What is a possible cause of a longitudinal crack in a submerged arc weld bead?

• A. Use of damp flux
• B. Specified pre-heat temperature not used
• C. Arc voltage used was too high
• D. Weld bead was very deep and narrow

Answer: (D)

A longitudinal crack in a submerged arc weld bead can indeed be attributed to the weld bead being very deep and narrow. This particular geometry can create a high-stress concentration in the weld metal and the heat-affected zone (HAZ). When the bead is deep, it typically undergoes higher cooling rates, leading to greater thermal stresses. A narrow bead may also exacerbate the issues related to solidification and cooling, making it more prone to cracking.

In the context of welding, such cracks usually originate from the combination of thermal expansion and contraction, along with the solidification processes that lead to a high degree of local stress. The design of the weld bead influences its ability to accommodate these stresses without cracking. Therefore, when a weld has a narrow profile and a significant depth, it often compromises its ability to manage those stresses effectively, resulting in the formation of longitudinal cracks.

Other factors mentioned in the other answer choices can cause issues in the weld, but they do not directly lead to the formation of a longitudinal crack in the way that the geometry of the weld bead does.