Scraper Trap

Scraper Trap

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.

Have you considered the value of using rotary PD pumping technology?

Midstream facility managers and operators around the globe have realized that volumetric, rotary PD pumps are something they can capitalize on in these services. Having one machine that can efficiently transport heavy, medium and lightweight oils with high pressure boost capabilities, while at the same time delivering a near constant, pulse free flow rate, provides the system control and reliability that end users demand. These strengths, coupled with the tremendous turndown flow range of rotary PD pumps and their inherent high suction lift capability, make them an ideal fluid-conveying solution for your Scraper Trap systems.

Suitable pump types:

Three-Screw Pumps and External Gear Pumps

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