Temperature of air pocket in Type3 composite vessel during ambient hydraulic cycling test

Abstract

The purpose of this study is to improve reliability and reproducibility of ambient cycling test by properly making corrections to the test procedure. No standard for certifying high-pressure vessels such as NGV2-2007 and ISO11439 clearly specifies the pre-processing steps of the ambient cycling test. For example, special care is necessary in order not to permit air to remain in the vessel when filling it with fluid. To show the possibility that such air pocket weakens the material strength of the vessel, temperatures in a 106 L Type III composite vessel for CNG, half-filled with water, were measured and recorded during the ambient cycling test with the pressure range from 2.5 to 25.9 MPa at the frequency of 6 cycles per minute. It was found that there was a temperature difference of around 10A degrees C between the air pocket and the water, and that the upper part of the liner faced the repeated temperature change of 40A degrees C. Due to such a sharp change in temperature, No Pass that has nothing to do with the purpose of the test would occur. Therefore, it is suggested that the air pocket be completely removed.