How Lubricant Issues Can Affect Pump Bearing Life
When it comes to your company’s refinery operations, there’s little to no time for downtime. This especially holds true for one of the most critical pieces of equipment inside the typical refinery: the centrifugal pump. With predictive maintenance and monitoring, it’s possible to achieve average mean times between failures (MTBFs) of 2.5 to 10 years, depending on the type and role of centrifugal pump.
Bearing lubrication plays an important role in ensuring long pump life, and the condition of the lubricant itself will determine the working life of the pump, as well as the type of maintenance that’s required. As you manage your refinery operations, you can use the following as a reference guide for understanding how different lubricant states affect pump operation over the long run.
Using the Incorrect Quantity
Using the incorrect amount of lubricant in centrifugal pump operation can also have a remarkable effect on overall performance and longevity. The correct quantity of oil required for a particular pump depends on its original lubrication method and the application of the pump itself. These lubrication methods include oil splash lubrication and pure/purge oil mist.
Lubricant starvation often leads to surface contact due to a lack of lubricant film strength. This, in turn, leads to a thermal runaway condition where the thermal expansion of bearing materials creates increased metal-on-metal contact, which further exacerbates thermal conditions. This eventually eventually leads to catastrophic failure of the pump.
Using too much lubricant could lead to excess churning, allowing air entrainment to take place and accelerate oxidation issues. Excessive lubricant levels can also interfere with oil splash lubrication. For instance, the flinger discs would no longer be able to splash lubricant if the ring itself becomes submerged in oil.
Maintaining optimal lubricant levels is essential for ensuring the longevity of the lubricant itself as well as that of the equipment being lubricated. These levels are normally determined by the equipment manufacturer specifications and preferred practices.
Lubricant Contamination
Most premature bearing failures can be linked to lubricant contamination of some sort, whether through moisture, particulates or air entrainment. Each type of contamination has its own set of effects on the lubricant and internal pump components:
- Particulate contamination can cause lubricants to become abrasive to mating surfaces and fatigue other components through localized pressure.
- Water contamination can lead to corrosion and destroy the lubricant’s ability to form a lubricating film for metal surfaces, resulting in excessive wear and tear of components.
- Air entrainment often leads to a loss in film strength and interferes with heat transfer. It also leads to poor oil compressibility, cavitation and oxidation.
Particulate contamination usually occurs when certain components made of soft metals, such as brass oil rings, wear and create particle debris that’s later introduced into the bearings. Meanwhile, pressure differentials could lead to the introduction of water or air into the pump’s oil sump via vents and seals. Lubricant contamination could even occur during maintenance and rebuild periods due to improper handling of pump components or preexisting contamination of oils during storage or dispensing.
Using the Wrong Lubricant
The main problem with using the wrong lubricant involves disparities in viscosity and how they can negatively impact bearing life and operation. Proper and long-lasting bearing function often depends on the correct lubricant thickness, ensuring that the roller elements and other contact surfaces remain separated from one another.
It’s important to use the correct viscosity lubricant based on the operating loads, temperatures and speeds of the rotating parts in question. Otherwise, a disparity in viscosity could result in the lubricant becoming degraded by excess heat and chemical change. As a result, the lubricant is no longer able to effectively provide a barrier against metal-on-metal bearing contact.
The above lubrication issues can have a tremendous impact on the average MTBF of centrifugal pump equipment. Understanding the importance of proper lubrication can go a long way towards ensuring a reliable environment for your refinery equipment, such as pump skids.
