Purpose of the development
The objective of the project was to develop a safe, automated technology for the pneumatic pressure testing of CO₂ refrigeration systems, including simultaneous or immediately subsequent leak testing and the proper recovery of the test gas for reuse. In accordance with the normative requirements (Pressure Equipment Directive PED, BGI 619 Information Sheet T039, and AD 2000 Information Sheet HP 30), the pressure resistance test is to be conducted in increasing pressure stages up to 1.1 times the maximum permissible operating pressure. The leak test is performed, on the one hand, during the holding time of the strength test as an (automated) pressure drop test (coarse leak test). On the other hand, when the test pressure is reduced to the maximum permissible operating pressure, the manual fine leak test can be performed by the tester using electronic leak detectors. Formier gas (95 percent nitrogen, 5 percent hydrogen) was selected as the test gas for the assembled functional prototype, as this test gas (which is inexpensive compared to helium) allows high test pressures to be generated, the hydrogen it contains is easily detectable using standard detection technology, and the test gas is non-flammable/non-explosive. The target for test gas recovery was >90 percent. To minimize the inherent risk potential of the gas pressure test during the strength test, the development of an automatic (remote) control system was necessary. The control system should also include test logging. The developed testing technology was to be validated using a functional prototype to be constructed (test specimen volume 10 L, test pressure up to 143 bar). The process itself was to be scalable for larger test specimen volumes (up to 800 L).
Benefits and Solutions
The developed method allows strength tests to be performed safely on CO₂ refrigeration systems or refrigeration systems operated with so-called high-pressure refrigerants, in compliance with the requirements of the Pressure Equipment Directive (PED). The strength test is performed as a pneumatic test. The inherent risk associated with such a test (in the event of structural component failure during the strength test) is drastically reduced by the automated, remote-controlled process, as automation now ensures that no personnel need to be present in the danger zone (near the test specimen) during the strength test. Furthermore, the automated process allows for the objectification of the strength and (rough) leak testing. The actual data (pressures, times, leakage rates) are logged. It is possible to conduct a parallel test on multiple test specimens. The combination of strength and leak testing saves test gas and time. Test gas recovery (recovery rates of 93 percent have been achieved) leads to significant savings in test gas compared to simply venting from test gas cylinders and reduces the time required for handling hundreds of test gas cylinders to just a few (refillable) cylinders.
Target audience and target market
During the project, a combination of a safe strength test and a two-stage leak test was carried out. The result was a functional prototype that is largely ready for the market and can be scaled to accommodate various test specimen sizes. This provides a solid foundation for commercialization. Already during the project, two partners were secured who provided financial support for the development and, through their technical expertise, helped incorporate user-specific requirements into the project.
During the project, valuable insights were gained regarding the handling of high-pressure gases. This included, among other things, the relevant regulations and their application in the practical construction of the functional prototype. This knowledge can be very effectively applied when addressing research topics involving so-called high-pressure refrigerants such as CO2.
