Causes and Preventive Measures of Stainless Steel Welded Pipe Defects (1)
- By:Iris Liang
There will be some defects in the welding process of stainless steel welded pipes. The defects of stainless steel welded pipes will lead to stress concentration, reduce bearing capacity, shorten service life, and even cause brittle fracture. The general technical regulations stipulate that cracks, incomplete penetration, incomplete fusion, and surface slag inclusions are not allowed; defects such as undercuts, internal slag inclusions, and pores cannot exceed a certain allowable value, and defects that exceed the standard must be thoroughly removed and welded. repair. The causes, hazards and preventive measures of welding defects of common stainless steel welded pipes are briefly described as follows.
1. The weld size does not meet the requirements
Weld size does not meet the requirements mainly refers to weld reinforcement and reinforcement difference, weld width and width difference, misalignment, post-weld deformation and other dimensions that do not meet the standards, uneven weld height, uneven width, and large deformation Big wait. The inconsistency of the weld width will not only cause the appearance of the weld to be unattractive, but also affect the bonding strength between the weld and the base metal; if the weld reinforcement is too large, it will cause stress concentration, and if the weld is lower than the base metal, it will not get enough reinforcement. Joint strength; wrong side and excessive deformation will distort the force transmission and cause stress concentration, resulting in a decrease in strength.
Causes: improper bevel angle or blunt edge and uneven assembly gap of stainless steel welded pipe; unreasonable selection of welding process parameters; low level of welder's operating skills, etc.
Preventive measures: choose the appropriate groove angle and assembly clearance; improve the assembly quality; select the appropriate welding process parameters; improve the welder's operating technology level, etc.
Due to incorrect selection of welding process parameters or incorrect operation process, the groove or depression formed by the melting of the base metal along the weld toe is called undercut. The undercut not only weakens the strength of the welded joint of the welded pipe, but also easily causes cracks due to stress concentration.
Causes: Mainly because the current is too large, the arc is too long, the angle of the electrode is incorrect, and the method of transporting the electrode is improper.
Preventive measures: choose the appropriate welding current and welding speed when welding with electrode arc welding.
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3. Not penetrated
Incomplete penetration refers to the phenomenon that the root of the welded joint is not completely penetrated when the stainless steel welded pipe is welded. Incomplete penetration will cause stress concentration and easily cause cracks. Important welded joints are not allowed to have incomplete penetration.
Causes: The groove angle or gap is too small, the blunt edge is too large, and the assembly is poor; the welding process parameters are improperly selected, the welding current is too small, the welding speed is too fast; the welder's operation technique is poor, etc.
Precautionary measures: correct selection and processing of groove size, reasonable assembly, ensuring clearance, selecting appropriate welding current and welding speed, improving welder's operating technical level, etc.
4. Not fused totally
Incomplete fusion refers to the incomplete melting and bonding between the weld bead and the base metal or between the weld bead and the weld bead during fusion welding. The lack of fusion directly reduces the mechanical properties of the joint, and severe lack of fusion will make the welded structure unable to bear at all.
Causes: Mainly due to the high speed and low welding current when welding stainless steel welded pipes, the welding heat input is too low; the welding rod is eccentric, the angle between the welding rod and the weldment is improper, and the arc pointing is deflected; there is rust and dirt on the side wall of the groove, Incomplete slag cleaning between layers.
Preventive measures: Correctly select welding process parameters, operate carefully, strengthen interlayer cleaning, and improve the level of welder operation skills, etc.
5. Welding tumor
Weld lump refers to the metal lump formed by the molten metal flowing to the unmelted base metal outside the weld during the welding process. The weld bead not only affects the shape of the weld seam of the stainless steel welded pipe, but also often has slag inclusions and incomplete penetration at the site of the weld bead.
Causes: The blunt edge is too small and the root gap is too large; the welding current is large and the welding speed is fast; the welder's operating skill level is low, etc.
Preventive measures: choose appropriate welding process parameters according to different welding positions, strictly control the size of the fusion hole, and improve the welder's operating technology level, etc.
Based on our experience, there are at least 10 reasons. Today we have a look the first 5 ones. Please follow our website for update.
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