DEFECTS IN WELD
The quality of weld depends on many factors:A. undercutting is caused by high amperage
B. porosity is caused by fast travel or dirty material surfaces
C. slag included in bead is caused by low amperage and short arc
D. lack of fusion is caused by low amperage and improper edge preparation
E. overlap is caused by electrode shaking
Surface defects perpendicular to tensile force are usually more dangerous than an inner defect of the same size. Lack of fusion, D is the sharpest and the most dangerous defect.
The quality of manual welding is usually less than that for other methods. Some imperfections that are not dangerous:
A. Electroslag welding: 0.56 defects / 10 meters.
B. Automated welding under flux: 2.5 defects / 10 meters.
C. Electric arc manual welding: 35 defects / 10 meters.
A. Incomplete penetrationB. Excess metal handing
C. Curved weld
D. Narrow weld at underside
Incomplete penetration means that tensile force lines meet obstacles on their path, causing high stress concentration. Other defects from the list do not cause high stress concentration.
Better melting takes place if there is a gap between the parts of Tee-weld. Residual stresses and cracking are smaller in this situation.
A. Cracking: toe, longitudinal, transverse, and underbead cracksB. Incomplete fusion
C. Undercutting and underfilling
D. Surface damage: small droplets and arc strike (electrode touch)
Cleaning the weld area prior ro welding improves the fusion of weld and base parts. The operation can guard against incomplete fusion, B.
A surface defect E in the heat-affected zone can be considered the most dangerous defect in the Tee-joint.
Residual tensile stresses in the vertical plate is less than in the first instance. The second instance is poor for heavy welded construction, showing lack of ductility through the thickness of the material.
Friction welding of steel bars. The bars are rotated relative to each other and squeezed together. A. Uniform weld is preferential
B. High pressure or low speed
C. Low pressure or high speed
Two defects can be considered as one if the distance between them is on the order of it's own size. The depth of the defect is more important than the length.
