10 phenomena most easily overlooked in welding processes and operations

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During the welding process, there are many things to pay attention to; any oversight could lead to serious mistakes. Details determine success or failure; attitude changes one’s life. 1. Failure to select the optimal voltage during welding operations. [Symptom] During welding, whether it is for root pass, filling pass, or finish pass, the same arc voltage is used regardless of the size of the groove. This may result in failure to achieve the required penetration depth and weld width, as well as defects such as undercut, porosity, and spatter. 【Measures】 Generally, depending on different circumstances, choosing either a long arc or a short arc accordingly can yield better welding quality and work efficiency. For instance, during root welding, a short arc should be used to achieve better penetration; whereas during filler or cap welding, the arc voltage can be appropriately increased to obtain higher efficiency and wider weld width. 2. Failure to control the welding current during welding. [Symptom] In order to speed up the process, no bevel is used for the butt joints of medium-thick plates during welding. The strength indicators decline, failing to meet the standard requirements; cracks appear during the bending test. This compromises the performance of the weld joints and poses a potential hazard to structural safety. 【Measures】During welding, the welding current should be controlled in accordance with the values specified in the process evaluation; a variation of 10–15% is allowed. The size of the root bevel should not exceed 6 mm. During butt welding, when the plate thickness exceeds 6 mm, a groove must be prepared for welding. 3. Failing to pay attention to the welding speed and welding current, as well as to using the electrode diameter appropriately. [Symptom] During welding, no attention is paid to controlling the welding speed and current, nor is there proper coordination regarding the electrode diameter and the welding position. When performing root pass welding on fully penetrated corner joints, due to the narrow root dimension, if the welding speed is too high, there isn’t enough time for gases and slag at the root to be expelled. This can easily lead to defects such as lack of penetration, slag inclusions, and porosity at the root ； During cap welding, if the welding speed is too high, pores are also likely to form ； If the welding speed is too slow, the weld reinforcement will be excessively high, resulting in an uneven appearance ； When welding thin sheets or welds with small root gaps, a too slow welding speed can lead to issues such as burn-through. 【Measures】The welding speed has a significant impact on welding quality and production efficiency. When selecting it, an appropriate welding speed should be chosen in conjunction with the welding current, the position of the weld (root pass, fill pass, cap pass), the thickness of the weld, and the groove dimensions. A higher welding speed can be utilized to improve productivity, provided that full penetration is achieved, gases and slag can be easily removed, the weld does not suffer from burn-through, and good weld shape is maintained. 4. Failure to control the arc length during welding 【Phenomenon】 During welding, the arc length is not appropriately adjusted according to factors such as the groove configuration, number of weld passes, welding method, and electrode type. Due to improper use of the welding arc length, it is difficult to obtain high-quality welds. 【Measures】To ensure weld quality, short-arc welding is generally used during welding. However, the appropriate arc length can be selected depending on the specific situation in order to achieve the best welding quality. For example, in V-groove butt joints and fillet joints, a shorter arc should be used for the first layer to ensure full penetration and prevent undercutting; a slightly longer arc can be used for the second layer to fill the weld. When the weld gap is small, a short arc should be used; when the gap is large, the arc can be slightly longer to increase the welding speed. The overhead welding arc should be as short as possible to prevent molten iron from flowing downward ； When welding in the vertical or horizontal position, to control the pool temperature, it is also necessary to use a low current and a short arc. Furthermore, regardless of the welding method used, it is important to maintain a basically constant arc length during the welding process, in order to ensure that the weld width and depth are consistent throughout the entire weld. 5. Failure to control welding deformation during welding 【Phenomenon】During welding, no attention is paid to controlling deformation by considering factors such as the welding sequence, personnel arrangement, groove design, selection of welding parameters, and operating methods; as a result, significant deformation occurs after welding, making correction difficult and increasing costs. This is especially true for thick plates and large workpieces, where correction is challenging, and mechanical correction methods can easily cause cracks or layered tearing. Flame correction is costly, and improper operation can easily overheat the workpiece. For workpieces with high precision requirements, failing to implement effective measures to control deformation can result in the installation dimensions not meeting the required standards, which may even lead to rework or scrapping. 【Measures】Adopt a reasonable welding sequence, select appropriate welding specifications and operating methods, and also implement counter-deformation and rigid fixation measures. 6. Multi-layer welding is carried out in a discontinuous manner, with no attention paid to controlling the interlayer temperature. [Symptom] When welding thick plates in multiple layers, if proper control of the interlayer temperature is not ensured – for example, if too much time passes between layers and welding continues without re-preheating – cold cracks are likely to form in those layers ； If the interval time is too short and the interlayer temperature is too high (above 900°C), it will also affect the properties of the weld and the heat-affected zone; this can lead to coarse grains, resulting in a decrease in toughness and plasticity, and pose potential risks to the joint. 【Measures】When welding thick plates in multiple layers, it is necessary to strengthen the control of the interlayer temperature. During continuous welding, the temperature of the base material being welded should be monitored to ensure that the interlayer temperature remains as close as possible to the preheating temperature; the maximum interlayer temperature should also be controlled. The welding time should not be too long; in the event of a welding interruption, appropriate post-heating and holding measures should be taken. When welding resumes, the preheating temperature should be appropriately higher than the initial preheating temperature. 7. Welding the next layer without removing slag from multi-layer welds or addressing defects on the weld surface 【Problem】When welding thick plates in multiple layers, if slag and defects are not removed after each layer is welded, the next layer is welded directly, which can lead to defects such as slag inclusions, pores, and cracks in the welds, reducing the strength of the joint. It also causes spatter during the welding of the next layer. 【Measure】When welding thick plates in multiple layers, welding should be carried out continuously for each layer. After each layer of weld is completed, the slag, surface defects on the weld, and spatter should be removed promptly. Defects such as inclusions, pores, and cracks that can affect the quality of welding must be completely eliminated before continuing with welding. 8. Insufficient weld leg dimensions in butt or fillet combined welds where penetration is required. [Symptom] In butt or fillet combined welds such as T-joints, cross joints, and fillet joints that require penetration, if the weld leg dimensions are insufficient, or if the weld leg dimensions of the welds connecting the web to the upper flange edges in crane beams or similar components for which fatigue analysis is required are insufficient, then both the strength and stiffness of the welds will not meet the design requirements. 【Measures】For butt joint combinations such as T-joints, cross joints, and corner joints that require full penetration, sufficient weld leg dimensions must be ensured in accordance with the design requirements; generally, the weld leg size should not be less than 0.25t (where t is the thickness of the thinner plate at the joint). For crane girders or similar webs designed with fatigue checks, the root size of the welds connecting them to the upper flange is 0.5t, and shall not exceed 10 mm. The allowable deviation for welding dimensions is 0–4 mm. 9. Inserting electrode tips or iron pieces into the joint gap during welding 【Phenomenon】Since it is difficult to fuse the electrode tips or iron pieces with the materials being welded during welding, welding defects such as lack of fusion and insufficient penetration occur, reducing the strength of the connection. If rusted electrode tips or iron pieces are used for filling, it is difficult to ensure consistency with the material of the base metal ； Using welding rod ends or iron pieces contaminated with oil, impurities, etc. as filler will cause defects such as pores, slag inclusions, and cracks in the weld. All these situations will **reduce** the quality of the weld at the joint, failing to meet the quality requirements for welds specified in the design and standards. 【Measures】 (1) When the assembly gap of the workpiece is large but remains within the specified allowable range, and when the assembly gap exceeds twice the thickness of the thin plate or is greater than 20 mm, the recessed areas should be filled using surfacing methods to reduce the assembly gap. It is strictly prohibited to use filled electrode tips or iron blocks for patch welding in the joint gaps. (2) When marking parts for machining, it is necessary to leave sufficient cutting allowance as well as allowance for welding shrinkage after cutting. The dimensions of the parts should be controlled properly; increasing gaps should not be used to maintain the external dimensions. 10. Failing to pay attention to the welding sequence for components with intersecting welds 【Phenomenon】For components with intersecting welds, proper consideration is not given to arranging the welding sequence by analyzing the effects of welding stress release and welding stress on component deformation; instead, welding is carried out in a random manner in both longitudinal and transverse directions. As a result, the longitudinal and transverse welds restrict each other, generating significant thermal contraction stresses that cause the plate to deform and become uneven, and may also lead to cracks in the welds. 【Measurements】For components with intersecting welds, a reasonable welding sequence should be established. When welding multiple intersecting welds, the transverse welds that experience greater contraction deformation should be welded first, followed by the longitudinal welds. This way, when welding the transverse welds, they are not constrained by the longitudinal welds, allowing the contraction stresses in those transverse welds to be released without restriction. This reduces welding deformation and ensures the quality of the welds. Alternatively, the butt welds can be welded first, followed by the fillet welds