Checking the Pulse of Welding Inconel

A few things to look for when selecting a TIG welding system in this application include:

• Direct Current Electrode Negative (DCEN) capabilities: As with many nickel-based alloys, DCEN is recommended for this process. There are dedicated DC TIG inverters, such as the Maxstar® 200, that will work perfectly in shops dedicated to welding Inconel or other common DC processes, such as stainless.

However, if you also weld other common materials such as aluminum, TIG inverters such at the Dynasty® 200 offer both alternating current (AC) and DC capabilities.

• Arc starting characteristics: Old transformer-style TIG machines generate a burst of current during starts that helps initiate the arc but also can damage the base metal. To compensate, welders often use a starting block positioned behind the piece to absorb some of the current.

Inverters, conversely, allow welders to regulate that output down to a microsecond to the exact amount of starting amperage (as low as one amp, depending on the power source) needed to light the arc without damaging the base material.

• Pulsing capabilities: Pulsing capabilities have improved substantially since the days of the larger transformer-based machines. Older TIG technology is limited to pulsing at about 20 pulses per second. Newer TIG inverter technology allows high speed DC TIG pulsing (up to 500 pulses per second with a Maxstar 200 and up to 5,000 pulses per second with a Dynasty 350, by example).

Having the ability to control pulsing up to that range allows the operator to reduce average amperage and heat input, helping to control penetration, reduce distortion and reduce cracking (more heat = larger grain structure = greater chance of cracking).

With typically sluggish alloys like Inconel, pulsing helps agitate the puddle. By bringing the pulse rate up, agitating the puddle and increasing the travel speed you can tighten the grain structure and achieve a stronger weld.

• Use a gas lens: A gas lens replaces the standard collet body in a TIG torch and improves the flow and coverage of the shielding gas around the tungsten, the arc and the weld pool. This helps create a calm, well protected weld puddle.

• Crater Control: Craters typically occur at the end of the weld and can lead to cracking. This is typically caused by reducing the welding power and removing the filler rod too quickly, causing the weld to cool rapidly.

TIG inverters with crater control functions automatically reduce the current for you at the end of the weld – highly recommended in this application.

PULSED MIG EVOLVES IN CLADDING OPERATIONS
Inconel wires are used extensively in cladding applications in high temperature and corrosive plant environments to extend the life of carbon steel pipes, adding years of service with an overlay of the existing pipe.