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Monday
Jul052010

Pumping Tank Cars

     The transfer of a damaged Rail Car is a precise operation requiring more than one talent. It has been accomplished safely by railroad personnel, so there are many time proven techniques the Haz-Mat Responder can assist with on scene. A transfer is an option when damage to the car prevents it from being moved to either a loading “rack” {fixed site train car loading area} for proper unloading, or be reset on its “trucks” {wheels} by train riggers, to continue on its way. These techniques are preferred, as there is a great risk to life and environmental contamination from portable pumping operations. Hazardous materials in rail tank cars can be divided into two general categories.

1] Products with a vapor pressure of less than, < 40 psi, usually found as liquids and,

2] Products with a vapor pressure greater than, > 40 psi, found as liquefied compressed gas. There are three {3} basic techniques that are used in pumping damaged rail cars due to de-railment,

1] the transfer of contents pneumatically

2] pumping the contents mechanically and,

3] a combination of both strengths.

These techniques need assessment and evaluation by a railroad specialist. You should be affluent with all three types to be able to contribute questions, favoring the outcome of the operation.

     For all techniques there are some commonalities. 1] All lines and fittings for gas, air, and hazardous product must have matching fittings and be chemically compatible. This minimizes field failure when product is in the line. 2] Check valves and manned shut-off valves must be placed at every “juncture” {pump, tanks, etc,} to minimize contaminant release in the event of a system break-down during transfer. 3] Product conduit {lines, sight glasses, pressure gauges} must be “purged” {flushed out} with the appropriate inert gas prior to and after product flow. 4} Appropriate PPE {Personal Protective Equipment} must be worn before, during and after the transfer. 5} all equipment must be electrically bonded and grounded. 6] If tank contents have cooled below their flow temperature, a steam generator must be available to heat the tank cars. 7] The use of sight glasses and pressure gauges are preferred to monitor product level and interior tank pressures or vacuum.

     From the drawings you can clearly see that a pneumatic transfer pressurizes the vapor line from the “bad” car by forcing product out through the liquid line into the “good car”. The primary drawbacks to this system are, 1] a large quantity of air or inert gas is required, 2] air pneumatic pumps tend to freeze in cold weather {due to moisture in the atmosphere} and 3] you are pressurizing a damaged car. While the first two may be conquered, the third is always suspect even with seasoned railcar damage assessment “technicians” on scene. While this may be unlikely due to the intrinsic strength of these rail cars, never the less, it is a gamble after the extreme trauma from a de-railment.

     Liquid transfer by pumping also has its challenges. Pumps tend to seize up with thicker products {see number 6}. If “Blanketing” is required by the product, inert gas such as Nitrogen may need to be simultaneously pumped into the “headspace” or “outage” of both cars. “Blanketing” is needed for selected products to prevent them from reacting with the atmosphere, this is referred to as a “pad”, for the product.  Additionally, a vacuum pump may have to create vacuum in the “good” car to reduce its’ atmosphere, before the product is loaded.

     A combination method can be used combining the best of both. Here, the atmospheric pressure inside both cars is monitored with gauges to insure the pressure or vacuum does not exceed the strengths or needs of the system. By creating “slight” pressure in the “bad” car and “slight” vacuum in the “good” car, you increase the product feed to the intake pump, while creating a more effective flow discharge rate into the “good” car. Remember, with increased flow rate comes increased static electricity. Paramount with all procedures involves “bonding” both cars together and properly “grounding” the entire system before transfer begins. This must be done to minimize the potential for a stray coronal ignition spark.

                                               Haz Mat Mike 

 



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