November 2009 Vol. 236 No. 11
Features
First Robotic Device To Inspect Unpiggable Gas Transmission Pipeline
Full deployment and inspection of unpiggable pipelines has been achieved with Explorer II. Explorer II is an untethered, modular, remotely controllable, self-powered inspection robot for the visual and non-destructive inspection of 6- and 8-inch natural gas tranmission and distribution system pipelines.
The heart of this system is a Remote Field Eddy Current (RFEC) sensor able to measure the pipeline’s wall thickness. In addition, two fisheye cameras at each end of the robot provide high-quality visual inspection capabilities for locating joints, tee-offs, and other pipeline configuration. The robot is launched, operated, and retrieved under live conditions and can negotiate diameter changes, bends and tees up to 90 degrees as well as inclined and vertical pieces of the pipeline network. In its first full deployment of the system, more than 2,000 feet of a pipeline were successfully inspected.
Explorer II is the result of collaboration between industry and government in the wake of the enactment of the 2002 PHMSA/DOT ruling regarding the inspection of natural gas transmission pipelines. In order to address the need to inspect pipelines not inspectable (unpiggable) using conventional technologies, NYSEARCH, the R&D organization within the Northeast Gas Association, the National Energy Technologies Laboratory (NETL) of the U.S. Department of Energy, and the PHMSA division of the U.S. Department of Transportation invested in the development of a state-of-the art system for the inspection of pipelines in the 6- to 8-inch range.
Following a competitive review of proposals from various organizations, this funding consortium selected the National Robotics Institute at Carnegie Mellon University in Pittsburgh to develop a robotic platform able to carry into a pipeline a RFEC sensor which was developed by the Southwest Research Institute in San Antonio. Following the development and extensive testing of the prototype system in the laboratory and in the field, Explorer II was deployed for its first full pre-commercial inspection of a live unpiggable transmission pipeline by Invodane Engineering, of Toronto, Ontario, Canada.
The safeguarding of the integrity of the pipeline network in the United States is primarily driven by the pipeline integrity management rule for gas transmission pipelines issued by the Office of Pipeline Safety (OPS) of the U.S. Department of Transportation (DOT) on Dec. 12, 2003. Gas transmission pipelines in High Consequence Areas (HCA), i.e. areas with substantial population in the vicinity of pipelines, need to be assessed by their operators on a periodic basis. A variety of tools may be used to carry out this assessment including inline inspection tools (pigs), hydrotesting, and direct assessment. Other technologies are allowed on the condition that they provide equivalent to the above methods’ assessment of the pipe’s condition.
The most important issue facing the industry in fulfilling its obligations under this rule is the inability of or lack of technologies able to provide inline inspection of pipelines that cannot be inspected using conventional smart pigs. The most prominent reasons that render a pipeline unpiggable are flow rates that are lower than needed to propel a pig or the presence of obstacles (such as valves, mitered bends, back-to-back in and out of plane bends) that may make the use of a pig impossible.
Figure 1: Explorer II – a modular, untethered, remotely controlled system for the live inspection of unpiggable transmission pipelines.
Explorer, shown in Figure1, consists of 11 modules organized on a symmetric design. At its two ends reside the modules carrying the fisheye cameras and lighting system. The fisheye cameras, with a 190-degree field of view, allow for the visual inspection of the pipeline and the driving of the robot. The lighting system uses high-efficiency, low-power LCDs, the intensity of which is controllable so that power consumption can be minimized when lighting is not needed. Also residing on the robot are sondes, which provide the option for the location of the robot from above ground, as well as the wireless receivers and transceivers that allow for the robot to communicate with and stream video images and data from its sensors to the operator.
Figure 2 is a view inside the pipeline from the operator’s computer. The remaining modules shown in the figure include battery modules, locomotive modules and the RFEC sensor. The locomotive modules are equipped with high-friction wheels providing sufficient traction so that the robot can travel up and down vertical segments of pipelines.
Figure 2: View inside the pipeline on the operator’s computer.
The RFEC sensor consists of an excitation coil and multiple sensors. The excitation coil generates the electric field that induces the electric currents that are detected by the sensors in the coil’s remote field. These sensors detect the electric currents and variations in the distribution are translated to wall thickness measurements and thus detections of anomalies in wall thickness due to corrosion and mechanical damage.
The modular design allows for the negotiation of bends and tees in the pipe (including that of mitered 90-degree bends). It also allows for the future addition of more modules that will enhance the capabilities of this tool, which is launched and retrieved under live conditions using a specially designed launcher. The launcher, consisting of a 10-foot-long pipe rated at 750 psig, is attached to the pipeline using a TD Williamson off-the-shelf 45-degree fitting. A sandwich valve between launcher and fitting provides the needed isolation of the launcher from the rest of the pipeline network. Figure 3 shows the launcher attached to the TDW fitting on a live 8-inch pipeline.
In order to warranty the safe operation of the system, a deployment and operational procedure is followed that is based on the absence of any contact between natural gas and air. After the launcher is installed on the TDW fitting and valve, it is purged of air through the use of a vacuum pump. The launcher is then filled with nitrogen, followed by the opening of the sandwich valve and a small valve at the top of the launcher. The high-pressure natural gas displaces the nitrogen in the launcher. Once the launcher is filled with natural gas, the robot is ready to be launched. A similar procedure is followed during robot retrieval. (See main article image at top.)
Assembly of the Explorer II prototype platform system and the RFEC modules were completed in early 2007. The platform and sensor were integrated thereafter and tested extensively in the laboratory. Successful completion of laboratory testing was followed by the field testing of the system in live pipelines. The experience gained in these deployments was used to redesign the system in 2008 and early 2009 in order to increase the system’s reliability and ruggedness.
An example of a recent deployment includes a two-day activity where Explorer II was launched in late September 2009 in Brookville, PA in an 8-inch transmission pipeline operated by National Fuel Gas Company. The pipeline operates at 140 psig and experiences low flow rates, which renders it unpiggable. Explorer II was deployed into the pipeline and inspected a total of 2,000 feet of the pipeline over two days. Preliminary analysis of the acquired data indicates a full set of data was successfully acquired.
Future Plans
Two additional deployments of Explorer II under live conditions are planned for the winter of 2009 and the spring of 2010. Full commercial inspection of pipelines will begin in mid-2010.
Acknowledgements
Explorer II would not have become a reality without the dedication, support and commitment of the members of NYSEARCH, collectively and individually. The unwavering support and commitment of Robert Smith and James Merritt of PHMSA/DOT have been critical in the development and field deployment of this technology. Our thanks also to Richard Baker of NETL/ USDOE for his support of the prototype platform development effort. Finally, special thanks to Martin Wallace and his group at the National Fuel Gas Company in Brookville, PA for their substantial and dedicated support of the field deployment of Explorer II.
Contact information: Daphne D’Zurko, Executive Director, NYSEARCH, Vice President, RD & D, Northeast Gas Association, (973) 265-1900 x214, ddzurko@northeastgas.org.
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