Method for preparing multilayer metal composite pipe

A method for preparing a multilayer metal composite pipe, comprising steps of:

• 1) grinding external surfaces of metal blank pipes (101) to eliminate oxide films on the external surfaces and spiral joints caused by a previous process;
• 2) grinding internal surfaces of the metal blank pipes (101) to eliminate oxide films on the internal surfaces and quality defects caused by the previous process, and producing micro-grooves on the internal surfaces of the blank pipes;
• wherein no micro-groove is produced on an internal surface of an innermost pipe of the multilayer metal composite pipe;
• 3) cleaning the internal surfaces and the external surfaces of metal blank pipes (101) ground in the step 2 to remove grits, metal burrs and the oil stains;
• 4) assembling the metal blank pipes (101) cleaned in the step 3 with internal and external clearances to form a multilayer metal blank pipe;
• 5) reducing the diameter of the multilayer metal blank pipe through a drawing die (4), and fully contacting adjacent pipe layers in the multilayer metal blank pipe to form an interference fit, thereby obtaining a layered composite pipe blank (102) by drawing to reduce the diameter;
• 6) fusing pipe end gaps of the layered composite pipe blank (102) with a high-speed friction welding head (5), and sealing by welding to prevent internal and external surfaces of adjacent pipe layers of the layered composite pipe blank (102) from oxidizing;
• 7) applying multiple sets of the high-speed friction welding heads (5) on surfaces of the layered composite pipe blank (102) with sealed pipe ends to fuse gaps between corresponding friction welding areas, thereby realizing the multi-point friction welding on the pipe surfaces of the layered composite pipe blank (102);
• 8) overall heating the layered composite pipe blank (102) after friction welding;
• 9) processing the heated layered composite pipe blank (102) with large deformation treatment through the four-roller cross-rolling, so that the internal and external surfaces of the adjacent pipe layers are metallurgically composited;
• 10) straightening the layered composite pipe blank (102) after the four-roller cross-rolling to eliminate bending and flattening problems caused during cooling as well as to eliminate an internal residual stress;
• 11) processing the straightened layered composite pipe blank (102) with plastic deformation and crushing metal crystal grains through the two-roller cold-rolling, so as to obtain a layered composite pipe (103) with a reduced diameter;
• 12) cleaning the rolled layered composite pipe (103) to remove surface oil stains;
• 13) brightening the degreased layered composite pipe (103) to reduce oxide scales on a surface of the metal pipe;
• 14) processing the brightened layered composite pipe (103) with the surface grinding to eliminate surface oxide films and pipe surface quality problems caused by the previous steps, and then polishing;
• 15) cleaning internal and external surfaces of the polished layered composite pipe (103) to remove surface grinding head grit and metal burrs;
• 16) performing ultrasonic detecting on the cleaned layered composite pipe (103) to obtain metallurgical bonding information of the internal and external surfaces between adjacent pipe layers of the layered composite pipe (103), and discarding an unqualified layered composite pipe (103) having unqualified metallurgical areas;
• 17) performing the ultrasonic detecting on the surfaces of the cleaned layered composite pipe (103) to obtain crack defect information of the layered composite pipe (103) after deformation, and discarding the unqualified layered composite pipe (103);
• 18) sampling and testing the qualified layered composite pipe (103);
• analyzing mechanical properties, grain sizes, and corrosion resistances of each pipe layer, and evaluating metal pipe performance;
• for the layered composite pipe (103) with unqualified metal structure performance, repeating the steps 11-18 until the qualified layered composite pipe (103) is obtained;
• and
• 19) sizing and packaging the qualified layered composite pipe (103) to facilitate transportation and avoiding corrosion by harmful substances.