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Explorer II – Wireless Self-powered Visual and NDE Robotic Inspection System for Live Gas Pipelines
Project Number

The goal of this project is to enhance the reliability and integrity of the Nation’s natural gas infrastructure through the development, construction, integration and testing of a long-range non-destructive evaluation (NDE) inspection capability in a modular robotic locomotion platform (Explorer II). The Explorer II will have an integrated inspection sensor (developed under a separate project) to provide enhanced in-situ, live, and real-time assessments of the status of a gas pipeline infrastructure. The Explorer II system will be capable of operating in 6-inch- and 8-inch-diameter, high-pressure (piggable and non-piggable) distribution and transmission mains. The system will also be enhanced to form an “extended” platform with additional drive and battery modules allowing the system the potential to carry alternative sensors that are heavier or more drag intensive than the current technology.

Explorer II (base platform) with integrated remote field eddy current inspection sensor
Explorer II (base platform) with integrated remote field eddy current inspection sensor
Explorer II with remote field eddy current inspection sensor in open position
Explorer II with remote field eddy current inspection sensor in open position



Carnegie Mellon University (CMU) - Pittsburgh, PA

Northeast Gas Association (NGA) - New York, NY

Southwest Research Institute (SRI) - San Antonio, TX


With an aging gas pipeline infrastructure, utilities face an ever-increasing need for more frequent inspections of the distribution network. At present, in the case of a leaking pipeline, the operator has to make a decision as to whether to spot or section repair a line and to reline it or replace it, based on in-situ evidentiary data (i.e., maps, historical repairs, leak surveys, corrosion data, etc.). Remote visual inspection holds promise to become the most effective method to assess internal pipe conditions. For this reason, the industry has concentrated resources to develop internal pipe inspection robots. Recognizing this need and the possibility of developing an advanced long-range, un-tethered gas main inspection system for in-situ assessment and pipe-network cataloging, CMU engaged in a study of potential configurations and technologies that could be integrated into such a robotic system. The result of this effort is Explorer, a real-time, remotely controlled, modular, visual inspection robot system for the in-situ inspection and imaging of live 6- and 8-inch diameter gas distribution systems. Using scripted routines and a combination of its onboard driving arms and steering joints, Explorer is designed to travel through straight pipe and pipe diameter reductions, as well as negotiate elbows, sharp bends, and tees. The system is sealed and purged, thus providing safe operation in natural gas environments, and is capable of negotiating wet and partially filled (i.e., water- or mud-filled) piping.

The current research builds upon a previous project in which CMU built and successfully tested the Explorer I robot. In June 2004, Explorer I was placed into a low-pressure, 8-inch gas main owned and operated by Con Edison in Mount Vernon, NY. The robot successfully inspected 2,150 feet of pipe that was originally installed in 1890. Cameras mounted on each end continually transmitted visual images to an external monitor over the wireless connection. On October 8, 2004, the robot successfully inspected a mile-long length of live natural gas distribution main in Brockport, NY.

Explorer II (base platform) train layout with module identification. “Extended” Platform to include additional drive and battery modules.
Explorer II (base platform) train layout with module identification. “Extended” Platform to include additional drive and battery modules.



Real-time inspection of live gas pipelines using advanced NDE sensors, currently not possible with traditional sensor transport methods, is a critical goal with the potential to dramatically increase the ability of industry to understand the state of their natural gas distribution systems. This technology has the potential to enhance the overall safety, reliability, and integrity of the natural gas infrastructure by providing a state-of-the-art tool for inspecting virtually all piping systems. Enhanced evaluation of piping conditions will more readily identify areas of concern, which can be corrected to minimize the chances of leak or rupture, reducing public and environmental risk and increasing the reliability of gas delivery to consumers.

Accomplishments (most recent listed first)

Initiated in October 2004, this project focused on development of design and integration concepts. Accomplishments to date include the following:

Base X-II Platform (October 2004 – September 2007)

  • Participation in preliminary robot/sensor integration team activities to define team interaction methodologies, integration parameters, and schedules.
  • Provision of initial integration parameters, including identification of available size, weight, volume, power, and communications limitations for the projected design of Explorer II. This information was used as the basis for determining common robot/sensor interfaces.
  • Completion of a preliminary design review where the development of new electronic camera system software and other sensors for high-pressure pipe were defined.
  • Implementation of preliminary pressure testing of critical components as required to finalize subsystem/system design.
  • Participation in preparation of a consensus set of integration parameters to be used by all platform and sensor developers and incorporation of integration parameters in overall platform design.
  • Completion of detailed final mechanical, electrical, and electronics design of all components, subsystems, and systems, such that detailed engineering drawings can be created and parts manufactured or purchased.
  • Presentation of a detailed review of final platform design to DOE-NETL and NGA for review and approval. Design review covered all aspects of the proposed final design.
  • Receipt of approval of final design and authorization to proceed to Phase II prototyping activities.
  • Completion of final engineering designs.
  • Completion of full prototype build.
  • Completion of software development for system control and operation.
  • Participation in a kickoff meeting for a sensor selected for initial integration (SWRI’s Eddy Current sensor).
  • Successful completion of operability and maneuvering tests with the prototype unit (with mock sensor module) in a non-pressurized pipe loop at CMU.
  • Completion of system launch testing from a 45 degree launch chamber including successful demonstration of prototype launch operability and launch sequence software functionality.
  • Completion of integration and testing of the Explorer II platform with the remote field eddy current inspection sensor.
  • Demonstration of remote launch, maneuvering, obstacle handling, pipeline inspection and retrieval of Explorer II with the integrated remote field eddy current inspection sensor in a non-live pipeline at CMU.
  • Successful completion of live pipeline demonstration of the Explorer II platform with integrated NDE sensor. The robot underwent multiple launch, obstacle handling, survey and retrieval sequences during testing of the integrated system in a live 8", 100 psig steel natural gas main belonging to National Fuels in Brookville PA during the week of September 10-14, 2007.

Extended X-II Platform (October 2007 – September 2008)

  • Completed engineering area layout and pipe network upgrade necessary for “extended” platform work.
  • Completed final design for “extended” platform hardware and system configuration.
  • Completed build of additional platform modules (steering and battery).
  • Completed design of a dummy sensor (Magnetic Flux Leakage sensor) for use in testing of the extended platform. Dummy sensor to accurately represent expected weight and drag characteristics of an MFL sensor.
  • Completed plan for software development for the “extended” platform.
  • Successfully demonstrated the operational capabilities (phusical and software) of the “extended” platform with onboard mock MFL sensor (magnetic drag equivalent to anticipated MFL sensor) in non-live pipeline.
  • Successfully modified system software and hardware to allow switching between operation modes to permit deployment of the platform with different physical configurations depending on mission.
  • Demonstrated that the platform could successfully handle the magnetic drag of an MFL sensor without excessive drain on system power or issues with “magnetic anchoring” as the system navigated obstacles
  • Provided (as part of final report) recommendations for any future development of actual MFL sensors for use on the X-II platform to assure optimum system performance.

In 2006, the Explorer technology earned one of the prestigious R&D 100 Awards from R&D Magazine. The R&D 100 Awards are presented annually to the 100 most technologically significant products introduced into the marketplace over the past year.

Current Status

All work under this project has been completed and is reportedin the final report which can be accessed from the Additional Information section below.

EXPLORER II platform modules
EXPLORER II platform modules

This project was initially awarded funding under cooperative agreement resulting from a Broad Agency Agreement solicitation. The initial award was made in September 2004.

Project Start
Project End
DOE Contribution


Performer Contribution


Contact Information

NETL - Richard Baker ( or 304-285-4714
CMU - Hagen Schempf ( or 412-268-6884)

Additional Information

Final Project Report [PDF-6.36MB]