Materials of Construction

Caustic soda solution users are responsible for building and maintaining a properly designed storage and handling system which meets applicable safety and regulatory requirements. Each caustic solution user is responsible for determining which construction materials are suitable for its individual facility.

For 50% caustic soda solution, carbon steel, carbon steel with a protective coating, stainless steel metals, nickel, and nickel alloys can all be successfully used for equipment construction.

Mild carbon steel butt-welded tanks are commonly used at temperatures below 120°F (49°C) where an increased level of iron impurity is not a problem. Welding should be done with appropriate rods such as those containing 1/2% molybdenum. Annealing to prevent stress corrosion cracking is not required for 50% caustic soda solution storage tanks unless temperatures greater than 120°F (49°C) are expected. See the Caustic Soda Service Graph.

For 50% caustic soda solution with temperatures above 160°F (71°C) materials of a nickel or nickel alloy construction should be used. Other metallurgies such as austenitic stainless steels (304L, 316L), ferritic stainless steels, and duplex stainless steels have been successfully used, however, higher corrosion rates and the risk of chlorine stress crack corrosion make these metals less desirable.

Fiberglass reinforced plastic (FRP) for caustic soda solution storage equipment should be used after careful consideration of process conditions and consultation with the resin supplier. Without proper protection, caustic soda solution can readily attack the glass fibers and weaken the structural integrity of equipment resulting in equipment failure.

FRP has successfully been used for highly iron sensitive processes when used with a synthetic surface veil and an appropriate corrosion barrier. Some of the vinyl ester and epoxy resins have good resistance for caustic soda service within certain temperature and concentration limits. The resin selection should be carefully reviewed, especially if the process caustic concentration is greater than 20%.

Aluminum, magnesium, zinc, tin, chromium, bronze, brass, copper, and tantalum are incompatible with caustic soda solution and should not be used.

Galvanized (zinc coated) materials should not be used in caustic storage and process areas. For iron sensitive processes, the application of a protective coating (epoxy resin, thermoplastic), bonded alloy (nickel, nickel alloy), or an elastomer liner (natural rubber, neoprene) have all been successfully used. See Tank Linings for additional information.

For additional information on storage tank materials of construction, review The Chlorine Institute, Inc. Pamphlet 094 "Sodium Hydroxide Solution and Potassium Hydroxide Solution (Caustic): Storage Equipment and Piping Systems." This pamphlet and additional resource materials can be purchased through the Chlorine Institute web site or send your request via fax to (703) 741-6068.

Caustic Soda Service Graph (33KB PDF)

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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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Each caustic solution user is responsible for determining which construction materials are suitable for its individual facility. For 50% caustic soda solution, carbon steel, carbon steel with a protective coating, stainless steel metals, nickel, and nickel alloys can all be successfully used for equipment construction. Mild carbon steel butt-welded tanks are commonly used at temperatures below 120°F (49°C) where an increased level of iron impurity is not a problem. Welding should be done with appropriate rods such as those containing 1/2% molybdenum. Annealing to prevent stress corrosion cracking is not required for 50% caustic soda solution storage tanks unless temperatures greater than 120°F (49°C) are expected. See the Caustic Soda Service Graph. For 50% caustic soda solution with temperatures above 160°F (71°C) materials of a nickel or nickel alloy construction should be used. Other metallurgies such as austenitic stainless steels (304L, 316L), ferritic stainless steels, and duplex stainless steels have been successfully used, however, higher corrosion rates and the risk of chlorine stress crack corrosion make these metals less desirable. Fiberglass reinforced plastic (FRP) for caustic soda solution storage equipment should be used after careful consideration of process conditions and consultation with the resin supplier. Without proper protection, caustic soda solution can readily attack the glass fibers and weaken the structural integrity of equipment resulting in equipment failure. FRP has successfully been used for highly iron sensitive processes when used with a synthetic surface veil and an appropriate corrosion barrier. Some of the vinyl ester and epoxy resins have good resistance for caustic soda service within certain temperature and concentration limits. The resin selection should be carefully reviewed, especially if the process caustic concentration is greater than 20%. Aluminum, magnesium, zinc, tin, chromium, bronze, brass, copper, and tantalum are incompatible with caustic soda solution and should not be used. Galvanized (zinc coated) materials should not be used in caustic storage and process areas. For iron sensitive processes, the application of a protective coating (epoxy resin, thermoplastic), bonded alloy (nickel, nickel alloy), or an elastomer liner (natural rubber, neoprene) have all been successfully used. See Tank Linings for additional information. For additional information on storage tank materials of construction, review The Chlorine Institute, Inc. Pamphlet 094 "Sodium Hydroxide Solution and Potassium Hydroxide Solution (Caustic): Storage Equipment and Piping Systems." This pamphlet and additional resource materials can be purchased through the Chlorine Institute web site or send your request via fax to (703) 741-6068. Caustic Soda Service Graph (33KB PDF) back 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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