The gas cylinder hydro test is a crucial gas cylinder testing procedure, ensuring the qualification of the gas cylinder and its safety in daily use. Gas cylinders, as pressure vessels that carry compressed or liquefied gases, come in many types. Based on their working pressure rating, gas cylinders can be divided into low-pressure gas cylinders and high-pressure gas cylinders. Based on their materials and structure, they can be divided into welded gas cylinders and seamless gas cylinders. Different types of gas cylinders require different gas cylinder hydro test methods.
Gas Cylinder Hydraulic Burst Test
The gas cylinder hydraulic burst test aims to verify the material strength and structural integrity of the gas cylinder body. It requires a gas cylinder hydraulic burst test machine, and the testing process consists of two stages.
The first stage is the gas cylinder hydraulic test. Firstly set a testing pressure on the machine, typically 1.5 times the cylinder’s working pressure. Then start the machine to pressurize the gas cylinder to the testing pressure and then maintain the pressure. During the pressure holding period, if the gas cylinder doesn’t crack and its internal pressure drop is within your allowable range, it proves that the gas cylinder has a safety margin for normal use and is qualified.
The second stage is the gas cylinder burst test to detect the cylinder’s burst pressure, which is the ultimate pressure that the cylinder body can withstand. Use the machine to pressurize the gas cylinder until it cracks. The pressure that causes the cylinder body to crack is the gas cylinder’s burst pressure.
The gas cylinder hydraulic burst test is simple to operate and applicable to all types of gas cylinders, yet it cannot accurately reveal minor damage to the cylinder. Therefore, it is more suitable for low-pressure gas cylinders, namely welded gas cylinders, such as LPG tanks, refrigerant tanks and FM200 extinguisher cylinders.
Water Jacket Method Gas Cylinder Hydro Test
The water jacket method gas cylinder hydrostatic test aims to perform gas cylinder volumetric expansion test, thereby detecting its volume expansion rate and determining whether the cylinder is qualified. And the gas cylinder water jacket test requires a gas cylinder hydrostatic test machine with a water jacket filled with water.
First, fill your gas cylinder with water, then place it in the water jacket and seal the water jacket. Now start the machine to pressurize the gas cylinder in two stages. The first stage is to pressurize the gas cylinder to its nominal working pressure and maintain the pressure for a while, normally 1 mintute at least. And the second stage is to pressurize the gas cylinder to 1.5 times its nominal working pressure and the maintain the pressure again. During the pressure holding period, the gas cylinder expands due to internal pressure, forcing some water from the water jacket into the measuring cup. After pressure relief, the cylinder partially returns to its original shape, and some water in the measuring cup flows back into the water jacket. The amount of water remaining in the measuring cup is the residual volume deformation of the gas cylinder. The machine automatically calculates the cylinder’s deformation rate to determine its qualification. Generally speaking, if a gas cylinder’s deformation rate exceeds 10%, the gas cylinder can’t serve any longer.
The water jacket method eliminates the influence of environmental factors on the testing process, thus accurately reflecting the deformation of the gas cylinder. Therefore, the test results are more comprehensive and accurate. It is important to note that this method is specifically designed for high-pressure cylinders, namely seamless gas cylinders, such as compressed gas cylinders, breathing tanks and Co2 fire extinguishers.
Direct Expansion Method Gas Cylinder Hydrostatic Test
The direct expansion method as cylinder hydrostatic testing has the same test objective and test method as the water jacketed method described above. However, it cancels the water jacket, thus environmental factors significantly interfere with the testing process, leading to poor test accuracy. Therefore, this method was phased out by policies and regulations many years ago, and we will not elaborate on the testing procedures here.
Which Gas Cylinder Hydro Test Method is Suitable for Me?
The purpose of the water jacket method gas cylinder testing is to evaluate the deformation rate of a gas cylinder, thus determining whether the gas cylinder can serve refilling gas. It is only applicable to high-pressure gas cylinders, namely seamless gas cylinders. Furthermore, it is suitable for old gas cylinders that have been used for a period of time. The purpose of the gas cylinder hydraulic burst test is to verify the material strength of a gas cylinder, and it is applicable to all gas cylinders, regardless of whether they are new or old.
Frequently Asked Questions
Why use water as the test medium in gas cylinder pressure testing?
Both water and gas can be used as testing media in gas cylinder testing. Water’s incompressibility allows for a smooth release of energy without generating shock waves, posing a very low risk. In contrast, the compressibility of gas causes the accumulated energy to be released instantaneously, potentially generating destructive shock waves. Therefore, from a safety perspective, using water as the test medium is much safer than using gas. Only the low-pressure test, such as gas cylinder sealing test, namely gas cylinder leaking test, utilizes gas as the test medium.
Why pressurize gas cylinder in two stages during gas cylinder hydro test?
In gas cylinder hydrostatic testing, we need to pressurize gas cylinder in two stages. Firstly, pressurize the cylinder to its working pressure, and then pressurize the gas cylinder to 1.5 times its working pressure. The purpose of this is to avoid pressurizing too quickly, which could lead to localized stress concentration inside the gas cylinder, and prevent the detection of potential defects, thus affecting the accuracy of the test results.
How to distinguish between low-pressure and high-pressure gas cylinders?
Low-pressure gas cylinders refer to cylinders with a nominal working pressure less than 8MPa, typically referring to welded gas cylinders. Common examples include LPG cylinders, butane tanks, propane tanks, FM200 cylinders, DCP extinguisher cylinders. High-pressure cylinders refer to cylinders with a nominal working pressure higher than or equal to 8MPa, typically referring to seamless gas cylinders. Various compressed gas cylinders, SCBA tanks, Scuba tanks, Co2 extinguishers are high-pressure gas cylinders.
What is the gas cylinder hydrostatic test interval?
Oxygen cylinder hydrostatic test interval is 1 year. LPG cylinder hydrostatic test interval is 3 years. The hydrostatic test interval for hydrogen cylinders, Co2 cylinders, nitrogen cylinders and acetylene cylinders is 5 years. Of course, different countries may have different regulations.
