Under conditions involving high-salinity slurries, the isolation sleeves of magnetic drive pumps frequently wear down to the point of perforation. The root cause is not a single factor such as corrosion or erosion, but rather a composite failure resulting from the combined effects of abrasive wear, crystallization-induced blockage in the clearance, electrochemical corrosion, and eddy current heating. Many field sites simplistically attribute this to medium corrosion, overlooking the friction caused by crystal deposits within the rotor clearance. Failures are often progressive: localized scratches first appear on the isolation sleeve, followed by thinning, and finally a sudden perforation.

The isolation sleeve of a magnetic drive pump is sandwiched between the inner and outer magnetic rotors. During normal operation, there is a tiny annular gap between the isolation sleeve and the inner rotor, into which a small amount of medium enters to form a lubricating film. High-salt concentrated mother liquor contains a large number of suspended salt crystals. Once these particles seep into the gap, the confined space and very low fluid velocity make it difficult for them to be carried away, causing them to remain trapped between the inner wall of the isolation sleeve and the surface of the inner magnetic rotor. As the rotors rotate at high speeds, the solid particles act like countless tiny abrasives, continuously grinding and cutting against the inner wall of the isolation sleeve, causing abrasive wear that gradually thins the wall thickness of the isolation sleeve. The higher the hardness of the slurry particles and the more uniform their particle size distribution, the faster the grinding rate. When silicate gel precipitated from the plate heat exchanger enters the pump housing along with the salt crystals, the erosive effect is further amplified.

The medium within the gap remains stagnant and is continuously heated, causing slight evaporation of moisture. This makes it easier for salts to undergo supersaturated crystallization within the narrow annular gap. As crystals continuously adhere and accumulate, the effective clearance between the rotor and the isolation sleeve gradually decreases. Once the clearance narrows, the original liquid lubrication film is disrupted, leading to localized dry friction between the rotor and the isolation sleeve, and a sharp rise in temperature at the friction points. These localized high temperatures, in turn, accelerate salt crystallization, creating a vicious cycle of crystal accumulation, gap narrowing, friction-induced heating, and further crystallization. When crystal accumulation reaches a certain level, the internal magnetic rotor comes into direct contact with the isolation sleeve, causing it to be scraped and damaged within a short period. This phenomenon is particularly pronounced under operating conditions with high concentration ratios, where large amounts of mother liquor crystals precipitate after the pump has been shut down and left idle. After shutdown, the crystals settle and solidify within the clearance; the moment the pump is restarted, hard crystal blocks directly scratch the inner wall of the isolation sleeve.

During operation of the magnetic drive pump, the external magnetic field passes through the isolation sleeve. The metal isolation sleeve generates eddy current losses, resulting in continuous heat generation, with the heat concentrated in the body of the isolation sleeve. When pumping clean water or pure solutions, the flowing medium within the gap can dissipate the heat generated by eddy currents; however, when pumping high-salt slurries, the gap becomes clogged with particles and crystals, obstructing the flow of the medium and causing heat exchange and cooling to fail, resulting in a continuous rise in the temperature of the isolation sleeve itself. High temperatures not only reduce the mechanical strength of the isolation sleeve material—making it more susceptible to abrasion by particles—but also accelerate electrochemical corrosion. High-salt mother liquor has very high electrical conductivity. Corrosive ions, such as chloride ions, accumulate in scratches on the inner wall of the isolation sleeve and in crevices where scale has adhered, leading to under-scale corrosion. This causes pitting corrosion in areas that have already been thinned by abrasion. As abrasive particles continuously erode the surface, the pitting corrosion pits deepen. The combined effect of these two factors results in a wall thickness reduction rate that is far faster than that caused by corrosion or abrasion alone.

There is also impact wear caused by operational disturbances, which is often overlooked. During the low-temperature evaporation and discharge phase, the concentration of the mother liquor itself fluctuates dynamically, with crystal content varying between high and low levels. At the same time, fluctuations in the vacuum system can introduce vapor, causing intermittent cavitation in the pump. The collapse of tiny bubbles generated by cavitation creates impact loads that cause fatigue spalling of the material on the inner wall of the isolation sleeve, forming microscopic pits. These pits are more prone to trapping solid particles, becoming the starting points for abrasion and pitting corrosion. Once microscopic perforations appear in the isolation sleeve, the high-salt slurry enters the outer magnetic rotor chamber directly, corroding the outer magnetic steel. As the magnetic steel demagnetizes, the pump immediately loses torque and becomes unable to convey the material.

On-site identification of this type of failure exhibits distinct characteristics: upon disassembling the magnetic drive pump, the inner wall of the isolation sleeve reveals fine, dense, annular scratches running in the direction of rotation, with localized pitting and salt crystal deposits accumulated in the gaps. In cases of purely chemical corrosion, the scratches are less pronounced, and the damage is primarily characterized by extensive, uniform thinning. Failure locations are mostly concentrated in the middle section of the isolation sleeve—the area with the highest eddy current heating and the most severe medium stagnation.

The corresponding control and selection strategies are as follows: prioritize the use of non-conductive silicon carbide isolation sleeves to eliminate eddy current heating and reduce composite damage caused by temperature rise at its source; control the upper limit of concentrate concentration in the discharge mother liquor to avoid excessively high crystal concentrations; and ensure thorough agitation before discharge to prevent large amounts of crystals deposited at the bottom of the tank from entering the pump housing all at once; Minimize the duration that crystal-laden mother liquor remains in the magnetic drive pump chamber; promptly flush and purge the pump chamber after shutdown to prevent salt crystals from solidifying within the clearances; Install pre-filters in the piping to intercept large crystal particles and reduce the number of hard particles entering the rotor clearance; in terms of operating parameters, avoid prolonged operation of the pump at low flow rates, as insufficient cooling flow through the rotor clearance at low flow rates prevents the dissipation of eddy current heat, significantly increasing the risk of wear-induced perforation.