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One of the leading causes of accidental spills of propane is a pull-away at a transfer area. The term pullaway refers to an accident caused by a bobtail or transport “pulling away” from the transfer point while the hoses are still connected. A pull-away may break the hose or even pull out the piping network, creating a large propane leak and possible fire. To avoid these problems, most transfer areas use bulkheads and emergency shut-off valves (ESVs).
In this module you will learn to identify:(1) Operating characteristics of bulkheads (2) Operating characteristics of emergency shut-off valves
Identifying Operating Characteristics of Bulkheads
Bulkheads— are located where the plant hoses connect to a large piping network where transports & bobtails are loaded & unloaded.
• Bulkheads are normally made from steel beams and reinforced concrete, and often are surrounded by large steel or concrete posts to prevent vehicles from colliding with the critical piping.
• NFPA 58 and many state and local codes stipulate that a stanchion should be able to withstand a force from any direction sufficient to cause the worst mechanical or structural damage to be on the vehicle side of the transfer point.
Bulkhead maintenance is limited to inspection of fittings, valves, and stanchions for structural integrity and propane leaks, especially in the event of a pull-away.
Emergency Shut-Off Valves (ESVs) are (one type of) valves that may be used to automatically stop the flow of propane in the event of a pull-away.
NFPA 58 requires that the valves be installed in the liquid or vapor lines of certain piping systems within 20 ft. of the junction of hose and rigid piping. In some plants, ESVs are often installed at the bulkheads for loading bulk trucks and unloading transports. In addition, they are installed at the hose junctions on tank car unloading risers.
New provisions for transfer area protection require the installation of ESVs to protect against hose failure resulting from a number of circumstances, including ruptures, exposure to fire, and pullaways.
Mechanical Emergency Shut-off Valves— Because the main valve disc is spring loaded and directly in the propane flow path, the valve also functions as an excess flow check valve.
Pneumatic Emergency Shut-off Valves – There are certain valves available today which are truly pneumatic ESVs; that is, the pneumatic operator is an integral, internal part of the valve.
Pneumatic Emergency Shut-off Valves – There are certain valves available today which are truly pneumatic ESVs; that is, the pneumatic operator is an integral, internal part of the valve.
• Manufacturer's literature details the requirements and procedures for maintenance and repair.
• An annually documented test of the ESV is required by NFPA 58.
• ESVs should be inspected frequently for gas leakage at all body seams, plus the connections to piping and hose.
• The pneumatic control system should be checked frequently for proper operation; check for leaks by pressurizing the system and checking all connections with liquid leak detector or a soapy water solution.
• Conduct frequent tests of the closing feature of the ESVs under simulated conditions.