A welder must know the design of machines and apparatuses for arc welding when using alternating and direct current; methods and main techniques of tack welding; joint preparation forms for welding; cylinder structure; colors, paints, and handling rules; gas-shielded welding rules and safety provisions for welding; maintenance rules for welding machines; types of welded joints and seams; rules for preparing the edges of items for welding; types of edge preparations and weld symbols on drawings; basic properties of electrodes, metals, and alloys being welded; purpose and conditions for using measuring and testing devices; causes of welding defects and prevention methods; design of non-consumable electrode welding torches in shielding gas; structure of welding machines and welding chambers used; requirements for the welding seam and surfaces after oxygen cutting (planing); properties and significance of electrode coatings; basic types of weld inspection; methods for selecting electrode grades based on steel grades; causes of internal stresses and deformations in welded items and preventive measures; types of defects in welds and methods for their prevention and correction; principles for selecting welding modes according to instruments; grades and types of electrodes; and mechanical properties of the metals being welded.