Faced with the need to inspect a high value pipeline asset due to previous failures and an overall unknown condition, an engineer is presented with the need to balance collecting data inexpensively while ensuring the data provides a quality adequate to make an effective decision.
Ideally, we want perfect information and we want it to be free. In reality, this is seldom the case; however sometimes we find that inexpensive information is more costly that quality information. An ongoing project in Ohio is one such example.
An Ohio utility owns a 12-in. Ductile Iron Cement Lined force main that conveys a lime slurry substance from a treatment plant to an open quarry. The total distance is approximately 90,000 ft with a plan to inspect it in smaller sections. The high consequence of failure and the utility’s previous inexperience with the condition assessment tool’s available prompted them to hire Brown & Caldwell as a consultant to develop an appropriate approach. A three-phase plan of attack was developed to gain confidence in both the ability of these condition assessment tools to be deployed within the pipeline system and the reliability of the reported information.
Phase One was designed to look at a pipeline within the system with similar characteristics as the lime slurry line, but in a low consequence area. Verification digs would be performed to assess the accuracy of the condition assessment report. Phase Two would inspect a lower-consequence 14-in. lime slurry line to gain confidence that the product within the pipeline would not present any unforeseen problems. Phase Three would begin inspecting the original lime slurry line in sections.
After vetting the available condition assessment techniques and the reliability of the data they provide, Brown & Caldwell recommended to the utility that PICA Corp. be hired for the Phase I work. PICA’s SeeSnake inspection tools employ an electromagnetic technology called Remote Field Testing (RFT) to measure the remaining wall thickness of ferrous pipelines. Wall thickness is measured every 1/10 of an inch, 360-degrees around the pipe’s circumference. This level of resolution allows decision-makers the information needed to properly plan future pipeline reliability.
Phase I was performed during September 2014. The utility was able to identify approximately 1,700 ft of 12-in. water main that could be taken out of service during the night to allow for an inspection tool to pass through the line. Because the goal of Phase I was to closely mimic the approach for the lime slurry line, the parties wanted to “free-swim” a tool through the line. This required pig launch and pig receive infrastructure to be installed on the 12-in. water main (photo above).
Environmental Enterprises Inc. (EEI) provided the civil work and Flowmore Services provided a light cleaning service using foam swabs propelled by water pressure.
PICA’s inspection was performed on the night of Sept. 16, 2014. To collect high-resolution data, an inspection speed of approximately 15 ft per minute was used, resulting in an inspection time of under two hours. The inspection data was sent off-site for analysis while the work site was restored by EEI.
The report stated that the average wall thickness of the pipeline was more than 90 percent remaining wall; however average wall thickness is often deceiving because it can mask deep, localized defects. The 12-in. water main perfectly illustrated this shortcoming of average wall assessments. The analysis of the Phase I data indicated a few areas of interest; so two Bell and Spigot pipe sections were selected for verification purposes.
Pipe I was located approximately 1,362 ft from the launch location and highlighted three defects along the invert of the pipe with remaining wall thickness measured at 3 percent, 15 percent and 16 percent. Pipe II was located 1,400 ft from the launch and highlighted three defects, also mostly along the invert, measuring 9 percent, 16 percent and 16 percent remaining wall thickness. The average wall thickness for these pipe sections measured between 84 percent and 87 percent remaining wall.
In summer 2015, all parties reconvened and excavated these two sections of pipe. These pipe sections were removed by the utility and sent to Corrosion Testing Laboratories (CTL) for analysis. CTL’s extensive laboratory analysis confirmed the PICA reports with very high correlation. As one example, a cross-sectional analysis of Pipe Two can clearly see the invert corrosion. CTL measured nominal pipe thickness as approximately 346-in., but the wall thickness at the invert was measured at .098-in. The reported axial location of the defects was also highly correlated.
With these results in hand, the Utility and Brown & Caldwell were gaining confidence in the condition assessment approach. The next step was to inspect a lime slurry line to see if the effluent created any issues for the inspection tool’s deployment. A recent pipeline construction project had made 18,172 ft of 14-in. lime slurry Ductile Iron pipe redundant, which provided the perfect candidate for inspection. Fortuitously, Robinson Construction had recently cleaned the line as part of a separate contract, so most of the launch fittings had already been installed. The 14-inch line relieves itself into an abandoned quarry and the plan was to simply collect the SeeSnake tool as it emptied into the quarry.
The Phase II inspection was completed in May 2015. The tool again traveled at 15 ft per minute, resulting in an inspection time of 20 hours. PICA technicians tracked the tool from above ground approximately every 1,500 ft and collected the tool in the early afternoon the following day. The inspection data was presented to Brown & Caldwell, which performed further engineering analysis, fitness-for-service reports and life-expectancy models. This report is being formally presented to the utility in March 2016.
After verifying the accuracy of the inspection data during Phase I and verifying the ability of these tools to travel extended distances through lime slurry pipelines, Phase III received the green light. Due to the extreme length and existing pipeline features, the 90,000 ft of 12-in. lime slurry main has been broken down into shorter sections for inspection. The first round of inspection took place in October 2015. More than 5,500 ft of pipe was inspected. The analysis has recently been shared with B&C, which will continue its enhanced engineering analysis. Preliminary information will be shared with the pipeline owner in March 2016 and the subsequent sections will continue to be inspected over the coming year.
To date, this phased approach has built the confidence needed to tackle the daunting task of inspecting 90,000 ft of pipeline. More importantly, the quality of the information will empower the project managers and engineers to make informed decisions regarding high-value, high-consequence assets.
Chris Garrett manages U.S. Operations for PICA Corp. He is based in Miami, Fla.