Why is there a weld bead excess height, and why is it necessary to control this excess height? The expert explained it clearly!

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01 The role of weld height: There should be a weld height during the welding process. Because the outermost layer serves to insulate and slow down cooling, it plays a significant role in refining the grain structure and reducing welding stress. It is also a collection area for impurities such as pores. 02 Disadvantages of excessive height: Pressure vessels should avoid sudden changes that could lead to local stress concentration. Furthermore, the residual height must have defects, and such defects are likely to be the nuclei for the formation of fatigue cracks. Crack source → fatigue propagation → fracture. China and Japan once conducted joint experiments and found that equipment with residual height had a service life 2.0 to 2.5 times shorter than that of equipment without residual height after grinding. 03 Requirements for residual height per standards: 1) JB4732 requires grinding for fatigue-prone equipment, while there are specific limits for other types of equipment. Basically, it doesn’t affect the soldering; polishing is not required. 2) China’s **standard GB150 specifies this as follows, as shown in the tables and diagrams: Grinding. Good appearance quality is one of the reasons for the success of foreign products in the market. Additionally, polishing prevents environmental corrosion, avoids excessive stress concentration, and extends the service life of welds. 05 Suggestions for dealing with excess height: Polishing is indeed a good option. The standard represents the minimum requirement; therefore, it is recommended to polish important equipment or those that require significant investment, while there is no need to polish equipment with lower investment costs. 06 Hazards of excessive weld bead height: Stress corrosion cracks tend to form at the weld toe. The stress concentration in butt joints is primarily caused by the weld bead height; in butt joint welds, the stress is highest at the weld toe. The greater the excess height of the weld, the more severe the stress concentration, and as a result, the strength of the welded joint decreases. After welding, the excess height should be trimmed down as long as it remains above the level of the base material; this helps to reduce stress concentration, and in some cases it can even increase the strength of the welded joint. 07 An excessive excess height of the external weld seam makes it difficult to carry out anti-corrosion treatment; when using epoxy resin and glass cloth for anti-corrosion purposes, a high excess height of the external weld seam hinders proper compression at the weld toe. At the same time, the higher the weld, the thicker the anti-corrosion layer must be; since standards specify that the thickness of the anti-corrosion layer is determined based on the top of the outer weld, this increases the cost of anti-corrosion measures. 08 Excessive height of the internal welds leads to increased energy losses for the transported medium. When the inner surface of the welding pipe used for transportation is not coated for corrosion protection, the excessive height of its internal welds results in greater frictional resistance against the transported medium, thereby increasing the energy consumption of the pipeline. 09 Control measures for weld excess height: Adjust the welding wire energy and check whether it is appropriate; this is generally done by examining acid-etched samples of the welded joints. First, check the degree of overlap between the internal and external welds; second, check the width of the weld bead’s waist.