A: For a general overview of this process see our website page on Flux Cored Arc Welding Tips and other pages referenced thereby.
FCAW is often perceived as a low cost process, even for Hobby and Home work, in that shielding gas is not required (flux cored wire is self shielded), thus reducing equipment cost and simplifying procurement of consumables.
For industrial applications shielding gas (for steel mostly Argon with 8-25 %CO2) is almost always employed, with remarkable influence of the gas mix on the arc and on the resulting welds.
It is also claimed to be easier to master than Gas Metal Arc Welding (GMAW), in that only basic skills are required to obtain acceptable welds in all positions. Penetration and deposition rate are higher than for Shielded Metal Arc Welding.
The often cited additional advantage is that flux cored filler material, by virtue of special ingredients in the flux can be more tolerant to the presence of rust or mill scale on the steel.
The production of thicker smoke and fumes is considered an advantage when welding outdoors because an occasional light breeze would not remove the shielding effect around the weld. It can be a nuisance and a health risk if welding indoors, unless fume extraction is in place to protect the welder.
Slag has to be removed in any case after welding and before any additional weld is done on top of the deposited weld beads.
When using traditional constant voltage power supplies the polarity selected is mostly DCEP (Direct Current Electrode Positive) that gives a stable arc, low spatter (at the correct voltage), a good weld bead profile and optimum penetration
It is important to know which metal transfer mode is used. At lower currents the short circuit transfer mode is operating, usually when welding steel less than 3 mm (1/8") thick.
Spatter is best controlled by using voltage adjustment to obtain a crisp, consistent crackle sound. One should learn from practice to recognize the correct sound associated with short circuit welding.
As an indication, the starting voltage for short circuit applications with flux cored wire of size 0.8 - 1.0 - 1.2 mm(0.030 - 0.035 - 0.045") is 16 to 18 V.
The corresponding wire feed speed could be 1.8 to 10.7 m/min (70 to 420 inch per minute), that would provide 50 to 170 Amps, 65 to 200 Amps, and 130 to 220 Amps for the three wire sizes.
If the crackle of the weld consists in a soft plop sound with some spatter, reduce voltage one volt at a time until the correct sound is generated and spatter is eliminated.
If on the contrary the sound is harsh and explosive with no soft sounds, then increase one volt at a time until spatter is substantially reduced.
With higher current levels the metal transfer becomes the spray mode. Here the arc length should be kept minimal and again one should strive to obtain the consistent crackling sound already described.
Voltage for spray mode would preferably be between 24 and 34 V, a good starting point would be 30V.
For 1.0 mm (0.035") wire size the wire feed speed could be between 10.7 and 14.2 m/min (420 and 560 ipm) that would provide 215 to 300 Amps for a normal stickout (electrode extension) between 13 to 16 mm (1/2 to 3/4").
For 1.2 mm (0.045") wire size, the wire feed speed could be between 8.9 and 16 m/min (350 and 630 ipm) that would provide between 250 to 360 Amps. Voltage adjustment in spray mode goes in opposite direction relative to short circuit mode.
Decreasing voltage (one volt at a time) shortens the arc, but too low a value will bring the electrode to plunge in the weld pool with consequent spatter. Then the voltage should be increased again until the optimum is reached and spatter is substantially reduced.
A: Yes, definitely. As the pipe is thick, the process used will most probably beeither Gas Metal Arc Welding or Submerged Arc Welding which are both providinghigh weld deposition rate.
In order to guarantee the highest quality the rootpass, however being done, has to be back gouged, that is ground for all itslength until sound metal is found. This grinding operation with a portablegrinder can best be performed unhindered from the outside. Therefore the rootpass has to be laid down first from the inside of the pipe.
Additional tips:please note that, for longitudinal welds, run out tabs have to be provided at both ends. Furthermore thefirst weld (from the inside as explained) will start at one end for a length ofabout 150 mm (6 inches) only. This short weld will prevent distortion andoverlapping of the edges under the shrinkage strains caused by the long weld.
Then its inner end has to be ground clean to permit perfect blending with theupcoming weld that will start at the other end of the pipe and proceed towardsthe already welded short stretch. Once the root weld is completed and backgougedthe filler passes will be performed as convenient.
