Steel Structure Welding Specification

Steel structure processes from material preparation, assembly, welding, to inspection

Steel Structure Manual Arc Welding Construction Standard

Based on the standards:

Unified Standard for Acceptance of Construction Quality of Building Engineering GB50300-2001

Code for Acceptance of Construction Quality of Steel Structure Engineering GB50205-2001

Method and Grading of Ultrasonic Testing for Steel Welds GB11345

Radiography and Quality Grading of Steel Fusion Welded Butt Joints GB3323

Ultrasonic Testing Method and Quality Grading for Welds of Steel Truss with Welded Ball Nodes JBJ/T3034.1

Ultrasonic Testing Method and Quality Grading for Welds of Steel Truss with Bolted Ball Nodes JBJ/T3034.2

Technical Regulations for Welding of Building Steel Structures JGJ81

1. Scope

This standard applies to manual arc welding of steel structures in general industrial and civil building projects.

2. Construction Preparation

2.1 Materials and Main Equipment

2.1.1 Welding Rods: The model should be selected according to the design requirements and must have a quality certificate. They must be baked before welding as required. It is strictly forbidden to use welding rods with peeling coatings or rusty cores. If not specified in the design, when welding Q235 steel, E43 series carbon steel welding rods should be used; when welding 16Mn steel, E50 series low-alloy structural steel welding rods should be used; low-hydrogen type welding rods (alkaline welding rods) should be used for important structures. After baking according to the instructions, they should be placed in an insulation bucket and used as needed. Acidic and alkaline welding rods must not be mixed.

2.1.2 Striking Plate: When using bevel joints, a striking plate is needed. The material and bevel type of the striking plate should be the same as the weldment.

2.1.3 Main Equipment: Welding machine (AC/DC), welding cables, welding tongs, face shield, small hammer, welding rod drying oven, welding rod insulation bucket, wire brush, asbestos strip, thermometer, etc.

2.2 Working Conditions

2.2.1 Familiarize yourself with the drawings and conduct welding process technical briefings.

2.2.2 Before welding, check the validity period of the welder's qualification certificate, which should verify the welder's ability to perform the welding work.

2.2.3 On-site power supply should meet the requirements of welding power.

2.2.4 When the ambient temperature is below 0℃, the preheating and post-heating temperatures should be determined according to the process test.

3. Operating Process

3.1 Process Flow:

Job preparation → Arc welding (flat, vertical, horizontal, overhead) → Weld inspection.

3.2 Steel Structure Arc Welding:

3.2.1 Flat Welding

3.2.1.1 Select a qualified welding process, welding rod diameter, welding current, welding speed, arc length, etc., and verify through welding process testing.

3.2.1.2 Clean the weld joint: Before welding, check whether the bevel and assembly gap meet the requirements, whether the tack welds are firm, and whether there are any oil stains or rust on the weld.

3.2.1.3 Baking of welding rods should meet the specified temperature and time. Welding rods taken from the oven should be placed in the welding rod insulation bucket and used as needed.

3.2.1.4 Welding current: Select the appropriate welding current based on factors such as weld thickness, welding layers, welding rod model, diameter, and welder proficiency.

3.2.1.5 Striking the arc: The striking and finishing points of fillet welds should be at the ends of the weld, preferably greater than 10mm. The arc should not be struck randomly. After striking the arc, the welding rod should immediately be pulled away from the weld area, maintaining a 2-4mm gap between the welding rod and the component to generate an arc. For butt welds and combined fillet welds, striking plates and finishing plates are installed at both ends of the weld. The arc must be struck on the striking plate before welding to the weld area. For intermediate joints, the arc should be struck 15-20mm ahead of the weld joint, the weldment should be preheated, and then the welding rod should be retracted to the beginning of the weld. The weld pool should be filled to the required thickness before proceeding with welding.

3.2.1.6 Welding speed: Requires uniform welding speed to ensure uniform weld thickness and width. When viewed through the face shield, the molten metal and slag in the weld pool should maintain an equal distance (2-3mm).

3.2.1.7 Arc length: Determined by the welding rod model. Generally, the arc length should be stable and unchanged. For acidic welding rods, it is generally 3-4mm; for alkaline welding rods, it is generally 2-3mm.

3.2.1.8 Welding angle: Determined by the thickness of the two weldments. There are two aspects to the welding angle: 1. The angle between the welding rod and the welding direction is 60-75°; 2. There are two cases for the angle between the welding rod and the left and right sides of the weld. When the thickness of the weldments is equal, the angle between the welding rod and the weldments is 45°. When the thickness of the weldments is unequal, the angle between the welding rod and the thicker weldment should be greater than the angle between the welding rod and the thinner weldment.

3.2.1.9 Finishing the arc: At the end of each weld, the crater should be filled, and the arc should be drawn in the opposite direction of welding to leave the crater inside the weld bead to prevent undercut. After welding, the striking plate should be cut off using gas cutting and smoothed; it must not be knocked off with a hammer.

3.2.1.10 Slag Removal: After welding the entire weld seam, remove the slag. The welder must perform a self-inspection (including appearance and weld seam dimensions, etc.) to ensure there are no problems before moving to another location to continue welding.

3.2.2 Vertical Welding: The basic operational process is the same as for flat welding, but the following points should be noted:

3.2.2.1 Under the same conditions, the welding power supply current is 10%~15% less than that of flat welding.

3.2.2.2 Use short-arc welding; the arc length is generally 2-3mm.

3.2.2.3 The electrode angle is determined by the thickness of the workpiece. If the thickness of the two workpieces is equal, the angle between the electrode and the left and right directions is 45°; if the thicknesses of the two workpieces are unequal, the angle between the electrode and the thicker workpiece should be greater than the angle on the thinner side. The electrode should form a 60°~80° angle with the vertical plane, with the arc slightly upward, blowing towards the center of the weld pool.

3.2.2.4 Crater Filling: When welding reaches the end, use the trailing arc method to fill the crater, and stop the arc by moving the arc to the center of the weld pool. Strictly prohibit the crater from being left to one side. To prevent undercut, lower the arc and change the angle of the electrode, so that the electrode is perpendicular to the workpiece or the arc blows slightly downward.

3.2.3 Horizontal Welding: Basically the same as flat welding, the welding current is 10%~15% less than that of flat welding under the same conditions, and the arc length is 2-4mm. For the electrode angle, in horizontal welding, the electrode should be tilted downward at an angle of 70°~80° to prevent molten iron from falling. The electrode angle can be adjusted appropriately according to the different thicknesses of the two workpieces, and the angle between the electrode and the welding direction is 70°~90°.

3.2.4 Overhead Welding: Basically the same as vertical and horizontal welding. The angle between the electrode and the workpiece is related to the thickness of the workpiece. The angle between the electrode and the welding direction is 70°~80°. Small current and short arc welding should be used.

3.3 Low-Temperature Welding in Winter:

3.3.1 When arc welding is performed at an ambient temperature below 0℃, in addition to complying with the relevant regulations for normal temperature welding, the welding process parameters should be adjusted to ensure slow cooling of the weld seam and heat-affected zone. If the wind speed exceeds level 4, windbreak measures should be taken; joints that have not cooled after welding should be kept away from ice and snow.

3.3.2 For steel structures, preheating and post-heating should be used to control the interlayer temperature to prevent welding cracks. When the working temperature is below 0℃, process testing should be conducted to determine the appropriate preheating and post-heating temperatures.

4. Quality Standards

4.1 General Provisions

4.1.1 This chapter applies to the engineering quality acceptance of steel component welding and stud welding in the fabrication and installation of steel structures.

4.1.2 Steel structure welding projects can be divided into one or more inspection batches according to the principles of dividing inspection batches for corresponding steel structure fabrication or installation projects.

4.1.3 For carbon steel structures, weld flaw detection should be carried out after the weld seam has cooled to ambient temperature; for low-alloy steel structures, it should be carried out 24 hours after welding is completed.

4.1.4 After welding, the welder's steel stamp should be stamped on the weld seam and specified locations according to the process.

4.2 Steel Component Welding Projects

I. Main Control Items

4.2.1 The matching of welding materials such as electrodes, welding wires, fluxes, and electroslag welding nozzles with the base metal should comply with the design requirements and the provisions of the current national industry standard "Technical Regulations for Welding of Steel Structures" JGJ81. Before use, electrodes, fluxes, metal-cored wires, nozzles, etc. should be baked and stored according to their product instructions and welding process documents.

Inspection Quantity: 100% inspection.

Inspection Method: Check the quality certificates and baking records.

4.2.2 Welders must pass the examination and obtain a qualification certificate. Certified welders must weld within the scope of their examination qualification items and approvals.

Inspection Quantity: 100% inspection.

Inspection Method: Check the welder's qualification certificate, its approved scope, and validity period.

4.2.3 The construction unit should conduct welding process evaluation for the first time use of steel, welding materials, welding methods, and post-weld heat treatment, and determine the welding process according to the evaluation report.

Inspection Quantity: 100% inspection.

Inspection Method: Check the welding process evaluation report.

4.2.4 Full penetration welds of Class I and Class II should be inspected for internal defects using ultrasonic testing. When ultrasonic testing cannot determine the defects, radiographic testing should be used. The internal defect grading and testing methods should comply with the provisions of the current national standards "Method of Manual Ultrasonic Testing for Steel Welds and Grading of Test Results" GB11345 or "Radiography of Steel Fusion Welded Butt Joints and Quality Grading" GB3323.

For welded spherical node trusses, bolted spherical node trusses, and circular pipe T, K, and Y-shaped node related line welds, their internal defect grading and testing methods should comply with the provisions of the current national standards "Ultrasonic Testing Method and Quality Grading for Welded Spherical Node Steel Trusses" JBJ/T3034.1, "Ultrasonic Testing Method and Quality Grading for Bolted Spherical Node Steel Trusses" JBJ/T3034.2, and "Technical Regulations for Welding of Steel Structures" JGJ81.

The quality grade and defect grading of Class I and Class II welds should comply with the provisions of Table 4.2.4.

Inspection Quantity: 100% inspection.

Inspection Method: Check the ultrasonic or radiographic testing records.

Table 4.2.4 Quality Grade and Defect Grading of Class I and Class II Welds

Weld Quality Grade Class I Class II

Internal Defect Ultrasonic Testing Evaluation Grade Ⅱ Ⅲ

Inspection Grade B Grade B Grade

Flaw detection rate 100% 20%

Internal defect radiographic testing evaluation level Ⅱ Ⅲ

Inspection level AB AB

Flaw detection rate 100% 20%

Note: The counting method for the flaw detection rate should be determined according to the following principles: (1) For factory-made welds, the percentage should be calculated for each weld, and the flaw detection length should not be less than 200mm. When the weld length is less than 200mm, the entire weld should be inspected; (2) For field-installed welds, the percentage should be calculated according to the number of welds of the same type and the same welding conditions, and the flaw detection length should not be less than 200mm, and there should be at least 1 weld.

4.2.5 For butt and fillet welds of T-joints, cross-joints, corner joints, etc., that require full penetration, the weld leg size should not be less than t/4 (Figures 4.2.5a, b, c); the weld leg size of the connection weld between the web and the upper flange of the crane beam or similar components with fatigue calculation requirements is t/2 (Figure 4.2.5d), and should not be greater than 10mm. The allowable deviation of the weld leg size is 0～4mm.

Inspection quantity: Full inspection of data; 10% random check of similar welds, and not less than 3.

Inspection method: Visual inspection, random check measurement with weld gauge.

Figure 4.2.5 Weld leg size

4.2.6 The weld surface shall not have cracks, weld beads, etc. Level 1 and Level 2 welds shall not have surface pores, slag inclusions, crater cracks, arc scratches, etc. Level 1 welds shall not have undercut, incomplete fusion, root shrinkage, etc.

Inspection quantity: Randomly inspect 10% of similar components in each batch, and not less than 3; in the inspected components, each type of weld shall be randomly inspected by the number of welds 5%, and not less than 1; each inspection 1 place, the total number of inspections shall not be less than 10.

Inspection method: Visual inspection or inspection using a magnifying glass, weld gauge and steel ruler. If there is any doubt, use penetration or magnetic particle inspection.

Ⅱ General items

4.2.7 For welds that require preheating before welding or heat treatment after welding, the preheating temperature or post-heating temperature should comply with the provisions of the current national standards or be determined through process tests. The preheating zone is on both sides of the weld bead, and the width on each side should be more than 1.5 times the thickness of the weldment, and should not be less than 100mm; the post-heat treatment should be carried out immediately after welding, and the holding time should be determined according to the plate thickness at 1h per 25mm plate thickness.

Inspection Quantity: 100% inspection.

Inspection method: Check pre- and post-heating construction records and process test reports.

4.2.8 The appearance quality standards of Level 2 and Level 3 welds shall comply with the provisions of Table A.0.1 in Appendix A of this standard. Level 3 butt welds shall be inspected for appearance quality according to the standard for Level 2 welds.

Inspection quantity: Randomly inspect 10% of similar components in each batch, and not less than 3; in the inspected components, each type of weld shall be randomly inspected by the number of welds 5%, and not less than 1; each inspection 1 place, the total number of inspections shall not be less than 10.

Inspection method: Visual inspection or inspection using a magnifying glass, weld gauge and steel ruler.

4.2.9 The allowable deviation of weld dimensions shall comply with the provisions of Table A.0.2 in Appendix A of this standard.

Inspection quantity: Randomly inspect 10% of similar components in each batch, and not less than 3; in the inspected components, each type of weld shall be randomly inspected by 5% of the number of welds, but not less than 1; each inspection 1 place, the total number of inspections shall not be less than 10.

Inspection method: Check with weld gauge.

4.2.10 For fillet welds formed into a concave shape, there should be a smooth transition between the weld metal and the base metal; for fillet welds processed into a concave shape, no cutting marks should be left on their surface.

Inspection quantity: Randomly inspect 10% of similar components in each batch, and not less than 3.

Inspection method: Visual inspection.

4.2.11 The weld appearance should meet the following requirements: uniform shape, good forming, smooth transition between weld beads and weld beads, and between weld beads and base metal, and slag and spatter are basically cleaned.

Inspection quantity: Randomly inspect 10% of similar components in each batch, and not less than 3; in the inspected components, each type of weld is randomly inspected by 5% of the quantity, and the total number of inspections shall not be less than 5.

Inspection method: Visual inspection.

Steel structure fabrication (installation) welding engineering quality inspection standard

Item Serial Number Item Allowable Deviation (mm) Inspection Method

Main control item 1 Welding material type, specification Article 4.3.1 Check product qualification certificate, Chinese marking and inspection report (full inspection)

2 Retest of welding materials Article 4.3.2 Check the retest report (full inspection)

3 Material matching Article 5.2.1 Check the quality certificate and baking record (full inspection)

4 Welder certificate Article 5.2.2 Check welder qualification certificate and its scope of approval, validity period (all welders)

5 Welding procedure specification Article 5.2.3 Check the welding procedure specification report (full inspection)

6 Internal defects Article 5.2.4 Check the weld flaw detection record (full inspection)

7 Combined weld dimensions Article 5.2.5 Visual inspection, random check measurement with weld gauge (full inspection of data, 10% random check of similar welds, and ≥3 places)

8 Weld surface defects Article 5.2.6 Visual inspection or inspection using a magnifying glass, weld gauge and steel ruler. If necessary, use penetration or magnetic particle inspection.

General item 1 Appearance quality of welding materials Article 4.3.4 Visual inspection (1% random check by quantity, and ≥10 packages)

2 Preheating and post-heat treatment Article 5.2.7 Check test report (full inspection)

3 Weld Appearance Quality Clause 5.2.8 Inspection by observation or using a magnifying glass, weld gauge, and steel ruler (Clause 5.2.8)

4 Weld Dimension Deviation Clause 5.2.9 Inspection by observation (Clause 5.2.9)

5 Concave Fillet Welds Clause 5.2.10 Inspection by observation (10% random check of similar components, and ≥3 pieces)

6 Weld Appearance Clause 5.2.11 Inspection by observation (Clause 5.2.11)

5. Finished Product Protection

5.1 After welding, do not strike or hit the joint, and do not pour water on freshly welded steel. Slow cooling measures should be taken at low temperatures.

5.2 Do not arbitrarily strike an arc on the base material outside the weld.

5.3 All components must be correctly aligned before welding, and shims and clamps must not be moved arbitrarily to prevent dimensional deviations of the components. Concealed welds must complete the concealed inspection procedures before the next concealed process can be carried out.

5.4 Low-temperature welding should not immediately remove slag, and should wait for the weld to cool down before doing so.

6. Quality Issues to Note

6.1 Dimensions exceeding allowable deviations: For insufficient weld length, width, thickness, center line offset, bending, etc., the relative positional dimensions of the welding part should be strictly controlled, and welding should only be allowed after passing inspection and careful operation during welding.

6.2 Weld cracks: To prevent cracks, appropriate welding process parameters and welding procedures should be selected, avoiding the use of large currents, sudden flame extinguishing, and the weld joints should overlap by 10～15mm. Moving or striking the weldment is not allowed during welding.

6.3 Surface porosity: Welding rods should be baked at the specified temperature and time, the welding area must be cleaned, and appropriate welding current should be selected during welding, reducing the welding speed to allow the gas in the molten pool to escape completely.

6.4 Weld slag inclusion: Multi-layer welding should remove slag layer by layer, and the operation should use the correct rod and appropriate arc length. Pay attention to the flow direction of the slag; when using alkaline welding rods, the slag must be left behind the slag.

7. Quality Records

7.1 Welding material quality certificate.

7.2 Welder qualification certificate and number.

7.3 Welding process test report.

7.4 Welding quality inspection report, ultrasonic and radiographic testing records.

7.5 Design changes and negotiation records.

7.6 Concealed works acceptance record.

7.7 Other technical documents.

8. Safety and Environmental Protection Measures

8.1 The casing of the welding machine must be well grounded, and the power supply installation and removal should be carried out by an electrician.

8.2 The welding machine should have a separate switch. The switch should be placed in a rainproof switch box, and gloves should be worn and sideways operation should be performed when switching.

8.3 The welding tongs and cables must be well insulated. The connection must be firm, and gloves should be worn when changing welding rods. When working in wet locations, stand on an insulating rubber pad or wooden board.

8.4 It is strictly forbidden to weld on pressurized containers or pipes, and the power supply of energized equipment must be cut off before welding.

8.5 When welding containers or pipes that store flammable, explosive, or toxic items, they must be thoroughly cleaned, and all openings must be opened.

8.6 When welding in a closed metal container, the container must be reliably grounded, well ventilated, and supervised by personnel. It is strictly forbidden to introduce oxygen into the container.

8.7 When preheating workpieces for welding, heat insulation measures such as asbestos cloth or baffles should be used.

8.8 Cables and ground wires are prohibited from contacting steel wire ropes, and steel wire ropes or electromechanical equipment should not be used as ground wires. All ground wire joints must be securely connected.

8.9 When changing the site and rotating the cable, the power must be cut off, and the cable must not be held while climbing a ladder.

8.10 When removing slag and using arc air gouging to clean the root, protective glasses or a face shield should be worn to prevent iron slag from splashing and injuring people.

8.11 When multiple welding machines are concentrated in one place for welding, the welding platform or workpiece must be grounded, and there should be light shielding plates.

8.12 Thorium tungsten electrodes should be placed in a sealed lead box, and when grinding thorium tungsten electrodes, gloves and masks must be worn, and the dust should be removed promptly.

8.13 The upper shell of the carbon dioxide gas preheater should be insulated, and the terminal voltage should not exceed 36 volts.

8.14 Outdoor welding operations should be stopped during thunderstorms.

8.15 Flammable and explosive items should be cleared around the welding site, or covered and isolated.

8.16 When welding in an area where flammable or combustible gases or liquids are diffused, it must be permitted by the relevant authorities before welding.

8.17 At the end of work, the power of the welding machine should be cut off and the operation site should be inspected to ensure that there is no fire hazard before leaving.