Tube connecting plate and shell failure of welded joints of structural factors

Study: Hong Junhua Wang Xianjun Xiaqiu Ping

Abstract: The properties of welded joints and experimental factors, adjusting the structure parameters and the corresponding welding parameters, to prevent defects in welded joints, increase joint mechanical properties, thereby enhancing the product life, reduce losses and save the material.

Keywords:: welded joint, failure analysis, structural factors
Heat exchanger products fixed tube plate without flange connection with the shell of welded joints is the main welded joints on the product, manufacturing process defects in the internal organization of welded joints, such as slag, porosity, incomplete fusion, not penetration, cracks and coarse microstructure, etc., will affect the mechanical properties of welded joints, but also affect the reliability of product, to the unnecessary use of units of the economic loss is not ignored. welded joint performance by influencing factors analysis and experiment, adjusting the structure parameters and the corresponding welding parameters, to prevent defects in welded joints, increase joint mechanical properties, thereby enhancing the product life, reduce losses and save the material.

1 of the problem
In the production process, the welded structure parameters, welding parameters, pre-preparation and operation of welding and other factors will affect the way the quality of welded joints in welding by controlling the related technical parameters necessary to control the internal quality of welded joints to maximize the mechanical properties of welded joints. In many technical factors, structural parameters and welding parameters the greatest impact on the quality of welded joints, for which changes in groove size of the impact on the quality of welded joints and welding process parameters on the quality of welded joints is the main topic.

Through the groove of different sizes with the same welding parameters in the welded joints welded joints, mechanical properties, welding stress distribution changes, compare the quality of welded joints of the structure of the smallest size, select the best technical parameters.

2 to determine the size of groove
Product design and size of groove shown in Figure 1, in which size tube dray side 0.25��, and the case group after the groove gap 0.4��1, depending on the thickness of the concrete in the country have clearly defined standards .

The subject of the production units based on the actual situation, �� and ��1 values in Table 1. According to data in the table, press <<Steel Pressure Vessels>> the relevant provisions of the standard, you can calculate the tube size and side scooters groove gap size, are also listed in Table 1.

In this experiment, in order to reduce the workload, the specimen into a groove the size of side group, maximum take 6mm, the minimum take 1mm. Although the value differ from the national standards, but meet the welding process to ensure welding joint quality of the requirements, the accuracy of test results is not obvious.

Simulation Test and Measurement 3
To ensure the structural parameters of welded joints of the organization, stress and mechanical properties of the test results so accurate, in the welding process, welding parameters remain the same requirements.

The structure of the test specimen and the structure of the actual use of similar products. For the detection of welded joints including HAZ of welded joints stress, mechanical properties and heat affected zone analysis.

3.1 Stress Test
Stress test, stress release method used.

Welded joints by welding heat affected zone or Area with the strain at the point of the test, calculate the stress at that point. This method is relatively simple test, test equipment required is simple. Although data are not accurate enough, but the same specimen test data a contrast, is fully in line with the project requirements.

Test, for the stress of heat affected zone is relatively accurate and has contrast, test selection 5mm welded joints on both sides of weld toe parallel to the welded joints at the centerline of the straight line as the position of the welding stress test, and the spacing of 5mm a test point, both sides of the ends of the measuring 6.

3.2 Mechanical Performance Test
Stress test specimen by mechanical processing methods processed into tensile test specimens to test their mechanical properties. Reposted elsewhere in the Research Papers Download http://www.hi138.com 4 Data Analysis
4.1 test points from the stress and the relationship between welded joints
The above data show that the different distances from the welded joint between the points of stress are different. From the more recent fusion line, the greater the stress, the farther away from the fusion line, the stress is smaller. That produce more high temperature zone stress.

4.2 groove spacing on the stress
The impact of the corresponding groove pitch is also more obvious, can be seen from the table, the greater the groove spacing, stress also significantly increased, the maximum clearance at the stress (the stress value for the minimum clearance of 3.5 times. From theory on the analysis, the greater the groove, more metal to be filled, the heat effect of welding the longer the higher the temperature, resulting in greater stress.

4.3 groove spacing on the mechanical properties of
Can be seen that the groove spacing on the mechanical properties of small, but the groove spacing of defects have a greater impact. Both have done a macro-metallographic sample examination, the smaller groove spacing, lack of penetration defects tend to increase. Therefore, the groove spacing indirectly affect the strength of welded joints and reduce fatigue.

5 metallographic analysis
Groove in the corresponding maximum and minimum slope-side port side of the sample were taken for metallographic analysis, comparing the base metal microstructure, very small differences in organizational change. Can be seen, because the materials used for ordinary carbon steel (tube plate and tube materials are chosen Q235-B, the organization of such materials in the heating, the growing tendency is not obvious. can be considered, groove spacing on the heat-affected zone of welded joints and metal structure of a little. or, for welded joints and heat affected zone metal structure welded joint failure caused by factors in the phenomenon of welding defects and stress than the impact is much smaller.

6 Conclusion
Through the above analysis, the tube connecting plate and shell important factor in the failure of welded joints, the groove size is one of them. Because the groove size on the generation of internal defects of welded joints and heat affected zone the size of the welding residual stress has significant impact, groove the greater the increase the likelihood of welding defects, welding residual stress increases. in the welding practice, you can choose the right groove size, together with the reasonable welding process parameters to minimize the welded joint and heat affected zone of the welding residual stress, you can reduce the occurrence of such failure, thereby reducing economic losses in production.

References
[1] TRANSACTIONS. Welded structure and assessment of fracture behavior of [M]. Beijing: China Machine Press, 2000,6.

[2] National Committee for Standardization of Pressure Vessel Committee. GB150-1998, steel pressure vessel [S].

[3] National Committee for Standardization of Pressure Vessel Committee. GB151-99, shell and tube heat exchanger [S].

[4] Chen Chu. Welding design Concise Manual [M]. Beijing: China Machine Press, 1997,3. Links http://www.hi138.com Research Papers Download