NIST Industrial Impact

Company: Gas Processors Association, Tulsa, Oklahoma
Business: Represents member companies who produce, process, and distribute natural gas and natural gas products
Number of Employees: Approximately 60 member companies

When Kepler came to the startling conclusion that planets rotate around the sun in elliptical orbits, not circular ones as everyone had believed, he owed plenty of thanks to his employer Tycho Brahe. Brahe had spent years measuring planetary positions with unprecedented precision. Had that precision been a fraction of a percent less, Kepler almost certainly would have failed to discern the unexpected orbital shape.

Now, there are countless down-to-earth reminders of how important precision can be, including one that has brought the Gas Processors Association's (GPA) member companies into alliance with researchers at the National Institute of Standards and Technology (NIST). The collaboration, which began in 1989, goes by the descriptive title of Volume Correction Factors Project.

The industrial problem that brought the two organizations together originated with disagreements between the companies that sell so-called liquid natural gas products such as ethane, propane, butane, pentane, isohexane, and their blends (which condense into liquid when extracted from natural gas) and those who purchase often huge amounts of these to use as fuel or chemical feedstocks. Says Dale Embry, a senior engineering specialist with Phillips Petroleum Co. in Bartlesville, Okla., and GPA liaison on the project: "The settlement of disagreements between the buyers, sellers, and regulators were tying up resources that could be better spent on other projects." By the late 1980s, the problem was getting expensive enough to move the GPA into action.

The technical basis of the discrepancy resides in calculations used to determine the quantity of the liquid product, which for practical reasons is always metered by volume, rather than mass. But since the density of liquids varies with the temperature, which means that a gallon of the same product packs a different mass of product on a hot day than it does on a cold day, the metered volumes need to be corrected to a standard set of conditions that everyone agrees to. Though actual corrections are relatively small, the financial consequences are great because the quantities of material produced and sold are so large.

Members of the GPA decided they needed to re-evaluate the correction tables they had been using since the 1950s when they were compiled by an engineer at Gulf Oil Co. Doing that meant preparing liquid product samples of precisely known compositions and then carefully measuring their volumes and masses in the range of temperatures at which these liquids might be pumped into a buyer's tanker. In the late 1980s, when they contacted NIST, they believed the corrections carried a 1 percent uncertainty. To halve that uncertainty, they needed measurement experts, which they knew they could find at NIST. Moreover, since many GPA member companies are multinational, they wanted to develop correction standards that would stand up to the scrutiny of foreign standards organizations. "This was another crucial reason to work with NIST," Embry says.

Beginning in 1989, the company contracted with a team of researchers at NIST's Boulder, Colo., facility to measure the density of liquid natural gas components and their mixtures. Collaborators at the Colorado School of Mines have used the detailed data, which even account for the portion of material that vaporizes into the free space of a tank, to generate sophisticated mathematical models that GPA members can use to calculate corrections with a maximum uncertainty of 0.5 percent. That is a factor of two to four improvement when compared to the previous methods. The new lower uncertainty translates into annual savings of tens of millions of dollars due to reduced claims tracking and settlement, Embry says.

In a letter to W. Mickey Haynes, a NIST researcher who had worked on the project since its inception, Embry wrote that "we have gotten a bargain from your laboratory in terms of the quantity of data measured for the money that we have contributed." In the letter, he points out that the data "have resolved many discrepancies in the [previously] available data." Moreover, he says, the improved data and correction calculations even have allowed companies to keep open some operating stations that would have required costly upgrades in metering systems to improve measurement accuracy. "With the new data, we will be able to continue to use less expensive metrology with reduced uncertainty," Embry says.

Precise measurement, it seems, is the key to discovering the cosmic paths of planets, cost-saving methods for major industries, and, undoubtedly, a few other things in between.