Tarrant Regional Water District (TRWD) and Pure Technologies U.S. (Pure) have a long history of working together to keep the water transmission mains in the Dallas-Fort Worth (DFW) area in good operating condition.
The partnership began 17 years ago with mutual development of electromagnetic technology to inspect prestressed concrete cylinder pipe (PCCP). One of Pure’s first electromagnetic inspection prototypes was developed (with funding assistance from American Water Works Research Foundation [now Water Research Foundation (WRF)], commercialized (with assistance from TRWD) and first pulled through TRWD’s pipeline on a little red wagon!
TRWD is one of the largest raw water suppliers in DFW with large-diameter pipelines that transport water from the East Texas Cedar Creek and Richland-Chambers Reservoirs. TRWD provides water to almost two million people and spans an 11-county area in North Texas.
Electromagnetic technology platforms recognized around the world
Since 1999, TRWD has utilized Pure's advanced inspection and condition assessment services to evaluate than 240 miles of PCCP. Over the years, TRWD has deployed a variety of inspection platforms to determine the condition of their critical supply lines. This includes PipeDiver, a free-swimming electromagnetic inspection technology, Sahara, an acoustic leak and gas pocket detection tool, and a manned electromagnetic tool equipped with PureEM to collect full circumferential data of the pipe wall.
The condition assessment data is compiled with a Geographic Information System (GIS) deliverable, which provides TRWD with detailed information that is used to implement a targeted pipeline repair and replacement strategy.
TRWD utilizes Pure Technologies’ cost-effective Assess and Address approach to target specific pipes for repair or replacement that are near the end of their service life, as opposed to replacing entire sections of pipe in good condition. In addition, this proactive approach allows TRWD to document significant savings over a complete pipeline replacement strategy.
This year, Pure conducted a non-destructive evaluation of high-risk sections of the Cedar Creek Pipeline, using electromagnetic inspection technology. The purpose of the 2016 inspection was to determine if the pipe’s condition had changed since previous inspections (dating back to 2003) in order to develop a degradation curve to help determine remaining useful life.
This year’s inspection covered a cumulative distance of 10 miles and spanned 2,234 individual pipes in Section 11 of the Cedar Creek Pipeline. To facilitate a direct comparison between previous inspection results and the 2016 inspection, the previous data was re-analyzed and updated to comply with current analysis methodologies.
Calibration begins with a baseline condition assessment
Effective analysis of electromagnetic data requires an understanding of how the electromagnetic signal behaves when no broken wire wraps are present (i.e., baseline condition) and comparing the baseline condition to the signal received from the pipe when broken wire wraps are detected.
The electromagnetic signal is sensitive to the physical properties of a particular pipe (i.e., wire diameter and spacing, presence of shorting straps, cylinder thickness, etc.). Pipes with the same diameter, but different design specifications exhibit different signal properties or “baselines.” Additionally, these pipes will display electromagnetic signals that respond differently when broken wire wraps are present.
To understand how the data signal responds in varying conditions, Pure performs a calibration scan on pipes similar to the inspected pipe. The calibration process involves scanning a pipe with properties as close to the properties as in situ pipe.
Once the baseline has been established, additional scans are performed on the pipe to determine:
- Resolution of the system when the number of broken wire wraps changes
- Optimal system settings used for that particular pipe
Distress signals compared to calibration curve
A calibration curve is created from this information and incorporated into Pure’s analysis software. A data analyst measures a distress signal, and compares it to the calibration curve to quantify the number of broken wire wraps represented by that signal. The distressed regions of each inspected pipe are then identified, measured and compared against the calibration curves to quantify the number of broken wire wraps within each distressed region.
In addition to calibration, TRWD performs pipe forensics each year to verify broken wires from the pipes that are replaced. A comparison is made from the results and the reported broken wires, including total wire break count and wire break count by location. This has given TRWD great confidence in the analysis over the years.
TRWD reacts to results with more confidence in pipeline infrastructure
Of the 2,234 pipes inspected in Section 11 of the Cedar Creek Pipeline, a total of 185 pipes (8 percent) had electromagnetic signals consistent with broken wire wraps, ranging from 5 to 200 broken wire wraps.
A comparison between previous inspection results and 2016 results has given TRWD a better understanding on the current condition of the pipeline, and shows that a total of 75 pipes (41 percent of the total 185 pipes with broken wire wraps) have become newly distressed since the earlier inspection. A total of 49 pipes exhibited an increase in broken wire wraps. Furthermore, one (1) pipe that was previously reported as distressed has now been replaced.
Since 2000, a total of 271 pipes have been replaced during planned maintenance based on the results from Pure inspections. As a result, TRWD has noticed a dramatic decline in failures since the late 90s doing a risk-based prioritization and replacement/rehab program, in addition to implementing cathodic protection, pressure transient surge reduction measures, and pipeline protection measures from external loads.
TRWD is extremely proactive when it comes to understanding their pipeline infrastructure. They take pride in their ability to locate and repair leaks, and repair or replace damaged pipes during routine maintenance schedules - rather than in emergency situations.