The D1.1 code does not permit GMAW welding in which mode?

The correct answer is that the D1.1 code does not permit GMAW welding in the short-circuiting transfer mode. This is because the short-circuiting transfer mode, while useful in certain applications particularly for thinner materials, often results in lower quality welds in terms of penetration and potential for defect formation. In high-stress applications or structural welds where integrity and strength are critical, using this mode could lead to weld failures or compromised structures.

In contrast, the other modes of GMAW such as spray transfer mode, globular transfer mode, and pulse transfer mode are permitted under D1.1 because they provide better control over the heat input and penetration, resulting in a higher quality weld that is more suitable for structural applications. Spray transfer is known for its high deposition rates and is ideal for thicker materials, while globular transfer typically operates at higher currents and can be used for various thicknesses, albeit with caution for cleanliness. Pulse transfer mode offers advanced control over heat and can be beneficial for preventing burn-through on thin materials while still achieving good penetration in thicker sections.