Weld bead, large

Resinoid-bonded wheels find wide use in heavy-duty snagging operations where large amounts of metal must be removed quickly, in cutting-off operations, portable disk grinding (as for weld-beads), roU grinding, and vertical spindle disk grinding. 

Jagged, spongelike metal loss was present downstream of a weld bead (Fig. 12.16), and again in the region of diameter increase (Fig. 12.17). Metal loss was most severe near the weld bead, where weld repairs from the external surface had closed a large perforation. 

Figure 15.6 Weld bead site at which radiography indicated a large pit. (Magnification 7.5x.)...

Stresses from welding result principally from the effects of differential thermal expansion and contraction arising from the large temperature difference between the weld bead and the relatively cold adjacent base metal. Shrinkage of the weld metal during solidification can also induce high residual stresses. Unless these residual stresses are removed, they remain an intrinsic condition of the weldment apart from any applied stresses imposed as a result of equipment operation. 

Welding is a primary source of residual stresses principally because of large temperature differences between the weld bead and the rela-... 

Residual stresses caused by large temperature differences between the weld bead and adjacent metal can be reduced by preheating the metals to be welded, especially if the sections are thick, or by stress-relief-annealing following the welding procedure. Proper welding techniques, especially the use of appropriate weld filler metals to minimize weld-metal shrinkage, can minimize residual stresses. 

Large differences in microstructure between parent metal, heat-affected zone and weld bead. Sharp changes in mechanical properties give local stress concentrations. 

Weld corrosion (Section 9.5) Crevice corrosion at butt welds due to poor penetration has already been discussed and was shown in Fig. 9.1(a). Conversely, if there is a large weld bead protruding in the pipe bore, erosion/cor-rosion can occur downstream due to the turbulence produced over the weld bead (Fig. 9.8). In either case, the fault probably lies in the incorrect spacing of the butts at welding. 

Cyclone Roughness Large weld beads, etc., can also reduce cyclone efficiency. If the solids flow along the wall of a cyclone encounters a large protuberance such as a weld bead, the weld bead acts as a type of ski jump and causes the solids to be deflected farther into the center of the cyclone, where they can be thrown into the vortex and carried out of the cyclone. In small pilot or research cyclones, this is especially common, because the distance between the wall of the cyclone and the vortex tube is very small. Because of their... 

Soft microstructures can be obtained by using steel with low contents of carbon and alloying elements (including manganese) to reduce the hardenability of the HAZ. Additionally, the use of a large weld bead, thin plate, and preheat will reduce the quenching rate in the HAZ. After a bead has been deposited the HAZ can be softened by tempering either as a result of subsequent weld runs or by a postweld heat treatment (PWHT or stress relief). 

In thin section, medium carbon and C-Mn steels can be welded using the procedures recommended for mild and C-Mn steels given already in this chapter. Such procedures ensure that sufficiently large weld beads are made so that the cooling rate is slow enough to avoid certain HAZ hardness levels. 

Drains should always be located at the lowest point in a tank and the joint between the tank and the drain pipe should be designed to permit free drainage (Fig. 11.14). Such design avoids the presence of protruding weld beads that could trap residues or moisture inside the tank. The use of sumps in large tanks is a useful way to mitigate... 

Observations Metallographic examination showed a large number of pits, most of the pits were about 6-13 mm (1/4-1/2 in) from the weld bead at the outlet. 

As to point 1, the toe of the weld bead is the most critical point as crack starter because of its concentration factor that can be quite high in case of bad welds with large reinforcement or sharp corners. 

Large weld beads can cause cracking. Weld penetration can be controlled by using a backing strip when using high currents. 

Molten-bead sealing is suitable particularly for making large areas of polyethylene sheeting by welding several widths. 

The important process parameters include gas temperature and flow rate, extrudate temperature and flow rate, and pressure. While the applications for extrusion and hot gas welding are similar, extrusion welding can improve productivity when welding thick members because it can fill the even large V-grooves with one or two passes instead of applying multiple beads. 

This presents itself as an interruption, perhaps of considerable length or with sections of the insideweld seam, which should instead be uniform after the first bead. In pipes with a sufficiently large diameter to permit internal accessibility it is visible to the naked eye and, in some cases, the intact bevel is visible (a welding process for instantaneous repair of the fault from the inside) is recommended. It may be caused by incorrect geometrical dimensions of the bevel, incorrect welding parameters, bad fit up (excessive misalignments) or poor operator skill. 

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