THE WORLD IS NOT FLAT: TIPS TO IMPROVE OUT-OF-POSITION WELDING (Part One)
Fabricators often need to weld out-of-position when working with large/heavy weldments and with pipe, which requires adjusting the electrode angle, puddle manipulation, body position and equipment settings. The first in this two-part series by Ken Alrick of Thermadyne takes beginning TIG knowledge to an intermediate/advanced level by comparing right and wrong methods of making these adjustments.
Posted: September 19, 2011
Fabricators often need to weld out-of-position when working with large/heavy weldments and with pipe, which requires adjusting the electrode angle, puddle manipulation, body position and equipment settings. The first in this two-part series takes beginning TIG knowledge to an intermediate/advanced level by comparing right and wrong methods of making these adjustments.
Everybody learns to weld in the flat position, but advancement in the skilled welding trades requires learning to weld in the horizontal (2F, 2G*), vertical (3F, 3G), overhead (4F, 4G) and 45 deg fixed (6G) positions. Further, codes and weld procedure specifications in the power generation, petrochemical and process piping industries call for both TIG and stick process. Of course, structural steel welding also heavily involves all-position stick welding.
In short, the more processes on which an apprentice or journeyman can become qualified, the greater their income potential. Part One of this discussion emphasizes the mechanics for welding out-of-position for TIG welding and, next month, Part Two will focus on stick welding.
Pipe welding is considered the ultimate all-position application: the position changes constantly as the operator works around the circumference of the pipe, covering the flat, overhead, horizontal and vertical positions. As a result, the TIG mechanics described in this article are largely applicable to both pipe and plate.
Sharing his experience on the mechanics of welding is Todd Hidde, the shop superintendent for the Pipe Fabrication Division of J. F. Ahern Co. (Fond du Lac, WI) and a journeyman with UA Local 400. Hidde has been welding for 29 years and supervises a crew of up to 40 welders. Ahern is ranked the 25th largest mechanical contractor in the country according to Contractor magazine’s 2011 Book of Giants. In addition to supplying prefabricated piping for internal mechanical projects, its Pipe Fabrication Division supplies more than $25 million of piping annually to outside mechanical contractors, owners and municipalities for industrial, power, utility and water/wastewater projects. It holds ASME “PP” and “U” stamps, a National Board “R” stamp and welds to ASME codes B31.1, B31.3, B31.9 and API-1104 codes.
“Before discussing welding in various positions, it is useful to review what the operator needs to accomplish,” says Hidde. He notes three key tasks:
(1) Achieve required penetration at the root of the weld. For an open root joint on pipe, this requires complete penetration through to the backside of the joint. On plate, the procedure generally involves gouging out the backside of the weld and completing the joint from the backside.
(2) Have good tie-in at the toes of fillet weld without any undercut. On a groove weld, this especially means good sidewall fusion.
(3) Produce a weld bead face that conforms to codes and specifications, being neither too concave nor convex. A rule of thumb states that the bead crown should be no more than one electrode diameter high and no more than three diameters wide (or “dime wide, nickel high” when using a 1/8 in diameter electrode).
When welding in the flat position, gravity pulls the molten pool into the root opening, making penetration easier. In all other positions, the molten weld puddle wants to roll out of the joint. For this reason, Hidde says that, “Out-of-position groove welds tend to be more difficult than fillet welds. Operators need to concern themselves with directing the molten metal at the bottom of the root and tying in to the sidewalls vs. just having good tie-in at the toes of a fillet weld.”
VARIABLES TO CONTROL
When welding out of position, operators must rely on their skill to deposit filler material and use the force of the arc direct the weld puddle into the joint. Chris Brownlee regularly works with Hidde. He is a CWI and weld process specialist for Weld Specialty Supply Corp. based out of Fond du Lac. Brownlee notes that operators can control weld puddle and weld bead profile by manipulating the following variables:
- Amperage. Reduce amperage by 15 percent for out-of-position welding.
- Arc length. Generally, arc length should equal electrode diameter. Because voltage is directly proportional to arc length, operators often hold a shorter arc to reduce heat when welding out-of-position.
- Electrode work angle. The angle of the electrode relative to the joint. TIG welders also must concern themselves with filler rod angle (more on this later).
- Direction of travel. Usually described in terms of push/forehand or drag/pull/backhand. TIG welding always uses a push technique.
- Electrode travel angle. The angle at which the electrode travels (e.g., how far back the torch is tipped; more below).
- Electrode (torch) manipulation. More on this below.
- Travel speed.
REFERENCE POINT: FLAT POSITION
Setting aside the technical terms, pipe fabricators commonly use a clock face reference to welding positions. When the pipe can be fixed in a positioner and rolled, operators in the “flat” position typically hold the torch at 1:30 to 2 o’clock. In this position, the combination of gravity and weld puddle surface tension helps “pull” the molten metal off the end of the filler rod and into the root.
6 O’CLOCK, OR OVERHEAD POSITION
“When welding overhead, operators need to manipulate the puddle faster or it will fall into the cup,” says Hidde. Manipulation refers to the zigzag motion of the torch. The welder’s wrist/forearm motion most closely resembles that of an infinity symbol. Rhythm is the key to cup walking (or a good freehand). Hidde says that, “Good rhythm has a 1-2, 1-2 metronome-like tempo. Journeymen can help inexperienced welders by counting out the tempo and even grabbing their hand and showing them the motion.”
When cup walking, the cup rests directly on the top of the joint. For this reason, start with perhaps a #6 or #7 cup and increase cup size after the root or hot pass. Set the electrode in the root opening or bottom of the joint, start the arc in the center of the joint, establish the puddle and place a small amount of pressure on the cup. Slide the left side of the cup forward about 1/16 in using the right side of the cup as the pivot point. As the cup pivots, direct the tungsten at the left edge of the joint (toward the leading edge of the cup) and pause momentarily. Next, slide the right side of the cup up 1/16 in, move the electrode across the root, direct it at the right side, pause and repeat the steps described.
The timing, pauses and movement involved with cup walking are as intricate as a waltz. Things happen quickly in any position and need to happen even faster when welding overhead. “Fast manipulation keeps the puddle and its freeze rate under control,” says Hidde. “Slow manipulation either causes the filler metal to pile up or puts too much heat into the joint and blows open the ‘window’ or ‘keyhole’.”
WINDOWS, TRAVEL SPEED AND TIE-IN
When welding an open root joint, operators look for several things. First, they look for a window or keyhole to open up in front of the arc and close behind it as fusion occurs. The objective is to maintain a consistent window size by achieving the optimum balance between travel speed and filler rod feeding rate.
Browlee notes that, “Another indicator of a quality weld is that as the molten puddle ties into the sidewalls, it starts circulating. Impurities and non-worrisome elements such as silicon rise to the top of the puddle and become clearly visible.” If this “scum line” of impurities circulates, it indicates good tie-in. A still puddle usually means little or no sidewall fusion, which is a common bigger mistake.
5 O’CLOCK: THE HAZARD ZONE
The 5 o’clock position is the most hazardous. Hidde says beginners fail here for two reasons. “First, as a transition zone, it’s the least practiced, being neither overhead, nor vertical nor flat. Second, it is where their 6 o’clock position becomes stretched and uncomfortable.”
Browlee adds, “An uncomfortable operator should stop before the cup slips or the tungsten becomes contaminated because the operator dipped it into the weld pool or pushed the filler rod into it. If the tungsten becomes contaminated, stop, grind out any flaws and redress the tungsten. Electricity likes to come off a point, and a contaminated tungsten cannot precisely direct arc force.”
Other “uncomfortable” errors include holding the filler rod too perpendicular to the pipe (which could lead to excessive reinforcement) or holding the filler metal too far in front of the arc and removing it from shielding gas coverage. It’s always better make a short weld and stay in control through frequent repositioning than it is to make a longer weld that might have a flaw.
3 O’CLOCK SLOW DOWN
As operators approach the 3 o’clock position, they can slightly reduce manipulation speed compared to overhead welding. In this position, the puddle freezes and provides a “shelf” on which additional molten weld metal can be stacked without falling out of the joint. For a horizontal weld, remember to direct the arc slightly more toward the top of the joint.
Once the torch position reaches 2 o’clock, gravity takes over and helps pull the puddle into the joint and makes it easier to direct at the sidewall. Return manipulation speed to normal.
In conclusion, beginning welders need to learn different manipulation speeds for different positions and the freeze rate of the metal. They need to learn how gravity affects the weld puddle in terms of how it falls into the root opening, how it affects penetration and how their manipulation enables good sidewall fusion.
“The only way to understand welding mechanics and how they affect the weld puddle is to get under the hood and practice – a lot,” says Hidde.
* F = fillet weld, G = groove weld
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