Metal Cavitation

Cavitation can silently damage metal surfaces over time, so spotting early warning signs is essential for preventing costly failures in pumps, turbines, and fluid-handling equipment.

• Surface Pitting: Tiny, crater-like holes or rough patches often appear on impellers, valves, or propellers — usually in high-velocity or low-pressure zones.
• Unusual Vibration or Noise: Cavitation often causes a “rumbling” or “gravel-like” sound inside pumps or flow systems, along with abnormal vibration.
• Drop in Performance: A sudden loss in flow rate, pressure, or efficiency may indicate cavitation is disrupting normal fluid dynamics.
• Localized Erosion: Cavitation can accelerate wear in specific areas, especially downstream of flow restrictions or sharp turns in piping systems.

Routine inspections and monitoring for these symptoms help catch cavitation damage early — before it leads to severe pitting, metal fatigue, or total part failure.

Pitting corrosion is a localized form of attack where small, deep cavities form on a metal surface. It’s especially dangerous because it can lead to structural failure without significant overall material loss. Common causes include:

1. Chloride Ions: Found in saltwater, de-icing salts, and cleaning agents — chlorides can break down protective oxide films, initiating pits.
2. Metallurgical Defects: Inclusions or inconsistencies in the metal can act as initiation sites for pit formation.
3. Stagnant Conditions: Crevices, deposits, or low-flow zones create isolated chemical environments that accelerate pitting.
4. Elevated Temperatures: Heat increases the aggressiveness of corrosive reactions, making pitting more likely.
5. Low pH Levels: Acidic environments can destabilize passive films, exposing fresh metal to localized attack.

How to prevent pitting corrosion:

• Use resistant materials: Choose alloys like stainless steel or titanium, especially grades with molybdenum for improved resistance.
• Apply protective coatings: Surface treatments create a barrier between the metal and corrosive environment.
• Control the environment: Reduce stagnation, maintain cleanliness, and prevent buildup of corrosive agents.
• Use cathodic protection: In critical systems, this method helps reduce the electrochemical activity that drives pitting.

Targeted material selection and proactive surface protection can greatly reduce the risk of pitting and extend component service life.

Pump cavitation happens when local pressure in the pump falls below the fluid’s vapor pressure, causing the liquid to vaporize into bubbles. As these bubbles enter higher-pressure zones, they collapse violently — producing shockwaves that damage internal components over time.

Main Causes of Cavitation in Pumps:

1. Insufficient Net Positive Suction Head (NPSH): If NPSHa is lower than NPSHr, cavitation is likely. This often results from low suction pressure or poor system design.
2. High Fluid Temperature: Warmer fluids vaporize more easily, increasing the chance of bubble formation at lower pressures.
3. Overspeeding the Pump: Operating above rated speed lowers suction pressure, encouraging cavitation.
4. Suction Line Restrictions: Blocked filters, undersized piping, or obstructions reduce inlet pressure and fluid flow.
5. System Design Flaws: Long suction lines, sharp bends, or improperly located valves create turbulence and localized pressure drops.
6. Air Entrainment: Trapped air bubbles can disrupt flow and mimic cavitation-like damage.

Prevention Tips:

• Maintain proper NPSH by managing suction conditions.
• Limit fluid temperature and avoid excessive pump speeds.
• Design systems with smooth, short suction paths and properly sized piping.
• Clean and inspect filters and inlets regularly.
• Prevent air from entering the system through seals or leaks.

When cavitation is unavoidable, applying protective coatings like Thin Dense Chrome can reduce erosion and extend the lifespan of critical pump components.