Material selection starts with the process
Stainless steel grade cannot be selected from the product name alone. Concentration, impurities, chloride level, pH, temperature, aeration, cleaning chemicals, residence time and the possibility of deposits all affect corrosion behaviour. The fabrication route, weld condition and required surface finish must also be considered.
A practical comparison
| Grade | Typical strengths | Points to review |
|---|---|---|
| AISI 304 | General-purpose food, water and mild chemical duties | Limited resistance where chlorides or aggressive cleaning media are present |
| AISI 316 | Improved pitting resistance through molybdenum addition | Still requires a duty-specific corrosion review |
| AISI 316L | Low-carbon grade preferred for many welded fabrications | Welding quality, pickling and passivation remain important |
Chlorides, temperature and deposits
Pitting and crevice corrosion risk generally rises with chloride concentration, temperature and stagnant conditions. Deposits, gaskets and poorly drained details can create local environments that are more aggressive than the bulk fluid. A material that performs in a clean laboratory sample may behave differently in a production tank with heat, oxygen gradients and cleaning cycles.
Welding and surface condition
The selected grade is only one part of corrosion performance. Weld procedures, heat tint removal, pickling, passivation, surface roughness and fabrication cleanliness influence the finished equipment. Carbon-steel contamination during grinding or handling should be prevented, particularly for hygienic and high-purity duties.
Information required before selection
Provide the full formulation and likely contaminants, minimum and maximum operating temperatures, cleaning chemicals and concentrations, pressure or vacuum, expected service life, product-contact finish and any applicable customer or regulatory specification. Where corrosion risk is uncertain, coupon testing or specialist materials advice may be appropriate.