Specification and standard for nondestructive testing of welds professional testing organization

Date：2022-04-20 17:30:00Views：749

Weld quality standard

1、 Guarantee project

1. The welding materials shall meet the design requirements and relevant standards, and the quality certificate and baking records shall be checked.

2. The welder must pass the examination, and check the certificate and examination date of the welder's corresponding welding conditions.

3. Class I and II welds must be subject to flaw detection and meet the design requirements and the provisions of construction and acceptance specifications. Check the weld flaw detection report.

4. Grade I and II welds on the weld surface shall be free of cracks, weld beading, burn through, crater and other defects. Grade II welds shall be free of surface pores, slag inclusions, craters, cracks, arc scratches and other defects, and grade I welds shall be free of undercut, incomplete welding and other defects.

2、 Basic items

1. Weld appearance: the weld appearance is uniform, the transition between weld bead and weld bead and between weld bead and base metal is smooth, and the welding slag and spatter are removed.

2. Surface porosity: Grade I and II welds are not allowed; The allowable diameter of grade III weld is ≤ 0.4t for every 50mm of weld length; 2 pores ≤ 3mm; Pore spacing ≤ 6 times of pore diameter.

3. Undercut: Grade I weld is not allowed.

Class II weld: undercut depth ≤ 0.05T and ≤ 0.5mm, continuous length ≤ 100mm, and total undercut length on both sides ≤ 10% of weld length.

Class III weld: undercut depth ≤ 0.5m LT, and ≤ LMM.

Note: t is the thickness of thinner plate at the connection.

3、 Finished product protection

1. It is not allowed to smash the joint after welding, and it is not allowed to water the steel just welded. Slow cooling measures shall be taken under low temperature.

2. It is not allowed to strike an arc on the base metal outside the weld at will.

3. Welding can be carried out only after various components are calibrated, and the sizing block and fixture shall not be moved at will to prevent dimensional deviation of components. For the welds of concealed parts, the next concealed process can be carried out only after the concealed acceptance procedures are completed.

4. Low temperature welding is not allowed to remove slag immediately. It should be carried out after the weld is cooled down.

4、 Quality problems needing attention

1. The size exceeds the allowable deviation: the relative position and size of the welding part shall be strictly controlled for the deviation such as insufficient length, width and thickness of the weld, offset of the center line and bending. The welding can be carried out only after it is qualified, and careful operation shall be carried out during welding.

2. Weld crack: in order to prevent cracks, appropriate welding process parameters and welding procedures shall be selected to avoid high current and sudden flameout. The weld joint shall be 10 ~ 15mm long. It is allowed to move and knock the weldment during welding.

3. Surface porosity: the welding rod shall be baked according to the specified temperature and time, and the welding area must be cleaned. During the welding process, appropriate welding current shall be selected to reduce the welding speed and make the gas in the molten pool escape completely.

4. Weld slag inclusion: the welding slag shall be removed layer by layer during multi-layer welding, and the strip shall be transported correctly and the arc length shall be appropriate. Pay attention to the flow direction of slag. When using alkaline electrode, the slag must be left behind the slag.

5、 Quality record

This process standard shall have the following quality records:

1. Quality certificate of welding materials.

2. Welder certificate and number.

3. Welding procedure test report.

4. Welding quality inspection report and flaw detection report.

5. Design change and negotiation records.

6. Acceptance records of concealed works.

7. Other technical documents.

Weld grade classification and NDT requirements

Different quality grades of welds shall be selected according to the importance of structure, load characteristics, weld form, working environment and stress state according to the following principles:

1. In the components requiring fatigue calculation, all butt welds shall be fully welded, and their quality grade is:

1) The transverse butt weld or T-shaped butt and fillet combined weld with force perpendicular to the length of the weld shall be class I in tension and class II in compression;

2) Longitudinal butt welds with forces parallel to the length of the weld shall be class II.

2 . In the components that do not need to calculate fatigue, the butt weld with the same strength as the base metal shall be fully welded, and its quality grade shall not be lower than grade II in tension and grade II in compression.

3 . For heavy duty working system and lifting capacity Q ≥ 50t, the T-joint welds between the web and L-edge of the crane beam and between the chord on the crane frame and the gusset plate shall be fully welded. The weld form is generally the combined weld of butt joint and fillet joint, and its quality grade shall not be lower than grade II.

4 . The quality grade of fillet weld or partial penetration butt and fillet combination weld used for 'I' joint without penetration and fillet weld used for lap joint is:

1) For structures that directly bear dynamic load and need to check fatigue and intermediate working crane beams with crane lifting capacity equal to or greater than 50t, the appearance quality standard of welds shall meet grade II;

2) For other structures, the appearance quality standard of welds can be grade II.

Visual inspection is generally used for appearance inspection. Crack inspection shall be supplemented by 5x magnifying glass and carried out under appropriate light conditions. Magnetic particle flaw detection or penetration flaw detection can be used if necessary. Measuring tools and caliper shall be used for dimension measurement.

The appearance quality of welds shall meet the following requirements:

1 . The primary weld shall be free of defects such as incomplete welding, root shrinkage, undercut and poor joint. The primary weld and secondary weld shall be free of defects such as surface porosity, slag inclusion, crack and arc scratch;

2. The appearance quality of secondary welds shall not only meet the requirements of paragraph 1 of this article, but also meet the relevant provisions in the following table;

3. The appearance quality of grade III welds shall comply with the relevant provisions in the table below.

For full penetration welds, the inspection of internal defects shall meet the following requirements

1 . 100% inspection shall be conducted for class I welds, and the qualification level shall be class II or above of class B inspection in the current national standard manual ultrasonic flaw detection methods and quality classification methods for steel welds (GB 11345);

2 . Spot check shall be carried out for class II welds, and the proportion of spot check shall not be less than 20%. Its qualification level shall be class III and above of class B inspection in the current national standard manual ultrasonic flaw detection methods and quality classification methods for steel welds (GB 11345);

3 . NDT is not required for grade III welds with full penetration;

4. The ultrasonic flaw detection method and defect classification of welded spherical joint grid welds shall comply with the provisions of the current national standard JG / t203-2007 ultrasonic flaw detection and quality classification method of steel structures;

5 . The ultrasonic flaw detection method and defect classification of bolt ball joint space truss welds shall comply with the provisions of the current national standard JG / t203-2007 ultrasonic flaw detection and quality classification method of steel structures;

6. In addition to the relevant provisions of article 7.3.3 of GB50205-2001, the NDT results of electroslag welding welds of box member diaphragms shall also be tested for weld penetration width and weld offset according to Appendix C;

7. The ultrasonic flaw detection method and defect classification of T, K and Y joint welds of circular pipe shall comply with the provisions of Appendix D of GB50205-2001 standard;

8 . When radiographic inspection or ultrasonic inspection specified in the design document cannot judge the nature of the defect, radiographic inspection can be used for inspection and verification;

9. Radiographic testing shall comply with the provisions of the current national standard radiography and quality classification of steel fusion welded butt joints (GB 3323), and the quality grade of radiography shall meet the requirements of grade ab. The qualification grade of grade I weld shall be grade II and above in radiography and quality classification of steel fusion welded butt joints (GB 3323), and the qualification grade of grade II weld shall be grade III and above in radiography and quality classification of steel fusion welded butt joints (GB 3323).

10. Surface inspection shall be carried out under one of the following conditions:

1) When cracks are found in appearance inspection, 100% surface inspection shall be conducted for similar welds in this batch;

2) When cracks are suspected in appearance inspection, surface flaw detection shall be carried out for the suspected parts;

3) When surface flaw detection is specified in the design drawing;

4) When the inspector deems it necessary.

Ferromagnetic materials shall be tested for surface defects by magnetic particle flaw detection. If magnetic particle testing cannot be used due to structural or material reasons, penetrant testing can be used. Magnetic particle flaw detection shall comply with the provisions of the current national standard magnetic particle inspection method of welds and classification of defective magnetic traces (JB / T 6061), and penetrant flaw detection shall comply with the provisions of the current national standard penetrant inspection method of welds and classification of defective magnetic traces (JB / T 6062). The qualification standards of magnetic particle flaw detection and penetrant flaw detection shall comply with the relevant provisions of visual inspection.

The grade I and II welds with full penetration required by the design shall be inspected for internal defects by ultrasonic flaw detection. When ultrasonic flaw detection cannot judge the defects, radiographic flaw detection shall be adopted. The classification and flaw detection method of internal defects shall comply with the provisions of the current national standard manual ultrasonic wave flaw detection methods and classification of flaw detection results of steel welds gb11345 or radiographic photography and quality classification of steel fusion welded butt joints gb3323.

The internal defect classification and flaw detection methods of welded ball joint space truss welds, bolt ball joint space truss welds and circular pipe T, K and Y-point intersection welds shall respectively comply with the provisions of the current national standards JG / t203-2007 ultrasonic flaw detection and quality classification method of steel structures and jgj81 technical specification for welding of building steel structures.

The quality grade and defect classification of grade I and II welds shall comply with the provisions in the following table.

1、 Grade II weld quality grade and defect classification

Note: according to the different bearing conditions of the structure, the quality of welds is divided into three quality grades in the current national standard code for design of steel structures (GBJ17). Generally, ultrasonic flaw detection and radiographic flaw detection can be used for the detection of internal defects. Radiographic testing has the advantages of intuitiveness and good consistency. In the past, people thought that radiographic testing was reliable and objective.

However, the cost of radiographic testing is high, the operation procedure is complex and the testing cycle is long. Especially, most of the steel structures are T-joints and corner joints, the effect of radiographic testing is poor, and the detection rate of radiographic testing for cracks, incomplete fusion and other harmful defects is low. Ultrasonic flaw detection is just the opposite. The operation procedure is simple and fast, has good adaptability to various joint forms, and has high detection sensitivity to cracks and incomplete fusion. Therefore, ultrasonic flaw detection is adopted for the internal quality control of steel structures in many countries in the world, and radiographic flaw detection is generally not adopted.

With the increasing application of large space structures, the corresponding ultrasonic flaw detection method and defect classification are given in the current national industry standard technical specification for welding of building steel structures jgj81 for the weld detection of thin-walled large curvature T, K and Y-type intersecting joints. The weld flaw detection of space truss 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.

This specification requires 100% inspection of class I welds with full penetration, and local inspection of class II welds is determined as sampling inspection. The fabrication of steel structure is generally long. Flaw detection shall be carried out for each weld according to the specified percentage, and the provision that each part is not less than 200mm is beneficial to ensure the quality of each weld.

However, the installation welds of steel structure are generally not long. Most of the welds are beam column connection welds, and the length of each weld is mostly between 250-300mm. It is feasible to use the counting and sampling inspection of the number of welds.

1. The weld leg size of T-shaped joint, cross joint, fillet joint and other butt and fillet combined welds requiring penetration shall not be less than t / 4; The weld leg size of the connecting weld between the web and the upper flange of the crane beam or similar components designed with fatigue checking calculation requirements is t / 2 and shall not be less than 10mm. The allowable deviation of weld leg size is 0-4 mm.

Inspection quantity: check all data; Spot check 10% of similar welds and no less than 3.

Inspection method: observation inspection, spot check and measurement with weld gauge.

Note: 1 For T-type, cross type, fillet joint and other butt and fillet combination welds requiring full penetration, in order to reduce stress concentration and avoid excessive weld leg size, the requirements for different weld leg sizes of static load structure and dynamic load structure are determined with reference to the provisions of relevant specifications at home and abroad.

2. The weld surface shall be free of cracks, weld beading and other defects. Primary and secondary welds shall be free of surface pores, slag inclusion, crater cracks, arc scratches and other defects. The primary weld shall be free of undercut, incomplete welding, root shrinkage and other defects.

Inspection quantity: spot check 10% of each batch of similar components, and no less than 3 pieces; Among the components to be sampled, 5% of each type of weld shall be sampled according to the number of welds, and there shall be no less than 1 weld; One inspection shall be conducted for each item, and the total number of spot checks shall not be less than 10.

Inspection method: visual inspection or inspection with magnifying glass, weld quantity regulations and steel ruler. In case of doubt, penetrant or magnetic particle inspection shall be adopted.

Note: considering that the weld bearing requirements of different quality grades are different, all defects that seriously affect the weld bearing capacity are strictly prohibited. This article lists the appearance quality requirements that seriously affect the weld bearing capacity into the main control items, and gives the appearance qualified quality requirements.

Due to the importance of class I and II welds, there shall be specific requirements for surface pores, slag inclusion, crater cracks and arc scratches. Undercut, incomplete welding, root shrinkage and other defects have a great impact on dynamic load, so class I welds shall not have such defects.