The CNG cylinder hydrostatic test is to verify whether a CNG cylinder is qualified, thus ensuring that it can safely continue to be refilling natural gas and store the compressed natural gas. As well known, CNG cylinders are made of various materials, and their nominal working pressure is usually 20MPa. Therefore, CNG cylinders are classified as seamless gas cylinders, namely high-pressure cylinders. Therefore, we need to use water jacket method to perform CNG cylinder hydro test.
What is Water Jacket Method CNG Cylinder Hydro Test?
The water jacket method CNG cylinder hydrostatic test is also known as CNG cylinder volumetric expansion test. It is to immerse a CNG cylinder in a sealed water jacket, and pressurize it. Then measure the amount of water overflowing from the water jacket, thereby calculating the residual deformation rate of the CNG cylinder. Generally speaking, if the deformation rate of a CNG cylinder exceeds 10%, the CNG cylinder can no longer be used.
CNG Cylinder Hydro Test Procedures
A gas cylinder hydrostatic test machine with a water jacket is an essential equipment for CNG tank hydro test. It is highly recommended to use a stainless steel water jacket, as it will not produce metal shavings after long-term use, thus preventing scratches on expensive CNG cylinders.
First of all, fill clean water to your CNG cylinder and immerse it into the water jacket , then seal the water jacket with a lid. Start the hydrostatic test machine to pressurize the CNG cylinder in two stages. Firstly pressurize CNG cylinder to its nominal working pressure, then continue to pressurize the CNG cylinder to 1.5 times its nominal working pressure, and maintain the pressure. During the pressure maintaining period, the CNG cylinder will expand due to internal high pressure, so some water in the water jacket will flow to a measuring cup. After pressure relief, the CNG cylinder will partially return to its original state, therefore, some water in the measuring cup will flow back to the water jacket. The amount of water remaining in the measuring cup represents the amount of deformation of the CNG cylinder. Finally, the hydrostatic test machine will automatically calculate the deformation rate of the CNG cylinder. If the deformation rate exceeds 10%, the machine will determine the CNG cylinder unqualified.
