Measurement of individual layers and entire thickness of fuel tanks for automobiles multilayer plastic

The Challenge

Many tanks for automobiles are manufactured with a construction of multilayer plastic, typically consisting of two structural layers of high density polyethylene (HDPE) that surround a thin barrier layer. The purpose of the barrier layer is to prevent the slow loss of petrol vapor through the polyethylene wall . The structural layers of HDPE have a thickness in the range between 0.1” and 0.2” (2.5 to 5 mm), and the barrier layer EVOH is typically between about 40μ to 250μ. For manufacturers of tanks it’s necessary to measure both the thickness and the depth of the barrier layer.

The Solution

The goal is to measure the thickness of the individual layers and their total thickness. The proposed solution involves the use of an ultrasonic generator (Digital Pulser / Receiver) with cable, and PC software for management and measurement. The measurement is done manually by placing the probe in the selected points of the tank, thanks to a liquid that allows the propagation of the ultrasonic wave; and this is coupled to the surface of the tank. The signal obtained is made up of several return echoes which are reflections of each individual layer. Once you get the signal, the software developed by MaGyc identifies the echo of interest and measures the thickness. The software uses different measurement parameters for each layer so as to have a single value for each layer, thus managing to measure a large number of different layers.
This technology is not just limited to the thickness measurement of tanks, but it is also used in the on-line measurement of multilayer pipes, typically fuel hoses.

Specifications:

Wall thickness total measurable: min. 2mm – max. 8mm
EVOH barrier measurable thickness: min. 40μ – max. 250μ
Accuracy: ± 10-15μ max. as a function of the total thickness of the tank.

Project Details

TechniqueUltrasound
DATE2014
TAGSUltrasound, multilayered plastics