Engineering | What's Next

Material Specifications & Regulations

Dangers of LPG

LPG may leak as a gas or a liquid. If the liquid leaks it will quickly evaporate and form a relatively large cloud of gas which will drop to the ground, as it is heavier than air. LPG vapours can run for long distances along the ground and can collect in drains or basements. When the gas meets a source of ignition it can burn or explode.

Cylinders can explode if involved in a fire.

LPG can cause cold burns to the skin and it can act as an asphyxiant at high concentrations.


The regulations are framework in character. They lay down general requirements but rely for detailed guidance upon codes of practice which may be approved from time to time by the Health and Safety Authority. These regulations apply in addition to any other requirements under relevant statutory provisions.

  • LPG must be stored in adequate location wherein vessels or cylinders are suitably positioned having regard to the relevant codes of practice
  • LPG plant must be designed to appropriate standards and be properly installed and commissioned by competent persons
  • Plant must be fitted with adequate safety and monitoring control devices and operated by competent persons
  • Occupiers must notify the gas supplier of any structural or other changes which might affect the gas installation
  • There must be a suitable programme of maintenance and testing by competent persons
  • Plant must be identifiable and accessible for maintenance
  • Records of maintenance and tests must be kept
  • Precautions must be taken to prevent fire and explosion including appropriate protection of storage vessels
  • Installations must have appropriate security measures to prevent deliberate interference
  • Incidents involving death or hospitalisation, fire or explosion or a significant release of LPG must be reported to the Authority and records of such incidents must be kept

Components of a Pressure Railcar Loading Spot

  1. Loading Arm System
  2. Angle Valves
  3. Stabber Pipe
  4. Gangway

Loading Arm System

Loading arms allow the transfer of fluid to and from a tank through a system made up of pipe, hose, and/ or valves. When transferring a pressurized fluid, a liquid loading arm is needed and at times a vent line.

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Angle Valves

Angle valves feature self centering valve seats that deliver positive shutoff while reducing the number of potential leak paths and long term reliability. Angle valves reside on pressure railcars. It is the primary connection point for loading operations.

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Stabber Pipe

The assembly that is part of the loading arm system is known as the stabber pipe (or stinger) which connects to the angle valves. Angle valves have a standard 2" FNPT connection which constrains the stabber pipe to 2" in diameter.


Safety Access Equipment

Safety access equipment provide fall protection when the operator ascends to the top of the railcar during loading/unloading procedures. The safety access equipment and loading arm system must work in concert.

Loading the OPW Way

1. Determine the Type of Stabber Pipe Needed



A single piece stabber pipe is typically used when the loading arm connection is to be horizontally oriented relative to the railcar, whereas a two piece stabber pipe is vertically oriented. Note that single piece stabbers have one half, and two piece stabbers have two halves.

2. Build the First Half of the Stabber Pipe

2a. Start with the Connection

Identify the angle valve valve’s connection size. They typically feature 1", 2", or 3" FNPT threaded connections, where there are two product (liquid) valves and one vapor valve. For LPG, itit’s predominantly a 2" connection. This means that loading is constrained by the 2" diameter flow path.

2b. Assess the Piping Material and Accessories

Option 1

2" LT CS SCH 80 FNPT BE, 18-19" OAL

Option 2

FISHER ESV, N562-16, W/ 4'" OAL SCH 80 SMLS CS 1

After identifying the angle valve connection size, begin building the first half of the stabber pipe needed for the application. This half of the stabber pipe is typically threaded into the angle valve independently before connecting it to the loading arm or a second half of the stabber pipe, which is integrated into the loading arm.

Option 1 is the simplest.
Option 2 allows for the integration of a Fisher™ Snappy Joe™ for emergency shutoff of the loading operation

3. Build the Second Half of the Stabber Pipe

3a. Determine the Fluid Loss Permissable to the Environment While Loading

This component will ultimately be part of the second half of the stabber pipe and will connect to the first half. The decision will be dependent on the implications of fluid loss on the operator and environment, along with the required operator ergonomics for loading efficiency.

For LPG, we recommend utilizing a Dry Disconnect to minimize spillage and enhance ergonomics of the loading procedure thereby creating a closed loop system.

3b. Choose Your Loading Arm Connection Orientation
1. Horizontal
2. Vertical

The orientation of the loading arm connection from this step will determine how it connects to the first half of the stabber pipe. It will either connect horizontally or vertically. This is strictly dependent on the preference of the loading procedure for the operator.

4. Assemble the Stabber Pipe

The Stabber Pipe is available for use in either a single-piece or two-piece configuration. Those wishing to purchase a single-piece Stabber Pipe need to specify the required parameters in the Angle Valve Connection, First Half Type, First Half Type Adaptor and Loading Arm Adaptor fields. In addition to those fields, anyone in need of a two-piece Stabber Pipe must also identify values for the Second Half Coupler, Second Half Type, Elbow and Second Half Vertical parameters.

5. Determine Loading Configuration



The stabber pipe assembled in step 3 will be integrated into the loading arm, however, it should be decided whether the loading procedure will done in single or dual configuration. Dual configurations, also known as bullhorn, allow for more efficient loading through two product angle valves.

Loading Arm Solutions

The most common loading arm solutions are the below arms. Learn more about each solution.

Safety Breakaways

Tthe breakaway is engineered within the loading arm system to add another layer of safety for operators and the environment. It serves as a separation device to keep the fluid in the internals of the system in the event of an accidental pull away.

Why OPW?

For more than 125 years, OPW has been defining what’s next in the transport and safe handling of high-value fluids around the world, and OPW Engineered Systems is a leader in the design, engineering, manufacturing and servicing of loading-arm equipment and systems.

5 Reasons to Choose OPW Loading-Arm Solutions

  1. Local factory support combined with 100-plus years of field experience that ensures the best outcome
  2. OPW’s 125+-year commitment to protecting people and the environment while enhancing business performance
  3. In-house machining, welding, X-ray, assembly, testing and packaging with all components “Made in the USA”
  4. The “OPW Promise” that guarantees the job is not completed until all expectations are met
  5. Streamlined part selection that reduces ordering, delivery and installation time, along with maintenance, repair and inventory costs


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