What is required for joint preparation before welding?

For effective welding, it is crucial that the joint surfaces are free of contamination. Contaminants such as dirt, oil, rust, moisture, paint, and other foreign materials can interfere with the welding process by affecting the quality of the weld. If the surfaces are contaminated, they can create defects in the weld, such as porosity, inclusions, or poor penetration, which can compromise the integrity and strength of the welded joint. Ensuring that the joint surfaces are clean allows for optimal fusion between the metals being welded, leading to stronger and more reliable welds.

The remaining options, while they may involve various practices in different contexts, do not fundamentally address the primary requirement for joint preparation before welding. Roughening the surfaces might help in some specific cases, but it is not a universal requirement. Heating the surfaces typically applies to particular materials or processes and is not a general necessity for all welding. Coating surfaces with protective layers might be relevant in certain applications but does not pertain to joint preparation specifically before welding.