Tips, tricks, and techniques for mastering the use of T-8 welding wire

There’s tough, and there’s offshore tough. All-position welding of critical structural applications—such as the TKY joints in offshore construction, pipe structures, bridges, and storage tanks—require filler metals with excellent low-temperature impact toughness and low amounts of diffusible hydrogen.

Users that want a combination of high productivity and simplicity often choose a flux-cored arc welding (FCAW) electrode classified as AWS E71T-8. Commonly known as T-8 wire, this self-shielded, cored electrode eliminates the need to supply shielding gas and offers up to 2.5 times the productivity of shielded metal arc welding electrodes. The deposition rate of a 5/64-in.-dia. wire is 2.4 to 5.1 lbs./hr., compared to about 2.6 lbs./hr. for a 1/8-in.-dia. 7018 electrode.

Furthermore, a T-8 wire with 1% added nickel is not as sluggish as 2% Ni wire, resulting in good puddle control. It provides low-temperature toughness; the Charpy V-notch strength is least 125 ft.-lbs. at -40 degrees F (170 joules at -40 degrees C) and a tensile strength of at least 75,000 PSI (517 MPa). Several T-8 electrodes also carry the H8 designation, indicating less than 8 ml of diffusible hydrogen per 100 g of deposited weld. A vacuum-sealed foil package preserves the wire’s integrity as long as the vacuum remains intact.

For all its benefits, T-8 wire can cause some welding challenges, often because it uses equipment and techniques associated with welding with AWS E7T-1 gas-shielded FCAW wires. A few recommendations and tips can help welders avoid common pitfalls, use optimal techniques, maximize productivity, and obtain better results.

Voltage Control

T-8 wire has a narrower voltage operating window than other FCAW wires. The sweet spot may vary by 3 V or less. As such, they require a constant-voltage (CV) power source. In fact, welding codes with seismic requirements specify using a CV power source.

Note that it’s acceptable to use a voltage-sensing (VS) style feeder paired with a CV power source. Compared to using a constant-speed feeder, VS feeders eliminate the need for a power supply/control cable between the power source and the feeder. The design simplifies cable management in portable applications, eliminating a cable that could get damaged. The trade-off for simplicity is that VS feeders only control wire feed speed, so users must return to the power source to adjust voltage.

For maximum control and arc stability, welders should use a constant-speed feeder. These feeders offer wire feeding performance that is inherently precise, better arc stability, better arc starts and stops, controls for voltage and wire feed speed at the feeder, and advanced functions such adjustable run-in speed and burnback control.

Three Pitfalls

When setting up a system for T-8 wires, operators often encounter three pitfalls.

Flux-cored arc welding wire T-8 excels in providing tough, durable welds for things like TKY joints in offshore construction, pipe structures, bridges, and storage tanks. Getty Images

They set polarity to direct current electrode positive because gas-shielded T-1 wires use this setting. Self-shielded T-8 wires require direct current electrode negative.

They often use the wrong electrode extension. This wire should have a stickout of ¾ in. During welding, the stickout may increase to 1.25 in., but it’s best to keep it as close to ¾ in. as possible. Total contact-tip-to-work distance should be about 1 in.

They don’t follow the wire manufacturer’s recommended settings. T-8 wires sound different than T-1 wires. Operators may be tempted to increase voltage to achieve a familiar sound, but too much voltage causes porosity (the sound of a properly tuned arc comes up at the 2:35 mark of the video). Feeders with digital displays make setting and returning to the proper parameters much easier.

If the recommended settings don’t provide the expected outcome, the problem might be a voltage loss caused by undersized or worn cables, a poor ground clamp, or a worn contact tip.

Welding Technique

Another factor in a quality weld is the welder’s technique. Many offshore applications require mastery of the 6G position. The position seems intimidating, but it is really just a combination of the other welding positions with transitions between them. For this reason, operators should practice for the 6G test by first mastering other positions, especially vertical-up and vertical-down, which many welders find to be the most challenging.

For welding vertical-up, the welder needs to build a shelf of slag to support the weld pool. To achieve a good shelf, the welder should direct the wire straight into the joint or use a slight backhand technique by pointing the torch downward at an angle of about 5 degrees during upward movement. The operator may use the slightest amount of wiggle to ensure tie-in at the toes of the weld but should never weave or otherwise manipulate the torch laterally. Such motions can entrap slag.

For welding vertical-down, the welder should reduce the parameters slightly, particularly voltage, and consult the manufacturer for recommended settings for the application. To counteract the pull of gravity on the weld pool, the welder should tip the torch upward at a 5-degree angle and use a backhand technique while moving it downward. A slight amount of wiggle can promote tie-in at the toes of the weld, but again a weave is not to be used. As with vertical-up, the operator should run straight stringer beads for all welding passes, from root to cap, and plan welding passes so that the finished weld has no more than 1/16 in. of reinforcement.

Regardless of position, maintaining a proper torch angle is the most important factor for success. To do this, the welder needs to move his arm, shoulders, and head in harmony while traveling around the pipe circumference. Coupling the correct angle with proper stickout and the correct system can help welders achieve all of the productivity and quality benefits offered by T-8 wires.