High-Precision Nondestructive Testing Solution for Measuring the Thickness of Grooves and Curved Surfaces on Automotive Plastic Fuel Pipes.

High-Precision Nondestructive Testing Solution for Measuring the Thickness of Grooves and Curved Surfaces on Automotive Plastic Fuel Pipes.

The safety, reliability, and environmental performance of an automotive fuel system fundamentally depend on the stability of its key connecting component—the plastic fuel filler pipe. 

As the “channel” for fuel delivery, the plastic fuel pipe must strictly comply with design specifications in terms of wall thickness. If the thickness is too thin, the pipe may lack sufficient strength and become prone to leakage under fuel pressure or vibration, posing safety risks. Conversely, if the wall is too thick, it will increase the overall vehicle weight and manufacturing cost, and may even affect assembly compatibility. Therefore, accurately measuring the thickness and internal structure (such as multi-layer conditions) of plastic fuel pipes is a critical step in ensuring the quality of automotive components.

Recently, an automotive parts manufacturer commissioned us to conduct testing on its plastic fuel filler pipe samples. The primary objective was to evaluate whether the wall thickness meets the design specifications and to verify whether any delamination defects exist between the upper and lower layers at the inspected locations.

1. Testing Requirements

Measurement Scope:

Thickness measurement must cover the outer curved surfaces and groove areas of the plastic fuel pipe, while simultaneously detecting any potential delamination within the dual-layer structure.

Accuracy Requirement:

The allowable measurement error must be ≤ ±0.03 mm, which significantly exceeds the precision of conventional non-metallic material testing and therefore requires a specialized solution.

Testing Method:

The entire process must be nondestructive to avoid damaging the sample structure, ensuring the samples remain reusable or suitable for archival purposes after testing.

2. Key Challenges

Material Attenuation:

PP (polypropylene) is a material with high ultrasonic attenuation, which weakens signal transmission and echo reception.

Curved Surface Coupling Difficulty:

The outer arc surface of the fuel pipe has a large curvature range (diameter 10–20 mm), making it difficult for the probe to achieve consistent coupling.

Limited Space in Grooves:

The contact width of the groove area is only 2–5 mm, with a depth of 6 mm. The narrow geometry prevents stable probe placement and easily results in ultrasonic blind zones, making it difficult to capture signals from the groove bottom interface.

3. Customized Measurement Solution

In response to the characteristics of the workpiece and the associated testing challenges, we developed a customized solution based on “probe adaptation for different areas + differentiated coupling methods.” This ensures that the measurement accuracy meets the required standards across all regions of the component.

Outer Curved Surface:

Measured using a contact method combined with a small-diameter probe.

Performance (as shown below):

The measurement repeatability error is ≤ ±0.025 mm, meeting the ±0.03 mm accuracy requirement. The operation is efficient and user-friendly, with each measurement point taking only 3–5 seconds.

Groove Area:

Measured using an immersion-type probe. To fundamentally address coupling difficulties and blind zones, a focused immersion ultrasonic probe is used. This enables the ultrasonic energy to be precisely concentrated on the target area within the groove, ensuring accurate detection.

4. Instrument Selection

Instrument Used

The PM5 Gen3 Ultrasonic Thickness Gauge by Yushi Instrument was selected for this testing project. Its multi-mode adaptability and strong anti-interference design serve as the core foundation for achieving high-precision measurements.

Multi-Mode Measurement Switching:

The instrument allows seamless switching between contact and immersion modes, enabling both outer curved surface and groove inspections without replacing the device, significantly improving operational efficiency.
Additionally, the dynamic gain adjustment function automatically compensates for signal attenuation, ensuring that even weak echoes are accurately detected.

Wide Application Adaptability:

Beyond automotive plastic fuel filler pipes, the instrument can also be applied to thickness measurement of plastic pipelines, composite material components, and non-metallic containers, offering an integrated nondestructive testing solution for industries such as automotive, chemical, and home appliances.

5. Testing Conclusion

By implementing the customized solution of small-diameter probes for curved surfaces and focused immersion probes to overcome groove blind zones, combined with the technical support of the Yushi Instrument PM5 Gen3 Ultrasonic Thickness Gauge, we successfully achieved high-precision nondestructive testing of both the outer curved surfaces and groove areas of automotive PP plastic fuel filler pipes.

This solution not only addresses the measurement challenges of non-metallic components with complex geometries (curved surfaces and narrow grooves) but also provides automotive parts manufacturers with a reliable quality control method, helping them mitigate fuel system safety risks at the source and ensuring the safety and environmental performance of vehicle operation.