Which weld type requires the design drawing to specify the required effective throat?

Which weld type requires the design drawing to specify the required effective throat?

• A. Fillet welds
• B. Backing welds
• C. Groove welds without backing
• D. Partial Joint Penetration groove welds

Answer: (D)

The key idea here is that the load-c carrying capacity of a weld groove depends on how much material actually fuses across the joint—the effective throat. For partial joint penetration groove welds, the strength is controlled by this specific throat dimension, which determines how much of the joint thickness is welded. Because the actual penetration can vary, the design drawing must specify the required effective throat to ensure the weld can carry the intended load. Fillet welds rely on the fillet throat set by the leg sizes (often expressed as leg length), so the drawing focuses on leg dimensions rather than an explicit effective throat. Groove welds with backing plates are designed to achieve full penetration, with the backing helping control penetration, so an explicit effective throat on the drawing isn’t the primary control. Groove welds without backing can vary in penetration, but the crucial, explicit specification of an effective throat is most characteristic of partial joint penetration groove welds to guarantee the intended strength.

The key idea here is that the load-c carrying capacity of a weld groove depends on how much material actually fuses across the joint—the effective throat. For partial joint penetration groove welds, the strength is controlled by this specific throat dimension, which determines how much of the joint thickness is welded. Because the actual penetration can vary, the design drawing must specify the required effective throat to ensure the weld can carry the intended load.

Fillet welds rely on the fillet throat set by the leg sizes (often expressed as leg length), so the drawing focuses on leg dimensions rather than an explicit effective throat. Groove welds with backing plates are designed to achieve full penetration, with the backing helping control penetration, so an explicit effective throat on the drawing isn’t the primary control. Groove welds without backing can vary in penetration, but the crucial, explicit specification of an effective throat is most characteristic of partial joint penetration groove welds to guarantee the intended strength.