Stress and Temperature Effects on Ultrasonic Properties in Cross-Linked and High Density Polyethylene

[+] Author and Article Information
Don E. Bray

 Don E. Bray, Inc. College Station, Texas P. O. Box 10315, College Station, TX 77842-0315debray1@brayengr.com

John Vela1

 Don E. Bray, Inc. College Station, Texas 77842-0315

Raed S. Al-Zubi

 Poly Processing Company, 8055 South Ash Street, French Camp, CA 95231


Present address: Ruhrpumpen, Inc., La Porte, TX

J. Pressure Vessel Technol 127(3), 220-225 (Mar 15, 2005) (6 pages) doi:10.1115/1.1990214 History: Received January 31, 2005; Revised March 15, 2005

Cross-linked polyethylene is widely used in the manufacturing of rotationally molded tanks for the agriculture, petroleum, and chemical industries. These tanks are exposed to a number of environmental effects, which can lead to material degradation. Measuring ultrasonic wave speed change in the outer wall of the tank is a method that shows promise for evaluating the ultraviolet (UV) degradation effects. In order to evaluate the UV effects in the field, however, the effect of stress and temperature on the wave speed first must be established. A series of tests was performed to establish the ultrasonic properties in cross-linked as well as linear polyethylene at a range of temperatures from 6°Cto44°C (22°Fto112°F). The change is linear, as expected. For the stress tests, the velocity decreased with tension, also as expected. Tests were performed from approximately 689kPato9.6MPa(100to1400psi). Results from these tests were incorporated into the overall algorithm used for evaluating tank degradation.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

(A) Mold charging; (B) Mold rotation and heating; (C) Mold rotation and cooling; (D) Product removal (demolding).

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Figure 3

Pulse echo tests for velocity and attenuation

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Figure 4

Cross-link black sample for thermal measurements

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Figure 5

Ultrasonic probe setup

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Figure 6

Apparatus for application of tensile stress to cross-linked polyethylene samples

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Figure 7

CLB samples with strain gauge

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Figure 8

(A) Wave speed (m/s) vs temperature for CLB; (B) Wave speed (m/s) vs temperature for CLN; (C) Wave speed (m/s) vs temperature for LN; (D) Wave speed (m/s) vs temperature for LG

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Figure 9

ΔV∕V versus stress for polyethylene samples



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