forms of damage, the information collected using PipeDiver was accurately verified and was very useful for PDMWD. In addition, the anomalies that indicate a pipe class shift provide the District with valuable information about their system that was previously unknown.
Based on the results of the condition assessment, PDMWD determined that a large replacement or renewal project was unnecessary and could be deferred. This allows the the District to be confident in the condition of this pipeline while maintaining safe and reliable service for its end-users.