AWS G2.5-G2.5M:2012 pdf download.Guide for the Fusion Welding of Zirconium and Zirconium Alloys
4.3 Zirconium Weld Discontinuities. Zirconium, like all metals, is susceptible to certain welding discontinuities; how-ever, the range of possible discontinuities is much less than for steel fabrication. Solidification cracking, a common dis-continuity in stainless steel and aluminum welds, is not found in zirconium; the same applies for liquation and reheat cracking. Most of the discontinuities encountered in zirconium welds can be traced to the use of incorrect welding parameters, poor cleanliness, or incorrect gas shielding. These items can result in discontinuities such as lack of fusion,incomplete penetration, and underfill. Porosity can also be encountered, typically as a result of hydrogen absorption due to surface contamination. Gas metal arc welds are susceptible to similar discontinuities but are also prone to spatter, fur-ther increasing the risk of contamination. Plasma arc welds are susceptible to the same discontinuities as gas tungsten arc welds. In the keyhole mode of operation, incomplete penetration results in gross tunnel porosity. Autogeneous keyhole welds in thick zirconium typically exhibit a minor amount of underfill that can be corrected by using a GTAW capping pass. Visual inspection is probably the most effective method and should always be used, regardless of other inspection requirements.
5. Arc Welding Processes
The practices described in this document are limited to the gas tungsten arc, gas metal arc, and plasma arc welding pro-cesses. These gas-shielded processes are well suited for joining zirconium and zirconium alloys provided that the gas shielding arrangement adequately protects the molten weld area and hot base metal from the atmosphere. AIll three of these processes can be performed using manual, semi-automatic, or automatic equipment in a chamber or an open-air environment with the use of auxiliary inert gas shielding. Other processes, including laser, electron beam, resistance, and friction welding, are also used on zirconium and offer advantages for specific applications. Many of the principles dis-cussed are applicable to these other joining processes.
5.1 Gas Tungsten Arc Welding (GTAW). The GTAW process is the most commonly used joining process for zirconium and its alloys. An arc between the tungsten electrode and the surrounding base metal generates the heat for welding.Inert gas from the torch controls the arc characteristics and protects the tungsten electrode and weld puddle from the atmospheric contamination of zirconium. Welds can be made autogenously (i.e., without filler metal) or with the addi-tion of wire. GTAW can be performed in all positions and is the primary process used for orbital pipe welding of zirco-nium. GTAW-P (with pulsation) is commonly used and is particularly advantageous for limiting heat input into a weld.Higher productivity variants of GTAW, such as the hot-wire GTAW process, increase the deposition rate by preheating the wire, providing improved productivity for multipass welding of thicker sections of zirconium.AWS G2.5-G2.5M pdf download.