GB/T 38681-2020Seamless corrosion resistant alloy pipes and tubes for industrial furnace (English PDF)

6.2.1 Smelting method

The alloy shall be smelted by electric arc furnace plus external refining (or electroslag remelting). After agreed by the supplier and purchaser and indicated in the contract, other smelting methods that meet the requirements of this Standard may also be used.

6.2.2 Pipes and tubes making method

6.2.2.1 Hot rolled or hot forged round bars shall be used for alloy ingots used for pipes and tubes making. The parts of the round bar material equivalent to the alloy ingot head and tail shall be fully removed.

6.2.2.2 Alloy pipes and tubes shall be manufactured by hot extrusion or cold rolling (drawing).

6.3 Delivery status

6.3.1 Alloy pipes and tubes shall be heat treated and pickled for delivery. See

Table 4 for recommended heat treatment system. All alloy pipes and tubes that have undergone integral grinding, boring or heat treatment in a protective atmosphere may not be pickled.

6.3.2 As required by the purchaser, after agreed by the supplier and purchaser and indicated in the contract, NS3306 alloy pipes and tubes can be stabilized after solution treatment. The stabilization treatment system is determined by the supplier and the purchaser through consultation.

6.4 Mechanical properties

6.4.1 The room temperature longitudinal tensile properties of the alloy pipes and tubes in the delivery state shall meet the requirements of Table 4.

6.4.2 As required by the purchaser, after agreed by the supplier and purchaser and indicated in the contract, alloy pipes and tubes with wall thickness not less than 2.5mm can be tested for Rockwell hardness or Brinell hardness. The hardness value is determined by the supplier and the purchaser through consultation.

6.4.3 As required by the purchaser, after agreed by the supplier and purchaser and indicated in the contract, alloy pipes and tubes can be subjected to high temperature tensile test. The specific test temperature and mechanical properties are determined by the supplier and the purchaser through consultation.

Where, H - Distance between two parallel pressing plates after flattening, in millimeters (mm); alpha - Deformation coefficient per unit length, taking 0.09;

S - Nominal wall thickness of the alloy pipes and tubes (calculated according to the minimum wall thickness when ordering according to the minimum wall thickness), in millimeters (mm);

D - Nominal outer diameter of alloy pipes and tubes, in millimeters (mm).

6.5.2 Flaring

The alloy pipes and tubes with a nominal outer diameter not greater than 150mm and a wall thickness not greater than 10mm shall be subjected to flaring test. The taper of the top core of the flaring test is 60°. The outer diameter flaring rate of the sample shall be 22%. There shall be no cracks or gaps in the sample after flaring.

6.5.3 Bending

Alloy pipes and tubes with a nominal outer diameter greater than 168.3mm shall be subjected to bending test. There shall be no cracks or gaps in the sample after bending.

6.6 Grain size

The average grain size of NS1102 and NS1104 alloy pipes and tubes shall be level 5 or coarser. As required by the purchaser, after agreed by the supplier and purchaser and indicated in the contract, other designations of alloy pipes and tubes can be tested for average grain size and the qualified level is determined by the supplier and the purchaser through consultation.

6.7 Non-metallic inclusions

use other levels for acceptance.

6.10 Ultrasonic testing

6.10.1 The alloy pipes and tubes shall be subjected to ultrasonic testing, and its acceptance level shall meet the requirements of U2 level in GB/T 5777-2019.

6.10.2 As required by the purchaser, after agreed by the supplier and purchaser and indicated in the contract, ultrasonic testing can use other acceptance levels.

6.11 Penetration testing

6.11.1 Penetrant testing shall be carried out on the repaired surface defects of alloy pipes and tubes.

6.11.2 As required by the purchaser, after agreed by the supplier and purchaser and indicated in the contract, penetrant testing can be performed on the outer surface, end and reachable inner surface of the alloy pipes and tubes.

6.11.3 Penetration testing shall meet the quality level I requirements of other components in NB/T 47013.5-2015.

6.12 Surface quality

6.12.1 There shall be no cracks, folds, chaps, delamination and scars on the inner and outer surfaces of the alloy pipes and tubes. These defects shall be completely removed. The actual wall thickness at the removal site shall not be less than the minimum value allowed by the wall thickness.

6.12.2 The allowable depth of the straight line on the inner and outer surfaces of the alloy pipes and tubes shall meet the following requirements:

a) Cold rolled (drawn) alloy pipes and tubes: not more than 4% of the wall thickness, and not more than 0.3mm;

b) Hot extruded alloy pipes and tubes: not more than 5% of the wall thickness, and not more than 0.4mm.

6.12.3 Allow other defects that do not exceed the deviation under the wall thickness.