Thawing Frozen Caustic Soda Solution in Tank Cars

Tank cars in DOW Caustic Soda Solution service are insulated to help prevent freezing. However, since caustic soda solution freezes around ambient temperatures (50% solution begins to freeze at about 58°F (14°C)) transit delays during cold weather may cause some freezing. Therefore, it is always a good idea to check the solution temperature before unloading.

If the temperature of a shipment of 50% caustic soda solution is above 85°F (29°C), it can generally be unloaded without steaming. If the temperature is below 65°F (18°C), steaming is almost always necessary. Between 65°F (18°C) and 85°F (29°C), it is often a good idea to heat the car to reduce the viscosity of the solution for easier and faster unloading.

Often it is not necessary to heat the entire tank car because it is not the contents of the car that restricts the unloading, but only caustic soda solution which has frozen around the outlet valve. As a first step to steaming a caustic soda solution tank car, it may only be necessary to steam the area around the outlet valve with a steam lance. This is particularly true for bottom unloading.

If the caustic can still not be pumped after steaming the outlet valve, further heating of the contents of the car is necessary. All cars used to ship DOW Caustic Soda solution contain steam coils, which enable customers to safely and easily heat the contents of the car.

Using the guidelines below, this operation can effectively be completed:

As with any unloading operation for caustic soda solution, proper personal protective equipment (PPE) must be worn. This includes close-fitting chemical worker’s safety goggles, chemical resistant gloves, and a hard hat as minimum protection. See Personal Protective Equipment for more information.
The car must be vented to avoid pressure building up in the car. This can be done by opening the manway cover or the vent valve on the top of the car. (Use caution while opening the vent valve, wear proper PPE, slowly open the valve and stand away from the valve outlet to avoid any potential discharge.)
Steam supply must be regulated down to 15 psig (103 kPa) or less to prevent damage to the tank car interior lining.
A steam trap should be installed on the outlet steam coil to maximize heating efficiencies.

Continued heating after the caustic soda solution is liquefied will waste steam and may damage the interior protective lining of the tank car. The temperature of 50% caustic soda solution should never exceed 150°F (66°C) in a lined tank car.

Never apply heat to caustic soda solution by blowing steam directly into the tank car without the expressed permission of The Dow Chemical Company. Lined tank cars must not be used as mixing tanks.

Once the caustic soda solution is completely thawed, the tank car is ready for sampling and unloading. Shut off and disconnect steam lines to the steam coil before starting the unloading procedure.

CAUTION: Continued steaming of the coils after the solution falls below the heating coil surface will destroy the lining in the tank car. In extremely cold weather, continue steaming the bottom outlet valve until the caustic soda solution flow to storage has begun.

Note: The freezing and thawing of a caustic soda solution has no effect on the quality of the product. However, it is typical for the caustic soda solution to become cloudy due to precipitated salt.

In cold weather, it is usually necessary to preheat the unloading lines to prevent the lines from plugging. This can be done with a maximum of 15 psig (103 kPa) steam tracing or by electrical heat tracing. Either way, the unloading line should be well insulated.

All horizontal portions of the unloading line leading to the top of the storage tank should be free draining toward the tank. This will assure that this portion of the unloading line is empty except when unloading.

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.

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However, since caustic soda solution freezes around ambient temperatures (50% solution begins to freeze at about 58°F (14°C)) transit delays during cold weather may cause some freezing. Therefore, it is always a good idea to check the solution temperature before unloading. If the temperature of a shipment of 50% caustic soda solution is above 85°F (29°C), it can generally be unloaded without steaming. If the temperature is below 65°F (18°C), steaming is almost always necessary. Between 65°F (18°C) and 85°F (29°C), it is often a good idea to heat the car to reduce the viscosity of the solution for easier and faster unloading. Often it is not necessary to heat the entire tank car because it is not the contents of the car that restricts the unloading, but only caustic soda solution which has frozen around the outlet valve. As a first step to steaming a caustic soda solution tank car, it may only be necessary to steam the area around the outlet valve with a steam lance. This is particularly true for bottom unloading. If the caustic can still not be pumped after steaming the outlet valve, further heating of the contents of the car is necessary. All cars used to ship DOW Caustic Soda solution contain steam coils, which enable customers to safely and easily heat the contents of the car. Using the guidelines below, this operation can effectively be completed: As with any unloading operation for caustic soda solution, proper personal protective equipment (PPE) must be worn. This includes close-fitting chemical worker’s safety goggles, chemical resistant gloves, and a hard hat as minimum protection. See Personal Protective Equipment for more information. The car must be vented to avoid pressure building up in the car. This can be done by opening the manway cover or the vent valve on the top of the car. (Use caution while opening the vent valve, wear proper PPE, slowly open the valve and stand away from the valve outlet to avoid any potential discharge.) Steam supply must be regulated down to 15 psig (103 kPa) or less to prevent damage to the tank car interior lining. A steam trap should be installed on the outlet steam coil to maximize heating efficiencies. Continued heating after the caustic soda solution is liquefied will waste steam and may damage the interior protective lining of the tank car. The temperature of 50% caustic soda solution should never exceed 150°F (66°C) in a lined tank car. Never apply heat to caustic soda solution by blowing steam directly into the tank car without the expressed permission of The Dow Chemical Company. Lined tank cars must not be used as mixing tanks. Once the caustic soda solution is completely thawed, the tank car is ready for sampling and unloading. Shut off and disconnect steam lines to the steam coil before starting the unloading procedure. CAUTION: Continued steaming of the coils after the solution falls below the heating coil surface will destroy the lining in the tank car. In extremely cold weather, continue steaming the bottom outlet valve until the caustic soda solution flow to storage has begun. Note: The freezing and thawing of a caustic soda solution has no effect on the quality of the product. However, it is typical for the caustic soda solution to become cloudy due to precipitated salt. In cold weather, it is usually necessary to preheat the unloading lines to prevent the lines from plugging. This can be done with a maximum of 15 psig (103 kPa) steam tracing or by electrical heat tracing. Either way, the unloading line should be well insulated. All horizontal portions of the unloading line leading to the top of the storage tank should be free draining toward the tank. This will assure that this portion of the unloading line is empty except when unloading. 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.
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