An Evaluation Study of Leak Testing Technologies for Watertight Plate Heat Exchangers : Fast and sustainable leak testing technology for high energy efficiency products

Sammanfattning: Background: One part of manufacturing a Plate Heat Exchanger (PHE) is to leak test them before delivery. Today, helium is used extensively in leak testing. How-ever, it is unsustainable to use helium in leak testing, because of its non-renewability and therefore becoming more and more expensive. Also, this technology is relatively complex. At the same, PHEs are rising in demand due to lack of energy resources in Europe. Therefore, possibilities emerged for using air based leak testing technologies in upcoming test lines and that is why an evaluation needs to be done to find the most suitable technology. Objectives: The objective of this master’s thesis is to evaluate and identify the most suitable leak testing technology for validating the watertightness requirement of 10−3 mbar·l/s at 1 bar pressure difference. There is a scientific gap in comparing how different air based leak testing technologies perform with different volumes of the test vessels. This thesis will identify the most suitable air based leak testing technology by evaluating three technologies: Pressure Decay, Differential Pressure Decay and Vacuum Decay. With the main focus on how different volumes impacts the performance of each technology. Lastly, this study aims to determine an optimal test pressure that achieves the shortest cycle time for the selected test technology. Choosing the most suitable test technologies will result in fewer production break-downs and interruptions. Additional, being able to phase out helium in leak testing. Methods: The workflow for evaluating the different leak testing technologies began with the implementation and installation of each test setup and ensuring the reliability of the gathered data. After verifying the absence of leakage in the system, a simulated leak was calibrated to match the requirement’s leak rate. Four test vessels with original volumes of 0.10, 0.45, 1.66 and 2.50 l were utilized. Various tests were then performed to answer the research questions, including measurements of leak rate at different pressures, analysis of outgassing characteristics, and determination of cycle time. Finally, by utilizing concept scoring, the most suitable leak testing technology was identified with respect to the volume. Results: The exhibited results in this thesis manifest how the different leak testing technologies perform depending on the volume. The relationship between leak rates and overpressures was obtained, which was then utilized to derive the theoretical detection time. The cycle time and accuracy were determined across various volumes. According to concept scoring, Pressure Decay was deemed the most suitable leak testing technology in terms of six different criteria.   Conclusions: All three technologies were able to determine a leak rate corresponding to the watertightness requirement. From the evaluation, Pressure Decay was the most suitable technology to use across the majority of the volumes, with an accuracy below 15%. The test cycle times were optimizable by selecting an optimum testing pressure.  Therefore, being able to replace the helium leak testing in future test lines.