Patent ID: 6923900

Claim:
A method of forming an end-profile in the bore of a tube of creep resistant alloy, the method comprising: drawing, from a first end of the tube to a second end of the tube, an electrode having an external profile corresponding to a desired end-profile of the tube; applying, across a space between a target area of the tube and the electrode, a potential difference for driving an electric current between the tube and the electrode; passing an electrolyte along the tube to enable the electric current to flow and to cause metal from the surface of the target area of the tube to enter solution in the electrolyte; maintaining the rate of draw of the electrode along the tube so that the space between the target area of the tube and the electrode remains substantially constant; and selecting the creep resistant alloy to include the following constituents in percent by weight as indicated: carbon, 0.1-0.5; chromium, 20-35; nickel, 20-45; niobium, 0-2; tungsten, 0-5; additions, 0-1; and the balance containing iron.