Gas cylinder hydrostatic testing or hydro test is essential in gas cylinder manufacturing, periodical inspection and re-identification. It simulates a high-pressure environment by applying a certain pressure of water into the gas cylinder to verify whether the structural integrity and tightness of the gas cylinder meet the design requirements, thus ensuring the safety of the gas cylinder during daily use. Normally, the gas cylinder hydrostatic test includes three test methods: gas cylinder pressure strength test, direct expansion method gas cylinder volumetric deformation test, and water jacket method gas cylinder expansion test.
Gas Cylinder Pressure Test and Burst Test
The gas cylinder pressure strength test uses water as the test medium to pressurize a gas cylinders to 1.5 times its working pressure, and maintain the pressure for a period of time. Meanwhile, observe whether the gas cylinder has pressure drop, leakage, deformation or rupture, thus verifying the material strength and structural integrality of the gas cylinder.
Normally, gas cylinder pressure burst test comes after gas cylinder strength testing completed. And the gas cylinder burst pressure test aims to detect the ultimate pressure that the gas cylinder can withstand. Specifically, keep on pressurizing a gas cylinder until it cracks. At this time, the pressure that causes the gas cylinder to crack is the gas cylinder’s burst pressure.
- Test purpose: It can only assess the material strength and structural integrity of a gas cylinder.
- Features: simple operation, but may not accurately reflect the slight damage of the gas cylinder, and cannot assess the deformation of the cylinder body.
- Test object: only applicable to welded cylinders, namely low-pressure gas cylinders, such as LPG tanks, fire extinguisher cylinders, refrigerant tanks, butane tanks.
- Test equipment: Manual or automatic gas cylinder hydraulic burst pressure test machine.
Direct Expansion Method Gas Cylinder Expansion Deformation Test
This is an internal measurement method. It performs a hydrostatic test on the gas cylinder while measuring its volumetric deformation rate from the inside of the gas cylinder.That is, directly pressurize the cylinder with water of a given pressure, and detect the gas cylinder deformation rate by measuring the amount of water entering the cylinder during pressurization and the amount of water returned after depressurization, so as to judge whether the gas cylinder is qualified and can continue to be used.
- Test purpose: Detect gas cylinder deformation rate to determine whether the gas cylinder can continue to be used.
- Features: Test process is affected by environmental factors, so there will be a certain test deviation. Many countries have phased out this test method.
- Test object: Specially designed for high-pressure gas cylinders.
Water Jacket Method Gas Cylinder Hydrostatic Expansion Test
This is an advanced external measurement method for gas cylinder volumetric expansion deformation test. First of all, aill water in a gas cylinder and place it in water-jacket filled with water. Then pressurize the gas cylinder in two stages: pressurize cylinder to its working pressure, then pressurize the cylinder to 1.5 times its working pressure, and then maintain the pressure. During pressure holding period, gas cylinder will expand due to internal pressure, thus squeezing some water in the water jacket to a measuring cup. After pressure relief, the cylinder will restore partially, so some water in the measuring cup will return to the water jacket. The remaining water in measuring cup is the residual volumetric deformation of gas cylinder. In this way, we can easily calculate the gas cylinder’s volume deformation rate. Generally speaking, if the deformation rate of a gas cylinder exceeds 10%, there will be great danger in continuing to use the gas cylinder, so it must be scrapped.
- Test purpose: Detect gas cylinder deformation rate, thus determining whether the gas cylinder can continue to serve.
- Features: It eliminates the influence of environmental factors on the testing process and accurately reflects the deformation of the gas cylinder.
- Test object: Specially designed for high-pressure gas cylinders.
- Test equipment: Water Jacket Gas Cylinder Hydrostatic Test Machine.
The above three test methods all use liquid as the test medium to perform hydrostatic pressure tests on gas cylinders. In addition, there is a gas cylinder tightness test, which uses air or nitrogen as the test medium to check gas cylinder leak.
