The Dangers of Cavitation Damage

If you’re hearing an excess of grinding, rattling, or rumbling at work, you may have a pump cavitation problem on your hands. Cavitation commonly plagues many industries, including oil and gas, power, and chemical processing. This devastating process often goes undetected and can lead to wear, mechanical erosion, and increased maintenance costs. Left unchecked, cavitation can wreak havoc on not just your pumps but also your bottom line. 

HTS Coatings has treated and repaired all types of components for cavitation damage and prevention. Follow along with us as we dive into the dangers of cavitation damage and how to prevent this costly and noisy ordeal.

What is Cavitation Damage?

Cavitation damage, specifically in a pump, is defined as the formation and then subsequent rapid collapse of tiny vapor bubbles within the liquid being pumped. This action occurs when the pressure of the liquid drops below its vapor pressure. When the bubbles implode, they create powerful shockwaves that may cause substantial damage to the pump's internal parts, including the impeller, valve, mechanical seals, and pistons. Over time this process can greatly hinder a pump’s ability to perform effectively and lead to expensive repairs, unplanned downtime, and eventually, complete pump failure. Centrifugal pumps in particular struggle with cavitation damage due to their high-speed operation and low suction pressure conditions, which allow vapor bubbles to form easily.

How Does Cavitation Damage Occur?

Typically, cavitation begins on the suction or inlet side of a pump. This process can be broken down into three distinct phases:

1. Low Pressure: A low pressure state will occur as liquid enters the pump’s impeller and the velocity increases.

2. Vaporization: When the pressure drops below the vapor pressure of the liquid, the liquid will “boil” over at that lower pressure, even at more ambient temperatures. This reaction will facilitate the creation of small vapor-filled bubbles.

3. Implosion: The bubbles created by vaporization will then be carried by the liquid flow to a higher-pressure area of the pump, usually on the discharge side of the impeller. The increase in pressure causes the bubbles to suddenly and violently implode. This implosion will release a tremendous amount of localized energy in the form of a shockwave.

Eventually, these repeated shockwaves can cause erosion of the pump's most integral parts and elicit a distinct noise, which sounds similar to rattling gravel or grinding coffee beans.

One of the contributing factors to cavitation damage is insufficient net positive suction head (NPSH). NPSH is a measure of the pressure energy available at the pump's inlet. To avoid cavitation, the available NPSH (NPSHa) must be greater than the required NPSH (NPSHr) for the pump. This can most easily be accounted for during the design stage by calculating these  unit losses in the suction pipework and then deducting these losses from the suction head available to the pump.

What are the Dangers of Cavitation Damage?

Whether you work in mining or a hydropower facility, cavitation can throw a wrench into even the most tight-run operations. Over time, cavitation can weaken the structure of metal components, such as a centrifugal pump impeller, creating surface fatigue, pitting, and erosion.

In addition to the physical damage inflicted by cavitation, this process can also lead to decreased operational performance and efficiency of mechanical systems. As the physical components of a pump become damaged and fluid flow becomes more unstable, the system will require more energy to produce the same output, causing higher operational costs. Parts that have suffered high cavitation damage often emit intense rumbling, rattling, or grinding noises, which can be disruptive to operations. 

Furthermore, the implosions that create cavitation can cause machine equipment to vibrate significantly, resulting in loose components, misalignment, and exacerbated wear on other machine parts. The heat generated by the collapse of cavitation can create extreme temperatures, which can lead to degraded hydraulic fluid and stress nearby components. 

In extreme cases, cavitation can incite operational and financial risks, leading to costly repairs and unplanned downtime. Cavitation to integral parts such as impellers, seals, and bearings can be expensive and may necessitate a complete replacement. Cavitation damage can also reduce a component’s lifespan if left unaddressed. In addition, the cumulative damage inflicted on multiple parts can lead to complete system and/or equipment failure.

How to Prevent Cavitation Damage

The good news? There are ways to minimize and even prevent cavitation. By prioritizing design and regular maintenance while optimizing a few key preventative measures, you can protect your parts:

• Maintain Proper Flow Rates & Suction: Check to make sure pumps are operating at their designed flow rate and ask operations to regularly monitor the suction pressure to ensure it remains above the fluid’s vapor pressure.

• Proper Pump Alignment: The wrong pump alignment can worsen the effects of cavitation by exacerbating pressure imbalances and increasing vibrations.

• Monitor Net Positive Suction Head: In order to avoid the formation of vapor bubbles, the available NSPH (NSPHa) must be greater than the required NSPH (NSPHr).

• Utilize High-Quality Materials: Selecting pumps made from more durable materials such as stainless steel and corrosion-resistant alloys can help mitigate the damage caused by cavitation.

If the above steps cannot be taken due to other process issues, another way to prevent and mitigate cavitation damage is the use and application of wear-resistant coatings. Applying wear-resistant coatings, like thermal spray, or adding hardfacing to pump parts such as the impeller, casing, sleeve, or disc can greatly extend the life of the pump and decrease the risk of cavitation.

HTS Coatings has a long history of pump repair and preventive maintenance. Our skilled team has the knowledge and expertise to give new life to your most valuable parts. Instead of a costly replacement, we can repair damage to your pump shaft or fitting, giving these components an increased service life and lowering the risk of cavitation.

No matter your industry, understanding cavitation is an essential part of preserving your parts and optimizing your business for peak performance. By learning the intricacies behind this phenomenon and implementing preventive measures like thermal spray and suction pressure monitoring, you can set yourself up for a future free of cavitation catastrophes.