MECHANICAL AND CORROSION PERFORMANCE OF WELDED ALLOY 925 VIT IN SOUR ENVIRONMENT

摘要

The concept of vacuum insulated double-walled tubular products (VIT) has been employed over the years providing downhole temperature management. Transfer to applications requiring the combination of extreme sour service and high strength requires consideration of a different group of materials than previously used. Alloy 925 was chosen as a candidate tubing material due to its combination of corrosion resistance, fabricability, strength characteristics and economy. Fabrication of the VIT assembly requires welded joints. For the welded joints, the age-hardenable filler metal 725 was needed to ensure high strength and acceptable corrosion properties. Utilizing age-hardenable filler metal to join a different age-hardenable material required development of an optimum welding procedure and postweld aging practice to ensure the resulting weldments possessed the desired properties for VIT service. At post weld heat treatment of 1350°F (732°C) for four (4) hours followed by air-cooling, the welded alloy 925 VIT showed the desired strength and toughness, good low cycle fatigue strength and acceptable corrosion resistance in the sour environment.