Rotating Pressure Vessel Oxidation Test (RPVOT)

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The Rotating Pressure Vessel Oxidation Test (RPVOT) is a vital tool in evaluating the performance and longevity of lubricants and gears in high-pressure, high-temperature environments. It simulates the conditions that lubricants and gears may experience in real-world industrial applications and provides valuable insights into their performance under extreme conditions. In this post, we will discuss the RPVOT test method in detail, including its purpose, how it works, and how the results are analyzed and interpreted. We will also explore the importance of RPVOT testing for industrial businesses and the role it plays in ensuring the reliability and longevity of lubricants and gears in demanding applications. Understanding the RPVOT test and its results is crucial for making informed decisions about product selection and performance.

What is RPVOT?

RPVOT stands for the Rotating Pressure Vessel Oxidation Test. It is a test method used to evaluate the oxidation resistance of lubricants and gears under high-pressure and high-temperature conditions. It simulates the conditions that lubricants and gears may experience in real-world industrial applications, such as those in gas turbine engines. The RPVOT test involves rotating a pressure vessel at a high speed. This is all while the lab exposes the lubricant or gear sample to oxygen at a controlled temperature and pressure. The test measures the rate of oxidation and the formation of deposits on the lubricant or gear surface, which can indicate its potential performance and longevity in actual service. It is an ASTM standard test method (ASTM D943) and is usually used in industrial fields to evaluate lubricant performance and to compare different lubricants in the same operating conditions.

The Importance of the Rotating Pressure Vessel Oxidation Test

The importance of RPVOT depends on how important the impact of oxidation is in your facility. Lubricant oxidation results in:

  • Inadequate lubrication due to depletion of characteristic qualities
  • Thickening
  • Production of heavy deposits
  • Higher acid as seen by an increase in the Total Acid Number (TAN)

The test gauges an oil’s ability to withstand oxidation. So, if you want to know the useful life of your lubricant, RPVOT is an essential test. Additionally, it can help you compare new fluids side by side or when choosing oil change intervals in crucial applications. The classic oxidation resistance tests of the past occasionally required a year to provide a result. With results measured in minutes, RPVOT requires only a few hours to a day.

When Should You Perform RPVOT?

RPVOT is a powerful tool for monitoring the lifespan of oil. It calculates the remaining life of the oil in minutes, based on accelerated oxidative conditions. By tracking this information over time, power stations and other facilities with large oil-filled systems can plan ahead for oil changes, sometimes several months in advance. This not only helps them save time and resources but also enables them to measure the impact of partial oil changes.

How Does RPVOT Work?

The test functions by:

  1. The lab places a copper coil, a 50g sample of oil, and 5g of deionized water in a beaker. Then, the beaker is loaded diagonally into the pressure vessel.
  2. After sealing, oxygen flushes into the pressure vessel, and then 90 psi of oxygen is applied.
  3. At a temperature of 150°C, the vessel begins rotating. Every minute, the lab records the pressure inside the vessel. The pressure inside initially rises with the temperature. But, it can eventually double from the initial 90 psi.
  4. Next, the pressure within will stabilize. Oxidation involves oxygen molecules bonding with the oil. That means there is less gas in the air, and the pressure will begin to drop.

The most often used testing method measures up to a 25 psi reduction from the maximum pressure. However, some labs will agree with the client to end the test early after a set amount of time. Additionally, some labs may even charge a higher fee to run the RPVOT to completion.

A Useful Component of Lubricant Analysis

A crucial cause of lubricant degradation is oxidation. Acids and other insoluble oxidation products are produced as oil oxidizes. These byproducts might result in the formation of varnish or sludge. Furthermore, it may cover the bearing and oil cooler surfaces, which would prevent the bearings from being adequately cooled. Areas with strict tolerances, such as hydraulic control valves, can also develop coatings that cause operating problems. To monitor fluid health and determine the amount of remaining life, lubricant analysis using RPVOT is essential for lubricants with antioxidant additive packages.

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