Firstly, XRD residual stress measurements were performed on the weld metal cap pass after electrochemical polishing of the distorted superficial layer and on the face of the root pass
weld metal in the as-welded condition, as shown in Figure 2(b) (location 1) and in Figure 2(c).
The welding process comprised five passes: one root pass
, that is, the first layer of the girth weld seam, followed by one hot pass, that is, the second layer of the girth weld seam, and three subsequent passes, that is, 2 filler passes and 1 cap pass.
Nicholson: Lincoln Electric is renowned worldwide so I guess when I picked up my first Fleetweld 5P back in the late '80s to put in a root pass
would be the start of my pipelining career.
For the root pass
, since this is the first weld pass to be made, argon gas is used as backing gas on the pipe interior diameter to displace all oxygen from atmospheric air.
Vertical Up Welding face a welding speed reduction of 60-70 per cent when welding the same root pass
with basic vertical-up electrodes.
A DC arc is normally used for the root pass
to achieve full penetration.
Jepperson explains that welding procedures specified a root pass
with solid wire (MIG process) and then subsequent passes with flux-cored wire.
0402-20 GTAW Root Pass
Welding of 6% Molydenum Austenitic Stainless Steel Pipe--Open Root Joint with Hand-fed Filler.
Welders can complete a root pass
using STT[R] and then switch to a different welding process for the fill and cap when using an advanced multi-process welding power source like the company's Power Wave[R] 455M/STT[R].
* TIP 0402-20 "GTAW root pass
welding of 6% molybdenum austenitic stainless steel pipe--open root joint with hand-fed filler"