Robotic Inspection of “Inaccessible” Piping at Pump Station 03 in Alaska.


Diakont’s In-line piping solutions executive, Jonathan Minder, presented Tuesday at the American Petroleum Institute Inspection Summit in Galveston, Texas.

The event focused on Asset Integrity through Corrosion Management, Inspection and Engineering Technology as applicable the Petroleum Industry. His talk focused on the Robotic Inspection of unpiggable pipelines at Pump station 03 in the Trans Alaskan Pipeline (TAPS), far North of the Arctic Circle.

API inspection summit logo

2011 Crude Oil Leak

In 2011, a crude oil spill to containment at pump station 01 (PS01) led to a TAPS shut down to assess the leak. This led to a plan by Alyeska to inspect or replace all buried pipelines that could affect safe operation of TAPS. Because of their ability to inspect pipelines previously considered “unpiggable,” Diakont was selected to inspect the pipeline as PS03 using their robotic crawlers.

Project Overview

The pipeline at PS03 that required inspection presented multiple challenges. In addition to being underground, it was encased in sand-cement slurry and contained vertical sections, horizontal tees, back-to-back bends and elevation changes. Diameters included 26” and 36” steel pipelines, and the pipelines would need to be cleaned prior to inspection to remove crude oil residue.

PS03 Buried Pipe Function

Reconstructing the piping above ground would present a serious safety concern due to potential pressure surges. The underground line (relief line) connects the main line to a relief tank, which is used to absorb excess oil pressure. If a pump issue caused a pressure surge down the main pipeline, the resulting forces on the pressure-relief pipeline would be absorbed by the ground, preventing breakage and movement. In addition, keeping the underground pipeline below the relief tank keeps the pressure in the line high enough to prevent dangerous gas bubbles from effervescing out of the oil. Given the potential issues with reconstructing the pipeline above ground, the best option was to conduct In-line piping inspection.

In-Line Inspection Robotic Crawler

Diakont uses a self-propelled robotic crawler for inspecting unpiggable pipelines. It’s robust track system presses into the ID of the pipe for traction and allows it to navigate complicated pipe geometries. The robot is attached to an umbilical cable, which delivers power to the inspection tool and real-time inspection data to the NDE tech for analysis.

Each robotic crawler is capable of being equipped with multiple types of NDE sensors including Electromagnetic Acoustic Transducer (EMAT) for ultrasonic testing, Laser profilometry, and a video camera for visual inspection. Each of these were utilized in the inspection of PS03.

EMAT Ultrasonic Testing

EMAT ultrasonic testing consists of ultrasonic waves generated into the pipe wall that are then reflected back into the sensor. There is no contact with the pipe wall or couplant required, and the method can detect metal loss ≥ 0.04,” has a measurement accuracy ±0.02,” and can detect OD and ID corrosion, wall thickness, cracks, pitting, and axial slotting.

Laser Profilometry

Laser profilometry casts a laser grid onto the pipe interior, with surface variations shifting the laser position. This is a high-accuracy measurement system capable of detecting corrosion profiles, dents, and weld defects.

Tool Testing

Alyeska chose to test the robotic crawler on PS01, an out of commission station with similar configuration as PS03, before approving the tool. PS01 was characterized by 36” steel pipes, vertical sections, 90º bends, and manifolds with multiple offtakes. Diakont’s robotic crawler was able to successfully navigate all required pipe geometries, leading PHMSA to accept use of the tool for PS03 inspection.

Pre-Inspection Cleaning

To prepare for inspection, the pipeline needed to be thoroughly cleaned. This was done by flushing with hot crude, followed by diesel fuel used as a solvent within the line. Finally, a hot water high-pressure wash concluded the cleansing process. The end result yielded a pipeline interior that looked almost new.

PS03 Inspection

Diakont and Alyeska collaborated to create an inspection plan that comprised of five routes to access the piping systems of PS03. These included:

  • Suction relief line
  • Tank farm line
  • Discharge relief line 1st half
  • Discharge relief line 2nd half
  • Suction riser line

Inspection Process

The inspection plan was carried out as follows:

  1. Visual inspection to record pipeline geometry and document features
  2. Automatic EMAT run of entire length of pipe for anomaly detection
  3. Manual EMAT scans of all areas identified during automatic run with >0.04” of wall loss
  4. Laser profilometry of ID anomalies
  5. High resolution photographs of ID anomalies

Inspection Results

The inspection was completed smoothly and on schedule, and the pipe was found to be in good condition aside from two exterior dents and a gouge found in the suction relief line. Anomalies were validated against the original pipeline construction documentation, and there was no safety or integrity concern. PS03 was then returned to service immediately following inspection