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Flow and Solidification in an Undersea Pipeline

Flow and Solidification in an UnderSea Pipeline

This project was so unique that we requested permission from the client to publish it and present it at an ASME conference. This was done although the article required B&W (and not color) illustrations. Here the article is re-written more succinctly and accompanied by colored illustrations.

Problem statement

Molten asphalt was to be pumped across the Bay (in Calif) from a tanker to a storage facility. An undersea pipeline was to be used whcih was initially filled with a cold, medium weight oil. The asphalt was initially at 250oF and would be added, displacing the oil. The oil was at ambient conditions, i.e. 60oF.   The asphalt could not be heated higher and had the viscosity curve as outlined below.


Asphalt Viscosity vs. Temperature

Note that the viscosity is on a log scale, thus when the asphalt falls under about 90C or 194oF, it becomes quite viscous. Under 140oF it is basically a solid, impossible to pump and would effectively destroy the pipeline. However there are several contravening reasons as to why the asphalt pumping could work.
1) The asphalt is an excellent insultator, once it forms a coating around the inside walls of the pipeline heat loss thru the sides will be minimal. As fresh hot asphalt is flowing into the pipeline, heat loss will be negligable.
2) There is a phenemon in flow where the leading interface will curve inwards to form the walls of the depositing layer. Thus the cooled leading interface will constantly be replaced by fresh hot asphalt from the core and permit the asphalt to flow.

Modeling Results

asphalt characteristics after 50 seconds

As can be seen the asphalt / cold oil interface did NOT form that rolling characteristic and basically elongated into a cone. This amplified the exposed area for heat loss to the cold (60oF) oil and casued the asphalt at the interface to solidify.

asphalt characteristics after 175.7 seconds

Once this happened the additional pressure only caused further elongation at the center of the interface with more heat loss. Thus as the pressure residuals climbed it was concluded that the asphalt essentially solidified in the pipeline. Unfortunately after hearing this, the client decided NOT to use the pipeline to transport the molten asphalt. Thus a comparison with field measurement is not possible. We shall provide links to these illustrations in higher resolution presently.