Cast iron fittings shall not be used in which piping service?

• A. Oil
• B. Water
• C. Gas
• D. Steam

Answer: (A)

Cast iron fittings aren’t suited for oil service because their material properties and chemical compatibility don’t match hydrocarbons. Oil and other petroleum products can interact with cast iron in ways that make the fittings more prone to corrosion, cracking, or leakage, especially under the pressures and temperatures typical of oil piping. Cast iron is brittle and not reliable for handling the stress and thermal cycling that oil systems can experience, so tougher materials like steel or ductile iron are used for oil piping. In contrast, water and steam systems commonly use cast iron fittings because the fluids and operating conditions are more compatible with cast iron’s characteristics.