Material compatibility — fuming sulphuric acid (oleum): Select a suitable construction material for equipment handling oleum at typical ambient conditions.

Introduction / Context:
Fuming sulphuric acid (oleum) is highly concentrated H2SO4 containing free SO3. Correct materials prevent rapid corrosion and ensure safe storage and transfer in chemical plants.

Given Data / Assumptions:

• Service at ambient temperature (unheated storage/transfer).
• Oleum and very concentrated sulphuric acid form protective films on certain ferrous alloys.
• Chloride stress corrosion is not the dominant concern here.

Concept / Approach:
At high concentrations of H2SO4 and oleum, carbon steel rapidly passivates by forming a protective sulphate/oxide film, resulting in very low corrosion rates at moderate temperatures. Many austenitic stainless steels (e.g., 304) are not favored for strong sulphuric acid and oleum; nickel and Monel are also not typical selections for this medium in bulk equipment due to cost and specific corrosion behavior.

Step-by-Step Solution:
Match acid concentration and temperature to corrosion data.Select carbon steel for oleum at ambient conditions based on established industry practice.Rule out stainless 304 and nickel alloys that are vulnerable or uneconomic for this specific acid.

Verification / Alternative check:
Corrosion charts for sulphuric acid show a region of low corrosion rates for carbon steel at high concentrations and low temperature, including oleum storage tanks.

Why Other Options Are Wrong:
304 SS: susceptible in strong H2SO4. Nickel/Monel: not standard materials for oleum handling; unnecessary expense and sometimes poor performance.

Common Pitfalls:
Generalizing “stainless is best” without consulting acid concentration–temperature corrosion maps.

Final Answer:
Carbon steel