CEWELD  Zirconium Zr 702

Zirconium often is chosen for its resistance to corrosion from most organic and inorganic acids, salt solutions, strong alkalis, and some molten salts. It is especially suitable in many sulfuric, nitric, hydrochloric, and acetic acid applications. Backup Shielding. Backup shielding protects the molten root of the weld on the first pass and blankets the solidified weld during subsequent passes until the root surface temperature stays below 600 degrees F. Backup shielding also should be used on the back surface of sheet or plate less than 1/4 in. thick to prevent oxidation. Gas Requirements. Welding-grade argon (99.999 percent purity) usually is chosen for primary, secondary, and backup shielding, as well as for purging. Argon provides excellent arc stability, and because it is heavier than air, it blankets the weld and provides protection. Helium or argon/helium mixtures sometimes are used for torch shielding if added penetration is desired. Argon and helium mixtures also are occasionally employed for backup shielding and purging, in which helium's low density can effectively purge blind spaces. Gas Purity. Argon usually is purchased to 99.998 percent purity with a guarantee of less than 5 parts per million (PPM) oxygen, moisture, or total hydrocarbons. The dew point at the gas supply should not be more than -60 degrees F (-51 degrees C).