Evident LogoOlympus Logo
Resources
Application Notes
Back to Resources

Thickness Measurement of Automobile Fuel Tanks


Application: Measurement of individual layers and total thickness in multilayer plastic automobile fuel tanks.

Background: Most contemporary automobile fuel tanks are fabricated with a multilayer plastic construction, typically made of two structural layers of high density polyethylene (HDPE) surrounding a thin gas barrier layer made of ethylene vinyl alcohol (EVOH). The purpose of the barrier layer is to prevent the slow leakage of gasoline vapor through the polyethylene wall. The HDPE structural layers are typically in the thickness range 0.1 in. to 0.2 in. (2.5 to 5 mm), and the EVOH barrier layer is typically 0.004 in. to 0.012 in. (0.1 to 0.3 mm). Tank manufacturers need to measure both the thickness and the depth of the barrier layer.

Equipment: The Model 38DL PLUS ultrasonic thickness gage with the Multi-Measurement software option is recommended for simultaneous measurement of individual layers and total tank thickness in this application. With this software, the 38DL PLUS gage is capable of using separately programmed setups (including sound velocity, gain, and blanking settings) for each layer being measured to optimize performance. In this test, the gage is most often used with an M2017-RM (20 MHz) delay line transducer. Contact Olympus for gage setup assistance.

Typical Procedure: The waveforms below show measurements of structural and barrier layers in a typical automobile fuel tank using appropriate setups. The gage's frequency-based barrier measurement mode is used to read the barrier layer whenever its thickness is less than approximately 0.010 in. (0.25 mm). Barrier depth is measured with a conventional Mode 2 setup, and the thickness of the inner polyethylene layer is also measured in Mode 2. Thick barrier layers, greater than approximately 0.010 in. (0.25 mm) may also be measured in Mode 2. Note that because of low pass filtering effects in the outer polyethylene wall, the minimum measurable barrier thickness will usually be approximately 0.004 in. (0.100 mm).

The reflection ratio at the boundary between any two materials is determined by the relative acoustic impedances of those materials. Because virgin and regrind material have essentially identical acoustic impedances, it is not possible to separately measure regrind layers. Also, adhesive layers adjacent to barrier layers are generally too thin and/or too closely impedance matched to measure with ultrasonic techniques and cannot be resolved.


outer polyethylene layer


barrier layer (frequency domain measurement)


inner polyethylene layer

As with any ultrasonic thickness measurement, accuracy is dependent on proper sound velocity calibration. Velocity calibration must be performed for each material being measured, on samples of known thickness.


 

Olympus IMS

ProductsUsedApplications

The 72DL PLUS™ advanced ultrasonic thickness gauge delivers precision thickness measurements at high speed in a portable, easy-to-use device. Compatible with single element transducers up to 125 MHz, this innovative instrument is ideally suited to measure the thickness of ultra-thin materials, including multilayer paint, coatings, and plastic. It can simultaneously display the thickness of up to 6 layers.

Zaawansowany grubościomierz ultradźwiękowy 45MG dostępny jest ze standardowymi funkcjami pomiarowymi oraz z opcjami oprogramowania. Ten unikalny przyrząd jest kompatybilny z całą gamą głowic jedno- i dwuprzetwornikowych do pomiaru grubości firmy Olympus.
Wszechstronnego grubościomierza 38DL PLUS™ można używać z głowicami dwuprzetwornikowymi do wykonywania pomiarów skorodowanych rur oraz z głowicami jednoprzetwornikowymi do wykonywania bardzo precyzyjnych pomiarów grubości cienkich lub wielowarstwowych materiałów.
Grubościomierz z czujnikiem hallotronowym Magna-Mike™ jest wyposażony w sondę magnetyczną umożliwiającą wykonywanie dokładnych pomiarów materiałów nieżelaznych i cienkich, takich jak butelki z tworzywa sztucznego.
Sorry, this page is not available in your country
Let us know what you're looking for by filling out the form below.
Sorry, this page is not available in your country