Frankfort Electric Electomagmetic Em Assessment Ductile Iron
Commercial introduction of ductile iron pipe (DIP) began in the mid-1950s and was established as the most frequently selected material of choice for ferrous pressure pipe by the early 1970s. Due to the widespread use of DIP during a large expansion of pipeline infrastructure in the 1970s, there are many thousands of miles of pressurized DIP in operation today.
Water and wastewater utilities across the United States face a major funding gap related to buried pipeline infrastructure – the U.S. Environmental Protection Agency (EPA) estimates the difference between what is needed for infrastructure renewal, the majority of which is associated with buried pipe, and what utilities can afford to spend is between US$200 billion and $1 trillion over the next 25 years.
Like most of our buried infrastructure, this large ductile iron pipe (DIP) inventory has not been proactively managed since installation. This is primarily because many pipeline owners across the United States have had few financially-viable pipeline management options available, thereby leading to an operate until failure approach. Typically, once several failures occur along one of these pipelines, they are replaced without truly assessing the root cause of failure.
Although this run to failure and replacement approach is commonly applied, it often leads to two unnecessary outcomes. First, emergency responses to failures often have high costs for a pipeline owner and are also degrading public confidence in the service. In fact, the Water Research Foundation reports that small-diameter water main failures cost approximately US$10,000 for direct and social costs while large-diameter failures average US$1.7 million in direct costs alone.
Secondly, data from pipeline replacement programs throughout North America indicate that 70–90 percent of the pipe being replaced has remaining useful life. These two pieces of information lead to a simple conclusion – pipeline owners need a better management strategy to maximize operational and capital budgets by optimizing the life of these critical assets.
To do this, an owner needs to determine what assets they have, where they are, and how much life it has left. This can then drive sound, defensible decisions on the long-term management strategies for the pipelines. Part of this management strategy should be to implement a comprehensive condition assessment strategy locate, inventory, and assess the condition of the pipeline.
Pipe distress is related to localized problems, meaning pipelines rarely – if ever – fail systematically across their entire length. When a pipe fails, it is usually due to localized damage relating to internal or external corrosion, excessive loading, unexpected soil conditions, and design, manufacturing, or construction defects. This means that a near-failing pipe is likely adjacent to pipes that are in like-new condition.
In fact, data from condition assessment programs throughout North America shows that less than 5 percent of pipeline alignments have any distress while even less (less than 1 percent) require repair or replacement. Therefore, the ability to identify these isolated areas of distress is critical for owners in not only preventing pipe failures but also avoiding the expensive and unnecessary capital replacement of a pipeline with remaining life.
Current condition assessment technologies available to owners of metallic pipelines allow for the identification of these localized areas of distress across for full pipeline alignments. One example of this is a project recently completed for the Frankfort Electric and Water Plant Board (FEWPB).
Frankfort Assesses Ductile Iron Pipeline
In June 2013, FEWPB agreed to utilize an electromagnetic (EM) assessment technology on 700 feet of 1974 era DIP after the successful assessment of almost five miles of its prestressed concrete cylinder pipe (PCCP). The 700-foot section of 48-inch DIP runs directly from one of FEWPB’s water treatment plants and connects with the primary transmission main.
To identify distress along the DIP transmission main, FEWPB and Pure Technologies used a manned EM tool with 24 detectors to collect full circumferential data of the pipe wall. The tool uses PureEM™ technology and can accurately identify broad areas of corrosion in metallic pipes, which is the typical failure mode for DIP.
While the PureEM tool provides the owner with lower resolution than available high-resolution tools, it is a more operationally friendly technology deployment as it is not a full diameter device (as with the high resolution tools). Additionally, PureEM can be implemented via manned, robotic, or free-swimming deployment methods providing operational flexibility that was previously unavailable.
One Pipe Identified for Further Investigation
For FEWPB, the 700-foot inspection identified one pipe section with an anomaly representative of distress. Based on the assessment, FEWPB decided to excavate the pipe and validate the anomaly. Once uncovered, it was found that the section was resting on a damaged section of Reinforced Concrete Pipe (RCP). The damaged RCP section had exposed reinforcing steel, which led to visible galvanic corrosion on the ductile iron pipe section. The location of the external corrosion closely matched the location of the anomaly in the data.
Ultrasonic testing was then completed for the exposed pipe (including the anomalous area). The average median thickness of the non-anomalous pipe wall was 0.69 inches, which corresponds to Class 52 DIP, while the minimum thickness found in the anomalous areas was 0.45 inches, indicating up to 35 percent wall loss.
FEWPB completed its own evaluation of the structural implications of the wall loss and used determined that the pipeline was in serviceable condition under standard operating conditions. As a precaution FEWPB decided to coat the pipe with asphaltic coating and install a repair sleeve over the damaged area. Through the implementation of a proactive pipeline management strategy by using condition assessment , FEWPB was able to increase their confidence in the reliability of the asset, lower risk of continued operation, as well as defer costly (and unnecessary) operational or capital expenditures for the rehabilitation/replacement of the pipeline.
The City of Tarpon Springs, FL serves a population slightly less than 25,000. With limited resources and a mandate to provide both reliable water supply and wastewater collection for its customers, the City decided to assess the condition of one of its primary 14-inch ductile iron force mains that experienced a failure in summer 2013.
Introduced into the U.S. marketplace in 1955, ductile iron pipe (DIP) is pressure pipe commonly used for potable water and sewage distribution. The predominant wall material is ductile iron, a spheroidized graphite cast iron, although an internal cement mortar lining usually serves to inhibit corrosion from the fluid being distributed, and various types of external coating are used to inhibit corrosion from the environment.