Abstract: New methods of manufacturing coiled tubing result in increased useful life of the coiled tubing string by creating an enhanced strip-to-strip weld zone having load bearing and/or fatigue resistance properties substantially equal to or greater than the load bearing and/or fatigue resistance properties of the strip base material. The enhanced weld zone is transition into the nominal tubing to reduce stress concentration.

Abstract: New methods of manufacturing coiled tubing result in increased useful life of the coiled tubing string by creating an enhanced strip-to-strip weld zone having load bearing and/or fatigue resistance properties substantially equal to or greater than the load bearing and/or fatigue resistance properties of the strip base material. The enhanced weld zone is transition into the nominal tubing to reduce stress concentration.

Abstract: A hard corrosion resistant surface is provided on a ferrous substrate by first overlay welding onto the substrate surface a chromium containing ferrous material. The deposited overlay can then be machined. It is thereafter subjected to a carburization treatment at a temperature and for a time sufficient to cause the overlay to become converted to an austenitic material containing iron chromium carbides. After cooling, the carburized overlay material is heated for a time and at a temperature sufficient to cause the austenitic matrix material to precipitate secondary carbides and convert to a martensite matrix material upon cooling. It is also contemplated to initiate the aforesaid treatment with a suitably selected chromium containing ferrous material that thereby is not overlay welded.