Midwest Utility Uses Pipeline Inspection to Assess Its Ductile Iron Lines

A critical part of this assessment was to gather wall thickness measurements of the force main by using PICA Corp.’s patented SeeSnake technology. The SeeSnake tool traveled approximately 3,000 ft in a free-swimming manner collecting data on the condition of the pipe wall.

The section of pipe selected for assessment was Class 53, 12-in. ductile iron. Installed in 1984, it is responsible for transporting waste water between two treatment facilities. Donohue & Associates Inc. was contracted to provide engineering guidance to complete the assessment of the pipeline. Donohue in turn subcontracted Corrosion Control Technologies to provide cathodic protection analysis; Flowmore Services to provide pipe cleaning services; PICA Corp. to provide the SeeSnake; and Grunau Co. to provide civil work.

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Access to the pipeline was established at two locations: A “Launch” on the treatment plant; and a “Receive” located 2,928 ft away in an open field. At both locations Grunau cut into the 12-in. pipe and installed additional piping to launch and receive Flowmore’s cleaning equipment and PICA’s SeeSnake. The cleaning was successfully completed in October 2012 and PICA was mobilized by early November.

PICA crews began work on Nov. 12 by completing the pre-requisite safety training and familiarizing themselves with the pipeline’s environment. This initiation process involved walking above the pipeline and establishing suitable Above Ground Market (AGM) locations. The AGMs use an electromagnetic sensor to monitor the passage of the SeeSnake tool as it travels underground. These locations prove useful in case any repairs are required as a result of the inspection information. PICA technicians also used that afternoon to perform calibration exercises. When Grunau installed the receive piping, it was able to extract a 12-ft pipe that was used for calibration of the SeeSnake tool. Five machined defects were created at varying depths: 100 percent, 80 percent, 60 percent, 40 percent and 20 percent. Several RFT surveys were conducted on this pipe to determine the optimal operating frequency for the in-line inspection. The resulting data quality was excellent and PICA is able to report wall losses with normal confidence. In the absence of a calibration pipe, PICA is still able to use the in-situ pipe to perform a calibration; however this may slightly affect the accuracy of reported data by 5 to 10 percent.

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The schedule for Nov. 13 included a morning gauge run by PICA to prove the SeeSnake tool could safely pass through the pipe; followed by an afternoon run of the SeeSnake tool. PICA prepared all the necessary tools the evening before in anticipation of the day of inspection.

The morning of Nov. 13 was moderately cool for the time of year, sunshine and a slight breeze off Lake Michigan. Crews mobilized to site at 6:30 a.m. to begin preparing the pipeline. In order to propel the gauge pig and SeeSnake through the pipeline, Donohue and Associates was responsible for redirecting the flow of adjacent pipelines. Concurrently, Grunau prepared the launch and receive piping and PICA put the finishing touches on their gauge pig. The composition of the gauge pig is such that it mimics the SeeSnake’s travel through the pipeline. If the gauge pig encounters any obstruction in the pipeline, it will record that event. As a result of the cleaning process provided by Flowmore, the pipeline was without obstruction and the PICA gauge pig traveled the line without incident. Also encouraging was the fact that the gauge pig arrived at the receive location precisely on schedule according to the flow rates begin pumped into the line. Pumping between 300 to 400 gpm, the gauge pig traveled through the line in 50 minutes.

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By the afternoon, the crews prepared to launch the SeeSnake through the force main. PICA technicians turned the tool on and communicated to it via Bluetooth to ensure its proper operation. All of the diagnostics checked out and it was time to start. The SeeSnake is approximately 11 ft in length consisting of many modules. Along with battery and electronics modules the tool uses an exciter-detector setup to measure the pipe wall thickness. To slightly simplify the technology: the exciter module energizes an electromagnetic field and the detector module measures changes in the field as it passes through the pipe wall. Any changes in the metallic wall thickness will affect the travel of the wave. This allows the SeeSnake to precisely measure the pipe wall thickness 360 degrees around the circumference and less than every .5 in. in the axial direction. This provides a comprehensive look at the true integrity of the pipe. All of this technology is self-contained on the SeeSnake.

Grunau used a backhoe to lower the tool into the launch-side excavation pit and subsequently into the launch piping. The piping was bolted up, secured and pressurized. The parties calculated the optimal flow rates for the inspection as approximately 80 gpm. After four minutes, the first AGM recorded the tool passing beneath and the inspection was off and running. The team tracked the tool through the evening and until it reached the receive pit at 7:35 p.m. Flowrates were raised and the tool entered the receive piping where it was isolated from the main line and removed. The pipeline was reinstated to its normal operations and PICA began to download the data. The following morning the data was sent to the PICA Toronto office for analysis.
The PICA data returned some interesting artifacts about the section inspected. Most notable was the fact that there were two types of pipe installed. About halfway into the inspection (1,424 ft), the pipe wall thickness and joint length changed. The change in wall thickness was marginal and PICA was still able to successfully analyze all sections. In total, 155 pipe sections were analyzed. Neither section indicated excessive corrosion; although the launch section did see one pipe with a through-hole indication. The receive half of pipe did not see any defect indications deeper than 37 percent.

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The next step after inspection it to develop an engineering report for the utility incorporating all of the information discovered during this project. Certain sections of this pipeline were under cathodic protection (CP) and Corrosion Control Technologies has performed extensive work on the in-situ CP. PICA’s data will be used to help understand the effectiveness of this protection. The combination of these sets of research may result in future construction guidelines as well as attempting to highlight other areas in need of inspection.

Chris Garrett
is general manager at PICA Corp.

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