Case studies

Robotic Crawlers Inspect Unpiggable Piping at Gas Compressor Station Pipe Systems

Using advanced robotic in-line inspection crawlers, Diakont has been successfully inspecting gas compressor station piping systems since 2004, and has assessed over 375 miles of unpiggable facility piping.  Comprised of anywhere from 2000’ to 6000’ of pipe due to substantial mechanical and thermal stresses, compressor stations are difficult to inspect. Using proven, high-accuracy inspection methods, Diakont provides in-line pipe inspection services for these facilities to uncover potential hazards, including corrosion, lack of fusion on girth welds, and metal loss.

Problem

  • Gas compressor stations had difficult to access pipes that required inspection
  • Most pipelines within the gas system were installed in the 1970’s and 1980’s and required inspection
  • The anticipated pipe flaws were difficult to inspect so high resolution sensor technology was required

Solution

  • In-line robotic crawler with bidirectional capabilities
  • Hand loaded tool easily deployed and retrieved
  • Advanced NDE EMAT technology for assessing corrosion and metal loss

Results

  • Robotic ILI crawler successfully navigated difficult compressor station pipe systems
  • NDE EMAT sensors provided high accuracy data on pipe wall condition and corrosion defects
  • Pipeline operators monitored findings within allowable operating and repaired critical anomalies before putting pipelines back into service

 

Self-Propelled Solution for Unpiggable Lines

Compressor stations have several key elements centrifugal compressors, filters and scrubbers which are all connected via intricate piping systems that are impossible to inspect using traditional “smart pigs.”  For difficult piping such as these, Diakont has developed and frequently deploys robust robotic crawlers equipped with NDE sensor technology to perform in-line inspections.

Each crawler employs three tank-like tracks—two at the bottom of the tool for primary propulsion, and a third upper track that extends out as necessary to stabilize the tool in difficult geometries such as bends and inclined or vertical pipes. As the crawler is self-propelled and bi-directional, its ability to be deployed and retrieved through the same access point for each line section to be inspected is often a crucial factor in its selection process.

High-Resolution Sensor for Precision Imaging

In addition to the challenge of accessing difficult-to-reach areas of pipeline, a secondary problem commonly posed in in-line inspection is the difficulty of actually locating and measuring metal loss or pipe wall anomalies, a common cause of pipeline failure when left undetected and unrepaired. High-resolution sensor technology is required to thoroughly and accurately assess pipe wall integrity.

 Diakont’s robotic crawlers are equipped with a suite of high-resolution NDE sensors, allowing for the selection of the right tool for the right part of each inspection job. Chief among the technologies utilized by the crawlers is the EMAT Ultrasonic Testing (UT) method. The main operating principle of EMAT testing is electromagnetic-acoustic transmission and receipt of ultrasonic shear waves (SH), with linear polarization. Diakont uses EMAT UT testing in conjunction with their robotic inspection crawlers to detect and measure the following:

  • Metal loss anomalies and remaining wall thickness
  • Internal pipe wall anomalies

Configured with a direct beam, the EMAT tranducer sends a shear wave into the pipe wall at a 90° angle.  The travels through the pipewall and reflects back to the sensor.  The sensor measures the time-of-flight of the shear wave, providing high accuracy data on the remaining metal in the pipe wall.  See Figure 1 for a diagram of this operating principle.

 

Figure 1. Diagram of Direct Beam EMAT Signal Measuring Pipe Wall Thickness

Configured with an angle beam, the EMAT transducer sends a shear wave into the test material around the circumference of the pipe wall.  The shear wave signal travels through the test material and reflects back to the sensor when it encounters any cracking in the pipe wall.  See Figure 2 for a diagram of this operating principle.

Figure 2. Diagram Angle Beam EMAT Signal Detecting Crack in Pipe Wall

Deployed via the robotic crawler, all EMAT sensor data feeds back to the inspection technicians in real time via an umbilical cable, and pipeline operators are given same-day assessment results.

Inspection Results

Over the last decade of utilizing high-resolution EMAT technology to assess pipeline integrity, Diakont has located various pipe wall anomalies which were repaired by the operators before they caused pipeline failures.  Repairing these gas pipeline anomalies instead of blindly replacing the piping systems saved customers hundreds of millions of dollars.

 

Total
(2004-2015)

Number of inspected facilities

315

Scope of ILI

In-line Visual Examination, meters

300,408

Visual Measuring Inspection, number of girth welds

36,991

EMAT combined beam, meters

267,132

   

Repaired defects per ILI results

VMI, number of girth welds

2590

EMAT-DB (corrosion/lamination etc), defects

2313

EMAT-AB (SCC), defects

558

Table 1. Natural gas facility pipelines inspection by Diakont from 2004- 2015

The following images are actual corrosion detected in natural gas facility pipelines using EMAT NDE technology.

Figure 3: Corrosion 1.6 mm Deep  - Figure 4: Corrosion 1.5 mm Deep  -  Figure 5: Corrosion 1.1 mm Deep