Designing the Best Loading-Arm System for LPG Applications

By OPW | Jul 02, 2021

It was 10 years ago – April 2011, to be exact – that, according to the U.S. Energy Information Administration, a “mere” 2.33 million barrels of liquefied petroleum gas (LPG) was being transported monthly in the United States via railroad. By January 2020, however, 10.17 million barrels of LPG was being transported in railcars.

Physics has a lot to do with the popularity of using railcars for LPG transport. In its gaseous form, LPG has a volume that is 270 times that of its liquid state, making it more efficient to transport it in its more compact liquid form. Railcars, which must be pressurized in order to keep the LPG in a liquefied state, generally have a capacity of between 17,000 and 33,500 gallons (65,000 to 127,000 liters). This allows them to hold about 143,000 pounds (65 metric tons) of LPG. That means that a unit train with 100 high-capacity LPG railcars can move 3.35 million gallons of product in one run.

The challenge in getting these high volumes of LPG safely to and unloaded at the storage terminal is ensuring that pressure is not lost in the railcar, from the point at which it is filled to the point at which it is unloaded. For the operators of LPG storage terminals, this demands that they employ a loading-arm system that is compatible with LPG handling and transfer, with the development of a system that reliably delivers safe, pressure-sensitive and efficient operation the ultimate outcome.

OPW Engineered Systems, a product brand of OPW, is a leader in the design, engineering, manufacturing and servicing of loading-arm equipment and systems for use with high-value fluids like LPG. As such, OPW recommends three types of top-loading arms in LPG-handling applications:

  • “Bull Horn” Loading Arm: This configuration features a single arm that divides into dual connections that can be attached to a pair of product lines, giving the loading arm setup a “U” shape reminiscent of a bull’s horns. This setup allows the combination of two product connections into a single arm, which reduces the number of arms required.
  • Single-Line Boom Arm: These supported or unsupported arms feature a single product hose for those applications that do not require dual-unloading capabilities. The arms are designed for use in variable-reach applications, specifically those with longer reach requirements that may put undo strain on other loading-arm styles.
  • “A” Frame Loader: This style of loading arm offers flexibility, long reach and easy maneuverability. It can be stored in an upright, near-vertical position away from the railcar for safe clearance, while crossover of any obstructions can be readily achieved, which is ideal for rack setups that feature dual unloading lines. During unloading, the arm adjusts to the railcar’s elevation or tilt so that a tight connection can be made to the valves.

As a designer, engineer and manufacturer of complete loading-arm systems, OPW can also supply all of the ancillary components that an operator may desire. For railcar/angle valve connection points, OPW offers a variety of stabber-pipe options. Though OPW does not make Emergency Shutoff Valves (ESV), it can supply the “Snappy Joe” ESV (Model No. N562) from Fisher Control Valves with its loading-arm packages. In the safety breakaway arena, OPW has direct-pull and cable-release coupling models, both of which will separate in the event of a railcar pull-away incident that could lead to an LPG release. Finally, OPW offers ground-verification monitors from Civacon, another OPW company, that do not allow LPG transfer to commence if a proper ground is not achieved, or if grounding is lost during product transfer.

For more information on OPW Engineered Systems’ complete portfolio of Loading Arm Systems and components, please visit opw-es.com.

 

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