Which of these is the best strategy for ensuring that the liquid in the pipe will not vaporize under any circumstances?

Question

A pipeline extends out from a shore plant into the shipping lane of a river. It’s used to carry a pressurized liquid to the receiving ships. But often the pipeline isn’t in use for hours or even days at a time, and the liquid simply sits in the pipeline. At many times of the year, the temperature of the water in the river is high enough that the liquid in the pipeline could boil.
A. Use the van der Waals equation of state to find the critical point of the liquid, and then pressurize it above the critical pressure so it cannot vaporize.
B. Use the Peng-Robinson equation to determine the bubble point pressure of the liquid at the average temperature of the river, and pressurize the pipe to above this value.
C. Add a vent with a pressure relief valve to the pipeline, so that if the pressure exceeds a threshold value, material will be released.
D. Add more insulation to the pipe.
E. Each approach has a significant flaw.

Answer 1

A. Incorrect. The approach is sound conceptually but the van der Waals EOS does not predict vapor pressures at all well.
B. Incorrect. The average temperature of the river is not the right value to use—in a safety analysis you want to use the worst-case scenario.
C. Incorrect. While this will avoid a dangerous pressure buildup, the stated goal is to prevent vapor from forming. This will release the vapor as it forms.
D. Incorrect.Adding insulation will slow the rate of heat transfer, but will not change the temperature attained at thermal equilibrium, so this will not conclusively prevent boiling.
E. Correct. Each approach has a degree of logic but some flaw.