Welds should be selected according to the importance of the structure, load characteristics, weld form, working environment and stress state, etc., according to the following principles to select different quality levels:
1. Among the components requiring fatigue calculation, all butt welds should be penetrated, and their quality grades are:
(a) Transverse butt welds or T-shaped butt and fillet welds where the force is perpendicular to the length of the weld shall be level one when under tension and level two when under compression;
(b) Longitudinal butt welds whose force is parallel to the length of the weld shall be Class II.
2. For components that do not need to calculate fatigue, all butt welds that require strength with the base metal should be penetrated, and the quality level should not be lower than Class II when tensioned, and should be Class II when compressed
3. Heavy duty working system and lifting weight Q≥50t The T-shaped joint welds between the web and the edge of the crane beam and the upper chord of the crane frame and the gusset plate are required to be welded through. The weld form is generally a combination of butt joint and corner joint, and its quality level shall not be lower than Class II.
4. Fillet welds used in I-shaped joints that do not require penetration, or combined butt and fillet welds with partial penetration, and fillet welds used in lap joints, have the following quality levels:
(a) For structures that directly bear dynamic loads and require fatigue checking, and intermediate working crane beams with a crane capacity equal to or greater than 50t, the appearance quality standards of the welds should meet the second level;
(b) For other structures, the appearance quality standard of welds can be Grade II.
Visual inspection is generally used for visual inspection. The inspection of cracks should be carried out with a 5x magnifying glass and under suitable lighting conditions. Magnetic particle inspection or penetrant inspection can be used if necessary. Measuring tools and calipers should be used for size measurement.
The appearance quality of welds should meet the following requirements:
1. The first-level welds must not have defects such as underfill, root shrinkage, undercut and poor joints, and the first-level and second-level welds must not have defects such as surface pores, slag inclusions, cracks and arc scratches;
2. The appearance quality of the secondary weld shall not only meet the requirements of the first paragraph of this article, but also meet the relevant regulations in the following table;
3. The appearance quality of the third-level weld should meet the relevant regulations in the table below.
For welds with design requirements for full penetration, the inspection of internal defects shall meet the following requirements:
1. The first-level welds should be 100% inspected, and their qualification level should be the second and above of the B-level inspection of the current national standard "Manual Ultrasonic Testing Method and Quality Classification Method for Steel Welds" (GB 11345);
2. Second-level welds should be randomly inspected, and the proportion of random inspections should not be less than 20%. The qualified level should be the current national standard "Manual Ultrasonic Inspection Method and Quality Classification Method for Steel Welds" (GB 11345) B-level inspection and level III and Above grade Ⅲ;
3. Non-destructive testing is not required for three-level welds with full penetration.
4. Ultrasonic flaw detection method and flaw classification of welded spherical joint grid frame welds shall comply with the current national standard JG/T203-2007 "Ultrasonic flaw detection and quality classification method for steel structures".
5. The ultrasonic flaw detection method and flaw classification of the welds of the bolted spherical joint grid frame shall meet the requirements of the current national standard JG/T203-2007 "Ultrasonic flaw detection and quality classification method for steel structures".
6. In addition to the non-destructive test results of the electroslag welding welds of the box-shaped component partitions, the weld penetration width and weld offset shall be tested in accordance with Appendix C, in addition to the relevant provisions in Article 7.3.3 of the GB50205-2001 standard.
7. The ultrasonic flaw detection method and defect classification of the T, K, Y node welds of round pipes should meet the requirements of Appendix D of the GB50205-2001 standard.
8. When the design documents specify radiographic flaw detection or ultrasonic flaw detection, when the nature of the defect cannot be judged, radiographic flaw detection can be used for inspection and verification.
9. Radiographic testing should meet the requirements of the current national standard "Radiography and Quality Classification of Steel Fusion Welded Butt Joints" (GB 3323), and the quality level of radiography should meet the requirements of Class AB. The first-class weld qualification qualification level should be "Steel Fusion Welding Butt Joint Radiography and Quality Classification" (GB 3323) Class II and above, and the second-class weld qualification qualification level should be "Steel Fusion Welding Butt Joint Radiography" (GB 3323) And quality classification" (GB 3323) level III and above.
10. Surface inspection should be carried out in one of the following situations:
a. When cracks are found in visual inspection, 100% surface inspection of the same kind of welds in the batch shall be carried out;
b. When a crack is suspected in the visual inspection, surface flaw detection should be carried out on the suspected part;
c. When the design drawing stipulates surface flaw detection;
e. When the inspector considers it necessary.
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 welds into three quality levels. Generally, ultrasonic flaw detection and radiographic flaw detection can be used to detect internal defects.
Radiographic inspection has the advantages of intuitiveness and good consistency. In the past, people felt that radiographic inspection was reliable and objective.
However, radiographic inspection has high cost, complicated operation procedures, and long inspection cycle, especially in steel structures, which are mostly T-shaped joints and corner joints. The effect of radiographic inspection is poor, and the detection rate of radiographic inspections for hazardous defects such as cracks and unfusion Low.
Ultrasonic flaw detection is just the opposite. The operating procedure is simple and fast. It has good adaptability to various joint forms and has high sensitivity for cracks and unfused detection.
Therefore, many countries in the world adopt ultrasonic flaw detection for internal quality control of steel structures, and generally do not use radiographic flaw detection.
With the continuous increase in the application of large space structures, the corresponding ultrasonic flaw detection methods are given in the current national industry standard "Technical Specification for Welding of Building Steel Structures" JGJ81 And defect classification.
The flaw detection of the welds of the grid structure shall be carried out in accordance with the current national standard JG/T203-2007 "Ultrasonic flaw detection and quality classification method for steel structures".
This code requires 100% inspection of the first-level welds with full penetration, and the partial inspection of the second-level welds is determined as sampling inspection.
The steel structure is generally long, and each weld is inspected according to the specified percentage, and the requirement that each place is not less than 200mm is beneficial to ensuring the quality of each weld.
However, the installation welds of steel structures are generally not long. Most of the welds are beam-column connection welds. The length of each weld is mostly between 250-300mm. It is feasible to use the number of welds to count and sample.
1. T-shaped joints, cross joints, corner joints and other butt joints and corner butt combined welds that require penetration, the size of the weld leg shall not be less than t/4; the webs of crane beams or similar components that require fatigue check calculations are designed The size of the weld 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.
Inspection quantity: all data are inspected; 10% random inspection of similar welds, and no less than 3.
Inspection method: observe and inspect, spot check and measure with weld gauge.
Note: The above 1. For T-shaped, cross-shaped, corner joints and other butt joints and corner joints combined welds that require penetration, in order to reduce stress concentration and avoid excessive weld foot sizes, refer to relevant domestic and foreign regulations. The requirements for different welding foot sizes of static load structure and dynamic load structure are determined.
2. There shall be no defects such as cracks and weld bead on the surface of the weld.
The first and second level welds shall not have defects such as surface pores, slag inclusions, crater cracks, arc scratches, etc. And the first-level welds are not allowed to have defects such as undercuts, incomplete welds, and root shrinkage.
Inspection quantity: 10% of each batch of similar components shall be randomly inspected, and no less than 3 pieces; among the randomly inspected components, 5% of each type of weld shall be randomly inspected according to the number of pieces, and shall not be less than 1 piece; each piece shall be inspected 1 piece, The total number of spot checks should not be less than 10.
Inspection method: observe inspection or use a magnifying glass, welding seam quantity regulation and steel rule inspection, when there is doubt, adopt penetrant or magnetic particle inspection.
Note: The above-mentioned consideration of different quality levels of weld load requirements is different, any defects that seriously affect the weld load capacity are strictly prohibited. This article lists the main control items for the appearance quality requirements that seriously affect the weld load capacity, and gives the appearance qualified Quality requirements. Due to the importance of the primary and secondary welds, there should be specific requirements that are not allowed for surface pores, slag inclusions, crater cracks, and arc scratches. Defects such as undercut, under-welded, and root shrinkage have a great impact on dynamic load. Therefore, the first-level weld shall not have such defects.
