The above-ground tanks at the refinery serve as the temporary, downstream staging point for the crude oil that has traveled to this location via pipeline, rail car, truck tanker or ocean vessel. Apart from crude oil arriving via pressurized pipeline, all of the other aforementioned Transportation methods will require process pumps to unload their cargo and to transfer it to the Storage tanks. This crude oil inventory will support the smooth and around-the-clock operation of the refinery. Tank Loading systems handle this task.

As user experience bears out, seemingly simple services like Tank Loading systems can offer their challenges. Stripping rail cars and tanker vessels demands that the pumps regularly operate under very difficult inlet conditions with tight NPSH / NPIP margins, often managing vortexed air that has entered into the supply manifold due to low submergence of the takeoff connection fitted to the side of the tank below the tank liquid level. Depending on the regularity of the crude oil supply chain, these systems may be operated intermittently, demanding the repeated starting and stopping of drivers and pumps, increasing the potential for an unplanned discharge of process fluid.

A key part of the reliable operation of large, long distance crude oil transportation pipelines is the cleaning of the internal wall of the pipe itself, as well as the removal of settled solids. These substances, if not properly dealt with, can lead to the subsequent fractures of the pipe wall in the affected areas and costly environmental leakage. If fractures do not readily occur, the accumulated solids will inevitably create flow assurance problems within the pipeline by reducing the working volume of the pipeline, or even blocking the line altogether. These obstructions typically occur where the internal line velocities are reduced due to pressure drops across elbows and valves, or where due to topographical changes the solids are able to separate because of their differing density as compared to the crude oil. To prevent or remedy these conditions, a close-fitting, mechanical device equipped with scrapers and/or brushes called a “pig” is inserted into the pipeline and travels through the line by the energy provided by the mainline booster pumps, removing the undesirable contaminants. At a predetermined delivery point, the pig is isolated in a Scraper Trap vessel. The contaminated fluids collected are pumped from this vessel to a tanker truck for removal to a treatment facility.

As experience bears out, Scraper Trap systems have their challenges. By the nature of the service, the fluids being managed are contaminated with settled solids which are suspended in a viscous oil mixture. To further complicate this service, the Scraper Trap vessel when isolated is at full line pressure, meaning that the suction of the pump tasked to drain this vessel is immediately exposed to an extremely high suction pressure. Once a sufficient volume of fluid has been extracted from the vessel to reduce the internal pressure, a valve is opened to vent the tank, to facilitate the safe draining of the trap. To perform in this duty the pump used must have good suction lift capabilities, due to the high viscosity of the fluid being managed and the minimal vertical height between the underside the Scraper Trap and suction centerline of the pump. To complicate matters further, these services are intermittent, so the fluid-handling technology selected must be robust enough to reliably restart after a long, idle period.