Electric resistance welded clad steel pipe or tube and method of producing same

A method of producing an electric resistance welded clad steel pipe or tube, the method comprising:

• preparing a clad steel strip including a first layer made of carbon steel or low-alloy steel as base metal and a second layer placed on one surface of the first layer and made of stainless steel or a nickel-containing alloy as cladding metal;
• subjecting both transverse ends of the clad steel strip to groove machining, to form a groove;
• forming the clad steel strip into a pipe or tube shape, to obtain an open pipe or tube that is a cylindrical strip before welding;
• and
• electric resistance welding a pair of butted parts of the open pipe or tube facing each other, to obtain an electric resistance welded clad steel pipe or tube,
• wherein in the groove machining, the transverse ends of the clad steel strip are indented from a second layer side,
• the groove satisfies the following conditions:
• a clad interface between the second layer and the first layer turns from the second layer side toward a thickness center of the clad steel strip;
• a bevel angle θ1 on the second layer side is 10° or more and 50° or less;
• a groove depth d1 is 10% or more and 45% or less of a thickness t of the clad steel strip;
• and
• a projection clad ratio R1 defined by the following Expression (1) is 25% or more and 50% or less,
• R1=(tc1*+d1)/t×100(%) (1)
• where R1 is the projection clad ratio, tc1* is a thickness of the second layer at a root surface in mm, d1 is the groove depth on the second layer side in mm, and t is the thickness of the clad steel strip in mm,
• the electric resistance welding is performed by, while subjecting the pair of butted parts to gas shielding, butt pressing the pair of butted parts with an amount of upset of not greater than the thickness t of the clad steel strip, and
• the gas shielding is performed by blowing a shielding gas using a shielding-gas blowing nozzle having three or more slit-shaped gas outlets arranged in parallel with and adjacent to each other in a butting direction of the open pipe or tube at a position of 5 mm to 300 mm above upper ends of the butted parts of the open pipe or tube, under conditions that B is 0.5 m/s to 50 m/s and 0.010≤B/A≤10, where A is a gas release flow rate in m/s from a pair of first gas outlets located at both ends among the gas outlets, and B is a gas release flow rate in m/s from a second gas outlet other than the first gas outlets.