What are the methods for leak detection in stainless steel heat exchangers?

The leak detection system for stainless steel heat exchangers comprises three levels: online monitoring, offline detection, and destructive testing. Online monitoring technology, based on the pressure decay method, compares the pressure gradient changes between the tube side and shell side in real time, achieving a leak rate sensitivity of up to 0.1 kPa/min. For highly toxic media, mass spectrometry is used to detect the concentration of characteristic gases in the isolation chamber or outlet, with accuracy down to the ppm level. Ultrasonic flow meters can monitor abnormal deviations in the flow rate of the media on both sides, and a heat balance model established in conjunction with temperature sensor data can identify minute internal leaks. A conductivity meter or pH meter is installed at the shell-side outlet to capture water quality changes caused by the infiltration of media from the tube side.

Offline detection methods include helium mass spectrometry leak detection (sensitivity 10^-9 Pa·m³/s), fluorescence penetrant testing (detecting cracks as small as 0.01 mm), and eddy current testing (suitable for tube wall thinning analysis). During major overhauls, a hydrostatic test is required, with the test pressure being 1.25-1.5 times the design pressure and held at that pressure for at least 30 minutes. For plate heat exchangers, each plate can be disassembled and subjected to dye penetrant testing. Destructive testing mainly involves sampling and metallographic analysis, observing crack propagation morphology using an electron microscope to determine whether the leak originates from stress corrosion or fatigue damage. Intelligent diagnostic systems are becoming increasingly common, using vibration analysis, acoustic emission technology, and machine learning algorithms to achieve early leak warning and location. All detection data should be incorporated into an integrity management system (IMS) to establish a predictive model of leak risk over time.