Field experiments were made to determine a suitable exterior protective coating for an oil transmission pipe line to handle oil heated to 200 degrees F. The 41-mile line was 8-inch Schedule No. 30 pipe operated at normal working pressure of 600 to 800 psi with three combined heating and pumping stations spaced at approximately 13.5 miles. It was designed to transmit fuel oil from the refineries to a steam-electric generating station.
To test stability, four different coatings were applied to 20-foot lengths of 8-inch pipes connected in series and buried in the soil. Oil heated to 200 degrees F then was circulated through the pipe for approximately two weeks. Provision was made to apply an external pressure of 10, 50 and 80 psi by the use of suitable rods and weights at three spots on each of the coatings. Depressions formed were measured carefully throughout the test to determine their rate and magnitude on each coating. Open ditch sections approximately 2 feet long for each coating were provided to permit observation of sag which might take place on any of the coatings. After the experimental hot oil circulation was completed the ditch was opened and the coatings examined for distortion and adherence and electrical resistance measurements were made at the depression points.
Additional 40-foot pipe lengths with each of the four different coatings then were subjected to cold bending by standard field equipment to a total angle of approximately 20 degrees and a minimum radius of approximately twenty pipe diameters (14 feet 5 inches). After each bend, the coatings were examined for cracks and given “holiday detector” tests to supplement visual examination.
Due to its ruggedness and freedom from distortion during the test it was decided to recommend a ½-inch thick asphalt mastic coating using a 250 degree F melting point asphalt for the hot-oil pipe line exterior coating.
