10 Common Welding Problems and Solutions
1. Welding construction does not pay attention to select the best voltage
Phenomenon:
When welding, regardless of the backing, filling, cover, regardless of the size of groove, all choose the same arc voltage. This may not meet the requirements of the penetration, melting width, the occurrence of undercut, blowhole, spatter and other defects.
Measures:
Generally according to different circumstances should choose the corresponding long arc or short arc can get better welding quality and work efficiency.
2. Welding does not control welding current
Phenomenon:
When welding, in order to speed up the progress, for the thick plate butt weld to take no groove. The strength index drops, even can not reach the standard requirement, the crack appears in the bending test, which will make the performance of the welded joint can not be guaranteed, and pose potential harm to the structure safety.
Measures:
According to welding current control in process evaluation, 10 -15% floating is allowed, the size of groove blunt edge should not exceed 6mm. When the plate thickness is more than 6mm, the groove should be opened for welding.
3. Do not pay attention to welding speed and welding current, electrode diameter coordinated use
Phenomenon:
When welding do not pay attention to control welding speed and welding current, electrode diameter, welding position coordinated use.
Measures:
The welding speed has a great influence on the welding quality and the welding production efficiency, when selecting, match welding current, Weld position (backing welding, filling welding, cover welding) , weld thickness, groove size to select the appropriate welding speed, in order to ensure penetration, gas, slag easy to discharge, not burn through, on the premise of good shape, choose larger welding speed to improve productivity.
4. Do not pay attention to control arc length when welding
Phenomenon:
Arc length should not be adjusted according to groove form, welding layer number, welding form, electrode type, etc. . Due to improper use of arc length, it is difficult to obtain high quality welds.
Measures:
In order to ensure the weld quality, short arc operation is usually used in welding, but suitable arc length can be chosen according to different conditions to obtain the best welding quality, if v-groove butt, corner of the first layer should use shorter arc to ensure penetration, and no undercut phenomenon, the second layer can be slightly longer, to fill the weld. When the gap is small, the short arc should be used. When the gap is large, the arc can be slightly longer and the welding speed can be accelerated. In order to control the temperature of molten pool in vertical and horizontal welding, small current and short arc welding should be used.
5. Welding does not pay attention to control welding deformation
Phenomenon:
When welding, we don’t pay attention to control deformation from welding sequence, personnel arrangement, groove form, welding specification selection and Operation Method, which leads to large deformation after welding, difficult rectification and increased cost, especially for thick plate and large workpieces, it is very difficult to correct them. The high cost and difficult operation of flame rectification can cause the workpiece to overheat.
Measures:
Adopt reasonable welding sequence and choose appropriate welding specifications and operating methods, but also the use of anti-deformation and rigid fixed measures.
6. Multi-layer welding discontinuous welding, do not pay attention to control the temperature between layers
Phenomenon:
Thick plate multi-layer welding, do not pay attention to inter-layer temperature control, such as inter-layer interval time is too long, do not re-preheat welding easy to produce cold cracks in the inter-layer; High interlaminar temperature (over 900 ° C) will affect the properties of weld and heat affected zone (Haz) , which will lead to coarse grain size, decrease toughness and plasticity, and leave potential trouble for joint.
Measures:
The control of interlaminar temperature should be strengthened in thick plate multi-layer welding, and the base metal temperature should be checked during continuous welding so that the interlaminar temperature can be kept consistent with the preheating temperature as far as possible, the highest temperature between the layers should also be controlled.
7. Multi-layer weld does not remove weld slag and weld surface defects on the next layer of welding
Phenomenon:
Thick plate multi-layer welding, each layer after the completion of welding do not remove welding slag and defects directly to the next layer of welding, easy to cause weld slag inclusion, porosity, cracks and other defects, reduce the strength of the connection, at the same time will cause the lower layer of welding spatter.
Measures:
Thick plate multi-layer welding, each layer should be continuous welding. The slag, weld surface defects and spatter should be removed in time after each layer of weld is welded. The slag, gas hole, crack and other defects that affect welding quality should be removed thoroughly before welding.
8. The weld fillet size of butt joint or fillet combination required for penetration is insufficient
Phenomenon:
T-joint, cross-joint, corner joint and other requirements of penetration of the butt joint or corner butt joint combination weld, the size of the welding feet is not enough, the strength and rigidity of the weld can not meet the requirement of the design because of the insufficient size of the weld feet of the web and the upper flange of the crane beam or similar members.
Measures:
T-joint, Cross Joint, corner joint and other requirements of the fusion of the joint combination weld, should be in accordance with the design requirements, must have sufficient welding feet requirements, in general, the size of welding feet should not be less than 0.25 t (t for the connection of thin plate thickness) . For crane girders or similar webs with upper flange joints designed for fatigue verification, the weld pin size shall be 0.5 t and shall not be larger than 10mm. The tolerance of welding dimension is 0 ~ 4mm.
9. Plug the electrode head or iron block into the joint gap
Phenomenon:
Because it is difficult to fuse the electrode head or iron block with the welded parts, it will cause welding defects such as non-fusion, non-penetration, and reduce the joint strength. If it is filled with rusted electrode head and iron block, it is difficult to ensure that the material is the same as the base metal. These conditions will make the joint weld quality greatly reduced, and can not meet the design and specifications of the weld quality requirements.
Measures:
- When the assembly gap of the workpiece is large, but it does not exceed the allowed range, and the assembly gap is more than 2 times of the thickness of the sheet metal or more than 20 mm, surfacing welding method should be used to fill the depression or reduce the assembly gap. It is strictly forbidden to use the method of filling electrode head or iron block to repair welding in the joint gap.
- When drawing lines in machining, we should pay attention to leave enough cutting allowance and welding shrinkage allowance after cutting, control the size of parts, do not increase the gap to ensure the shape of the size.
10. Do not pay attention to the welding sequence of the cross-welded members
Phenomenon:
For the members with cross-welding seam, the welding sequence is arranged reasonably without paying attention to the analysis of the welding stress releasing and the influence of the welding stress on the deformation of the member, but the longitudinal and transverse welding is carried out at will, as a result, the longitudinal and transverse seams will restrict each other, produce large temperature shrinkage stress, deform the plate, make the plate surface uneven, and may cause weld cracks.
Measures:
Reasonable welding sequence should be established for components with cross welds. When there are several kinds of crossovers, the crossovers with large shrinkage deformation should be welded first, and then the longitudinal welds, so that the crossovers are not constrained by the longitudinal welds, the contraction stress of the transverse seam can be released without restriction, which can reduce the welding deformation and guarantee the weld quality, or welding the butt weld first and then the fillet weld.
Learn more our project quality managemet, QAQC and third party inspection (TPI), NDT practices thru below link.-