Which type of steels is prohibited according to API 650 Section 4?

• A. High carbon steels
• B. Rimmed or capped steels
• C. Alloy steels
• D. Stainless steels

Answer: (B)

According to API 650 Section 4, rimmed or capped steels are prohibited for use in the construction of welded tanks for oil storage. The prohibition stems from the fact that rimmed and capped steels are produced using processes that can lead to a segregation of alloying elements and non-metallic inclusions, which can negatively affect their mechanical properties, including toughness, ductility, and weldability. This quality concern is particularly critical for storage tanks that must withstand various environmental and operational conditions.

The guidelines in API 650 emphasize the importance of using materials that ensure structural integrity and safety. By specifying that rimmed or capped steels are not allowed, API 650 ensures that the steel used in tank construction adheres to quality standards that promote reliability and longevity of the tanks. Other steel types listed, such as high carbon steels, alloy steels, and stainless steels, may have their own set of limitations or requirements, but they are not outright prohibited in the same way rimmed or capped steels are.