Many sections of piping were previously constructed or are operated in ways that do not allow the use of inline inspection (ILI) tools of a traditional design. For more than 10 years, Diakont has focused on the development and deployment of tooling to support the inspection of these pipeline sections that were previously considered “unpiggable.”
The approach to inspecting these pipelines is through the use of tethered, robotic, crawler-type tools that use the non-contact electro-magnetic acoustic transducer (EMAT) method of ultrasonic inspection. Diakont tools employ an advanced form of multi-angle high-resolution EMAT UT, such that they are used as combination tools which, during a single run, detect and measure wall thickness, volumetric anomalies, and OD and ID corrosion, pitting, and cracking.
This article will present the details of a recent pipeline inspection conducted using robotic ILI tools.
Comprehensive Inspection Using Robotic ILI Tools
Diakont’s U.S.-based pipeline services group recently used robotic ILI crawlers to complete multiple inspection projects for a western natural gas pipeline operator. The project required reassessment as part of the operator’s Internal Corrosion Direct Assessment (ICDA) program. The line was deemed challenging to inspect for several reasons: the section of the pipe to be inspected was buried beneath a river crossing, therefore, it was not practical to excavate for external inspection, and the pipe had inherent geometries, such as multiple elbow fittings that disqualified the use of traditional flow-driven pigging tools. For these reasons, the pipeline inspection project necessitated the use of a robotic ILI tool.
The decision to conduct an internal inspection using a robotic tool was confirmed after the pipeline operator completed a preliminary internal visual inspection of the pipe section using a video crawler. This revealed indications of internal corrosion at a low point of the line of unknown depth or severity. As a result of these preliminary indications, the operator’s integrity engineers made the decision to conduct a comprehensive inline inspection using a robotic EMAT ILI tool. The ICDA inspection area had initially been established as only the area surrounding a sag elbow fitting, but based on the visual-only findings, the inspection area was extended to consist of the entire pipe section under the river crossing, including both the downstream and upstream sag elbows.
Tool Selection Process
The tool selection process for performing this challenging pipe section inspection was guided by the NACE SP0102 Standard Practice for Inline Inspection of Pipelines. The following primary tool characteristics were considered in the selection process:
- Performance with regard to detection, characterization and measurement of the types of anomalies pertinent to the inspection objectives.
- Operational capabilities, including the ability to traverse multiple elbow fittings and inclines, and the need to report in near real time.
- Expectation of tool reliability in consideration of the volume of experience and history of successful ILI runs.
Upon detailed review of the pipeline drawings, and establishing the inspection requirements collaboratively with the pipeline operator, the Diakont RODIS-28 robotic ILI tool was selected for the project (Figure 1). The self-propelled crawler has completed hundreds of inspection runs on piping systems which were historically considered unpiggable, including crossings, cased lines, compressor stations, tank farms and lines with vertical sections or significant diameter changes.
The semi-autonomous nature of the tool’s design makes it ideal for use in the inspection of challenging pipe sections. All operational aspects of the tool can be manipulated remotely and the resultant data is monitored in real time. This ensures that unanticipated factors do not cause total run failure. NDE (non-destructive evaluation) settings and methods can be adjusted throughout the examination to ensure inspection success in a single run.
The EMAT method of ultrasonic testing differs from the traditional piezoelectric method by the manner in which the acoustic waves are transmitted and received. Non-contact EMAT UT generates ultrasonic waves in the surface layer of the inspected material using electromagnetics. In the EMAT method, a permanent magnet creates a baseline magnetic field within both the transducer coil and the inspection object. When an alternating current is applied to the transducer coil, a shear wave is initiated at a specified angle in the inspected material. The characteristics of the waves echoed back to the EMAT sensors provide high-resolution information of the pipe’s condition.
The patented EMAT technology developed over the last decade uses a variety of frequencies and employs sophisticated signal processing, to produce high signal-to-noise ratio data. Diakont uses EMAT to perform high-accuracy inspection of materials for internal and surface defects, including detection and measurement of: OD and ID corrosion, wall thickness loss, and volumetric anomalies, as well as cracking and pitting.
EMAT UT is well-suited for use with robotic tools because no couplant or liquid product is required to be present in the line in order to conduct inspections.
Inline Inspection With EMAT
To gain access to the pipe, the operator dug a bellhole downstream of the crossing, purged the line and removed a 6-foot spool section. The RODIS-28 robotic ILI tool was launched by hand via the open pipe face and navigated upstream to the inspection area. The inspection area was established as the entire creek crossing, including the upstream and downstream sag elbows, and portions of the inclined sections on either side of the crossing.
The RODIS-28 tool was set to examine 100% of the scope at maximum resolution using 0°-incidence acoustic beams only, such that remaining wall thickness, OD and ID corrosion, and volumetric defects were detected, but not surface defects, such as pitting or stress corrosion cracking (SCC). First, the tool conducted an autoscan in the upstream direction of all the straight sections, and ring scans in the two elbow fittings. Throughout this initial scan, the Diakont NDE inspector reviewed the resultant data, monitored tool operation via telemetry and recorded the pipe’s geometric data, which was incorporated in the pipe feature list (PFL) report.
Following the initial autoscan, the operators navigated the tool back downstream, stopping at each indication and performing a detailed manual inspection using the remotely operated tool. It was at this time that anomalies were characterized and measured, and close-up ID image captures taken. Following the characterization, the tool navigated back to the launch point where the EMAT module was replaced with a laser visual measurement (VMI) camera, and the robot returned to the inspection area. The VMI camera was used to capture laser scans of the profile of the pipe ID surface at certain identified defect areas.
Following the VMI portion of the inspection, the tool navigated back to the launch point where it was manually removed from the pipe.
Inspection using the RODIS-28 tool confirmed that ID corrosion was present in the 5:00-7:00 area of the pipe, in and adjacent to the crossing’s downstream sag elbow. The NDE data indicated that some wall loss was present. The depth and area of the wall loss was shallow and wide, with a maximum depth less than 0.08 of an inch. Internal photos were captured of the ID corrosion anomalies to support the operator’s ICDA program and provide a benchmark for future inspections.
The inspection results were analyzed, and the data presented to the pipeline operator within hours of removing the tool from the pipeline. Since calculations determined that the pipeline’s failure pressure was still multiple times greater than its established maximum allowable operating pressure (MAOP), the operator’s ICDA process allowed the pipeline to be returned to service. A drip line was installed for future removal of any possible liquids at the low point, the spool piece replaced, a hydrotest conducted and the line returned to service.
In this example, the pipeline operator used results from robotic ILI to complete their reassessment obligation of an “unpiggable” pipeline section on an expedited timeframe, gain valuable and previously unknown data about the pipeline features, and validate the integrity of the line.
Robotic ILI tools with high-accuracy NDE sensors have proven through numerous inspections to be highly effective tools that supplement pipeline operators’ traditional flow-driven smart pigging activities. Robotic ILI tools are used in the portion of their pipeline systems that include sections with low flow, geometric challenges, or other parameters that make flow-driven pigging impossible or uneconomical. Robotic ILI is also valuable for use in performing detailed “remote examination” of pipe sections that cannot be excavated. As pipeline operators increase the portion of their systems which are to be inspected using ILI, the demand for this type of robotic inspection continues to grow.