Preliminary Conclusion: Low-power nighttime heat preservation and continuous negative pressure operation provide far better protection for heat exchange plates than breaking the vacuum and allowing the system to stand idle.

I. Breaking the Vacuum and Allowing the System to Stand Idle (The Primary Cause of Damage to Heat Exchange Plates)

A sudden drop in temperature causes concentrated precipitation of salts and silica colloids, which adhere to the plate walls.

After the vacuum is released during shutdown and heating ceases, the process fluid cools rapidly; the solubility of silica colloids drops significantly, leading to supersaturation of inorganic salts. Large amounts of microcrystals and silica gel settle and adhere to the corrugated flow channels of the plates, forming a dense scale layer. This scale layer isolates the metal from the process fluid, and the occluded gaps lead to chloride ion pitting corrosion and intergranular corrosion.

Gas-Liquid Dry-Wet Cycles Exacerbate Corrosion

When the chamber returns to atmospheric pressure, the plate sections above the liquid level are fully exposed to air. The residual concentrated salt film evaporates and dries, causing salt crystals to become lodged in the plate gaps and gasket grooves. When the unit is restarted the following day and re-wetted, the repeated alternation between dry and wet conditions causes the corrosion rate to increase exponentially.

Significant Alternating Thermal Stresses Damage Plates and Seals

When the unit is restarted the next day after complete cooling, the plates undergo rapid thermal expansion and contraction within a short period. The repeated deformation of the corrugated heat exchange plates can easily lead to micro-deformation due to stress, causing gasket fatigue and leakage. Corrosive media seeping into the gaps further erodes the plate material.

Static conditions without flushing allow scale deposits to take root and solidify

When the unit is idle with no circulating water flow, precipitated crystals are not removed by shear forces and adhere firmly to the plate surfaces. Even acid washing struggles to remove them completely, leading to continuous corrosion and thinning of the plate walls over time.

II. Low-power heat preservation and maintaining negative pressure operation (to protect the core advantages of the plates)

Constant Temperature Suppresses Supersaturated Crystallization

Maintaining the process fluid at a slightly elevated temperature keeps the solubility of silicic acid and inorganic salts high, preventing large-scale microcrystal precipitation. This reduces scale adhesion at its source and prevents under-scale corrosion.

Full Liquid Immersion Throughout, No Alternating Wet-Dry Cycles

Continuous negative pressure combined with gentle circulation ensures the plates are fully submerged in the process fluid, preventing the formation of dry salt films; A stable passivation protective film remains on the metal surface, significantly reducing the rate of chloride-induced electrochemical corrosion.

Stable temperature, minimal thermal stress

The plate temperature does not fluctuate significantly; thermal expansion and contraction are minimal. Stress on the corrugated plates remains moderate, preventing fatigue deformation and reducing the risk of corrosion in gaskets and plate welds.

Continuous flushing via gentle circulation prevents crystal deposition

Continuous low-flow circulation continuously removes small amounts of newly formed microcrystals, preventing their accumulation in dead corners of the heat exchange channels. No hard scale deposits cover the plates, ensuring the heat exchange surface remains clean at all times.

III. Additional Notes for Special Operating Conditions

If the feed solution contains high concentrations of highly corrosive chloride ions or silicate colloids: It is strictly prohibited to break the vacuum and leave the system idle overnight;

The vacuum may be broken only for short-term shutdowns lasting a few hours; for overnight or long-term idling, the system must be kept warm and under negative pressure.