Robotic non-destructive testing: Difference between revisions

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Robotic [[non-destructive testing]] (NDT) is a method of inspection used to assess the [[structural integrity]] of petroleum, natural gas, and water installations. Crawler-based robotic tools are commonly used for in-line inspection (ILI) applications in [[pipelines]] that cannot be inspected using traditional [[Pigging#Intelligent_piggingIntelligent pigging|intelligent pigging tools]] (or unpiggable pipelines).

Robotic NDT tools can also be used for mandatory inspections in inhospitable areas (e.g., tank interiors, subsea petroleum installations) to minimize danger to human inspectors, as these tools are operated remotely by a trained technician or NDT analyst. These systems transmit data and commands via either a wire (typically called an umbilical cable or tether) or wirelessly (in the case of battery-powered tetherless crawlers).

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Pipeline conditions that may prevent or hinder a flow-driven pig inspection include:

* Some pipe fittings (e.g., small-radius [[Piping_and_plumbing_fittingPiping and plumbing fitting#Elbow|bends]], [[Piping_and_plumbing_fittingPiping and plumbing fitting#Tee|tees]], [[butterfly valves]], [[Reducer|reducersreducer]]s) may be impassable for bulky inspection pigs.

** Technicians can manually adjust robotic tool travel speed, orientation, and configuration to navigate fittings that might trap or damage a free-flowing pig.

* Product flow may not be conducive to pig travel.

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* Limited tool access may impact use of traditional tools – smart pigs require special entry and exit points (called launchers and receivers, respectively), which may be permanently or temporarily installed.

** Some crawlers can be inserted via removed fittings or cut-out spools as small as 24” in length, providing greater flexibility in launch and retrieval options – these tools do not require special fixtures.

** Some crawlers are designed to enter and exit natural gas lines via [[Hot_tappingHot tapping|hot taps]], which can be placed at pipeline operator convenience without taking the line out of service.

** Even in pipelines that could feasibly accept a traditional smart pig, the ability of crawlers to perform short inspections inside specific areas of concern is much more efficient for pipeline operators than arranging a lengthy pig run just to reach the same small area.

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=== Electromagnetic Acoustic Transducers (EMAT) – milled steel ===

Main article – [[Electromagnetic_acoustic_transducer|Electromagnetic acoustic transducerstransducer]]s

[[File:DB EMAT.jpg|thumb|A transducer uses the direct beam method to discover anomalies in a pipe wall; the pink arrows represent the ultrasonic waves.]]

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=== EMAT – girth welds ===

[[Oxy-fuel_welding_and_cuttingfuel welding and cutting|Weld]] integrity is a crucial component of pipeline safety, especially girth welds (or the circumferential welds that join each section of pipe together). However, unlike the consistent molecular structure of milled steel, welds and their [[Heat-affected_zone|heat-affected zoneszone]]s (HAZs) have an [[anisotropic]] grain structure that [[Attenuation|attenuates]] ultrasonic signals and creates wave velocity variances that are difficult for ILI tools to analyze.

One angle-beam EMAT method employs a set of nine [[Time–frequency_analysisTime–frequency analysis|frequency-time]] (FT) scans on each side of the girth weld, where each frequency corresponds to a different input wave angle.<ref name="GWS">[http://www.energy.ca.gov/publications/displayOneReport.php?pubNum=CEC-500-2015-028 In-Line Inspection Technology to Detect, Locate, and Measure Pipeline Girth Weld Defects]. California Energy Commission, 2015. Web. Accessed 1 March 2016.</ref> The following figure shows a diagram of the inspection area covered by this method, where the green area represents the propagation of [[shear waves]] in the weld and surrounding metal.

[[File:GWS diagram.jpg|center|The principle of angle-beam EMAT use in pipeline girth weld assessment.]]

[[File:GWS FTM scan.jpg|thumb|upright|The frequency-time matrix for a lateral cylindrical hole in a pipe.]]

The tool merges each set of FT scans into a single frequency-time matrix scan to display weld conditions, with anomalies color-coded by severity.<ref name="GWS" /> This method of girth weld scanning is designed to detect the following [[Welding_defectWelding defect|weld defects]]:

* Planar defects (e.g., lack of fusion, cracks)

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[[File:Pipeline video inspection - pitting corrosion.png|thumb|A high-resolution camera image of an internal corrosion pit in a pipe wall.]]

Main article – [[Pipeline_video_inspectionPipeline video inspection|video inspection]]

Robotic NDT tools employ cameras to provide technicians an optimal view of the inspection area. Some cameras provide specific views of the pipeline (e.g., straight forward, sensor contact area on the metal) to assist in controlling the tool, while other cameras are used to take high-resolution photographs of inspection findings.

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Main article – [[surface metrology]]

Laser profilometers project a shape onto the object surface. Technicians configure the laser (both [[Angle_of_incidence_Angle of incidence (optics)|angle of incidence]] and distance from the object) to ensure the shape is uniform on normal metal. Superficial anomalies (e.g., pitting corrosion, dents) distort the shape, allowing the inspection technicians to measure the anomalies using proprietary software programs. Photographs of these laser distortions provide visual evidence that improves the data analysis process and contributes to structural integrity efforts.

=== Pulsed-Eddy Current (PEC) ===

Main article – [[Eddy-current_testingcurrent testing#Pulsed_eddy_currentPulsed eddy current|Pulsed-eddy current]]

Pulsed-eddy current (PEC) tools use a probe coil to send a pulsed magnetic field into a metal object. The varying magnetic field induces eddy currents on the metal surface. The tool processes the detected eddy current signal and compares it to a reference signal set before the tool run; the material properties are eliminated to give a reading for the average wall thickness within the area covered by the magnetic field. The tool logs the signal for later analysis.<ref>Robers, M.A. and R. Scottini. [http://www.ndt.net/article/ecndt02/251/251.htm Pulsed Eddy Current in Corrosion Detection]. June 2002. Web. Accessed 2 March 2016.</ref> The following diagram illustrates the principle of a typical PEC inspection tool.

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United States federal law requires baseline inspections to establish pipeline as-built statistics and subsequent periodic inspections to monitor asset deterioration. Pipeline operators also are responsible to designate high-consequence areas (HCAs) in all pipelines, perform regular assessments to monitor pipeline conditions, and develop preventive actions and response plans.<ref>[https://www.federalregister.gov/articles/2003/12/15/03-30280/pipeline-safety-pipeline-integrity-management-in-high-consequence-areas-gas-transmission-pipelines Pipeline Safety: Pipeline Integrity Management in High Consequence Areas (Gas Transmission Pipelines)]. Research and Special Programs Administration, 2003. Web. Accessed 1 March 2016.</ref>

State regulations for inspecting pipelines vary based on the level of public safety concerns. For example, a 2010 natural gas pipeline explosion in a [[2010_San_Bruno_pipeline_explosion2010 San Bruno pipeline explosion|San Bruno]] residential neighborhood led the [[California Public Utilities Commission]] to require safety enhancement plans from California natural gas transmission operators.<ref>Ng, Deana Michelle and Sharon L. Tomkins. [https://www.socalgas.com/regulatory/documents/r-11-02-019/Amended%20PSEP-12.2.11.pdf Amended Pipeline Safety Enhancement Plan of Southern California Gas Company (U 904-G) and San Diego Gas & Electric Company (U 902-M) Pursuant to D.11-06-017, Requiring All California Natural Gas Transmission Operators to File a Natural Gas Transmission Pipeline Comprehensive Pressure Testing Implementation Plan]. December 2, 2011. Web. Accessed 9 March 2016.</ref> The safety plan included numerous pipeline replacements and in-line inspections.

=== Tethered robotic ILI crawler application examples ===

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The federal [[Pipeline and Hazardous Materials Safety Administration]] (PHMSA) does not permit use of tetherless crawlers in HCAs due to the risk of getting stuck. Excavating buried pipelines to retrieve stuck tools beneath freeway crossings, river crossings or dense urban areas would impact the community infrastructure too greatly. Natural gas and oil pipeline operators therefore rely on tethered robotic ILI crawlers to inspect unpiggable pipelines.

Williams used a tethered robotic ILI crawler to inspect an unpiggable section of the [[Transcontinental_PipelineTranscontinental Pipeline|Transco Pipeline]] in New Jersey in 2015.<ref>[http://napipelines.com/robotic-crawlers-inspect-unpiggable-gas-pipelines-urban-area/ Robotic Crawlers Inspect Unpiggable Gas Pipelines in Urban Area]. North American Oil & Gas Pipelines. September 29, 2015. Web. Accessed 9 March 2016.</ref> The pipeline system ran beneath the Hudson River; construction of a new condominium development nearby created a new HCA, requiring Williams to create an integrity management program per PHMSA regulations.

[[Alyeska Pipeline Service Company]] inspected Pump Station 3 on the [[Trans-Alaska Pipeline System]] after an oil leak was discovered in an underground oil pipeline at Pump Station 1 in 2011.<ref>DeMarban, Alex. [http://www.adn.com/article/20150705/crawling-robot-patrols-alaska-pipelines-formerly-unpiggable-pipes Crawling robot patrols Alaska pipeline’s formerly ‘unpiggable’ lines]. July 5, 2015. Web. Accessed 9 March 2016.</ref> The spill resulted in a consent agreement between Alyeska and PHMSA requiring Alyeska to remove all liquid-transport piping from its system that could not be assessed using ILI tools or a similar suitable inspection technique. Because other ILI tools could not navigate the pipeline geometry common to each of the eleven pump stations along the pipeline, Alyeska received approval to use a tethered robotic ILI crawler manufactured by Diakont to complete an inspection project at Pump Station 3. This tool allowed Alyeska to only remove a few small aboveground fittings to permit crawler entry into the piping, saving the time and expense necessary to excavate hundreds of feet of pipe (some of which was also encased in concrete vaults) to inspect by hand.

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Nuclear power plants in the United States are subject to unique integrity management mandates per the Nuclear Energy Institute (NEI) NEI 09-14, Guideline for the Management of Buried Piping Integrity.

* The [[Cooper Nuclear Station]] in Nebraska performed buried pipe inspections to comply with these industry mandates as part of a 2010 nuclear power plant license renewal. Part of the plant pipeline integrity management program included inspecting a high pressure coolant injection (HPCI) line using a tethered robotic ILI crawler manufactured by Diakont.<ref>Bremer, David. [http://nuclearplantjournal.com/uploads/digital/MA13.pdf Robotic Pipe Inspection to Meet License Renewal Commitments]. Nuclear Plant Journal. March-AprilMarch–April 2013. Web. Accessed 9 March 2016.</ref>

* The [[South Texas Project Electric Generating Station]] performed an inspection of a service water pipe in 2014 using a [[GE Hitachi Nuclear Energy]] crawler.<ref>[http://www.neimagazine.com/features/featurepipe-surveying-solution-4562648/ Pipe surveying solution]. Nuclear Engineering International Magazine. April 27, 2015. Web. Accessed 10 March 2016.</ref>

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** The inspection crew can also manipulate the tool to maximize sensor reception in areas where the tool’s normal travel path would impact readings.

[[File:Applus ROV with INCOTEST.JPG|thumb|A [[Remotely_operated_underwater_vehicleRemotely operated underwater vehicle|remotely-operated vehicle]] (ROV) manufactured and operated by Applus to inspect pipelines on sea and subsea petroleum installations using a PEC module.]]

* Many inspection areas pose significant safety hazards to human occupants that can be eliminated or greatly reduced by robotic NDT tools:

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** Tension on a tethered crawler’s cable may limit tool movement after passing too many bends in pipeline applications, or after wrapping around roof supports during tank floor inspections.

* Many self-propelled pipeline inspection tools are slower than pigs that can flow with product.

* Unlike some [[Remote_control_vehicleRemote control vehicle|remote-control vehicles]] that are commercially available for rent or sale, robotic NDT crawlers require significant training before they can be used for formal inspection.

** Regulatory requirements often specify that inspection data must be gathered, analyzed, and collated for reporting by technicians who are certified as experts in the applicable inspection technology by an independent organization (e.g., the [[American Society for Nondestructive Testing]], the [[American Society of Mechanical Engineers]]).

* Many crawlers require the inspection area to be taken out of service and cleaned before operations.

** Continuous air-quality monitoring may be necessary during operations, up to provision of a blanket of inert gas (e.g., nitrogen) if the area contains especially flammable/explosive fumes.

** Loose debris (e.g., [[ferromagnetic]] dust, [[Paraffin_waxParaffin wax|paraffin]]) or internal corrosion can impact EMAT and MFL readings.

** These services can often be performed during scheduled outages, but special shut-down may be necessary if regulatory requirements do not align with other planned service outages.

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* [http://www.astm.org/ American Society for Testing and Materials]

[[Category:Robotics]]
[[Category:Nondestructive testing]]
[[Category:Technology]]