Trinity River Authority Condition Assessment C303 Pipeline
hese distinctions can make assessing BWP challenging for pipeline operators attempting to renew their large-diameter water transmission mains, since the methods for determining baseline condition in the similar-looking pipe types are different.
PCCP is a concrete pipe that remains under compression because of the prestressing wires, with the thin-gauge steel cylinder acting as a water membrane. With BWP, the cylinder plays a much larger role in the structural integrity of the pipe. BWP is essentially designed as a steel pipe with mild steel used to manufacture the steel cylinder and steel bars.
The high strength steel wire in PCCP is smaller in diameter and wrapped under higher tension, therefore corrosion makes it quite vulnerable to breakage. The mild steel bars in BWP are thicker in diameter and wrapped under less tension, therefore corrosion takes significantly longer to lead to breakage.
This was the case for Trinity River Authority of Texas (TRA), who owns and operates 8.5 miles of 30-inch BWP and PCCP that supplies raw water from Lake Arlington to the Tarrant County Water Supply Project Water Treatment Plant in Euless, Texas.
The 30-inch pipeline, in conjunction with a parallel 54-inch pipeline, conveys raw water to TRA’s 87 mgd Water Treatment Plant (WTP). Treated water produced at the WTP is then supplied to five cities in the mid-cities region between Dallas and Fort Worth including Bedford, Colleyville, Euless, Grapevine and North Richland Hills.
TRA had originally planned to replace this pipeline, but chose to assess and selectively rehabilitate the pipeline by finding solutions that could identify the most distressed areas. The pipeline, constructed in 1973, is made up primarily of BWP, although there are some sections of PCCP.
In November 2012, TRA began a condition assessment program with Pure Technologies that included transient pressure monitoring, acoustic leak and gas pocket detection, internal electromagnetic inspection, and structural condition assessment including finite element analysis.
After completing the inspections, TRA has verified and repaired three sections of BWP that were beyond the yield limit determined by BWP structural performance curves. During the verification, TRA and Pure determined that the distress areas identified in the structural assessment were accurate and the excavated pipe sections had bar breaks and corrosion.
The condition assessment project also identified four leaks and three gas pockets and although the four identified leaks were small (less than 2 gallons per minute), one was located in the front yard of a brand new church building and could have caused significant water damage had it not been repaired immediately by TRA. Water from this leak was visible at the surface 325 feet away from the actual leak location.
Through the use of condition assessment, TRA was able to selectively rehabilitate its assets for roughly 4 percent of the estimated $25 million replacement cost. The project has also allowed TRA to increase service reliability for customers in the region.
Pure Technologies is helping utilities manage their buried infrastructure through its Assess & Address which can often be implemented for only a fraction of the capital replacement cost.
After completing leak detection and structural condition assessment on 8.5 miles of PCCP and Bar-Wrapped Pipe, Trinity River Authority verified the results of inspection, finding three distressed pipe sections.
This study investigates the behavior of a deteriorating BWP under various levels of distress and various internal pressures. The results based on a 24-inch pipe transmission main, are used to define criteria to evaluate the performance of a damaged BWP. Based upon the finite element results obtained in this study, suggestions for future work are presented and discussed.