Overview
ISO 18069:2015 - Corrosion of metals and alloys - Method for determination of the uniform corrosion rate of stainless steels and nickel based alloys in liquids - defines a laboratory immersion test to estimate uniform corrosion rate, and to assess the ability of stainless steels and nickel‑based alloys to repassivate (passivate after activation) in intended liquids under atmospheric (aerated) conditions. It is intended for the chemical industry as an estimation method (not a qualification test) and can be used to produce iso‑corrosion diagrams and identify the temperature where corrosion rate exceeds 0.1 mm/a. The method is not intended for rates above 1 mm/a or for solutions containing halides (especially chlorides), which can cause localized corrosion.
Key topics and technical requirements
- Test sequence: three sequential immersion periods - 24 h, 72 h, and 72 h (with activation); mass is measured before and after each period.
- Activation: performed at the start of period 3 to evaluate repassivation. Accepted activation methods: potentiostatic, zinc contact, or HCl immersion (HCl activation recommended for strongly oxidizing solutions or ferrous sulfate).
- Measurement and calculation:
- Mass loss (Δm) measured with high‑precision balance (document specifies 0.0001 g accuracy).
- Corrosion rate rcor (mm/a) calculated from Δm, specimen area, exposure time, material density and the conversion factor 8760 h/year: rcor = (8760 · Δm) / (A · t · ρ).
- Equipment & controls: inert test vessels and holders, temperature control ±1 °C, stirring when needed, and potentiostat capability to control potential within ±1 mV when potentiostatic activation is used.
- Specimen preparation: orientation representative of service surface, edges minimized and ground (edges to at least P120 grit), cleaned by degreasing, rinsing with high‑purity water and ethanol, and air‑dried; specimens must form a stable passive film before testing.
- Test liquids: may be laboratory‑prepared (reagent grade chemicals + high‑purity water) or actual process solutions; take safety and vessel compatibility precautions.
Practical applications
- Material selection and lifetime estimation for stainless steels and nickel‑based alloys in process liquids.
- Development of iso‑corrosion diagrams and determination of critical temperatures where uniform corrosion exceeds 0.1 mm/a.
- Comparative corrosion screening of alloys under defined, aerated conditions to support design decisions in the chemical, petrochemical and processing industries.
Note: do not use this method to assess localized corrosion (pitting/crevice) or in chloride‑containing media where localized attack dominates.
Who uses this standard
- Corrosion engineers, materials scientists, metallurgists, laboratory technicians, OEMs and asset owners in chemical and process industries involved in materials selection, corrosion testing, and asset integrity management.
Related standards
- ISO 3696 - Water for analytical laboratory use
- ISO 8044 - Corrosion of metals and alloys - Basic terms and definitions
- ISO 17864 - Determination of the critical pitting temperature under potentiostatic control
Keywords: ISO 18069:2015, corrosion rate, uniform corrosion, stainless steels, nickel based alloys, passivation, corrosion testing, iso‑corrosion diagrams, chemical industry.