When leakage occurs at the plate sealing area during on-site operation and maintenance, is shutdown for major overhaul the only option? First check whether the clamping dimension is up to standard and whether the bolts are loose. Many leakage problems can be solved by retightening. The following is a checklist of key points for routine maintenance, for on-site operation reference.
During operation, the inlet and outlet pressure difference and flow velocity should be controlled to avoid overpressure and severe temperature shocks. An increase in pressure difference usually means fouling or blockage in the channels between plates, and it should be recorded promptly and cleaning arranged. Too low a flow velocity tends to aggravate scaling, while too high a velocity may erode the edges of the sealing gaskets. It is recommended to record the pressure difference reading once per shift, and arrange an inspection when it exceeds 20% of the initial value.
Plates are commonly made of 304 or 316L stainless steel; titanium is suitable for seawater or chlorine-containing media, and Hastelloy is used for highly corrosive conditions. Sealing gaskets are often selected from nitrile rubber, EPDM rubber, or fluororubber, and must match the medium temperature and chemical compatibility. When replacing gaskets, be sure to confirm the material code to avoid mixing them up.
During disassembly and inspection, bolts should be loosened evenly in a diagonal sequence to prevent plate deformation. It is strictly forbidden to loosen one side all the way down in one go. Each loosening amount should not exceed one third of the bolt travel, and the operation should be repeated until fully loosened. During reassembly, tighten gradually and evenly in the same sequence, and refer to the value marked on the nameplate for the final clamping dimension.
If the medium needs to be drained after shutdown, wait until the equipment temperature drops close to ambient temperature before doing so, to avoid uneven shrinkage of plates or gaskets caused by rapid cooling. During restart, first increase temperature and pressure slowly; the recommended rate of temperature change should not exceed 30°C per minute.
Spare plates and gaskets should be placed flat in a cool, dry place, avoiding heavy pressure and direct sunlight. After each maintenance, record the clamping dimension, the batch of replaced parts, and changes in operating pressure difference, so as to facilitate traceability and predict the next maintenance cycle.
