Explain the process of hydrostatic testing of fire suppression system cylinders and the associated acceptance criteria.

Hydrostatic testing of fire suppression system cylinders is a process used to verify the structural integrity and safety of the cylinders under pressure. It involves subjecting the cylinder to a pressure significantly higher than its normal operating pressure to detect any signs of weakness or leaks. The process begins with a visual inspection of the cylinder to check for any external damage, such as dents, corrosion, or cracks. Any cylinder with visible damage is typically rejected and not subjected to hydrostatic testing. The cylinder is then emptied of its fire suppression agent and connected to a hydrostatic test pump. The cylinder is filled with water, and the pressure is gradually increased to the test pressure, which is specified by the cylinder manufacturer and regulatory standards, such as those from the Department of Transportation (DOT) or Compressed Gas Association (CGA). The test pressure is typically 1.5 times the cylinder's service pressure. The cylinder is held at the test pressure for a specified period, typically one minute, while the cylinder is carefully monitored for any signs of leakage or deformation. The cylinder's expansion is also measured during the test. The expansion is the amount the cylinder's volume increases under pressure. Both temporary (elastic) and permanent (plastic) expansion are measured. After the test, the pressure is released, and the cylinder is inspected again for any signs of damage or deformation. The acceptance criteria for hydrostatic testing typically include the following: No visible leaks are allowed during the test. The cylinder must not exhibit any signs of permanent deformation or bulging after the test. The permanent expansion of the cylinder must not exceed a specified limit, typically 10% of the total expansion. If the cylinder passes the hydrostatic test, it is dried, re-labeled with the test date, and returned to service. If the cylinder fails the test, it must be removed from service and either destroyed or reconditioned according to applicable regulations. Hydrostatic testing is typically required every 5 or 12 years, depending on the type of cylinder and the applicable regulations. This periodic testing helps to ensure that the cylinders remain safe and reliable over their service life.