By -
Date 07-17-2000 22:35
I agree inpart that "worm-hole" porosity is used as a definition for "piping porosity" but usually the initial start of worm-hole porosity, as is being discussed preceedingly, begins as an elongated discontiuity from the root or depth of a weld. This will be eviedent while excavating the surface indication at the point where the worm-hole began.
From my experiences and as described by AWS B1.10-86R it resembles an elongated gas pocket extending from the root of fillet welds and groove welds (my observations) from the root upward toward the weld's surface.
I've encountered this type of porosity with SMAW while examining structural fillet welds and GMAW aluminum groove welds and GTAW inconel. When the welds were sectioned transverse through the weld, the elongated were very visable with the discontinuies resembling cone shaped cavities frozen in weld metal. That is, the very bottom of the discontinuity is much smaller in diameter the the top and is coned shaped. In structural fillet welds the discontinuity usually extends completey, or near completely throught the weld pass. In the aluminum plate groove welds the discontinuitities would never break the surface of the weld and when radiographed, the indications were veiwed as just being rounded indications in the image but upon sectioning the welds, the cone configurations were very evident.
Also I've encountered "worm-hole" porosity that was completely linear while GTAW welding sch 160 Inconel 690. It was a gas bubble trapped subsurface in a pass. Excavation proved that the indication was completely horizonal with no tail going verticle.