Mild steel corrosion and caustic

I don't know what 300+ steel means. I'm hoping you mean 303 or 304 stainless, both of which are rated excellent for 50% NaOH at 175F by Hoke.

This might increase confidence in the set-up. Mild steel is generally used in contact with NaOH solutions.

I am not sure of the corrosion rate, but I am confident that a 3M formerly Thortex Chemi-Tech EP coating would lower your total lifecycle cost and extend the life of the tank.

Get some coupons of the same steel you want to use, and partially submerge them in the same caustic solution you plan to use, cover the container, and look at the coupons every few days or once a week....

if you're talking about a Stainless Steel 3xx (304, 316) or Carbon - Low Alloy Steels then you can use it, look at this reference:

"Corrosion by caustic (sodium or potassium hydroxide) at all concentrations is easily handled at room temperature with a variety of metals and alloys, including carbon steels. It becomes increasingly more corrosive with increasing temperature and concentration. The useful safe limit of carbon steel is approximately 150^oF/65^oC, both with regard to caustic stress corrosion cracking (CSCC) and corrosion. Stainless steels are more resistant to general corrosion compared with carbon steel; however, they can suffer CSCC at approximately 250^oF/121^oC. "

Hope this help

S.

GA

Chemical Compatibility Database from Cole-Parmer United Kingdom (coleparmer.co.uk)

Yes. Microsoft Copilot does:

"The corrosion rate of mild steel exposed to a caustic solution can vary depending on several factors such as the concentration of the solution, the temperature, and the presence of other chemicals. However, I found some information that might be helpful:

• A discussion thread on GlobalSpec1 mentions a similar query where a user was designing a Mild Steel tank for holding 48% w/w of Caustic, NaOH at ambient temperature. However, the exact corrosion rate was not provided in the discussion.
• A document from the Nickel Institute2 mentions that steels can be subject to a form of stress-corrosion cracking in 55% caustic at as low as 50 °C (120 °F), with a corrosion rate of 1.3 mm/y (50 mpy).
• A study on the corrosion behaviour of Type 316L Stainless Steel in hot caustic aqueous3 mentions that exposure to room temperature environment showed parabolic weight loss behaviour, with corrosion rates of up to 0.4 mm/year. Higher NaOH concentrations and exposure temperatures resulted in a reduced stability of the electrochemical passivity domain, associated with higher corrosion rates.

Please note that these are general figures and the actual corrosion rate can vary based on specific conditions. It’s always a good idea to conduct tests under the specific conditions that the material will be exposed to. If you need more specific information, I recommend consulting with a corrosion engineer or a materials scientist."