Root Protection in Special Welding Process

The shielding gas flowing from the welding torch only provides oxidation protection on the upper side of the weld. Forming the underside of the weld by inert or reducing shielding gases prevents or reduces oxidation of the weld root and reduces or prevents tarnish (scale layers), which are the starting point of corrosion even in high-alloy steels. The forming gas additionally supports the forming of the root.

Carbon steel, stainless steel, Duplex and Superduplex, aluminium, and many other gases have different metallurgical characteristics and reactivity to air.

The choice of the inert gas or reducing mixture, must be made by following the compatibility criterion of the material to weld and critical aspects of the atmosphere generated inside the tank – tube to weld.

There are on the market, devices and analysers allowing a correct and safe use of the reducing gas, thus avoiding waste of gas or incorrect use, which voids the operatingresult.

Nippon Gases recommends the use of nitrogen or argon gas mixtures with small amounts of hydrogen. It must be ensured that the ambient air has been sufficiently evacuated from the seam area and that sufficient forming gas is supplied during the entire welding process without causing turbulent flow. When using hydrogen mixtures (reducing effect), even greater attention must be paid to the relevant safety rules during forming.