Consultant Response to Maddox is Faulty and Misleading - Gasoline is Compressible

Ms. Fitzgerald wrote in her July 31, memo to CUSD Trustees at paragraph 5:

Liquids are considered to be incompressible fluids. Therefore, increased fuel flow by fluid compression is not possible. The bulk modulus of gasoline is approximately 200,000 psig; therefore, to get just a 1% increase in volume, the pressure would need to be increased by an additional 2,000 psi above what the current operating pressure of the pipeline is.

Please understand that I’m not a hydraulic engineer. However, only a few minutes of research is needed to dispense with this argument.

First, while liquids are relatively incompressible compared to gases, they are not “incompressible”. In fact, there is quite a difference between the compressibility of gasoline compared to, say, water. The term “bulk modulus” is used to describe the “stiffness” of a fluid. Gasoline has a bulk modulus of 190,000 psig. The bulk modulus of water is between 310,000 psig and 340,000 psig, depending on salinity.

Thus, gasoline is not as “stiff” as water and a certain amount of pressure applied to gasoline will reduce its volume more than the same pressure will reduce an equal volume of water. Conclusion: liquids are compressible. This contradicts Ms. Fitzgerald’s main statement.

Next, the compressibility of a fluid is not a linear function. An uncompressed fluid (at 0 psig, atmospheric pressure) is easily compressed a small amount. However, it takes an increasing larger amount of effort to achieve more compression. The effort to go from 0 psig to 1 psig is far less than is required to go from 10 psig to 11 psig, and so on. In fact, the function is hyperbolic.

The Kinder-Morgan pipeline operates at 1400 psig. The volume of gasoline under consideration in the pipeline is a fluid cylinder that is at least 24 miles in length and 16-inches in diameter (considering only the section up to the high school).

The “increase in volume” discussed by Ms. Fitzgerald misses the point entirely. Her disingenuous argument obscures the actual danger.

In a pipeline rupture, the enormous energy that has been expended to compress Ms. Fitzgerald’s “incompressible” fluid is released instantaneously. The entire 24+ mile cylinder of fuel (plus more beyond the point of rupture) will “relax” back to atmospheric pressure, increasing in volume as it does so. During this process, any obstruction (e.g., earth) at the site of the rupture will literally be “blown away” and a geyser of aerosol gasoline will rise into the air.

As the fluid in the pipeline returns to atmospheric pressure, it must escape from the pipe because with relaxed compression, it occupies a larger space (or volume) than the container (the pipeline) that previously held it. At the point of rupture, the rate of fuel escape will be dramatically higher than the nominal flow rate of the closed pipeline past the same location. Given the length of the pipeline, this accelerated release will continue for some time until all of the fuel has returned to atmospheric pressure.

Ms. Fitzgerald then makes this statement:

...therefore, to get just a 1% increase in volume, the pressure would need to be increased by an additional 2,000 psi above what the current operating pressure of the pipeline is.

This is way off subject; so far off, in fact, that it is difficult to accept as a mistake. The volume differential that is of interest is the difference between that of the pipeline payload compressed to 1400 psig (normal pipeline operations) compared to that same payload at atmospheric pressure (during a rupture). This would be far more than 1% and the volume under consideration (24 miles x 16 inches) is immense.

Given this error, Ms. Fitzgerald should also reconsider her response to Mr. Maddox in paragraph 6. Maybe she spoke to the wrong person at Kinder-Morgan?