Which material is prohibited for use in pressure parts or welded components in API 650?

• A. Aluminum
• B. Steel
• C. Cast Iron
• D. Copper

Answer: (C)

The correct material that is prohibited for use in pressure parts or welded components in API 650 is cast iron. This prohibition is based on the material's properties, particularly its brittleness and tendency to crack under load or when subjected to stress. Cast iron does not perform well under the conditions typically encountered in welded tank applications, especially when pressure is involved. Its inability to handle dynamic loads and its lesser ductility compared to other materials like steel make it unsuitable for components that must ensure the integrity and safety of oil storage tanks.

In contrast, both steel and aluminum are commonly used in the construction of tanks due to their favorable mechanical properties and weldability. Copper, while also not typically used for welded tank construction, is not specifically prohibited and can serve certain applications in a non-pressurized context. The use of cast iron is specifically restricted to ensure safety and reliability in the storage of oil and other liquids.