DOW Caustic Soda Solution

Bottom 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.

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. If necessary, heat the bottom outlet valve and the 50% caustic soda solution. See additional directions on the Thawing Frozen Caustic Soda Solution in Tank Cars page.
  3. Remove the protective housing covering the air inlet and eduction pipe valves on the top of the tank car.
  4. Slowly and carefully, open the valve on the 1" air inlet connection to relieve and equalize the pressure in the car.
  5. Open the dome cover only if a retainer sample of 50% caustic soda solution must be taken from the car.
  6. If a retainer sample is taken, close the cover, making sure the gasket is properly and securely in place and the dome latches are securely fastened.
  7. Cautiously remove the plug from the external bottom outlet valve. It may be necessary to use a second backup wrench to prevent the external bottom outlet valve from turning while removing the plug from the valve.
  8. Connect the unloading line to the external bottom outlet valve.
  9. Open the external bottom outlet valve.
  10. Recheck to be sure the manway cover is fastened securely.
  11. 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.
  12. Open the internal bottom outlet valve by turning the valve rod handle on the top of the tank car and allow the 50% caustic soda solution to flow. NOTE: If the outlet valve handle does not turn with moderate pressure, it indicates that some frozen caustic soda solution remains in the bottom of the car and further steam is necessary. Do not attempt to force the handle.
  13. Check for leaks.
  14. If a leak is found, close the internal and external bottom outlet valves, stop the flow of pressurized air to the car, and relieve the air pressure on the car.
  15. Correct all air or caustic soda solution leaks by tightening or replacing the leaking piping or fittings.
  16. Apply air pressure to the car slowly. Open the external bottom outlet valve and then the internal bottom outlet valve until there is a suitable flow of caustic soda solution to the storage tank.
  17. Make air pressure adjustment, if needed, until the tank car is empty. NOTE: A drop in pressure, or the sound of rushing air indicates that the car is empty.
  18. 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.
  19. 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.
  20. Close the internal bottom outlet valve and the external bottom outlet valve.
  21. Visually inspect the car to confirm it is empty. See Empty Tank Car Confirmation for more information.
  22. Clear and disconnect loading hose.
  23. Clean out the unloading hose with steam or water inside the containment area.
  24. 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.