That's a wrap

By the early 1940s, cast iron pipe was losing its historic cachet as the go-to material for new buried infrastructure. Cast iron's replacement was bar-wrapped pipe (BWP), and it quickly gained acceptance as a reliable, durable and cost-effective pipe material for use in large-diameter transmission and sewer force mains.

Typically, BWP consists of a welded steel cylinder with reinforcing bars wrapped around the cylinder to provide strength. An internal concrete lining and external mortar coating provide corrosion protection to the steel components. The watertight membrane enables the composite pipe to withstand high internal pressures and the effects of external earth and traffic loads.

Until recently, BWP condition assessment proved difficult

Despite early adoption from many pipeline operators, the downside to BWP has been the difficulty to assess the pipe's condition, where failures are often precipitated by deterioration of the reinforcing bars and long periods of leakage that often go undetected.

It's now 70 years later, and the methods to assess the condition of bar wrapped pipe have only been recently developed and commercialized. On this forefront, Pure Technologies is recognized for its toolbox of condition assessment technologies that can identify broad areas of cylinder corrosion and bar breaks.

Two Texas cities join forces to assess shared BWP water supply line

In one specific case, the city of Irving (Water Quality Report, 2014) and a partnering agency in North Texas joined together to initiate a condition assessment project of their shared water supply line, made up primarily of bar-wrapped pipe. Constructed in 1955, the 48-inch Jamison Water Transmission Main is a critical non-redundant pipeline that conveys potable water to a combined population of 400,000 residences within the Dallas Fort-Worth Metroplex.

The two agencies worked side by side to implement an Assess and Address™ pipeline inspection protocol to determine the condition of the pipeline and to increase the utilities' reliability of water delivery.

The condition assessment utilized inline acoustic leak and air pocket detection, robotics with high definition CCTV and enhanced electromagnetic detection, transient pressure monitoring and non-linear Finite Element Analysis (FEA) of the steel cylinder corrosion and broken bar wraps.

The results concluded that 97 percent of the 583 pipes inspected had no detectable damage. Less than 3 percent of the total pipes inspected exhibited minor distress, of which 15 (2.5 percent) pipes exhibited thinner steel cylinder.

Through close collaboration, the two agencies were able to effectively manage a shared asset with the goal of preventing disruptive and expensive pipe failures. The information gained from the assessment will allow for the implementation of a cost-effective, long-term management plan to extend the life of the pipeline.

Trinity River Authority of Texas (TRA) evaluates 8.8 miles of critical BWP transmission main

In a second case involving BWP, Pure collaborated with Trinity River Authority on assessing the condition of a pipeline that is a critical link in the reliable delivery of drinking water to five cities within the Dallas-Fort-Worth Metroplex. The aging pipeline was scheduled for replacement due to previous failures and inability to be removed from service for repairs.

To understand the overall pipeline condition, TRA contracted Pure to inspect and evaluate the pipeline by conducting comprehensive hydraulic, leak detection and condition assessment on 8.8 miles of the 30-inch bar-wrapped pipe.

For the leak and air pocket assessment, TRA used the SmartBall® inspection tool, a non-destructive, free-swimming technology that measures the acoustic activity associated with leaks and gas pockets in pressurized pipelines. Regular leak detection inspections can help utilities identify leaks that may not be visible at the surface.

Increased reliability, reduced capital costs

For the structural inspection, TRA used PipeDiver®, a free-swimming electromagnetic tool that identifies bar breaks and broad areas of cylinder corrosion in BWP using PureEM technology while the line remains in service.

The inspection of the BWP identified 14 pipes with bar break damage and 72 pipes with electromagnetic anomalies resembling cylinder defects out of 1284 inspected pipes. By repairing specific pipe sections with deterioration, TRA was able to avoid replacing the entire pipeline at a high capital cost and continue providing reliable service to customers in the region.

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