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1. Scope: This technical standard applies to manual arc welding work for the fabrication and installation of steel structures in general industrial and civil construction projects. II. Construction Preparation 2.1 Materials and Main Equipment 2.1.1 Welding electrodes: Their models shall be selected in accordance with the design requirements, and they must come with quality certificates. Baking is performed before welding as required. Welding rods with flaked coating or rusted electrodes are strictly prohibited from use. When no specific requirements are given for the design, E43 series carbon steel structural welding electrodes are suitable for welding Q235 steel ； When welding 16Mn steel, E50 series low-alloy structural steel electrodes are recommended ； Low-hydrogen electrodes (alkaline electrodes) are recommended for welding important structures. After baking as instructed, place it in a insulated container for easy access whenever needed. Acidic welding electrodes and alkaline welding electrodes must not be used together. 2.1.2 Arc starting plate: An arc starting plate is required when using a groove for connection; the material of the arc starting plate and the type of groove should be the same as those of the welded parts. 2.1.3 Main tools: welding machines (AC and DC), welding cable, welding tongs, mask, hammer, electrode oven, electrode insulation container, wire brush, asbestos strips, thermometer, etc. 2.2 Operating Conditions 2.2.1 Become familiar with the drawings and conduct a welding process briefing. 2.2.2 Before welding, the validity period of the welder’s certificate should be checked to ensure that it confirms the type of welding work the welder is qualified to perform. 2.2.3 The on-site power supply shall meet the requirements for welding. 2.2.4 When the ambient temperature is below 0°C, preheating and post-heating temperatures shall be determined based on process testing. III. Operating Procedures 3.1 Process flow: Preparation for work → Arc welding (flat welding, vertical welding, horizontal welding, overhead welding) → Weld inspection 3.2 Arc welding of steel structures: 3.2.1 Flat welding 3.2.1.1 Select appropriate welding parameters such as electrode diameter, welding current, welding speed, and welding arc length, which are verified through welding process tests. 3.2.1.2 Cleaning the weld joint: Before welding, check whether the groove and assembly gap meet the requirements, and whether the tack welds are secure; there should be no oil or rust around the weld seam. 3.2.1.3 Welding electrodes should be baked at the specified temperature for the specified time. Once taken out of the oven, they should be placed in a welding electrode storage container and used as needed. 3.2.1.4 Welding current: Select an appropriate welding current based on factors such as the thickness of the workpiece, the welding layer, the type and diameter of the electrode, and the welder’s skill level. 3.2.1.5 Arc initiation: The start and end points of the arc in fillet welds should be at the ends of the weld, with a distance of more than 10 mm between them. Arc initiation should not be done casually; once the arc is established, the welding rod should be immediately pulled away from the weld area, maintaining a gap of 2–4 mm between the welding rod and the component in order to sustain the arc. For butt welds and fillet weld combinations, arc starting plates and lead plates are placed at both ends of the weld; the arc must be started on the arc starting plate before welding begins in the weld area. In the case of intermediate joints, the arc should be started 15–20 mm in front of the joint, the workpiece should be preheated first, then the welding rod should be moved back to the start of the weld. Only after the molten pool has reached the desired thickness can welding proceed forward. 3.2.1.6 Welding speed: Constant welding speed is required to ensure uniform weld thickness and width; from inside the mask, it is appropriate for the molten iron and slag in the weld pool to be at an equal distance of 2–3 mm apart. 3.2.1.7 Welding arc length: It is determined depending on the type of electrode; generally, it is required that the arc length remain constant. For acidic electrodes, a length of 3–4 mm is appropriate, while for basic electrodes, 2–3 mm is suitable. 3.2.1.8 Welding angle: It is determined based on the thickness of the two welded pieces. There are two aspects to the welding angle: one is that the angle between the welding electrode and the direction of welding progress is 60–75° ； Secondly, there are two possibilities regarding the angle between the welding rod and the workpiece: when the thicknesses of the workpieces are equal, the angle between the welding rod and the workpiece is 45° in both cases ； When the thicknesses of the welded parts are different, the angle between the welding rod and the side of the thicker part should be greater than the angle between the welding rod and the side of the thinner part. 3.2.1.9 Arc termination: At the end of each weld, after filling the crater, move the arc in the direction opposite to that of welding so that the crater is pushed into the weld bead, thereby preventing the crater from penetrating the metal. After welding is complete, the arc plate should be removed by gas cutting and polished smooth; it must not be knocked off with a hammer. 3.2.1.10 Slag removal: After the entire weld has been completed, the slag must be removed. Only after the welder has conducted a self-inspection (including checking the appearance and weld dimensions) to confirm that there are no issues can the work proceed to another location for further welding. 3.2.2 Vertical welding: The basic operating procedures are the same as those for flat welding, but the following points should be taken into account: 3.2.2.1 Under the same conditions, the welding current required is 10%–15% lower than that for flat welding. 3.2.2.2 Short-arc welding is used, with the arc length generally being 2–3 mm. 3.2.2.3 The electrode angle is determined based on the thickness of the workpiece. The thicknesses of the two welded pieces are equal, and the angle between the electrodes in the horizontal direction is 45° ； When the thicknesses of the two welded pieces are different, the angle between the welding rod and the thicker piece should be greater than the angle with the thinner piece. The welding electrode should form an angle of 60° to 80° with the vertical plane, with the corner arc slightly tilted upward and directed toward the center of the molten pool. 3.2.2.4 Arc termination: When welding is complete, the arc pit is filled using the arc extinguishing method, and the arc is moved to the center of the molten pool to be extinguished there. It is strictly prohibited to let the arc crater fall to one side. To prevent chipping, the angle of the arc transfer electrode should be lowered so that the electrode is perpendicular to the workpiece, or the arc should blow slightly downward. 3.2.3 Transverse welding: It is basically the same as flat welding; the welding current is 10%–15% lower than that used in flat welding under the same conditions, and the arc length is 2–4 mm. Regarding the angle of the welding rod, when welding horizontally it should be tilted downward at an angle of 70° to 80°, in order to prevent the molten iron from falling. Depending on the thickness of the two weld pieces, the angle of the welding rod can be adjusted appropriately, with the welding rod forming an angle of 70° to 90° with the direction of welding progress. 3.2.4 Upward welding: It is essentially similar to vertical and horizontal welding; the angle between the electrode and the workpiece depends on the thickness of the workpiece. The electrode should be at an angle of 70° to 80° to the welding direction, and it is advisable to use a low current and a short arc for welding. 3.3 Welding at low temperatures in winter: 3.3.1 When performing arc welding in an environment where the temperature is below 0°C, in addition to complying with the relevant regulations for welding at normal temperatures, the welding process parameters should be adjusted to ensure that the weld and the heat-affected zone cool down slowly. When the wind speed exceeds level 4, wind protection measures should be taken ； Uncooled joints after welding should be kept away from ice and snow. 3.3.2 To prevent welding cracks in steel structures, preheating is required to control the interlayer temperature. When the temperature at the work site is below 0°C, process tests should be conducted to determine the appropriate preheating and post-heating temperatures. IV. Quality Standards 4.1 Assurance Items 4.1.1 Welding materials shall meet the design requirements and relevant standard specifications; quality certificates and baking records shall be checked. 4.1.2 Welders must pass examinations, and it is necessary to check their certificates confirming compliance with the relevant welding conditions as well as the date of the assessment. 4.1.3 Welds of grades I and II must undergo flaw detection inspections and shall meet the design requirements as well as the provisions of the construction and acceptance specifications; the weld flaw detection reports shall be checked. 4.1.4 Grades I and II weld surfaces shall be free from defects such as cracks, weld beads, burn-through, and arc pits. Grade II welds must be free from defects such as surface pores, slag inclusions, cratering, cracks, and arc scratches, while Grade I welds must be free from defects such as undercutting and incomplete welding. 4.2 Base Project 4.2.1 Weld appearance: The weld shape is uniform, with smooth transitions between weld passes as well as between the weld passes and the base metal; slag and spatter are completely removed. 4.2.2 Surface pores: Not allowed in welds of grades I and II ； For grade III welds, the allowable diameter within every 50 mm of weld length is ≤0.4t ； And there are 2 pores ≤3mm ； The pore spacing is ≤6 times the pore diameter. 4.2.3 Edge biting: Not allowed in Class I welds. Grade II welds: the root undercut depth shall be ≤0.05t and ≤0.5mm; the continuous length shall be ≤100mm, and the total length of undercuts on both sides shall be ≤10% of the weld length. Grade III weld: root undercut depth ≤ 0.1t, and ≤ 1mm. Note: t is the thickness of the thinner plate at the joint. 4.3 Allowable deviation items are shown in the table. Image 5: Protection of Finished Products 5.1 It is not allowed to strike or damage the joints after welding, nor is it permitted to pour water on the freshly welded steel. Slow cooling measures should be taken at low temperatures. 5.2 Arcing shall not be performed arbitrarily on the base metal outside the weld. 5.3 Welding may be carried out only after all components have been adjusted properly; the shims and clamps must not be moved arbitrarily to prevent dimensional deviations in the components. Welds in concealed areas must undergo the concealed work acceptance procedures before the next concealed work can be carried out. 5.4 During low-temperature welding, slag removal should not be carried out immediately; it must wait until the weld has cooled down. VI. Quality issues that require attention 6.1 Dimensions exceeding allowable tolerances: Deviations such as insufficient length, width, and thickness of welds, offset of the center line, and bending must be strictly controlled; the relative dimensions of the welding area must be within acceptable limits before welding can proceed, and careful operation is required during welding. 6.2 Weld cracks: To prevent cracks from forming, appropriate welding process parameters and procedures should be selected; high current levels should be avoided, and the weld should not be extinguished suddenly. The weld joints should overlap by 10–15 mm, and it is not allowed to move or strike the welded parts during welding. 6.3 Surface pores: The welding rod should be baked at specified temperatures and for specified times; the welding area must be cleaned thoroughly. During welding, an appropriate welding current should be selected and the welding speed reduced to allow all gases in the molten pool to escape. 6.4 Weld slag inclusion: When welding in multiple layers, the slag must be removed thoroughly from each layer; proper wire feeding and an appropriate arc length should be maintained during the operation. Pay attention to the flow direction of the slag; when using alkaline electrodes, it is necessary to keep the slag behind them. VII. Quality Records This process standard shall include the following quality records: 7.1 Quality certificates for welding materials. 7.2 Welder’s certificate and number. 7.3 Welding process test report. 7.4 Welding quality inspection report, flaw detection report. 7.5 Design change and negotiation records. 7.6 Records of acceptance for concealed works. 7.7 Other technical documents. Arc welding of steel structures – Safety and environmental protection measures for welding: 1. The casing of the welding machine must be properly grounded, and the installation and removal of its power supply should be carried out by electricians. 2. The welding machine should have a separate switch. The switch should be placed in a rainproof enclosure, and gloves should be worn when operating it to avoid direct contact. 3. The welding torch and its cables must be well insulated. It should be connected firmly, and gloves should be worn when replacing the welding rod. When working in wet areas, one should stand on insulating rubber mats or wooden planks. 4. Welding is strictly prohibited on containers or pipes under pressure; power must be disconnected first before welding equipment that is still powered. 5. When welding containers or pipes that have stored flammable, explosive, or toxic substances, they must be thoroughly cleaned. And open all the openings. 6. When welding in a closed metal container, the container must be properly grounded, well-ventilated, and there must be someone to supervise the process. It is strictly prohibited to introduce oxygen into the container. 7. When preheating workpieces for welding, heat-insulating measures such as asbestos cloth or shields should be used. 8. The live wire and ground wire must not come into contact with steel wires; moreover, steel wires or mechanical and electrical equipment must not be used as the neutral wire. All ground wire connections must be firmly secured. 9. When changing the location and turning the handle wire, the power supply must be disconnected, and one must not climb to a higher height while holding the wire handle. 10. When removing slag and using arc air gouging to clean the root of a weld, protective glasses or a face shield should be worn to prevent iron slag from splashing and causing injury. 11. When multiple welding machines are used for welding together, the welding platform or the workpiece must be grounded. And there should be a light shield. 12. Thorium-tungsten electrodes must be placed in a sealed lead box. When grinding thorium-tungsten electrodes, gloves and a mask must be worn, and the dust must be removed promptly. 13. The upper shell of the carbon dioxide gas preheater should be insulated, and the terminal voltage should not exceed 36 volts. 14. Welding work in the open should be stopped during thunderstorms. 15. Flammable and explosive items should be removed from the area around the welding site, or covered and isolated. 16. Welding must be carried out in areas where flammable gases or liquids are present only with the permission obtained after inspection by the relevant authorities. Welding can be carried out only then. 17. Once the work is completed, the power supply to the welding machine should be turned off, and the work area should be inspected. Only after confirming that there is no risk of fire can one leave.