Diakont recently inspected an unpiggable section of a pipeline that had never been accessible for a major European natural gas pipeline operator. This inspection was crucial for the integrity management program because the natural gas pipeline was buried beneath a densely-populated urban area, making pipeline safety and reliability especially important. The high-consequence area (HCA) pipeline had not previously been inspected due to the limitations of traditional in-line inspection (ILI) methods.
Traditional flow-driven smart pigs were not suitable to inspect the pipeline for several reasons; the aging pipeline was built without pig launchers or traps, the line contained sections with complex geometry, and much of the pipeline length ran beneath roads, parks, and buildings that could not be excavated in the event of a pig getting stuck.
The 24”-diameter natural gas line was buried an average of 8 feet below grade, but the line was installed with over bends and sag bends that arch over numerous sewer lines. The inspection area included seven such sewer crossings with varying bend angles. Five of the sewer crossings were comprised of crossing sections ≤ 1.0 meter in length, leading to almost back-to-back 45° bends at each of these sewer line crossings, as shown in Figure 1.
The other two sewer crossings were comprised of pipe sections ≤ 1.7 meters, leading to 20° bends that crossed the sewer lines as seen in Figure 2. Aside from the sewer crossings, the pipeline bent around additional underground infrastructure elements, including a subway, power lines, and water lines via various horizontal and vertical directional changes. Most of these directional changes were 3D forged bends built according to European standard EN 10253-2 (equivalent to the long-radius forged bends of ASME B16). These qualities led the operator to deem this section of the pipeline impossible to inspect with flow-driven smart pigs, due to the risk of getting the tool stuck, or of speed excursions causing loss of data.
The pipeline operator selected Diakont’s robotic ILI crawler tools for the inspection because of their unique ability to negotiate unpiggable pipeline geometries. Using robust track systems connected to actuators, Diakont robotic ILI tools adjust their shape against the inner diameter (ID) of the pipe wall to maintain positive traction while navigating virtually all possible geometries, including back-to-back bends, 1.5D bends, unbarred tees, and vertical sections. Each crawler is connected to a mobile inspection suite via an umbilical cable that supplies power to the tool and relays integrity data back to non-destructive examination (NDE) Inspectors in real time.The umbilical cable can also serve as a means of emergency tool retrieval in the possible event of a malfunction.
Diakont’s ILI crawlers use NDE sensors to acquire integrity data, including electromagnetic acoustic transducer (EMAT) UT, laser profilometry, and high-resolution video.EMAT UT operates on the same principles as conventional UT, but EMAT UT does not require a liquid couplant.This makes EMAT UT ideal for assessing pipe wall integrity in natural gas pipelines, where operators try to minimize the amount of moisture introduced into the lines. Aside from pipe wall thickness,Diakont’s EMAT UT technology also detects and measures SCC, cracking, pitting, and mid-wall defects.The Diakont laser profilometry NDE module creates detailed mapping of the pipeline’s inner surface as well as detecting and measuring internal surface irregularities such as pitting. And video cameras on the robotic ILI tools support navigation and anomaly characterization.
Prior to performing the inspection, Diakont inspection engineers worked collaboratively with the operator’s integrity personnel to establish inspection objectives – to measure actual pipe wall thickness and characterize any defects. After performing a site walk-through and analyzing the pipeline drawings, the team jointly developed an inspection plan for the project comprised of multiple routes.
The pipeline operator excavated bell holes on the edges of the HCA to create access points for the robotic crawlers. The inspection routes started from these convenient locations and traversed through the pipelines, beneath the city to the HCA inspection locations.
Diakont mobilized inspection teams consisting of NDE Inspectors and Technicians, who operated the ILI tools from mobile diagnostic vans parked at the bell hole locations. Diakont personnel deployed the robotic crawlers into the bell holes using gantries.
Diakont technicians hand-loaded the compact crawlers horizontally into the pipe openings – these tools require no launchers and can be inserted via spool openings as small as 22” in length. The inspection crawlers then performed their runs, driving through the pipelines capturing integrity data and relaying the data to the mobile diagnostic vans, where technicians actively controlled the robots and were ready to modify the inspection procedures in the event of a significant finding.
The pipeline operator personnel were present throughout the inspections to secure the urban worksite and observe the inspection procedure. Diakont NDE Inspectors reviewed the integrity data in real-time throughout the inspection and appraised the pipeline operator of the progress and findings daily.
Diakont completed this critical inspection within the short available pipeline clearance timeframe. The inspection identified just three potentially-anomalous areas, all with <= 20% wall loss. Various mid-wall defects were also detected; however, all findings measured well within allowable operation limits. All of the findings were captured by the pipeline operator into their Integrity management program, and will be used as baselines in future inspections. With the pipeline integrity and operational safety validated, the pipeline operator proceeded to put the pipeline back into service.