PIPELINE IMAGING TECHNIQUES

Erosion in underground pipe systems can be caused by aging, damage, overloading, misuse, poor management, and neglect. If the wastewater system is damaged, infiltration (liquid movement inward) occurs. The system’s capacity and treatment capability decrease, hydraulic load increases, and naturally, costs for operations and maintenance rise. The evaluation and inspection techniques for infrastructure systems are varied, with their own advantages and obstacles.

Table: Techniques Used in Pipeline Evaluation

Rehabilitation of an infrastructure system is performed after collecting the following data:

• Pipe material type,
• Service type (e.g., wastewater, sewer, raw water),
• Information level (field, internal inspection knowledge) (plastic, iron, steel, etc.).

Visualization Methods for Infrastructure Systems:

1. Statistical Observation and Condition Assessment
   This method covers a range of techniques from dry air flow analysis to modern computer models. For wastewater leakage detection, certain techniques require a broader perspective. The data collected on flow can also help identify high-flow junctions using rainfall hydrographs. Seasonal flow predictions are also considered. The disadvantages of these techniques are the cost and time involved. Despite these drawbacks, they provide a good starting point for identifying problems and areas of concern.
2. Flow Imaging Systems
   Flow imagers (or meters) are useful as part of statistical model use but have limited accuracy due to changes in pipe size between manholes. The data gathered on water usage and wastewater discharges is usually statistical and may not be accurate enough for small-scale studies. When strategically placed, monitors can provide high-accuracy results.
3. Dye Test
   The dye dilution test, introduced in the 1960s, measures the dilution rate of a fluorescent dye added to the system. It is used where leakage into the channel is suspected. Additionally, recent developments allow for measuring the amount of leakage by placing a flow monitor at the modeling point.
4. Closed-Circuit Television System (CCTV – SSET)
   The use of color cameras, equipment miniaturization, low-light cameras, and the ability for cameras to tilt and rotate have made in-pipe imaging feasible over the past 20 years. This system is especially useful for examining leaks into channels but is visually limited for detecting leaks outside the channel. The limitations of CCTV can be addressed with a sonar system. The system records data in DVD format and is now widely used for detailed wastewater assessments.
5. Sonar
   Sonar is used to determine the pipe wall and surrounding soil profile. The results are often open to interpretation and require high operator experience. Sonar also indicates underwater flow regimes, making it useful for detecting leaks in overloaded pipes.
6. Ground Penetrating Radar (GPR)
   GPR operates by sending electromagnetic pulses into the ground. These pulses travel and reflect off interfaces between different materials. The time taken for reflections is measured to determine the depth and area of the target. The penetration of pulses depends on the soil type. The technique has been found to be less effective in detecting leaks in plastic water transmission pipes, but multi-sensor systems have shown promise in improving its effectiveness.
7. Infrared Thermography
   This technique involves flying over the area with an aircraft or walking with special equipment to detect leaks. While accurate results can be obtained, environmental conditions, especially rain, can interfere with its use. The method is also expensive.
8. Air Pressure Tests
   Commonly used in North America for wastewater pipe rehabilitation or replacement, air pressure testing measures leakage at joints and lateral connections. It is typically less useful for older systems due to the inability to measure air loss in old connections. However, newer robotic technologies have made it possible to apply this test to old pipes.
9. Water Tests
   Water testing provides the most accurate results for detecting both internal and external leaks, though it is time and labor-intensive and generally used as a last resort.

Infiltration (inward leakage) and exfiltration (outward leakage) are the two main issues that lead to increased pumping and treatment loads. The second major problem is the collapse of sewers. When groundwater leaks into a pipe through cracks, it increases the gap between the pipe and the surrounding soil. This weakened soil causes the ground above the pipe to collapse. Increased hydraulic capacity causes greater exfiltration and worsens the problem.

Figure: Structural Failures – Pipe cracks, misalignment at joints, and leakage (from left to right).

The Turkish Society for Infrastructure and Trenchless Technologies is committed to advancing construction methods and infrastructure systems. Through national and international collaboration, the association seeks to provide optimal solutions to manufacturers, users, and researchers alike.