Chapter 9 - Welding Defects - 9 Welding Defects 9 Welding...

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9. Welding Defects
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9. Welding Defects 108 Figures 9.1 to 9.4 give a rough survey about the classification of welding defects to DIN 8524. This standard does not classify existing welding defects according to their origin but only to their appearance. Defect Class: Shape Defects undercut open end crater weld reinforcement too small throat thickness start defects excessive seam width burn through undercut, continuous unfused longitudinal seam edge end crater with reduction of weld cross section nominal nominal surface defects at a start point weld is too wide through-going hole in or at the edge of the seam © ISF 2002 br-er09-01.cdr Figure 9.1 Defect Class: Cracks and Cavities longitudinal crack transverse crack star shaped crack porosity pore nest of pores line of pores worm hole in the unaffected base metal in the HAZ in fusion zone in weld metal in the unaffected base metal in the HAZ in weld metal in the unaffected base metal in the HAZ in weld metal globular gas inclusion many, mainly evenly distributed pores locally repeated pores pores arranged in a line elongated gas inclusion in weld direction © ISF 2002 br-er09-02.cdr Figure 9.2 Defect Class: Lack of Fusion, Insufficient Through-Weld insufficiently welded root one or two longitudinal edges of the groove are unfused insufficient through weld insufficiently welded cross section lack of fusion between passes root lack of fusion flank lack of fusion lack of fusion between weld passes or weld beads lack of fusion in the area of weld root lack of fusion between weld and base metal © ISF 2002 br-er-09-03.cdr Figure 9.3
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9. Welding Defects 109 A distinction of arising defects by their origin is shown in Figure 9.5. The development of the most important welding defects is explained in the following paragraphs. Lack of fusion is defined as unfused area between weld metal and base mate- rial or previously welded layer. This happens when the base metal or the pre- vious layer are not com- pletely or insufficiently molten. Figure 9.6 explains the influence of welding parameters on the devel- opment of lack of fusion. In the upper part, arc charac- teristic lines of MAG weld- ing are shown using CO 2 and mixed gas. The weld- ing voltage depends on welding current and is se- lected according to the joint type. With present tension, the welding cur- rent is fixed by the wire feed speed (thus also melting rate) as shown in the middle part of the fig- ure. Melting rate (resulting from selected welding parameters) and welding speed define the heat input. As it can be changed within certain limits, melting rate and welding speed do not limit each other, but a working range is created (lower part of the figure). If the heat input is too low, i.e. too high welding speed, a definite melting of flanks cannot be ensured. Due to the Defect Class: Solid Inclusions slag line single slag inclusions pore nest stringer type inclusions different shapes and directions irregular slag inclusions locally enriched © ISF 2002 br-er-09-04.cdr Figure 9.4 Welding Defects © ISF 2002 br-er-09-05.cdr spatters and
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