In the oil, gas and fuel industries, there are many test methods for the analysis of the products’ various parameters. One of the major types of petroleum analyzers is the vapor pressure tester, which provides a measure of the sample’s volatility. When a liquid has a physical interface with air, another gas or a vacuum, some of the molecules in the liquid will volatilize; that is, escape the liquid surface and exist in a vaporous or gaseous state. The pressure exerted by the vapor is a direct measure of how much of the substance exists as a vapor, and thus of the volatility. One important aspect of vapor pressure is that it increases with temperature.

For oil samples and fuels, vapor pressure is of great interest. For engines that run on liquid fuel, vaporized fuel readily combusts. At the same time, fuel that is too volatile can be dangerous or can lead to “vapor lock,” when volatilized fuel interrupts the proper functioning of a fuel pump. While automotive gasoline is fairly volatile at room temperature, other fuel oils can be quite viscous and require preheating if they are to combust properly.

The volatility of a particular sample is a complex combination of its chemical make-up and its temperature. Vapor pressure testers provide a means for testing this parameter. Various test methods exist in order to standardize the methodology, and all commercial vapor pressure analyzers conform to one or more test methods.

The measurement process depends on the method, but usually involves placing the sample in a piston chamber. When the piston is moved to expand the volume of the chamber, part of the sample volatilizes to fill the void. When equilibrium is reached, the pressure generated by the vapor is measured. Measurement can be made at a constant temperature or with various temperature profiles.

Vapor pressure testing is used with crude oil feedstocks, for quality control of finished fuels, and for monitoring oil pipelines and oil samples in the field. Some systems are designed for online use in refineries and other production facilities. Because of the relationship between temperature and volatility, different fuel blends are more commonly used in summer than in winter. Vapor pressure testing helps to ensure that the product has the correct properties. Other applications for vapor pressure tests involve liquid petroleum gas and other petroleum derivatives, such as solvents, for which volatility provides a measure of how rapidly a solvent will evaporate.

Most of the handful of vendors that provide petroleum analyzers offer vapor pressure instruments as one of their primary products. Grabner Instruments leads this market with several fully automated lab systems, as well as an online analyzer. Stanhope-Seta and Normalab are the other major vendors. Other market participants include Koehler Instrument, Orbis, PAC (Roper Industries), Petrotest (Anton Paar) and Tanaka Scientific. Market demand for lab vapor pressure analyzers was about $13 million in 2012.

Vapor Pressure Analyzers at a Glance:

Leading Suppliers

• Grabner Instruments (AMETEK)

• Stanhope-Seta

• Normalab

Largest Markets

• Petroleum

• Natural Gas

• Fuels

Instrument Cost

• $2,000–$20,000