Many chemical batch production, laboratory reaction and wastewater treatment facilities adopt intermittent power supply modes. Heating tubes are powered on to heat materials for a period, then cut off and stand by until the next batch of processing. This repeated cycle of heating, cooling, power on and power off creates unique hot-dry, wet-hot alternating environments on titanium tube surfaces. Although titanium has excellent inherent anti-corrosion ability, long-term intermittent power operation will subtly damage the surface passivation film, change local medium concentration and accelerate aging, which gradually weakens the original corrosion protection performance of the heating tube.
Frequent temperature fluctuation is the core factor damaging the titanium passivation layer under intermittent power. When energized, the tube surface temperature rises rapidly, and the liquid near the wall partially evaporates, concentrating chloride, acid and salt ions on local areas. After power cut, the temperature drops sharply, vapor condenses back into liquid and soaks the tube wall again. Repeated expansion and contraction of the oxide protective film caused by sharp temperature swings produce tiny micro-cracks on the film surface. Corrosive ions can penetrate these cracks and contact the titanium substrate, triggering slight local pitting that would not occur under constant stable power operation. Continuous power operation maintains a balanced mild temperature field and avoids such concentrated ion enrichment.
Intermittent standby static liquid aggravates crevice corrosion risks. During the long power-off standby interval, the liquid around the heating tube remains completely static without thermal convection stirring. Sediments, reaction precipitates and organic impurities slowly settle and attach to the lower half of the titanium tube, forming a covering layer. A sealed crevice environment is generated between the dirt and tube surface. Inside this gap, chemical ingredients keep reacting, forming highly corrosive concentrated micro-solution. Under continuous power supply, thermal circulation keeps the medium flowing and prevents long-term static sediment accumulation, while intermittent power greatly extends the static soaking time and speeds up crevice corrosion development.
Internal component aging indirectly worsens surface corrosion resistance. Intermittent power brings frequent current surges when starting heating each time. The internal resistance wire bears instantaneous impact current repeatedly, leading to slow oxidation and resistance rise. Internal insulating filler also expands and contracts repeatedly with temperature cycles, gradually loosening and reducing heat conduction efficiency. This causes uneven heat distribution on the tube outer wall, with some positions running far hotter than the design standard. Overheated areas have thinner passivation films and become preferential corrosion points, forming a vicious cycle of internal aging accelerating external surface corrosion damage.
Reasonable operation optimization can mitigate the negative impact of intermittent power supply. Low-power holding mode can be enabled during short standby intervals to maintain mild medium convection and avoid complete static liquid. Extend the preheating stage when restarting heating to reduce instantaneous temperature surges on the tube surface. Regular weekly surface cleaning removes settled sediments to eliminate crevice corrosion conditions. Install multi-point liquid flow baffles to weaken local medium concentration when the equipment is idle. These simple adjustments effectively stabilize the integrity of the titanium protective film.
表格
| Passivation film micro-cracks, corrosive ion penetration | Low-power heat preservation during short standby | |
| Static medium during power-off standby | ||
| Local ion concentration under heating-evaporation cycles | High-corrosion micro-area on tube surface |
Intermittent power supply mode comprehensively weakens the long-term anti-corrosion performance of titanium heating tubes from surface film structure, medium environment and internal component aging. Recognizing these changing rules and matching targeted operation optimization plans can effectively slow down corrosion progression. This ensures titanium heating tubes maintain stable service life and anti-corrosion advantages even in discontinuous batch production systems.
