Manufacturing and refurbishment processes for cold exchange tube bundles

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Part 1: Manufacturing Process of Tubes I. Inspection and Evaluation of Tubes and Various Accessories 1. Inspection of Tubes (1) All steel tubes shall comply with the requirements for heat exchange tubes specified in GB151-89; cold-drawn tubes of the higher grade or those of the ordinary grade as specified in the relevant standards shall be used. During visual inspection, the outer wall of the tube should be free from defects such as folds and cracks. In addition, physical and chemical tests, as well as verification of the manufacturer’s quality certificate and approval documents, are required; those that fail these tests shall not be used. a. GB8163-87 \"Seamless steel pipes for transporting fluids\" ； b. GB9948-88 \"Seamless Steel Tubes for Petroleum Cracking\" ； c. GB2270-80 \"Seamless Stainless Steel Tubes\" ； d. GB6479-86 \"High-pressure seamless steel pipes for fertilizers.\" (2) The hardness of the tube should be 30 HB lower than that of the tube sheet; otherwise, annealing treatment should be carried out within 150–200 mm of the tube end. (3) The expansion joint portion of the pipe shall have no longitudinal grooves, but transverse grooves with a depth not exceeding 0.1 mm are permitted. (4) The allowable dimensional tolerances for various parts of the steel pipe shall comply with the provisions of relevant standards. (5) The outer surface of the tube ends of the heat exchange tubes should be derusted. For welding, the rust removal length at the pipe end should be no less than the pipe diameter and also no less than 25 mm. For expansion joint connections, the pipe end must be rusted free until it has a metallic shine, and this length should be at least twice the thickness of the pipe sheet. (6) Due to length limitations of the pipes, each pipe can have one weld joint. The U-tube can allow for a second butt joint, with the shortest section not being less than one meter. A single-pipe hydrostatic test shall be conducted after welding, with the test pressure being 2 times the design pressure. 2. Inspection of tube sheets: (1) There shall be no longitudinal or spiral cutting marks that run through the tube holes; in the case of individual cutting marks, their distance from the edge of the hole must be at least 10 millimeters. The pipe holes should be cleaned thoroughly before threading the pipe. (2) The axis of the pipe hole in the tube sheet should be perpendicular to the plane of the tube sheet. (3) The allowable deviations for the diameter of the heat exchange tubes and tube holes are shown in Table 1. Table 1(a) Allowable deviations for the outer diameter of heat exchange tubes and tube hole diameters in Class I heat exchangers, in mm:
Heat exchange tubes – Outer diameter: 10, 14, 19, 25, 32, 38, 45, 57; Allowable deviations: ±0.15, ±0.20, ±0.30, ±0.45.
Tube sheet – Tube hole diameter: 10.20, 14.25, 19.25, 25.25, 32.35, 38.40, 45.40, 57.55; Allowable deviations: +0.15, 0, +0.20, 0, +0.25, 0.

Table 1(b) Allowable deviations for the outer diameter of heat exchange tubes and tube hole diameters in Class II heat exchangers, in mm:
Heat exchange tubes – Outer diameter: 10, 14, 19, 25, 32, 38, 45, 57; Allowable deviations: ±0.20, ±0.40, ±0.45, ±0.57.
Tube sheet – Tube hole diameter: 10.30, 14.40, 19.40, 25.40, 32.50, 38.50, 45.50, 57.70; Allowable deviations: +0.15, 0, +0.20, 0, +0.30, 0, +0.40, 0.

(4) When reusing old tube sheets, the tube holes may be slightly larger, but not more than 1.5 times the maximum allowable deviation for those holes. The method for repairing an old tube sheet is as follows: first, use gas cutting to cut the tube sheet off, then place it on a drilling machine and drill away the flared end from the front side; next, use a sledgehammer to break off the remaining tube end, pull out the tube ring that remains in the groove, and clean the oil and rust inside the holes of the tube sheet with fine sandpaper. Once this is done, the old tube sheet can be used again. (5) The grooves or flange surfaces of the old tube sheet should be smooth without any defects; if they do not meet these requirements, they must be processed before being reused. 3. Inspection of baffle plates and support plates: For commonly used Φ25mm pipes, the diameter tolerance of the pipe holes in the baffle plates and support plates shall not exceed Φ25.6+0.4-0mm. After drilling, the burrs around the pipe holes should be removed and the surfaces smoothed out. The repair of old baffles involves removing the tubes from the old tube bundle whose tube sheet has been taken off, taking out the baffles, and leveling them up (be careful not to damage the tube holes while leveling the baffles). Once they pass inspection, they can be reused. . The negative deviation of the outer diameter of the baffle plates and support plates shall not exceed the values specified in Table 2. Table 2: Outer diameter deviation of baffle plates and support plates, unit: mm, nominal diameter DN