Caustic soda solutions attack some materials and leave others untouched. Choosing the wrong tank, pipe, valve or gasket leads to leaks, contamination and, with some metals, flammable hydrogen gas. This guide summarises material choices for storing and handling caustic soda solutions.
Metals
| Material | Suitability |
|---|---|
| Carbon steel | Widely used for caustic storage at ambient temperature. At higher temperatures and concentrations it can suffer caustic stress corrosion cracking, so stress-relieved construction or other materials are used for hot service. |
| Stainless steel 304 / 316 | Good for most caustic duties, including food and higher-purity service. Watch chloride content in hot solutions. |
| Nickel and high-nickel alloys | Used for hot, concentrated caustic, such as evaporators. |
| Aluminium, zinc, galvanised steel, tin | Not suitable. Rapidly attacked, releasing hydrogen gas. |
| Copper and brass | Generally avoided; can be attacked and can contaminate the solution. |
Plastics and composites
- HDPE and polypropylene: widely used for tanks, IBCs and piping at moderate temperatures.
- PVC and CPVC: used for piping within their temperature limits.
- FRP: suitable when built with the right resin and a caustic-resistant inner layer; standard polyester FRP is not suitable.
Seals and gaskets
EPDM is commonly used for caustic service. PTFE is resistant to caustic at most strengths and temperatures. Some rubbers and elastomers swell or harden in caustic, so always check the supplier's chemical resistance chart for your concentration and temperature.
Tank design points
- Provide bunding to hold at least the tank contents.
- Fit a vent; consider a carbon dioxide trap to limit carbonate formation.
- For 50% lye in cool locations, add insulation and heating, because it crystallises at around 12 °C.
- Label the tank with contents, strength and hazard symbols.
- Place an eyewash and safety shower near filling and dispensing points.
Flakes avoid bulk storage
Many smaller users avoid bulk tanks altogether by buying 25 kg bags of flakes and dissolving only what they need. For sites in Oman, details of flakes 99% with ready stock in Barka are on our Oman caustic soda page.
