Welding Technology: Processes, Electrodes and Defect Control
Core concepts to master
A BTEB welding candidate must be able to match a process to its power source, filler and typical use. Know SMAW (manual metal arc): a flux-coated consumable electrode, constant-current supply, polarity chosen by electrode class. Know MIG/MAG (GMAW): continuous wire, DC reverse polarity (electrode positive), shielding gas - argon-rich for aluminium, CO2 or argon-CO2 mixes for carbon steel. Know TIG (GTAW): non-consumable tungsten electrode, separate filler, DCEN for steel, AC for aluminium to break the oxide film. Also understand oxy-acetylene gas welding, with a neutral flame for steel and a carburising flame for hardfacing.
Electrode coding is a favourite question area. In a designation such as E6013, the 60 means minimum tensile strength in ksi (about 430 MPa), the 1 is the usable position (1 = all positions), and the 3 encodes coating type and current. E6013 is a rutile electrode for general work on thin sheet; E7018 is basic (low-hydrogen) and must be stored dry and used on DC or AC. Low-hydrogen electrodes reduce the risk of hydrogen cracking in restrained joints.
Traps examiners set
Do not confuse polarity names: DCEN (straight polarity) puts more heat in the workpiece and gives deeper penetration; DCEP (reverse polarity) gives more heat at the electrode, better cleaning and shallower penetration. Questions often ask which polarity suits TIG on steel - the answer is DCEN. Another trap is naming a defect from its cause: porosity comes from moisture, dirt or poor gas coverage; slag inclusion from incomplete cleaning between passes; undercut from excessive current or wrong travel angle; lack of fusion from too low a current or too fast travel.
Worked rule of thumb
For a butt weld in 6 mm mild steel with E6013 on DC, a common starting current is about 30–40 A per millimetre of electrode core diameter; a 3.2 mm electrode therefore starts near 100–130 A, adjusted by bead appearance. Keep arc length roughly equal to the electrode core diameter.
Study approach
Practise reading electrode codes backwards and forwards, sketch each process's circuit, and link every defect to a current, travel or preparation cause.