Can Monel be welded?
Arc Welding Processes on Monel Alloys
As an alloy made primarily of nonferrous metals, oxyacetylene and other fuel gas welding techniques aren't applicable to Monel. The constituent nickel is likely to bond with atmospheric oxygen and hydrogen without the presence of some sort of shield gas or flux, creating porosity and inclusions. Joining Monel is best accomplished through electric arc welding. All types of arc welding provide a way to shield the molten metal and prevent the weld from being contaminated. While all types of arc welding can be used on Monel alloys, some welding processes are known to work better than others.
Welding Monel With SMAW
Shielded Metal Arc Welding (SMAW) or stick welding is by far the most common type of arc welding. Monel can be welded with SMAW using a high-nickel electrode and direct current. However, creating a smooth interior surface for the weld requires the use of a backing plate since SMAW offers no internal shielding of the molten metal. Monel is also especially vulnerable to cracking due to uneven heat, and SMAW welding inputs more heat than gas shielded methods of arc welding. Cracking is especially likely with open-groove welding that requires multiple passes using wide-ranging weave patterns to fill the joint. Monel also becomes contaminated if the molten weld pool is exposed to the atmosphere, and without inert shielding, contamination is harder to avoid. Deposition rates with the SMAW process on Monel are also not ideal.
Welding Monel with Gas Shielded Arc Welding
Gas shielded methods of arc welding have several characteristics that make them preferred for use with Monel. Gas coverage is critical when welding Monel. Similar to the way oxygen exposure can cause severe contamination when welding titanium and aluminum, nitrogen exposure to molten nickel and nickel alloys can cause severe porosity. Inert shielding gas like argon provides a medium that prevents the surrounding atmosphere from contacting the molten Monel. The gas can be pumped into the interior of a pipe or a pressure vessel, and the weld can be shielded from both sides. This ability to shield from both sides ensures a smoother interior weld surface and offers very little chance for nitrogen, oxygen, or carbon to contaminate the weld as long as the joint is prepared properly beforehand. Gas shielded arc welding also allows for more control of the heat input into the metal. The heat of the welding process can be changed by using a mixture of argon and helium, or argon and hydrogen as well. The continuous flow of shielding gas inside and out also improves weld penetration, reducing the potential for crevices and seams in the weld. Of the two types of gas shielded arc welding processes, GTAW is the superior of the two methods for the level of control it offers.
