Base Metal Preparation and Weld Quality
This domain covers fit-up and cleaning before the arc, plus the defects and inspection methods used to judge a finished weld. Exam items tend to link a preparation error to a specific discontinuity.
Joint preparation
Clean oil, paint, rust, moisture, and mill scale from the joint and at least 1 in of adjacent base metal. Use a dedicated stainless brush for stainless steel and a wheel that has not been contaminated by carbon steel. Bevel and root face follow the WPS; a common single-V groove for SMAW is 60° included, a 1/16–1/8 in root face, and about a 1/8 in root opening. Tack welds must be fused, cleaned, and feathered if they become part of the final weld.
Distortion and defects
Control distortion with balanced sequences, backstep, skip welding, pre-setting, clamping, and minimum heat input. Porosity is trapped gas; slag inclusion comes from poor interpass cleaning; lack of fusion is insufficient heat or wrong angle; incomplete penetration is a root-side problem; undercut is a melted groove at the toe; overlap is cold metal piled on the surface; cracks often involve hydrogen, restraint, or stress.
Inspection
Visual inspection comes first. Penetrant testing finds surface-breaking flaws; magnetic particle testing finds surface and near-surface flaws in ferromagnetic steel; ultrasonic and radiographic testing look for internal flaws.
Worked example: A 1/2 in plate has a 60° included V-groove, 1/8 in root opening, and 1/16 in root face. Depth to beveled = 1/2 − 1/16 = 7/16 in. Each side adds 7/16 × tan 30° = 0.252 in. Face width = 0.125 + 2(0.252) = 0.629 in, about 5/8 in. This checks whether the fit-up will accept the root pass and whether the bevel is per the WPS.
Traps: 60° included is not 60° per side; PT does not find internal defects; cleaning only the visible top of the joint leaves slag and porosity at the root.