Top Unloading by Air Pressure

Personal protective clothing and equipment must be worn throughout the preparation steps as well as during unloading. For specific information, see the Personal Protective Equipment section.

The illustration below illustrates a typical layout for unloading caustic soda solution through the eduction pipe by air pressure:
Top Unloading Caustic Soda by Air Pressure

Safety showers and eyewash fountains should be conveniently located, clearly marked and readily accessible to personnel in areas where normal operations or maintenance could expose personnel to caustic soda solution. Safety showers should be located directly above the eyewash fountains. Self-draining and heated safety showers and eyewash stations may be required in freezing conditions. Safety showers and eyewash fountains should be tested frequently for proper operation and especially before work begins in the vicinity. It is recommended that a horn or other such alarm device be installed at the safety shower so that it can be activated to summon help if use of the safety shower and/or eyewash fountain becomes necessary.

  1. Be sure the storage tank vent is clear and the tank has enough volume to hold the contents of the car while leaving at least 10% of the storage tank unfilled (freeboard).
  2. Remove the protective housing covering the air inlet and eduction pipe valves on the top of the tank car.
  3. Slowly and carefully, open the valve on the 1" air inlet connection to relieve and equalize the pressure in the car.
  4. Open the dome cover only if a retainer sample of 50% caustic soda solution must be taken from the car.
  5. If a retainer sample was taken, close the cover, making sure the gasket is properly and securely in place and the dome latches are securely fastened.
  6. Connect the unloading line to the discharge pipe valve connection.
  7. Connect the air supply line to the air inlet valve located on the top of the tank car. Open the air inlet valve and apply air pressure to the car slowly. Typical air pressure is 30 psi.
  8. Cautiously open the eduction pipe outlet valve until there is a suitable flow of caustic soda solution to the storage tank.
  9. Check for leaks.
  10. If a leak is found, close the eduction pipe outlet valve, stop the flow of pressurized air to the car, and relieve the air pressure on the car.
  11. Eliminate all air or solution leaks by tightening or replacing the leaking piping or fittings.
  12. Apply air pressure to the car slowly and open the eduction pipe outlet valve until there is a suitable flow of caustic soda solution to the storage tank.
  13. Make air pressure adjustments, if needed, until the tank car is empty. NOTE: A drop in pressure, or the sound of rushing air, indicates that the car should be empty.
  14. When the unloading line is completely drained, shut off the air supply line and allow the system to stand for a few minutes to relieve all internal pressure in the car. Let the discharge pipe drain.
  15. Close the air inlet valve, de-pressure the air inlet line, and then disconnect the air supply line fittings from the air inlet on the dome.
  16. Close the eduction pipe outlet valve.
  17. Visually inspect the car to confirm it is empty. See Empty Tank Car Confirmation for directions.
  18. Clear and disconnect loading hose.
  19. Clean out the unloading hose with steam or water inside the containment area.
  20. Prepare the car for return to Dow. See Empty Tank Car Return for more information.
The information contained above is supplemental to the Internet Disclaimer and is not intended to be all-inclusive as it relates to use, handling, storage, disposal and all other described activities. Recipients must make their own determination of suitability and are responsible for compliance with all applicable federal, state, provincial, municipal laws and/or other regulations. This information is offered solely for your consideration and verification and in no event will The Dow Chemical Company be responsible for damages of any nature whatsoever resulting from the use or reliance upon this information or the product to which this information pertains.