High-precision Non-destructive Testing Solution for Groove and Arc Surface Thickness of Automatic Plastic Fuel Pipes

The safety, reliability, and environmental performance of automotive fuel systems fundamentally depend on the stability of key connecting components-namely, the plastic fuel hoses. Serving as the "channels" for fuel transmission, the thickness of plastic fuel hoses must strictly conform to design standards. Excessively thin hoses can result in insufficient strength, making them prone to leaks under fuel pressure or vibration, thereby posing safety risks; conversely, overly thick hoses increase vehicle weight, raise manufacturing costs, and may affect compatibility during assembly. Therefore, precise inspection of the thickness and internal structure of plastic fuel hoses (such as layering) is a critical step in ensuring the quality of automotive components.

Recently, an automotive parts company entrusted us with testing samples of its plastic fuel pipes. The primary objective is to evaluate whether the product's thickness meets the design standards and to check for any delamination defects in the upper and lower layers of the tested sections.

The material of the plastic fuel hose tested this time is PP (polypropylene) plastic - although this material has excellent resistance to fuel corrosion and high and low temperatures and is a common choice for automotive fuel lines, as a non-metallic material, ultrasonic waves tend to experience energy attenuation when propagating through it, posing inherent challenges for high-precision measurements. The specific parameters of the workpiece are as follows:

1. Inspection Requirements

• Measurement Range: Covering the thickness of external curved surfaces and groove areas, while simultaneously checking for any delamination in the two-layer structure;
• Accuracy Requirement: Thickness measurement error must be ≤ ±0.03mm (far exceeding the accuracy of conventional non-metallic inspections, requiring a targeted solution);
• Inspection Method: Entirely non-destructive testing (to avoid damaging the sample structure, ensuring that the sample can be reused or retained after inspection).

2.Key Measurement Challenges

• Material Attenuation Effects: PP plastic is an ultrasonic attenuating material, and energy is easily lost during propagation, which may result in weak interface reflection signals and affect the accuracy of thickness calculations;
• Curved Surface Fitting Issues: The curvature of the outer arc surface varies greatly (diameter 10-20 mm), and conventional flat probes cannot fully conform, making coupling poor due to air gaps;
• Groove Space Limitations: The groove contact width is only 2-5 mm with a depth of 6 mm. The narrow space prevents stable probe contact, and deep grooves can create measurement blind spots, making it difficult to capture signals from the bottom interface.

In response to the characteristics of the workpiece and the challenges of inspection,we have adopted a customized solution of "adapting probes to specific sections with differentiated coupling methods" to ensure that measurement accuracy meets requirements in all areas.

1.External Curved Surface:Contact Method with Small-Diameter Probe

The core challenge of measuring external curved surfaces is the 'fit between the probe and the curved surface.' Therefore, a small-diameter specialized probe is selected, paired with high-viscosity ultrasonic couplant (to enhance the coupling effect between the probe and the workpiece surface, reducing air interference)

Effect: Measurement repeatability error ≤ ±0.025mm, meeting the ± 0.03mm accuracy requirement. It is also easy to operate, with single-point measurements taking only 3-5 seconds.

2. Grooved Area:Immersion Probe Measurement 

Due to the limited space in the groove area, which easily creates blind spots, a "water-immersed focused transducer" array is employed to fundamentally address coupling and blind spot issues. This method precisely focuses ultrasonic energy on the target area of the groove, avoiding interference from the groove walls. If delamination exists, an additional reflection peak at the "delamination interface" will appear, allowing intuitive defect assessment.

Effect: The delamination detection accuracy reaches 100%, effectively identifying internal structural defects.

For this inspection, the YUSHI PM Gen3 ultrasonic thickness gauge was selected. Its multi-mode adaptability and anti-interference design are the core supports for ensuring measurement accuracy:

• Multi-measurement mode switching: It can flexibly switch between "contact" and "immersion" modes, allowing the inspection of external curved surfaces and grooves without changing the instrument, thereby enhancing operational efficiency;
• The instrument features dynamic gain adjustment, which can automatically compensate for energy loss to ensure that weak reflected signals are accurately captured;
• Extensive scenario adaptability: In addition to automotive plastic fuel pipes, it can also be extended to thickness measurements of plastic pipelines, composite material components, non-metallic containers, and other scenarios, providing an integrated nondestructive testing solution for industries such as automotive, chemical, and home appliances.