Welded tube with excellent corrosion-resistant inner surface and method of producing the same

Abstract

Disclosed is a welded tube with an excellent corrosion-resistant inner surface, in which the inner surface including the bead part has a first plate layer of one metal material selected from Sn, Sn--Zn, Sn--Ni, Ni--P and Ni--B and the first plate layer is overcoated with a second plate layer of one metal material selected from Ni, Co and alloys based on the metals. The welded tube is free from exposure of the steel base out of the plate layer and is also free from cracks, pin holes, overplated spots and peeling of the plate layer. It has excellent corrosion resistance and good workability for working the terminals. The welded tube is produced by forming a first plate layer of Sn, Sn--Zn, Sn--Ni, Ni--P or Ni--B on at least one surface of a steel strip, then forming a second plate layer of Ni, Co or an alloy based on the metals over the first plate layer, shaping the thus plated steel strip into a tube by welding with the plated surface being inside and then heat-treating the tube.

Dependencies are inferred from the claim text.