The top ten issues most easily overlooked in welding

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1 Failing to select the optimal voltage during welding operations. [Symptom] During welding, whether it is for root pass, fill pass, or finish pass, the same arc voltage is used regardless of the size of the groove. In this case, it may not be possible to achieve the required penetration and width, leading to defects such as undercutting, pores, and spatter. 【Measures】Generally, depending on the different situations, choosing either a long arc or a short arc accordingly will yield better welding quality and work efficiency. For example, during root welding, a short arc should be used to achieve a better penetration depth; whereas during fill welding or cap welding, the arc voltage can be increased appropriately to obtain higher efficiency and weld width. 2. Welding: Welding current is not controlled. [Phenomenon] During welding, in order to expedite the process, no groove is prepared for butt welds on medium-thick plates. The strength parameters decrease, sometimes not even meeting the standard requirements, and cracks appear during bending tests; this results in an unguaranteed performance of the weld joints, posing a potential risk to the 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 made for welding. 3 Failing to pay attention to the welding speed and 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 a root pass on fully penetrated corner joints, due to the narrow size of the root area, if the welding speed is too high, there isn’t enough time for gases and slag to be expelled from that area, which can lead to defects such as lack of penetration, slag inclusions, and pores at the root ； When welding the cover, if the welding speed is too fast, pores are also likely to form ； If the welding speed is too slow, the weld bead height will be too high and its shape will not be regular ； When welding thin plates or welds with a small root face, a too slow welding speed can easily lead to burn-through and similar issues. 【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 burn through, and a good weld shape is obtained. 4. Failing to control the arc length during welding 【Phenomenon】 During welding, the arc length is not appropriately adjusted according to factors such as the groove profile, 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 circumstances 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 without undercutting; the arc length can be slightly longer for the second layer in order to fill the weld completely. A short arc is preferable when the weld gap is small; the arc can be slightly longer when the gap is large, allowing for an increased welding speed. The overhead welding arc should be as short as possible to prevent the molten iron from flowing downward ； When performing vertical or horizontal welding, low current and short arc welding are also used to control the pool temperature. 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 remain 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 cause the workpiece to overheat. For workpieces requiring high precision, failing to take effective measures to control deformation can result in their installation dimensions failing to meet the required specifications, and may even lead to rework or scrapping. 【Measures】Adopt a reasonable welding sequence and select appropriate welding specifications and procedures; in addition, use counter-deformation and rigid fixation measures. 6. Multi-layer welding is carried out discontinuously, 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 ductility, and it creates potential risks for the joint. 【Measures】 When performing multi-pass welding on thick plates, it is necessary to strengthen the control of the interpass temperature. During continuous welding, the temperature of the base metal being welded should be monitored to ensure that the interpass temperature remains as close as possible to the preheating temperature. The maximum interpass temperature must 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 When multi-layer welding is performed on thick plates, if the slag is not removed and defects exist on the weld surface before starting the next layer of welding, it is easy for defects such as slag inclusions, pores, and cracks to occur in the weld, which reduces the strength of the joint. Additionally, this can cause spatter during the welding of the next layer. [Measures] When welding multiple layers on thick plates, each layer should be welded continuously. 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 welding quality must be completely eliminated before continuing with welding. 8 Insufficient weld leg dimensions in butt or fillet combined welds requiring full penetration 【Phenomenon】In butt or fillet combined welds such as T-joints, cross joints, and fillet joints that require full penetration, if the weld leg dimensions are insufficient, or if the weld leg dimensions of the welds joining 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 welds that require full penetration, such as T-joints, cross joints, and corner joints, 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 verification requirements, 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 Welding: Inserting electrode tips or iron pieces into the joint gap. [Phenomenon] Since it is difficult to fuse the electrode tips or iron pieces with the materials being welded during 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 ； Filling with electrode stubs or iron blocks that are oily, contaminated, etc., can cause defects in the weld such as porosity, slag inclusions, and cracks. All these conditions can **degrade** the weld quality at the joint, failing to meet the quality requirements for welds as specified in the design and specifications. 【Measures】 (1) When the assembly gap of the workpiece is large but 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 welding rod ends or iron pieces 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 Failure 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 vertical and horizontal directions. As a result, the vertical and horizontal welds restrict each other, generating significant thermal contraction stresses that cause the plate to deform and become uneven, and it is also possible for cracks to appear in the welds. 【Measures】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, the welding of the transverse welds is not constrained by the longitudinal welds, allowing the contraction stresses in those transverse welds to be released without restriction, which helps reduce welding deformation and ensure weld quality. Alternatively, the butt welds can be welded first, with the fillet welds done afterward.