Thread Content
The welds should be assigned to different quality grades in accordance with the following principles, taking into account factors such as the importance of the structure, load characteristics, weld type, operating environment, and stress conditions. 1. In components for which fatigue calculations are required, all butt welds must be fully penetrated. The quality grade for such welds is as follows: 1) For transverse butt welds or T-shaped butt and fillet combined welds, where the force acts perpendicular to the weld length, they shall be of grade 1 when under tension and of grade 2 when under compression ； 2) Longitudinal butt welds whose acting force is parallel to the weld length direction shall be of grade 2. 2. In components for which fatigue calculation is not required, butt welds that are required to have strength equal to that of the base material must be fully penetrated; their quality grade shall be at least grade 2 when under tension, and grade 2 is preferred when under compression. 3. For cranes with a heavy duty operating regime and a lifting capacity of Q≥50t, full penetration is required for the T-joint welds between the web and the L-shaped flange, as well as between the upper chord members of the crane frame and the node plates. The weld configuration is generally a combination of butt welds and fillet welds, and their quality grade should not be lower than grade 2. 4. For ‘I’-shaped joints where full penetration is not required, as well as for butt and fillet weld combinations with partial penetration used in such joints, and for fillet welds used in lap joints, the quality grade is as follows: 1) For structures that are subject to dynamic loads and for which fatigue analysis is necessary, as well as for crane beams with a lifting capacity of 50 tons or more operating under medium-duty conditions, the visual quality standards for the welds shall meet grade 2 ； 2) For other structures, the visual quality standard for welds can be grade 2. Visual inspection is generally carried out by eye; the inspection for cracks should be done using a 5x magnifying glass under appropriate lighting conditions. When necessary, magnetic particle testing or penetrant testing can be employed, while dimension measurement should be performed using measuring tools and calipers. The visual quality of the welds shall meet the following requirements: 1. First-class welds must not have defects such as incomplete filling, root contraction, undercutting, or poor joint formation; first-class and second-class welds must not have surface defects such as pores, inclusions, cracks, or arc scratches ； 2 The visual quality of secondary welds shall, in addition to meeting the requirements of the first paragraph of this clause, also comply with the relevant provisions specified in the table below ； 3 The visual quality of grade 3 welds shall comply with the relevant provisions in the table below. For welds designed to achieve full penetration, the inspection of their internal defects shall meet the following requirements: 1 Grade 1 welds shall be inspected 100%, and their acceptable quality level shall be grade II or higher as per level B inspection of the current **standard \"Methods for Manual Ultrasonic Testing of Steel Welds and Quality Classification\" (GB 11345) ； 2 The secondary welds shall be subject to random inspections, with a sampling rate of not less than 20%; their acceptable quality grade shall be Grade III or higher as per Grade B inspection standards specified in the current standard \"Methods for Manual Ultrasonic Testing of Steel Welds and Quality Classification Method\" (GB 11345) ； 3 Fully penetrative grade 3 welds do not require non-destructive testing. 4 The ultrasonic testing methods for welds in welded spherical node trusses, as well as the classification of defects, shall comply with the provisions of the current standard JG/T203-2007 \"Ultrasonic Testing and Quality Classification Methods for Steel Structures\". 5 The ultrasonic testing methods for welds of bolted spherical grid shells, as well as the classification of defects, shall comply with the provisions of the current standard JG/T203-2007 \"Ultrasonic Testing and Quality Classification Methods for Steel Structures\". In addition to complying with the relevant provisions of Article 7.3.3 of standard GB50205-2001, the non-destructive testing results of the electroslag welded joints of the 6 box-shaped members’ partitions shall also include inspections of the weld penetration width and weld offset in accordance with Appendix C. 7 The ultrasonic testing methods and defect classification for the fillet welds at T, K, and Y joints of circular tubes shall comply with the provisions of Appendix D of standard GB50205-2001. 8 When the design documents specify that radiographic testing or ultrasonic testing cannot be used to determine the nature of defects, radiographic testing can be employed for inspection and verification. 9 Radiographic testing shall comply with the provisions of the current **standard \"Radiography and Quality Grading of Steel Fusion Welded Butt Joints\" (GB 3323); the quality grade of the radiographs shall meet the requirements of grade AB. The acceptable grade for first-class welds should be Grade II or above as specified in \"Radiographic Inspection and Quality Classification of Fusion Welded Butt Joints of Steel\" (GB 3323), while the acceptable grade for second-class welds should be Grade III or above according to the same standard. Surface inspection shall be conducted in any of the following situations: 1) When cracks are detected during visual inspection, 100% surface inspection of similar welds in that batch shall be carried out ； 2) When cracks are suspected based on visual inspection, surface flaw detection should be performed on the suspected area ； 3) When surface flaw detection is specified in the design drawings ； 4) When the inspector deems it necessary. Ferromagnetic materials should be inspected for surface defects using magnetic particle testing. Penetrant testing may be used only when magnetic particle testing cannot be employed due to structural or material reasons. Magnetic particle testing shall comply with the provisions of the current standard **\"Methods for magnetic particle inspection of welds and grading of defect traces\" (JB/T 6061), while penetrant testing shall comply with the provisions of the current standard **\"Methods for penetrant inspection of welds and grading of defect traces\" (JB/T 6062). The acceptance criteria for magnetic particle testing and penetrant testing shall comply with the relevant provisions for visual inspection. For grade 1 and grade 2 welds that require full penetration, ultrasonic testing shall be used to detect internal defects. When ultrasonic testing is unable to determine the presence of defects, radiographic testing shall be employed. The classification of internal defects and the testing methods shall comply with the current standards **“Methods for Manual Ultrasonic Testing of Steel Welds and Classification of Test Results” GB11345, or “Radiographic Testing and Quality Classification of Fusion Welded Butt Joints of Steel” GB3323. For the welds of welded ball-joint grid structures, bolted ball-joint grid structure welds, and the welds at the T, K, and Y intersections of circular tubes, the classification of internal defects and the methods for flaw detection shall comply respectively with the provisions of the current standard JG/T 203-2007 \"Ultrasonic Flaw Detection and Quality Classification Methods for Steel Structures\" and the \"Technical Code for Welding of Building Steel Structures\" JGJ81. The quality grades and defect classifications for grade 1 and grade 2 welds shall comply with the provisions in the table below. Quality grades for secondary welds and classification of defects: Depending on the load-bearing requirements of the structure, the current **standard ‘Code for Design of Steel Structures’ GBJ17 classifies the quality of welds into three different grades. The detection of internal defects can generally be achieved using ultrasonic testing and radiographic testing. Radiographic inspection has the advantages of being intuitive and providing good consistency; in the past, it was considered reliable and objective. However, radiographic testing is costly, has complex procedures, and requires a long inspection time. Especially in steel structures, where T-joints and corner joints are common, the effectiveness of radiographic testing is poor, and its ability to detect harmful defects such as cracks and lack of fusion is low. Ultrasonic testing is the opposite in this regard: it has a simple and fast operation procedure, is well-suited to various types of joints, and possesses high sensitivity in detecting cracks and lack of fusion. As a result, many countries around the world use ultrasonic testing for controlling the internal quality of steel structures, and radiographic testing is generally no longer used. With the increasing use of large-scale spatial structures, regarding the weld inspection of thin-walled, highly curved T, K, and Y-type intersections, **the current industry standard, the ‘Code for Welding Technology of Building Steel Structures’ JGJ81, provides corresponding ultrasonic inspection methods and defect classification systems. The flaw detection of welds in grid structures shall be carried out in accordance with the provisions of the current standard JG/T203-2007 \"Ultrasonic Flaw Detection and Quality Grading Method for Steel Structures\". These specifications require 100% inspection of first-class welds that must be fully penetrated, while partial inspection of second-class welds is specified as a sampling inspection. The fabrication of steel structures is generally a lengthy process; flaw detection is carried out on each weld according to a specified percentage, with a requirement of at least 200 mm per location, which is beneficial for ensuring the quality of each weld. However, the welds used in the installation of steel structures are generally not long; most of them are welds that connect beams to columns, and the length of each weld is usually between 250–300 mm. It is feasible to conduct sampling inspections by counting the number of welds. 1. For butt and fillet combined welds that require full penetration, such as T-joints, cross joints, and corner joints, the size of the weld leg should not be less than t/4 ； The root thickness of the weld joining the web to the upper flange of crane girders or similar members that are subject to fatigue checks is set at t/2, and shall not be less than 10 mm. The allowable deviation for the weld leg size is 0-4 mm. Number of inspections: Full inspection of all materials ； 10% of welds of the same type shall be sampled, with a minimum of 3 welds. Inspection method: Visual inspection, with random sampling and measurement using a weld gauge. ] Note: For the butt and fillet combined welds of T-shaped, cross-shaped, corner-jointed joints, etc., where full penetration is required, in order to reduce stress concentration and avoid excessively large weld leg sizes, the requirements for weld leg sizes in static and dynamic load structures have been determined with reference to relevant domestic and international standards. 1. For butt and fillet combined welds that require full penetration, such as T-joints, cross joints, and corner joints, the size of the weld leg should not be less than t/4 ； The root thickness of the weld joining the web to the upper flange of crane girders or similar members that are subject to fatigue checks is set at t/2, and shall not be less than 10 mm. The allowable deviation for the weld leg size is 0-4 mm. Number of inspections: Full inspection of all materials ； 10% of welds of the same type shall be sampled, with a minimum of 3 welds. Inspection method: Visual inspection, with random sampling and measurement using a weld gauge. ] Note: For the butt and fillet combined welds of T-shaped, cross-shaped, corner-jointed joints, etc., where full penetration is required, in order to reduce stress concentration and avoid excessively large weld leg sizes, the requirements for weld leg sizes in static and dynamic load structures have been determined with reference to relevant domestic and international standards.