Procedures for Hydrostatic Testing of Air Cylinders
Hydrostatic testing is used for initial qualification and periodic re-qualification of air cylinders. This testing method is performed according to U.S. Department of Transportation and Transport Canada regulations for the manufacture, use and transport of pressurized cylinders. Hydrostatic testing determines proper and safe cylinder performance under operating pressure, presence of degradation and presence of structural damage. Different testing methods include the water jacket method, direct expansion method, proof pressure method and the ultrasonic test method.
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Proper Function at Operating Pressure
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Proper function at operating pressure is determined by cylinder percent expansion values obtained through application of water and test pressure conditions. Cylinders with expansion values within the manufacturer set limit point will be qualified for use. Cylinders with expansion values that are not within manufacturer acceptable range will be condemned. The equation used to determine percent expansion is (Permanent Expansion/ Total Expansion) x 100 = Percent Expansion
Test Cylinder Structure Flaws
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Presence of cylinder flaws is determined through visual inspection, which applies the use of pressure or ultrasonic probes. The cylinder will be condemned if any flaws that may inhibit proper and safe cylinder operation are detected.
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Water Jacket Method
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A cylinder is filled with water and loaded into a sealed chamber known as a test jacket. The test jacket is filled with water and connected to an expansion measuring system. Test pressure is applied and held for 30 seconds to inflate the cylinder. When the pressure is released, the cylinder deflates, and total and permanent expansion values are used to calculate the percent expansion.
Direct Expansion Test Method
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A direct expansion test connection is attached to the neck of a water-filled cylinder. Additional water is pumped into the cylinder to achieve test pressure conditions. Total expansion value is determined through volume of water required to reach test pressure. The permanent expansion is determined through measurement of the water volume expelled when the pressure is released. Both values are used to calculate percent expansion.
Proof Pressure Test
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The proof pressure test is also known as modified hydrostatic testing. This method is performed as periodic maintenance or re-qualification.Test pressure is applied to the cylinder, and it is visually and manually inspected for degradation, damage and presence of leaks.
Ultrasonic Test Method
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The ultrasonic test method does not use the application of water or pressure. An ultrasonic inspection probe examines the cylinder as it rotates on a rolling rack. The probe uses ultrasonic energy to detect any flaws or degradation in the cylinder structure.
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