Welding technology-Base material preparation

Base Metal Preparation is very important for weld quality. For Base Metal Preparation, the metal surface and the area within 50 mm of the weld joint must be clean. They must have no scale, rust, grease, moisture, or other bad things. These things can cause weld cracks and holes. So Base Metal Preparation asks for a clean surface.

Base Metal Preparation lets you prepare grooves in different ways. You can use machining, thermal cutting, arc gouging, chipping, or grinding. But if you use thermal cutting for Base Metal Preparation, the groove surface has a roughness limit. For steel up to 100 mm thick, the drag line depth must be ≤0.2 mm. For steel thicker than 100 mm, it must be ≤0.3 mm. If the drag line is deeper than that, or if there are notches or grooves, you must remove them by grinding or welding repair. So Base Metal Preparation says you cannot leave bad cuts.

Base Metal Preparation also covers rolling defects like laminations and cracks. You must check them with non‑destructive testing (NDT). For a laminate defect on the groove edge, if its length is over 25 mm, you measure its depth. If the depth is ≤6 mm, you grind it out. If the depth is >6 mm, you grind it out and then weld repair it. But if the defect depth is over 25 mm, you use ultrasonic testing. Then the defect is okay only if the defect area (a × d) is ≤4% of the cut steel section area. If not, you reject the steel plate. For internal laminate defects, if they are far from the groove (≥25 mm) and small, Base Metal Preparation says no repair is needed. But if they are too close (<25 mm), you must repair them. If a laminate defect is a real crack and its length and depth are ≤50 mm, you repair it. But if the crack depth is over 50 mm or the total crack length is over 20% of the plate width, Base Metal Preparation says you reject the steel.

One more thing about Base Metal Preparation: thin rust, thin coatings, or thin oxide layers from cutting are not a big problem. They have little water, so a multi‑pass weld or higher heat can let the gas escape. But loose scale or heavy rust has a lot of water, so it can cause holes. That is why Base Metal Preparation has strict rules for cleaning.

In short, Base Metal Preparation ensures the steel is clean, cuts are smooth, and defects are fixed or rejected. This stops cracks, holes, and bad fusion. So always follow Base Metal Preparation.