In selection discussions for chloride-containing media conditions, designers often ask about the applicable boundaries of brazed stainless steel heat exchangers. The following points are listed from the perspective of maintenance and precautions for selection reference.
Brazed stainless steel heat exchangers are not suitable for media with high chloride ion concentrations. During selection, chloride ion concentration and medium temperature must be assessed as combined conditions; a single indicator cannot serve as the basis for judgment. Under conditions of relatively high concentration and relatively high temperature, the risk of pitting corrosion increases significantly, and the material scheme should be adjusted in advance or the heat exchanger structure should be changed.
Under chloride-containing conditions, the pitting corrosion resistance of 316L material grade is superior to that of 304. Design and selection personnel should evaluate whether to use 316L material based on the chloride ion concentration in the medium, temperature, and operating cycle. For 304 material, the upper limit of chloride ion concentration must be checked more cautiously to avoid pitting perforation after long-term operation.
For chloride-containing media or frequent cleaning conditions, the material and cleaning scheme should be communicated with technical personnel in advance. Frequent cleaning may introduce chloride ions from cleaning agents or cause mechanical and chemical effects on brazed welds. The cleaning scheme must specify the type, concentration, temperature, and rinsing method of the cleaning agent to prevent the cleaning process from becoming a cause of pitting corrosion.
Brazed welds are key connection points of the heat exchanger. During maintenance, attention should be paid to whether there are leakage traces, surface discoloration, or sediment accumulation near the welds. Any abnormality should be recorded promptly and re-inspection arranged; operation with increased pressure should not continue before the cause is identified.
Fluctuations in inlet and outlet temperature, pressure, and flow rate should be included in daily records. When parameters deviate from design values, it is necessary to determine, in conjunction with medium conditions, whether additional stress or corrosion risk is caused to the heat exchanger. The recorded data can serve as a basis for subsequent adjustment of maintenance cycles.
