The plates of diffusion-bonded plate heat exchangers are typically made of 304 or 316L stainless steel, with a design pressure of 2.5 MPa and a design temperature of -40°C to 200°C. In on-site operation and maintenance, it is recommended to use the inlet-outlet temperature difference, pressure drop, and medium flow rate as the three baseline data items for daily inspection, recording them once per shift and comparing them with the initial commissioning data. When the temperature difference narrows by more than 10% or the pressure drop increases by more than 15%, an inspection should be arranged.
Q: How should signs of blockage in the plate channels be handled? A: The channels of a diffusion-bonded plate heat exchanger are formed by hydraulically inflating two plate blanks after diffusion bonding, and the channel shape is directly related to the medium characteristics. Before cleaning, the medium side should be confirmed, and cleaning agents incompatible with the plate material should be avoided. For 304 or 316L stainless steel plates, neutral cleaning liquid may be used for circulating flushing, and the pressure should not exceed 80% of the design pressure. If the scale in the channels is relatively thick, a low-flow, long-duration circulation method is recommended to avoid impact on the plate welds from instantaneous high pressure.
Q: How can the risk of plate leakage be judged in daily operation? A: Diffusion-bonded plate heat exchangers have no rubber gasket seals; the plate periphery is a welded structure. Maintenance personnel should focus on checking the outer edge welds of the plates and the interface flanges for signs of seepage. It is recommended to wipe the outer surface of the plates with a clean cloth every month and observe whether any medium residue remains. If rust marks or wet traces are found near the welds, the heat exchange unit should be isolated promptly and a pressure test arranged.
Q: What should be noted when adjusting the medium flow rate? A: Unlike removable plate heat exchangers, which rely on rubber gaskets for sealing and require space for plate withdrawal, diffusion-bonded plate heat exchangers are compact in structure, but valves should be operated slowly when adjusting flow to avoid pressure surges. The design pressure of 2.5 MPa is the upper limit, and daily operation is recommended to be kept within 2.0 MPa. When the ambient temperature in winter is below -40°C, the medium in the plates should be drained to prevent frost heave damage to the channels.
Q: How should short-term and long-term shutdowns be handled respectively? A: For short-term shutdown (within 7 days), the medium may be kept filled and the inlet and outlet valves closed; for long-term shutdown, the medium should be drained, the channels flushed with clean water and blown dry, and blind plates installed at the interfaces. Before recommissioning, a low-pressure leak test should be carried out, and after confirming there is no leakage, the pressure should be gradually raised to the operating pressure.
