Welded Threaded Pipe Fittings

During the welding process of threaded pipe fittings,the following problems often occur due to various factors such as materials,processes,and operations:

Appearance defects

Bite the edge

Phenomenon:Groove or groove marks formed at the boundary between the weld edge and the base metal.

Reason:Excessive welding current,long arc,fast welding speed,improper welding rod angle,etc.Excessive current can cause excessive melting of the base material at the edge of the weld seam,while an excessively long arc can lead to dispersed arc force,resulting in uneven melting of the weld seam edge.

Harm:Weakens the strength of welded joints,easily leads to stress concentration at the biting edge,reduces the fatigue life of pipe fittings,and may cause crack propagation when subjected to load,resulting in pipe failure.

Weld bead

Phenomenon:Metal nodules formed during the welding process when molten metal flows onto the unmelted base metal outside the weld seam.

Reason:Excessive welding current,slow welding speed,improper swinging of welding rod,etc.When the current is too high,the amount of molten metal is too much and it is easy to flow outside the weld seam;Slow welding speed can cause the molten pool to stay for too long,increasing the possibility of metal flow.

Harm:Affects the appearance quality of the weld seam,making the surface of the weld uneven,and the organization of the weld bead uneven,which may have defects such as slag inclusion,reducing the performance of the welded joint.

stoma

Phenomenon:Holes present in the weld metal,usually circular or elliptical in shape.

Reason:There are impurities such as oil stains,rust,and moisture on the surface of the welded parts,the welding material is damp,the protective gas is impure or the flow rate is insufficient,and the welding speed is too fast.These factors can lead to the generation of gas during the welding process,and if the gas fails to escape from the molten pool in a timely manner,it will form pores.

Harm:It reduces the effective bearing area of the weld,lowers the strength and toughness of the weld,and may also become the origin point of cracks,affecting the sealing and service life of the pipe fittings.

Slag inclusion

Phenomenon:The slag present in the weld seam is a non-metallic inclusion.

Reason:During the welding process,the slag did not completely float out of the molten pool,such as incomplete interlayer cleaning during multi-layer welding,low welding current,and too fast welding speed.Too low welding current will lower the temperature of the molten pool,reduce the fluidity of the slag,and make it difficult to float out;If the welding speed is too fast,the slag will be covered by the solidified weld metal before it can float out.

Harm:Slag inclusion can reduce the strength and toughness of the weld seam,easily cause stress concentration,lead to the generation and propagation of cracks,and affect the performance of the pipe fittings.

Internal defects

Not fully welded

Phenomenon:The phenomenon of incomplete fusion between the base metal and the weld metal during welding.

Reason:welding current is too low,welding speed is too fast,groove angle is too small,blunt edge is too large,gap is too small,etc.These factors can lead to insufficient welding heat,which cannot fully melt the base material,resulting in incomplete penetration.

Harm:It seriously reduces the strength and load-bearing capacity of welded joints,and is prone to cracking in areas where welding is not fully penetrated under stress,causing damage to pipe fittings.It is a very dangerous welding defect.

Not fused

Phenomenon:The phenomenon of incomplete fusion between the weld metal and the base metal or between the layers of the weld metal.

Reason:During welding,the arc is blown off,the welding speed is too fast,the welding current is too low,and there are oxide scales or oil stains on the groove surface.Arc bias can prevent the arc from accurately heating the welding area,resulting in poor fusion;Impurities on the groove surface can hinder the fusion process.

Harm:Similar to incomplete welding,it can significantly reduce the performance of welded joints,affecting the reliability and safety of pipe fittings.

crackle

Phenomenon:Cracks appearing in welds or heat affected zones can be classified into different types such as hot cracks and cold cracks.

Reason:Hot cracking is mainly caused by the limited solidification shrinkage of the metal during the welding process,resulting in significant tensile stress,and the presence of low melting point eutectic materials in the weld metal;Cold cracking is related to factors such as the hardening tendency of the steel,welding stress,and hydrogen content.For example,when welding high-strength alloy steel,if the welding process is improper,it is easy to produce cold cracks.

Harm:Cracks are one of the most serious welding defects,which can rapidly reduce the strength and toughness of welded joints,making pipe fittings prone to fracture during use,leading to serious safety accidents.

welding deformation

Phenomenon:After welding,the shape and size of the pipe fittings change,resulting in bending,twisting,angular deformation,and other phenomena.

Reason:During the welding process,the weld seam and its surrounding area are subjected to uneven thermal effects,resulting in thermal expansion and contraction,which leads to the generation of welding stress.When the welding stress exceeds the yield strength of the pipe material,it will cause deformation of the pipe.Unreasonable welding sequence and insufficient rigid fixation can also exacerbate welding deformation.

Hazard:Welding deformation can affect the installation accuracy and performance of pipe fittings,increase the difficulty of subsequent processing and calibration,and may even cause pipe fittings to be unable to function properly,requiring reprocessing or scrapping.