Can the helium leak detection for refrigeration plate heat exchangers be replaced by a 24-hour airtightness test?
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JB/T8701 \"Plate Heat Exchangers for Refrigeration\" requires helium to be used for leak testing; for fully welded plate heat exchangers, the allowable leakage rate should not exceed 10-5 mbar L/s during internal leak tests, and not exceed 10-3 mbar L/s during external leak tests. 1. Is it possible to use an inert gas (such as nitrogen) to maintain pressure for 24 hours, thereby controlling the pressure drop and achieving the same level of tightness testing as that done with helium? 2. Can it be calculated using the formula: “Pressure drop during pressure holding time * volume of the hermetically sealed device / pressure holding time”? 3. The general acceptance criterion for a gas-tightness test is an average leakage rate of ≤0.2% per hour (calculated based on the absolute pressure, temperature, and holding time before and after the test). What value should this criterion be increased to in order to achieve the same level of tightness verification as that obtained using helium testing?
First, it is necessary to determine why helium leak detection is needed, as well as the principle behind it. Some cannot be replaced by airtightness; helium leak detection has much higher sensitivity
A Helium Mass Spectrometer Leak Detector is a term used in the gas industry; it is a mass spectrometer that uses helium or hydrogen as the gas for detecting leaks, with a gas analyzer being used to detect the presence of helium. Helium has low background noise, a low molecular weight and low viscosity, making it easy to pass through leaks and spread easily ； Furthermore, helium, being an inert gas from the helium group, does not corrode equipment; therefore, it is commonly used as a leak detection gas. This gas is sprayed onto the container under inspection, which is connected to a gas analyzer (set to respond only to helium). If there are leaks in the container, the analyzer will react, thereby indicating the location of the leaks and the amount of gas leaking.
Just one thing to mention regarding the factors involved in conducting a pressure-based airtightness test: it’s about how to calculate the volume deformation of the medium in the plate heat exchanger and of the container itself, which is influenced by atmospheric temperature.:)