What type of joints are vertical shell joints required to be?

• A. Fillet Joints
• B. Butt Joints
• C. Lap Joints
• D. Seam Joints

Answer: (B)

Vertical shell joints in welded tanks are required to be butt joints primarily to ensure structural integrity and load-bearing capabilities. Butt joints allow the edges of the two pieces of material—such as the tank shell sections—to meet directly, enabling a strong, continuous weld. This type of joint is critical in tank construction as it provides a smooth surface with minimal stress concentration, crucial for maintaining the tank’s ability to contain liquids safely under pressure or fluctuating temperatures.

Furthermore, butt joints are more suitable for maintaining the overall strength of the structure, preventing issues like leaks that may arise from weaker joint designs. This design choice also aligns with the requirements set forth in API 650, which emphasizes joint efficiency and performance in welded tanks for oil storage, ensuring that the tanks can withstand the operational stresses without compromising safety or structural reliability.