What Is It – Reid Vapor Pressure (RVP)

Although an obscure environmental data point, Reid vapor pressure is a critical factor when it comes to gasoline fuel supplies in the US. As such, it’s important that those in the fuel industry have a clear understanding of what Reid vapor pressure is and why it matters. In this edition of FUELSNews What is It Wednesday, we will explore the significance of Reid vapor pressure, how it is measured, and why it’s essential for ensuring compliance with regulations and product specifications. By the end, we promise you will have a deeper appreciation for Reid vapor pressure and its role in the fuel industry.

 

What is Reid Vapor Pressure?

Reid vapor pressure (RVP) is a measure of the volatility of gasoline and other petroleum products. It is defined as the absolute vapor pressure of the fuel at 100 degrees Fahrenheit (37.8 degrees Celsius), which is the temperature at which gasoline is stored and transported.

The RVP is measured in pounds per square inch (psi) or kilopascals (kPa). The higher the RVP, the more volatile the fuel, which means it evaporates more easily and can contribute to air pollution. The lower the RVP, the less volatile the fuel, which means it is less likely to evaporate and contribute to air pollution.

 

How is RVP calculated?

RVP can be measured using specialized equipment, but it can also be estimated using the product’s composition. One common method for estimating RVP is to use the boiling points of the individual components in the fuel, along with their vapor pressures. The RVP of the fuel is calculated as the sum of the vapor pressures of all the elements that boil at or below 100 degrees Fahrenheit (37.8 degrees Celsius).

The exact method for calculating RVP using this approach can vary depending on the specific composition of the fuel, but the general steps are as follows:

1. Determine the boiling points of all the individual components in the fuel.
2. Calculate the vapor pressures of each component at 100 degrees Fahrenheit (37.8 degrees Celsius) using a reference chart or equation.
3. Identify all the components that boil at or below 100 degrees Fahrenheit (37.8 degrees Celsius).
4. Sum the vapor pressures of all the identified components to get the RVP of the fuel.

It’s important to note that this is an estimation method, and actual RVP can vary depending on other factors, such as the presence of impurities or the accuracy of the vapor pressure data used. For this reason, the actual RVP of fuel is usually measured using specialized equipment to ensure compliance with regulations and product specifications.

 

What are the EPA RVP requirements?

The Environmental Protection Agency (EPA) sets RVP requirements for gasoline sold in the United States to reduce air pollution. The specific requirements vary depending on the region and time of year.

Generally, the EPA requires gasoline sold during the summer months, typically from June 1st to September 15th, to have an RVP of no more than 9.0 pounds per square inch (psi) or 62 kilopascals (kPa) in most areas. However, the requirement may be lower in certain parts of the country, such as high-altitude areas. The map below shows  the requirements as of 2017, though some areas have since been relieved from their special low-RVP requirements. Currently, the EPA only requires certain cities in Colorado, Nevada, Oregon, Texas, and Utah to utilize 7.8 psi RVP.

During the winter months, which is typically from October 1st to May 31st, the EPA allows gasoline to have a higher RVP in order to facilitate cold weather starting. In most areas, the RVP limit is 15.0 psi or 103 kPa.

 

 

These requirements are subject to change and may vary depending on the specific location and year. Gasoline retailers and distributors are responsible for ensuring that the fuel they sell meets the appropriate RVP requirements for the time of year and region.

 

Why is RVP important?

RVP is an important parameter in regulating gasoline and other petroleum products, as it affects the emissions from vehicles. Gasoline with a higher RVP is typically used in the winter, as it allows for easier starting in cold temperatures. In comparison, gasoline with a lower RVP is used in the summer to help reduce evaporative emissions.

This small regulation can have a significant impact on fuel supplies. Every spring, refiners, shippers, and distributors must purge their tanks of any high-RVP fuel to prepare for the June 1 conversion of all end-user tanks. That can create shortages in some areas if low-RVP gasoline does not arrive on time. On the other hand, a supplier with too much high-RVP on May 31 may need to heavily discount the fuel to avoid regulatory penalties on June 1. Imagine the challenge! A similar challenge occurs in September, as suppliers try to stock up on cheaper high-RVP fuel while only being able to sell low-RVP product through Sept 15. Converting each year is a logistics exercise at best… throw in a refinery outage or a hurricane, and it can quickly become a severe supply challenge.

Unique requirements add another layer of complexity. While most of the country switches to one blend of gasoline, certain pockets around the US require special RVP blends to meet local environmental requirements. During disruptions such as refinery outages, areas with unique RFG requirements may face more acute supply challenges than surrounding areas.

 

Does Canada also set RVP requirements?

Yes, Canada also has RVP requirements for gasoline sold in the country. The specific requirements are set by Environment and Climate Change Canada (ECCC) and are designed to reduce air pollution and protect public health.

In Canada, the RVP requirements are expressed in kilopascals (kPa) and vary depending on the season and geographic location. The summer RVP limit for most areas is 75 kPa, while the winter RVP limit is 77 kPa. The ECCC monitors compliance with these requirements and takes enforcement action against those who do not meet the standards.