Hydrostatic Pressure Testing Services
Alexander Chemical has the capabilities to manage and maintain your entire fleet of cylinders and ton containers to assure they are in compliance with current DOT regulations. We perform hydrostatic testing on a variety of sizes and configurations. In addition to pressure testing the cylinders we also perform a thorough visual inspection of the entire cylinder inside and out to ensure safety to our fillers and end-users. Our test system allows us to accurately calculate expansion measurements within minutes. We utilize calibrated cylinders for daily performance checks to assure that each time we perform the testing, we have confidence in our results. A 14” test head is utilized to provide the physical connection to the pressure vessel when testing cylinders. A test jacket is also an integral part of our testing process, which has been engineered to fit most standard industry size cylinders. When it comes to ton containers and also larger size cylinders, we perform a direct expansion test using an electronic expansion measuring system. These systems are very similar but measure different aspects.
What is a Hydrostatic Pressure Test?
Hydrostatic testing is designed to evaluate the structural integrity of a cylinder while it is under pressure. Our highly trained technicians will remove the cylinder’s valve and fill the vessel with water, pressurizing it to a level above its operating limit. The cylinder is then evaluated and measured to capture the amount of expansion. If the cylinder expands beyond acceptable limits, it must be taken out of service.
The cylinder being tested is filled with water and placed inside of a test jacket that is also filled with water. A test head is used to seal the system and also pressurize the cylinder in question. A digital scale is connected to this system and any water displaced from the system will be forced into the water basin connected to a high precision balance. The vessel is pressurized for a period of time and allowed to de-pressurize. The water level in the jacket is measured and if the level is greater it indicates that the vessel being tested has become deformed or distorted and hasn’t recovered to it’s original volume or another possibility is the pressurized cylinder has a leak that allowed the water inside to move its way into the jacket. In both cases we will see these results as failures if they don’t fall within the acceptable limits specified by the CGA standards.
All cylinders will have a DOT or ICC rating, which indicates the amount of PSI that they can hold. Most cylinders must be inspected every 3-5 years. Here are some examples of common ratings and testing periods.
DOT 3AA – A “star” will follow the most recent hydro test date.
What is Direct Expansion Testing?
This method of testing pressure vessels is usually reserved for larger containment vessels such as 1 ton or ½ ton gas cylinders. The ton containers are filled with water and the amount of water that is passed into the cylinder under pressure to achieve the specified test pressure is quantified with an expansion indicating device. When the cylinder is de-pressurized a specific amount of water is forced back into the measuring device when equilibrium is achieved, which provides the data to calculate permanent expansion. After the permanent expansion is calculated by subtracting the amount of liquid forced into the cylinder from the amount of water forced out of the cylinder after releasing pressure. Another calculation is performed to achieve the total expansion, this is done by determining the difference between the ability to compress the total volume of a liquid under pressure from the initial amount of water pushed into the ton container to reach the defined test pressure
At Alexander Chemical, we place our customers’ safety as the top priority. Contact us today to learn more about how we can help keep your employees and equipment safe with our cylinder hydrostatic testing services.