Cavitation erosion mainly occurs in liquid circulation systems with high flow velocity, pressure fluctuation and gas-liquid two-phase mixing. When local liquid pressure drops below the saturated vapor pressure, numerous tiny vapor bubbles form instantly. These bubbles collapse violently the moment pressure recovers, generating high-speed microjets and intense shockwaves that continuously impact the tube surface. The passive film is stripped and the matrix suffers plastic fatigue damage, forming honeycomb pockmarked pits on the pipe wall. With prolonged operation, pits interconnect and penetrate the wall, causing medium leakage. Cavitation damage features concentrated local material loss and no obvious external corrosion sources.
1. Microscopic Cavitation Damage Mechanism
When the flowing medium passes through sudden contraction, bends or low-pressure areas, local pressure declines rapidly and liquid vaporizes to produce a large number of cavitation bubbles. Once the fluid enters a high-pressure zone, bubbles implode within microseconds. The implosion releases powerful hydraulic shock and ultra-fine liquid jets striking the metal surface. Repeated impact induces cyclic compressive and tensile stress on the substrate, leading to fatigue crack initiation beneath the material surface. The chromium oxide passive film fractures and peels off continuously. Corrosive ions in the liquid invade the cracks, coupling mechanical fatigue with electrochemical corrosion to accelerate pit expansion. Eventually, dense cavities connect to form through-wall holes and cause equipment failure.
2. Typical Positions Vulnerable to Cavitation Erosion
Inlet sections directly connected to pump outlets with drastic pressure variation;
Elbow, reducer and sudden expansion pipe sections where flow field changes abruptly;
Liquid level line of heating tubes with alternating liquid immersion and vapor phase;
Areas with poor flow uniformity and local vortex dead zones;
Tube surface near throttling valves where pressure drops sharply.
3. Main Accelerating Inducing Factors
Excessive pump lift and flow rate leading to violent pressure fluctuation;
Excessively high liquid temperature lowering saturated vapor pressure and promoting bubble generation;
A large amount of dissolved air mixed in the circulating liquid;
Rough tube surface and welding defects serving as bubble nucleation sites;
Improper pipeline layout with frequent abrupt changes in pipe diameter and flow direction.
4. Multi-dimensional Whole-Link Prevention Technical Measures
① Optimize pipeline structure to smooth flow transition
Use gradual reducing and arc transition elbows instead of sharp right-angle bends to eliminate sudden pressure drop.
② Adjust operating parameters to suppress bubble formation
Reasonably control medium temperature and pump operating frequency to avoid pressure falling below vaporization pressure.
③ Install exhaust devices to remove dissolved gas
Set up automatic exhaust valves at system high points to discharge accumulated air and reduce bubble nucleation sources.
④ Improve surface finish of heating tubes
Implement electropolishing to reduce surface micro-pits and restrain initial cavitation bubble generation.
⑤ Strengthen local surface wear resistance
Perform laser cladding or nitriding treatment on high-risk cavitation areas to enhance anti-impact fatigue performance.
5. Prevention Effect Comparison Table
表格
| Pipeline & Operation Mode | Cavitation Erosion Risk | Recommended Optimization Plan |
|---|---|---|
| Sharp pipeline transition + high temperature high flow | Fast honeycomb pitting perforation | Restructure pipeline and add exhaust facilities |
| Smooth flow layout + periodic exhaust + parameter limitation | Effectively inhibit cavitation damage | Conventional circulating heating system standard scheme |
| Surface strengthening treatment + deaeration management | Minimal cavitation erosion tendency | Pump outlet and throttle nearby equipment preferred option |
Conclusion
Cavitation erosion of 316 heating tubes originates from shock damage induced by periodic bubble generation and collapse. The core prevention ideas are optimizing flow channel design to stabilize pressure, removing dissolved gas from the medium, limiting operating temperature and flow velocity, and eliminating surface defect nucleation points. Comprehensive transformation of piping design and standardized process operation can fundamentally eliminate through-wall leakage risks caused by cavitation erosion.
