Non destructive testing plan for metal pipelines

Pipelines are widely used in industrial production, not only as channels for conveying media, but also as an important means of safety protection. In order to ensure the safe operation of pipelines, non-destructive testing technology plays an important role in the design, manufacturing, installation, and maintenance stages of pipelines. This article will introduce a non-destructive testing scheme for pipelines and analyze the ultrasonic testing technology used in it.

Principles of non-destructive testing for metal pipelines

In metal pipelines, due to the flow of the medium, eddy currents are generated in the pipeline, resulting in sound flow, which leads to differences in acoustic impedance on the surface of the inner wall of the pipeline, resulting in varying degrees of attenuation of sound waves. Meanwhile, due to factors such as pipeline wall thickness and material type, there may be different types and quantities of defects in the pipeline, including cracks, incomplete welding, incomplete fusion, etc. Therefore, in the non-destructive testing scheme of pipelines, ultrasonic testing technology is used to locate and quantify defects. In metal pipelines, common types of defects include cracks, incomplete penetration, incomplete fusion, and leakage. Among them, cracks are one of the most common and easily detected defects. When using ultrasonic testing technology to detect cracks, two main methods are used: time difference method and echo method.

Instruments and equipment

• 1. Ultrasonic detector: portable, using A/B dual probes, capable of simultaneously detecting pipes of different diameters.
• 2. Data acquisition instrument: portable, connected to the upper computer through RS232 interface, capable of data acquisition and processing.
• 3. Signal analysis software: It can analyze and process the collected signals to obtain detection results.

Probe
At present, the commonly used ultrasonic testing instruments are ultrasonic probes, mainly used to detect defects in workpieces, including cracks, pores, inclusions, shrinkage cavities, etc. Due to the significant differences in acoustic impedance in metal pipelines, using different types of probes can improve detection accuracy and efficiency to a certain extent. The ultrasonic flaw detector used in this article adopts a fully digital multi-channel ultrasonic flaw detector, which not only can emit ultrasonic waves, but also has automatic gain control function and multiple automatic functions. In addition, the instrument has a high signal-to-noise ratio and can accurately locate the detection area.

Non destructive testing methods for metal pipelines

According to engineering requirements, the pipeline needs to undergo wall thickness measurement and weld quality inspection. Determine the location and type of defects by scanning the surface and near surface defects of the pipeline. Use ultrasonic technology to detect internal defects in metal pipelines. After determining the wall thickness of the pipeline, X-ray digital imaging technology is used to image the welds inside the pipeline, and the internal state of the pipeline is determined based on the detection results.

Test report

In the report, the following content needs to be listed:

• 1. Model of ultrasonic probe;
• 2. Operating frequency range;
• 3. Working voltage (rated voltage);
• 4. Probe size;
• 5. Instrument performance and system introduction.

For low alloy steel pipes, the probe model is 2A12T or 3A12T, the frequency range is 15kHz to 75kHz, and the detection depth range is 0.3mm-2mm.
For ultra-high and ultra-thick wall steel pipes, the probe model is 5A12T or 6A12T.