System for electrically heating fluid-conveying pipe lines and other structures

Claim 1

A pipe line heating apparatus comprising an electrically conductive fluid transport pipe having magnetic properties, at least one electrically conductive member having magnetic properties, said member being positioned on the outer periphery of said pipe to cover a portion of said outer periphery and cooperating with said pipe to define a hollow heat generating conduit that has a part of its wall in common with a portion of said pipe, an electrical conductor peripherally surrounded by said hollow conduit and extending along the outer periphery of said pipe, the effective length of said electrical conductor that is peripherally surrounded by said hoLlow conduit being electrically insulated from said hollow conduit, means providing a source of alternating current and having first and second terminals, said hollow conduit and said electrical conductor being serially connected across said first and second terminals to pass heat-producing alternating current through said hollow conduit and said electrical conductor for providing a currentproduced magnetic field around said electrical conductor, said magnetic field causing the current flowing in said hollow conductor to be concentrated at the inner periphery of said hollow conduit, the wall thickness of said conduit being greater then the penetration depth of the alternating current flowing therethrough, and spaced apart stitch welds extending along opposite sides of said electrically conductive member and fixing said electrically conductive member to said pipe, the stitch welds on one side of said electrically conductive member being staggered relative to the stitch welds on the other side of said electrically conductive member.