Improvement of product safety and quality in manufacturing of refrigeration plants and components.

High standards are set for the leak tightness of refrigeration products. To meet this requirement, the components must undergo rigorous testing. If these components are used under high pressure, for example in R744 systems, they must also be tested for strength. These tests are fundamentally different. Leak testing is a non-destructive test, in contrast to destructive strength testing.

At ILK Dresden, research on both testing methods was successfully conducted with the aim of combining the two processes. As a result, automated test benches were constructed. Depending on the specific testing task, the test benches are configured using modules for leak testing, strength testing, test gas recovery, measurement and control, and results management.

The combined test benches enable, for example, in CO₂ refrigeration systems, pressure strength testing followed by leak testing in compliance with all required safety measures. For the customer, this results in increased process reliability as well as savings in test gas costs (through test gas recovery) and reduced cycle times.

The developed method allows strength tests to be performed safely and in compliance with the requirements of the Pressure Equipment Directive, for example on CO₂ refrigeration systems or refrigeration systems operated with so-called high-pressure refrigerants. The pressure test is performed as a pneumatic test. The inherent risk associated with such a 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 pressure 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 parallel testing of multiple test specimens.

The combination of strength and leak testing saves test gas and time.

Test gas recovery (recovery rates > 93 percent have been achieved) leads to significant savings in test gas compared to simply overflowing from test gas cylinders and reduces the time required for handling hundreds of test gas cylinders to just a few (refillable) cylinders.

For the pressure test, the test specimen is connected to the test gas supply by the operator in a secure area (burst protection). The test gas—such as nitrogen—is then automatically introduced into the test specimen, with holding times observed. Once the test pressure is reached, a holding time is also observed before the test gas is vented from the test specimen. In parallel with the hold time at the pressure test pressure, a pressure drop test can be integrated as a preliminary test. By using a detectable test gas, such as helium, an intermediate step for manual leak detection by the tester can be introduced during the venting of the test gas. In this case, the test gas is vented only to a partial pressure. This manual test step requires a special safety concept in which access control allows entry to the test specimen. Subsequently, the test gas is completely vented. The necessary test gas is stored in a pressure accumulator. Test parameters can be recorded and archived. This test is possible both in a water bath and in secure rooms.

For economic reasons and to conserve resources, test gas recovery is recommended for large-scale test gas requirements, depending on the number and volume of test specimens. In this module, the test gas is compressed from the test specimen using a compressor system (which may consist of multiple stages) and stored in pressure-resistant storage cylinders. The storage pressure exceeds the burst test pressure. The test specimen is filled by overflowing the test gas from the storage tank. Due to the high pressure levels, a corresponding safety concept has been developed.

The design of the MSR module is complex because various test steps, including test gas recovery, must be integrated. The following subfunctions are programmed into the MSR module:

• Test specimen management: This involves identifying and assigning test specimens using barcodes. Data stored in a database for each test specimen determines the test parameters (pressure, leakage rate, etc.).
• Test sequence: The test sequence is largely automated and includes the evaluation of sensor data (pressure, leakage rate, etc.) and the control of actuators (valves, pumps, compressors). Separate test programs are stored for each test specimen type.
• Visualization: The tester can change certain parameters in the touch screen’s user interface. This screen displays the current test step and the actions to be performed by the tester (e.g., connecting or disconnecting the test specimen). Completed actions are manually confirmed on the screen.
• Access control: For safety reasons, the test area must not be entered during the strength test. Access control is managed by the MSR.
• Result evaluation: Test results (e.g., test pressure, test duration, determined leakage rates, etc.) are displayed to the tester.
• Test gas requirement: The MSR module detects whether test gas is missing from the storage tank and automatically refills it. If the refill cylinder is empty, a message appears on the user interface.
• Remote monitoring: The MSR module can be equipped with a remote monitoring system.

The modules described can be combined with one another depending on their test parameters. Various leak testing methods, each with their own specific characteristics, can be implemented. These can be combined with the strength testing, measurement and control, and results management modules. The test gas methods can also be combined with the test gas recovery module. A preliminary test (e.g., pressure drop test, ultrasonic test) can be performed prior to all test procedures. Furthermore, it is possible to conduct tests on multiple test specimens simultaneous.