Abstract
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 post-weld 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.
