Welding defects

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I. Porosity: Cause analysis: 1. The welding electrode or wire is damp; in particular, low-hydrogen electrodes are prone to developing porosity when damp. Additionally, the arc-starting agent at the tip of low-hydrogen electrodes may come off； 2. During arc interruption, the welding wire moves away from the molten pool too quickly, resulting in a lack of gas protection for the molten pool and the formation of crater pores ； 3. When re-igniting the arc, no effective grinding was performed, and welding was initiated at the weld bead formed prior to arc extinction ； 4. There is strong wind on site, and wind protection measures are inadequate ； 5. The weld area is contaminated with dirt, dew, or moisture ； 6. Welding rod offset or arc too long ； 7. The welding technique is not proficient enough. Prevention and control measures: 1. Welding electrodes or wires should be kept dry; low-hydrogen electrodes must be dried as required, retrieved in limited quantities, and stored in insulated containers. Any electrodes that are not used on the same day need to be dried again. For low-hydrogen electrodes, it is essential to ensure that the arc-starting agent is in good condition, and they should be handled carefully during loading and unloading to prevent the arc-starting agent from falling off or the coating from being damaged ； 2. When interrupting the arc, the welding rod should pause briefly at the interruption point or perform a back-welding motion to prevent the entry of harmful gases.
3. Upon re-igniting the arc, grind the defective areas of the crater using a grinding wheel until reaching the original interruption point; then start welding at the weld bead prior to the interruption, ensuring that it completely covers the area where the arc was interrupted ； 4. Appropriate wind protection measures must be in place; low-hydrogen welding electrodes are extremely sensitive to wind, so strict wind protection is necessary. Ultra-short arc welding should be used, and welding operations cannot proceed without such protection measures. Experience has shown that porosity can still occur even at wind speeds below level 2 ； 5. The pipe outlet must be kept clean and dry, free from rust, oil stains, impurities, etc ； 6. When the welding electrode is offset, the arc should be interrupted to replace the electrode and perform grinding ； 7. If the welder’s welding skills are not proficient, targeted training should be intensified to enable them to master the ability to control defects as soon as possible. II. Slag inclusions: Cause analysis: 1. A small groove angle, low welding current, high slag accumulation, or a fast welding speed result in rapid cooling of the weld pool, preventing the slag from rising to the surface of the pool and thus causing slag inclusions ； 2. If the root weld is too thin or has been over-ground, hot welding is prone to causing burn-through, so higher currents cannot be used. The root cleaning method was improper, resulting in angles on either side of the weld bead or excessively deep grooves. During rapid thermal welding, the slag that flows into the corners and deep grooves does not have enough time to rise to the surface, resulting in slag inclusions ； 3. The welder’s technique is improper: the welding rod is moved too quickly at the center and at the corners of the weld bead, resulting in insufficient depth of penetration in the molten pool; this leads to residual slag remaining or getting mixed together ； 4. The welding electrode is offset, resulting in poor fusion on the other side and the formation of slag inclusions ； 5. Contaminants on the electrodes and weld beads, if not removed properly, cause slag inclusions during welding ； 6. When welding in a downhill direction for vertical welds, the welding speed is high, and the electrode angle and welding technique are improper. Especially with low-hydrogen electrodes, during welding, \"rail-like slag inclusions\" tend to appear above and below the 3 o’clock position, that is, parallel strip-shaped slag inclusions appear on both sides of the weld bead. Prevention and control measures: 1. The alignment gap should not be too small; a higher current should be selected within the range of acceptable process parameters to ensure an adequate welding depth. Meanwhile, the welding speed should not be too fast ； 2. The root pass must not be too thin or over-ground; remove surface slag (or black spots) and level the joint. When cleaning the root pass, it is necessary to shape the weld bead into a \"U\"-shaped groove to avoid the formation of angles; this prevents slag from easily floating to the surface during welding. Grinding the root pass helps to ensure better control over heat input, thereby avoiding burn-through and slag inclusion ； 3. Welders should correct improper welding techniques, control the angle and amplitude of the welding rod movement, to ensure proper welding penetration ； 4. When the welding electrode is offset, the arc should be interrupted to replace the electrode and carry out grinding ； 5. Thoroughly clean the pipes and electrodes of any impurities or slag from previous weld passes. Before welding, remove any rough edges on the welds, any fallen slag, and dirt on the alignment tools, to prevent impurities from entering the welds. Throughout the welding process, a clear molten pool is maintained, ensuring good separation between the slag surface and the molten metal ； 6. When performing downhill welding for vertical welds, the welding speed should not be too fast to ensure proper penetration. Use the correct electrode angle and welding technique. Especially with low-hydrogen electrodes, more attention must be paid to the area around the 3 o’clock position during welding; the technique must be steady, and the welding angle should be controlled (it is recommended that the parallel angle at the 3 o’clock position be 10–15 degrees). The welding speed should not be too fast, in order to prevent the formation of parallel strip-shaped slag inclusions on both sides of the weld bead. III. Incomplete penetration: Cause analysis: 1. The welding current is too low, resulting in a shallow penetration depth; the welding speed is too fast, the pause time when moving the welding rod on either side of the weld is too short, or the angle of the welding rod is skewed to one side. As a result, the base material (root metal) or the interlayer metal does not melt sufficiently and remains uncovered by the filler metal ； 2. During root welding, an excessively small groove angle, narrow gap between joints, thick root face, significant misalignment, uneven pipe thickness, insufficient penetration depth, or improper welding technique can easily result in incomplete fusion of the root weld ； 3. During welding, an improper electrode angle causes the arc heat source to dissipate or deviate, resulting in lack of penetration on one side. Preventive measures: 1. In accordance with welding procedure requirements, control the groove dimensions and root face thickness; adjust the gap during alignment. The misalignment between pipes during butt jointing must be strictly controlled. Pipes with different wall thicknesses should be processed into a gradual slope as required ； 2. Select a higher current within the allowable process parameters to ensure adequate penetration depth. Adjust and properly control the welding torch angle and welding speed to keep the arc in the correct direction ； 3. Move the welding rod slightly more slowly along the edge of the groove, stay there for a slightly longer time, and ensure that the rod is in the correct position so that there is enough heat to melt the root edge of the base material as well as the metal from the previous layer of weld. When welding the root, pay attention to the shape of the weld pool; a full penetration is achieved when small circles appear at the front of the weld pool as welding progresses, which helps to ensure proper root penetration. IV. Lack of fusion (incomplete welding): Cause analysis: 1. The welding current is too low, the welding speed is too high, the pause time for moving the electrode on both sides of the weld bead is too short, or the electrode angle is skewed to one side; as a result, the base metal or interlayer metal fails to be adequately melted and is instead covered by the filler metal ； 2. When the gap between the joint surfaces is small, the thickness of the blunt edges is large or there is significant misalignment, together with an improper angle of the welding rod and incorrect welding technique, the penetration depth is insufficient and the welding speed is too fast; these factors can easily result in incomplete fusion of the root weld ； 3. Incomplete welding is mainly caused by improper oscillation of the electrode or wire; secondly, it is due to arc deviation. Prevention and control measures: 1. Use a higher current within the allowable parameters, adjust the welding torch angle and welding speed appropriately; move the torch more slowly along the edge of the groove and stay there for a longer time, so that sufficient heat is available to melt the base material and the metal from the previous weld layer ； 2. Adjust the alignment gap, reduce the thickness of the root edge and the amount of misalignment, so that the weld groove is smooth and the slag is completely removed ； 3. Adjust the electrode angle and ensure proper rod movement so that the arc is in the correct direction ； 4. To prevent incomplete welding, the electrode or wire must be moved properly; in case of arc deviation, replace the electrode first, grind out the defective area, and then proceed with welding. V. Weld penetration: Cause analysis: 1. Insufficient root weld thickness or excessive grinding, along with too high a current level ； 2. The molten pool temperature is too high; a slightly slow welding speed leads to burn-through ； 3. Improper angle of the welding rod (wire) ； 4. The wire feeding speed is not properly controlled, or wire skipping occurs, causing the welding wire to penetrate the molten pool and resulting in burn-through weld beads at the root. Prevention and control measures: 1. Ensure an appropriate root weld thickness; avoid excessive grinding, and adjust the current reasonably ； 2. When hot welding, if the temperature of the weld pool is too high, the welding speed should be increased appropriately to lower the temperature of the weld pool ； 3. Adjust the wire feeder properly to control the wire feeding speed and prevent wire skipping ； 4. During flat welding and overhead welding, the temperature of the molten pool must be strictly controlled; it should not be too high. Short arc welding is preferred, and the correct electrode angle should be used. It is recommended to change the angle at the 5 o’clock position in a timely manner ； 5. The alignment gap between the grooves should not be too large; the welding current should be set at a lower level. For semi-automatic welding, the two settings of the welding torch can be adjusted to the lower level. VI. Edge biting: Cause analysis: 1. Excessive welding current, overly long arc, and improper wire movement angle ； 2. When moving the welding torch, spend slightly more time on each side of the groove edge ； 3. During filling, the weld filler metal is too low, the overlay weld metal is too thick, the arc stays on the area for too long, and the high temperature in the weld zone causes undercutting. Preventive measures: 1. Select a current value slightly lower than the recommended range for the welding process parameters; control the arc length or perform short-arc welding. Maintain a uniform welding speed, keep the dwell time at the edges of the groove somewhat shorter, and pay attention to the welding angle ； 2. The final pass of filler metal should be slightly below the surface of the base material (0.5 mm–1 mm), so that the width profile of the cap bead is well-defined; this helps to control undercutting and ensures good overall appearance ； 3. For areas where the depth and length of weld undercut exceed the specified limits, it is advisable to grind them with a grinding wheel and then perform supplementary welding. VII. Arc crater in the weld bead: Cause analysis: 1. Improper arc interruption and termination, resulting in a depression at the end of the weld bead; the depth of this depression exceeds the specified limits, that is, it is lower than that of the base material ； 2. The weld pool metal is not fully filled, caused by ending the welding too quickly or using too high a current ； 3. When ending the arc at 6 o’clock, the weld bead temperature is too high, resulting in a short pause time. Prevention and control measures: 1. During arc termination, the welding electrode should pause briefly at the arc end or make a back-welding movement so that the deposited metal fills the weld pool ； 2. Use a grinding wheel for repair welding; the length of the repair weld should be no less than 50 mm. It is advisable to use low-hydrogen electrodes and move the electrode in a circular motion to fill the molten pool ； 3. When ending the arc at the 6 o’clock position, two people should not do it simultaneously; wait until the temperature drops a bit before welding to the joint to end the arc. Conversely, cratering or poor weld bead formation is likely to occur.   VIII. Analysis of crack causes: 1. Improper construction methods; when pipes are under stress or suspended over long distances, stress cracks are likely to occur at the weld start/end points (or areas of stress concentration) ； 2. Improper welding methods, along with repeated welding and grinding in certain areas, cause changes in the crystal structure of the base material, leading to an increase in hardness (brittleness) and a decrease in ductility ； 3. During root welding, if the aligner is removed too early, the molten metal in the weld pool does not have enough time to solidify completely, making cracks likely to occur at the end point of the weld ； 4. A large amount of misalignment causes the weld center line to shift, resulting in central cracks ； 5. The weld bead contains impurities; the vibration of the internal alignment device causes slag to fall on the weld bead, and this slag enters the molten pool during welding. The presence of such slag reduces the strength of the weld, increasing the likelihood of cracks at the root area ； 6. Dew formation on the pipe materials or moisture remaining in the welding materials that has not been dried out, resulting in a high level of diffused hydrogen in the welds ； 7. Regularly clean the expansion blocks at the ends of internal alignment tools to remove weld slag and dirt. This prevents them from falling into the weld pool and causing defects (such as porosity or poor fusion of molten metal), which would otherwise reduce the strength of the weld bead. The end of a welding electrode (where there is no coating) can be flattened and bent, then inserted into the interior of the overhead weld joint to scrape off any slag and impurities. This helps to prevent and minimize defects in the root pass of overhead welds. IX. Analysis of the causes of cracks during rework: 1. Cracks that occur after rework in winter are caused by improper preheating methods – either too low a temperature for local preheating or uneven heating throughout the area; furthermore, no insulation is provided after welding, resulting in a rapid drop in temperature ； 2. When reworking root welding, the current is high; improper operation leads to repeated welding and grinding ； 3. The pipeline may be under stress (internal or external stress) ； 4. Dew formation on the pipe materials and moisture absorption in the welding materials (the E8018-G welding rods used for filling and surfacing were not dried or kept warm); the high content of diffused hydrogen in the weld pool can lead to defects and a reduction in strength. Recommended measures for repairing cracks: 1. Apply proper heating, either by heating the entire area; after grinding the repair site, measure the temperature and apply additional heat to prevent the temperature of the weld seam from dropping too rapidly ；  2. Use a low current within the process parameters; dry and maintain the temperature of the filler rod E8018-G. 3. Remove impurities from within the pipe opening as much as possible, especially the roughness on the inner surface at the upward-facing part, welding slag, and dust ； 4. Try to relieve stress at the weld area; if necessary, use a pipe lifting machine to keep the pipe in a horizontal position ； 5. When root repair takes a long time, it is recommended to weld in segments by penetrating through the area completely, welding the ends first and then the middle, in order to eliminate and distribute weld stresses.   X. Analysis of the reasons for excessive weld bead height: 1. The welding speed was slightly too slow, and proper control over grinding after the final pass of filling was not achieved, resulting in excessive height of the top layer of weld beads ； 2. Improper wire feeding during flat welding and overhead welding, slow welding speed, inadequate control of the filler metal, as well as lack of experience or insufficient sense of responsibility.  Prevention and control measures: 1. Increase the welding speed in areas where excess height is likely to occur; weld and grind each layer to achieve the standard thickness, in order to prevent neglect of process control and post-weld quality inspection due to an attempt to speed up the work ； 2. For the final filling pass, maintain a thickness of 0.5 mm to 1 mm below that of the base material, thereby creating favorable conditions to prevent the excess height in the overlay weld from exceeding the specified limits ； 3. Grind the welds with excessive remaining height to achieve a smooth transition. XI. Analysis of reasons for excessive numbers of repairs and excessive grinding depth: 1. The welder repeatedly grinds and repairs the welds to address obvious quality defects that occur during the welding process, as well as local defects in the interlayer or surface areas ； 2. The welder carried out repairs on his own without notifying the quality inspector; the frequent repairs caused the weld material to become more brittle, its plasticity to decrease, and the structural strength to decline. 3. When using low-hydrogen electrodes to repair and fill surface defects, overheating of the weld bead can easily lead to porosity.  Prevention and control measures: 1. When dedicated quality inspectors or inspection supervisors discover such issues on site (that is, the welder repeatedly grinding and welding at one spot), they should stop this practice immediately and assign a welder with higher skill levels to address the defect ； 2. When using low-hydrogen electrodes for repair work, the temperature of the weld seam should not be too high; experience has shown that overheating the weld seam easily leads to the formation of pores. It is not advisable to start grinding and repairing the weld immediately – one should wait a while until the temperature of the weld seam drops to around 150 degrees Celsius before proceeding with grinding and repair. Weld seam details determine success or failure, especially in the welding process. Strengthening process control and reducing the formation of defects can effectively improve the first-pass welding success rate, as well as facilitate successful repairs. To control welding quality, it is first necessary to fully understand and analyze the causes of welding defects on site. Then, targeted preventive measures and control strategies should be implemented based on the actual conditions there, in order to avoid the occurrence of serious defects, reduce and eliminate welding imperfections, and effectively address quality issues such as pores, slag inclusions, lack of fusion, under-welding, over-welding, undercutting, cratering, cracks, and excessive weld height. Here, an analysis of the causes and reference control measures are provided for common defects and deficiencies, as well as quality issues that often arise during winter construction.