Small-diameter baseline inspector from IP Pipeline Technology

Authors:​​ Rita Gu, Kiki Jiang, IP Pipeline Technology, China

The commonly used traditional method for baseline inspection of newly built pipelines before production is to use an air compressor to drive the detector to run in the pipeline. Under this method, when the detector encounters bends or changes in wall thickness, it is easy to experience "gas surge" phenomenon. The phenomenon of "gas surge" refers to the sudden release caused by the accumulation of pressure in front of the resistance zone, which causes the speed of the detector to soar to over 10 meters per second. In these high-speed areas, the detection data is invalid. For baseline inspection of pipelines over 12inch, our company uses a self-propelled detector. If you are interested, please check our company's previous news. For pipelines under 12inch, self-propelled detectors are not applicable. For this situation, IP Pipeline Technology has successfully developed a small-diameter backpressure pneumatic geometric detector through long-term research and testing.

1. Design Principle​ The purely pneumatic design utilizes a cup-shaped component with a diameter smaller than the pipeline's inner diameter. In normal operation, it adopts a non-contact annular leakage mode, where the annular gap allows airflow to create a driving pressure differential between the front and rear of the inspector. This provides propulsion force while effectively mitigating speed fluctuations caused by gas bursts. Additionally, flexible steel brushes are integrated to ensure stable support. During operation, the compressible deformation characteristics of these brushes maintain smooth movement.

2. Pull Through Test Results​ Pull through tests conducted on a 8inch Aero caliper showed an operational resistance of approximately 20kg in straight pipe sections.

3. Working Mechanism​ The diameter-adaptive mechanism operates as follows:

• In standard pipe sections, Aero caliper is driven by gas pressure differentials.
• At a target speed of 5m/s, the gas-induced pressure differential balances the 20kg operational resistance, maintaining steady motion (per dynamic equilibrium equations).

4. Key Calculations​

• Pipe Cross-Sectional Area: A=πd2/4=0.33m2 (pipe inner diameter d=205mm).
• Effective Leakage Ratio: ϕ=10% (accounts for annular gap and brush clearance).
• Pressure Differential Requirement: Computational fluid dynamics (CFD) simulations determined a total leakage pressure drop coefficient of 10. To achieve the required 20kg thrust, a pressure differential ΔP=20kPa must be established.

5. Operational Parameters​

• Backpressure: 0.3MPa (operating pressure).
• Gas Flow Rate: Q=50m3/min (provided by the compressor at the launching end).
• Pipeline Length: 25km.

6. Pressure and Velocity Analysis​ As the inspector travels along the pipeline:

• Gas pressure decreases with distance.
• Flow velocity increases toward the downstream end.

The backpressure mode minimizes pressure/velocity differences between the pipeline’s start and end, stabilizing the driving differential and preventing erratic motion. This mode also allows higher pressure differentials at lower actual flow velocities, reducing speed disparities between the gas and inspector. The simulation confirms stable operation at 5m/s, with speed variations below 1.39m/s, ensuring high-quality geometric inspection in small-diameter pipelines.

This detector has been used multiple times in the newly built pipelines, and has demonstrated a highly stable operating speed in pipeline inspection, ensuring the quality of inspection data. Provide a stable and high-quality inspection solution for small-diameter newly built pipelines!