Weld quality standard
1. Guarantee Project
1. Welding materials should comply with design requirements and relevant standards, and quality certificates and baking records should be checked.
2. The welder must pass the examination and check the welder's certificate of conformity to the welding conditions and the date of assessment.
3. Class Ⅰ and Ⅱ welds must be inspected for flaw detection, and should meet the design requirements and construction and acceptance specifications, and check the weld inspection report.
4. Class Ⅰ and class Ⅱ welds on the surface of the welds must not have defects such as cracks, weld lumps, burn-throughs, and arc craters. Class II welds shall not have defects such as surface porosity, slag inclusions, craters, cracks, arc scratches, etc., and Class I welds shall not have defects such as undercutting and underwelding.
2. Basic items
1. Appearance of welding seam: the appearance of welding seam is uniform, the transition between welding bead and welding bead, welding bead and basic metal is smooth, and welding slag and spatter are removed.
2. Surface pores: Class I and II welds are not allowed; Class III welds have a diameter of ≤0.4t per 50mm length weld; and 2 pores of ≤3mm; the pore spacing is ≤6 times the hole diameter.
3. Undercut: Class I welds are not allowed.
Grade Ⅱ weld seam: Undercut depth ≤0.05t, and ≤0.5mm, continuous length ≤100mm, and total undercut length on both sides ≤10% of weld length.
Grade Ⅲ welding seam: Undercut depth ≤0.lt, and ≤lmm.
Note: t is the thinner board thickness at the connection.
3. Product protection
1. It is not allowed to hit the joint after welding, and it is not allowed to pour water on the steel just welded. Slow cooling measures should be taken at low temperatures.
2. Arbitrary arcing on the base metal outside the weld is not allowed.
3. After correcting various components, soldering is not allowed, and the horns and fixtures must not be moved at will, in order to prevent the size deviation of the components. Welding seams in concealed parts must go through concealed acceptance procedures before proceeding to the next concealed process.
4. Low temperature welding is not allowed to remove slag immediately, and should be carried out after the welding seam has cooled down.
4. Quality issues that should be noted
1. The size exceeds the allowable deviation: For the length, width, thickness and thickness of the weld seam, the center line offset, bending and other deviations, the relative position size of the welding part should be strictly controlled. After passing the qualification, the welding should be strictly controlled.
2. Weld cracks: In order to prevent cracks, suitable welding process parameters and welding procedures should be selected, avoid using large currents, and do not suddenly extinguish the flame. Weld joints should be 10 to 15 mm. Welding and percussion are allowed in welding. Weldment.
3. Surface porosity: The electrode is baked according to the specified temperature and time. The welding area must be cleaned. The welding current must be selected during the welding process to reduce the welding speed and allow the gas in the molten pool to escape completely.
4. Welding seam slag inclusion: Welding slag should be cleaned layer by layer, the strip should be correct during operation, and the arc length should be appropriate. Pay attention to the flow direction of the slag. When using alkaline electrodes, the slag must be left behind the slag.
V. Quality record
This process standard should have the following quality records:
1. Certificate of welding material quality.
2. Welder's certificate and serial number.
3. Welding process test report.
4. Welding quality inspection report and flaw detection report.
5. Design changes and negotiation records.
6. Acceptance record of concealed works.
7. Other technical documents.
Weld class classification and non-destructive testing requirements
Welding seams should be selected according to the following principles according to the importance of structure, load characteristics, welding seam form, working environment and stress status, etc.:
1. Among the components requiring fatigue calculation, all butt welds should be fully penetrated, and the quality level is:
1) For transverse butt welds or T-joint and fillet welds whose force is perpendicular to the length of the weld, the tension should be first class and the compression should be second class;
2) The longitudinal butt welds whose force is parallel to the length direction of the welds shall be Class II.
2. Among components that do not require fatigue calculation, all butt welds that require equal strength with the base metal should be fully penetrated, and the quality level should not be lower than Grade 2 when tensioned, and should be Grade 2 when compressed.
3. The heavy duty working system and the lifting capacity Q≥50t between the web of the crane beam and the L Ji edge and between the chord and the joint plate on the crane frame are required to be fully penetrated. The weld form is generally a combination of butt joints and fillet welds, and its quality level should not be lower than Grade 2.
4. The quality grades of fillet welds for partially welded'I'-shaped joints or partially welded butt and fillet welds and fillet welds used for lap connections are:
1) For mid-level crane beams that directly bear the dynamic load and need to be checked for fatigue and the lifting weight of the crane is equal to or greater than 50t, the appearance quality standards of the welds should meet the second level;
2) For other structures, the appearance quality standard of welds may be Grade II.
Visual inspection is generally performed by visual inspection. The inspection of cracks should be supplemented by a 5x magnifying glass and carried out under suitable light conditions. Magnetic particle inspection or penetration inspection can be used if necessary. Measurements and calipers should be used for size measurement.
The appearance quality of welds shall meet the following requirements:
1. The first-level welds must not have defects such as under-welding, root shrinkage, undercutting and poor joints. The first-level welds and second-level welds must not have defects such as surface porosity, slag inclusions, cracks and arc scratches;
2. In addition to the requirements of the first paragraph of this article, the appearance quality of the secondary welds should also meet the relevant requirements of the following table;
3. The appearance quality of the third-grade welds shall meet the relevant regulations in the following table.
For fully welded welds, the inspection of internal defects shall meet the following requirements
1. 100% inspection should be carried out for the first-grade welds, and the qualified grade should be the second-grade and above grade B inspection of the current national standard "Manual Ultrasonic Flaw Detection Method and Quality Classification Method for Steel Welds" (GB 11345);
2. The second-level welds shall be subject to random inspection, the ratio of which shall be not less than 20%, and the qualified level shall be the third-level and third-level inspections of the current national standard "Manual Ultrasonic Flaw Detection Method and Quality Classification Method for Steel Welds" (GB 11345) Ⅲ or above;
3. Non-destructive testing is not required for fully welded three-level welds;
4. The ultrasonic flaw detection method and defect classification of the welded joints of the welded ball joints shall comply with the provisions of the current national standard JG/T203-2007 "Ultrasonic flaw detection and quality classification method for steel structures";
5. The ultrasonic flaw detection method and defect classification of the welded joints of the bolt ball node grid shall comply with the provisions of the current national standard JG/T203-2007 "Ultrasonic flaw detection and quality classification method for steel structures";
6. In addition to the relevant provisions of Article 7.3.3 of GB50205-2001 standard, the non-destructive testing results of box-shaped member separator electroslag welding welds shall also be tested for weld penetration width and weld deviation according to Appendix C;
7. The ultrasonic flaw detection method and defect grading of T, K, Y joints of round tubes shall comply with the provisions of Appendix D of GB50205-2001 standard;
8. When the design document specifies that the radiographic inspection or ultrasonic inspection cannot judge the nature of the defect, radiographic inspection can be used for testing and verification;
9. The radiographic inspection shall comply with the provisions of the current national standard "Radiophotography and Quality Classification of Steel Fusion Welding Butt Joints" (GB 3323), and the quality level of radiography shall meet the requirements of AB level. The qualification level of the first-class welds shall be Grade Ⅱ and above of the “Steel fusion welding butt joint radiography and quality classification” (GB 3323), and the qualification level of the second-class welds shall be “Steel fusion welding butt joint radiography And quality classification (GB 3323) grade Ⅲ and above.
10. Surface inspection should be conducted in one of the following situations:
1) When cracks are found in visual inspection, 100% surface inspection of similar welds in the batch shall be carried out;
2) When cracks are suspected in visual inspection, surface inspection should be performed on the suspected parts;
3) The design drawings stipulate that surface flaw detection is required;
4) When the inspector deems it necessary.
Ferromagnetic materials should be inspected for surface defects using magnetic particle inspection. When the magnetic particle inspection cannot be used for structural reasons or material reasons, penetration inspection can be used. Magnetic particle flaw detection shall comply with the provisions of the current national standard "Welding Magnetic Particle Inspection Method and Classification of Defective Magnetic Traces" (JB/T 6061), and penetration flaw detection shall comply with the current national standard "Welding Penetration Inspection Method and Classification of Defective Traces" ( JB/T 6062). The qualification standards for magnetic particle inspection and penetration inspection shall comply with the relevant provisions of visual inspection.
The design requires that the fully welded first and second welds should be inspected for internal defects using ultrasonic flaw detection. When ultrasonic flaw detection cannot determine the defect, the radiographic flaw detection should be used. The internal flaw classification and flaw detection method should comply with the current national standard "Steel Weld seam manual ultrasonic flaw detection method and flaw detection result classification" GB11345 or "Steel fusion welding butt joint shooting and quality classification" GB3323.
The internal defect classification and flaw detection methods of welded ball node grid welds, bolted ball node grid welds and round pipe T, K, Y-shaped point intersecting line welds shall comply with the current national standard JG/T203-2007. "Ultrasonic flaw detection and quality classification method for steel structures", "Technical Specification for Welding of Structural Steel Structures" JGJ81.
The quality grade and defect classification of the first and second welds shall comply with the following table.
One and two grades of weld quality and defect classification
Note: According to the different load-bearing conditions of the structure, the current national standard "Code for Design of Steel Structures" GBJ17 divides the quality of the weld into three quality levels. The detection of internal defects is generally available for ultrasonic flaw detection and radiographic flaw detection. Radiographic inspection has the advantages of intuitiveness and good consistency. In the past, people felt that radiographic inspection was reliable and objective.
However, the cost of radiographic testing is high, the operation procedures are complicated, and the inspection cycle is long. Especially, the steel structure is mostly T-shaped joints and corner joints. The effect of radiographic inspection is poor, and the detection rate of radiographic flaw detection to cracks, unfused and other harmful defects low. Ultrasonic flaw detection is just the opposite. The operation procedure is simple and fast. It has good adaptability to various types of joints and high detection sensitivity for cracks and unfusion. Therefore, many countries in the world use ultrasonic flaw detection to control the internal quality of steel structures. No radiographic inspection is used.
With the increasing application of large-scale space structures, the corresponding ultrasonic flaw detection method is given in the current national industry standard "Technical Specification for Welding of Structural Steel Structures" JGJ81 for thin-wall large-curvature T, K, and Y-type intersecting joints. And defect classification. Weld flaw detection of the grid structure shall be carried out in accordance with the provisions of the current national standard JG/T203-2007 "Ultrasonic flaw detection and quality classification method for steel structures".
The requirements of this specification require 100% inspection of fully welded first-class welds, and partial inspection of second-class welds is designated as sampling inspection. Steel structure production is generally longer, and each weld is inspected at a specified percentage, and the requirement of not less than 200mm at each location is beneficial to ensure the quality of each weld. However, the welds for steel structure installation are generally not long. Most of the welds are beam-column-connected welds, and the length of each weld is mostly between 250-300mm. It is feasible to use sampling and counting for the number of welds. 1. For T-joints, cross joints, corner joints and other welded joints that require penetration and corner butt joints, the weld leg size should not be less than t/4; the webs of crane beams or similar members with fatigue check requirements are designed The size of the welding leg connected to the upper flange is t/2, and should not be less than 10mm. The allowable deviation of the solder foot size is 0-4 mm.
Number of inspections: full inspection of data; random inspection of similar welds is 10%, and no less than three.
Inspection method: Observe and inspect, and measure with spot weld gauge.
Note: above 1. For T-type, cross-type, fillet joints, etc., butt joints and fillet welds that require thorough penetration, in order to reduce stress concentration and avoid excessively large weld foot dimensions, refer to the relevant domestic and foreign regulations. The requirements of different welding leg sizes for static load structure and dynamic load structure are determined.
2. The surface of the welding seam shall not have defects such as cracks and welding lumps. The primary and secondary welds must not have defects such as surface porosity, slag inclusions, crater cracks, and arc scratches. And the first-level welds are not allowed to have defects such as undercut, under-weld, and root shrinkage.
Number of inspections: 10% of each batch of similar components shall be checked, and no less than 3; among the components to be inspected, 5% of each type of weld shall be inspected according to the number of strips, and no less than 1; each inspection shall have 1 The total number of spot checks should not be less than 10.
Inspection method: Observation inspection or inspection using magnifying glass, welding seam quantity regulation and steel ruler. When there is doubt, use penetration or magnetic particle inspection.
Note: The above considers the requirements of welds of different quality grades are different. All defects that seriously affect the load-bearing capacity of welds are strictly prohibited. This article lists the appearance quality requirements that seriously affect the load-bearing capacity of welds in the main control project and gives the appearance qualification Quality requirements.
Due to the importance of the first and second welds, there should be specific requirements for surface pores, slag inclusions, crater cracks, and arc scratches. Defects such as undercuts, underwelds, and root shrinkage have a great influence on dynamic load. Large, so the first-class welds must not have such defects.
The most comprehensive knowledge point on weld inspection in history
