What Are Welding Joints?
A welded joint is a joint where two or more parts are to be combined by welding. Or refers to a joint where two or more parts are connected by welding, including welds, fusion zones and heat affected zones. The fusion welded joint is formed by local heating by a high-temperature heat source. Welded joints consist of weld metal, fusion zone, heat affected zone and base metal. [1]
Welded joint
- Welding joint coefficient refers to the ratio of the strength of the butt welded joint to the strength of the base metal. It is used to reflect the extent to which the strength of the welded joint is weakened due to factors such as welding materials, welding defects, and welding residual stress. It is a comprehensive reflection of the mechanical properties of the welded joint. (In fact, the weld joint coefficient does not really reflect the degree of weakening of the material strength at the weld, but an empirical data that indicates the reliability of the quality of the weld.)
- Coefficient size
- Standards: National Standard, American Standard, and Japanese Standard are related to the type of welding seam, welding process and the strictness of non-destructive testing of welding seam. Same as ASME -1 in the United States and JISB8241 in Japan, GB150 stipulates that the welding joint coefficient should be based on the welding process characteristics of the welded joints of the pressure components of the vessel (weld type-single-sided or double-sided welding; with or without backing plate ), And the non-destructive testing spot check rate is determined, and only the butt weld is specified.
See Table 1:
Table 1 Welded joint coefficient
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- The mechanical properties of a welded joint depend on its chemical composition and organization. Therefore, the factors that affect the chemical composition of the weld and the structure of the welded joint all affect the performance of the welded joint.
- There are four main types of welded joints: butt joints, T-joints, corner joints, and lap joints. Sometimes there are some other types of joints in welded structures, such as cross joints, termination joints, crimp joints, bushing joints, oblique butt joints, lock bottom butt joints, etc. There are detailed regulations in the national standard GB 985-88.
Butt joint
- The joint where two weldments are relatively parallel is called a butt joint. This joint is an ideal joint form from a mechanical point of view. It has better stress conditions, less stress concentration, and can withstand large static or dynamic loads. One of the most commonly used joints in the structure.
- According to the thickness of the weldment, the welding method and the preparation of the groove, butt joints can be divided into two types: non-open groove butt joints and open groove butt joints. Common joints are shown in Figure 3-1.
- Butt joint
T T-joints
- The joint between the end face of one weldment and the surface of the other weldment forms a right angle or near right angle, which is called a T-shaped joint.
- T-joints are used more often in steel structures. As a contact weld, it can withstand forces and moments in all directions. When selecting, try to avoid single-sided fillet welds, because the root has a deep gap and the load capacity is very low. For weldments with higher requirements, a K-shaped groove can be used, and whether the root is welded through is determined according to the force. This is more economical than a weld with a large welding leg without opening the groove, and the joint has higher fatigue strength.