GB/T 21833.2-2020Seamless austenitic-ferritic duplex stainless steel tubes and pipes - Part 2: Pipes for fluid service (English PDF)

4.2 Length

4.2.1 Normal length

The normal length of the steel pipes is 3000 mm~12000 mm. According to the requirements of the purchaser, through negotiation between the supplier and the purchaser, and indicated in the contract, steel pipes of other lengths can be supplied.

4.2.2 Fixed length and multiple length

According to the requirements of the purchaser, through negotiation between the supplier and the purchaser, and indicated in the contract, steel pipes with fixed length, multiple length, or other specific length requirements can be supplied. The total fixed length and multiple length shall be within the normal length range.

For steel pipes delivered in multiple lengths, the cut margin shall be 5 mm~10 mm for each cut.

4.3 Bending

The bending of each meter of the steel pipe shall meet the following requirements:

a) When S<=15 mm, it is not more than 1.5 mm/m;

b) When S >15 mm, it is not more than 2.0 mm/m.

4.4 Out-of-roundness and uneven wall thickness

The out-of-roundness and uneven wall thickness of the steel pipes shall not exceed 80% of the tolerances of the outer diameter and wall thickness, respectively.

4.5 End shape

The end faces of both ends of the steel pipe shall be perpendicular to the axis of the steel pipe. It shall remove the cut burrs.

4.6 Masses

Steel pipes are delivered according to actual mass; can also be delivered according to theoretical mass. The theoretical mass of the steel pipe per meter is calculated according to formula (1).

5.2 Manufacturing method

5.2.1 Smelting method of steel

Steel shall be smelted by electric arc furnace plus external refining or converter plus external refining or electroslag remelting process. Through negotiation between the supplier and the purchaser, and indicated in the contract, other smelting methods can also be used.

5.2.2 Manufacturing method of steel pipe

The steel pipes shall be manufactured by hot-rolling (hot-extrusion) or cold-drawing (rolling) seamless production process.

5.3 Delivery state

5.3.1 Steel pipes shall be delivered after heat treatment and pickling. Steel pipes, which have been heat-treated in a protective atmosphere or ground (polished) as a whole, can be delivered without pickling.

5.3.2 See Table 3 for the recommended heat treatment system for steel pipes.

Through negotiation between the supplier and the purchaser, and indicated in the contract, heat treatment systems other than Table 3 can be used for steel pipes.

5.4 Mechanical properties

5.4.1 The longitudinal mechanical properties of steel pipes delivered in heat-treated state shall comply with the requirements of Table 3.

5.4.2 Steel pipes with a wall thickness of not less than 1.7 mm shall be tested for Brinell or Rockwell hardness. Their values shall comply with the requirements of Table 3.

5.4.3 According to the requirements of the purchaser, through negotiation between the supplier and the purchaser, and indicated in the contract, the steel pipes can be subjected to an impact test. The test temperature and impact absorbed energy are negotiated between the supplier and the purchaser.

5.5 Hydrostatic pressure

5.5.1 Steel pipes shall be subjected to hydrostatic pressure test one by one.

The test pressure is calculated according to formula (2). The maximum test pressure is 20 MPa. Under the test pressure, the pressure stabilization time shall be no less than 10 s. The steel pipe shall not leak.

Where: P - Test pressure, in megapascals (MPa);

S - The nominal wall thickness of the steel pipe, in millimeters (mm);

R - Allowable stress. It is 50% of the minimum Rp0.2 value specified in Table 3, in megapascals (MPa);

D - The nominal outer diameter of the steel pipe, in millimeters (mm).

5.5.2 The supplier can replace the hydrostatic pressure test with eddy current testing. During eddy current testing, the artificial defects of the comparative sample pipe shall comply with the provisions of the acceptance level E4H or E4 in GB/T 7735-2016.

5.6 Flattening

Steel pipes with a wall thickness not greater than 10 mm shall be subjected to flattening test. After flattening, the spacing H between two parallel pressing plates is calculated according to formula (3). After the sample is flattened, there shall be no cracks or gaps.

Where:

H - The distance between parallel pressing plates after flattening, in millimeters (mm); alpha - Deformation coefficient per unit length, 0.07;

S - The nominal wall thickness of the steel pipe, in millimeters (mm);

D - The nominal outer diameter of the steel pipe, in millimeters (mm).

5.7 Drift-expending

There shall be no cracks, folds, rolled folds, delamination, and scars on the inner and outer surfaces of the steel pipe. These defects shall be completely removed. The removal depth shall not exceed the lower tolerance of the nominal wall thickness. The actual wall thickness at the removal location shall not be less than the allowable minimum wall thickness. Other local defects not exceeding the lower tolerance of wall thickness are allowed.

5.13 Special requirements

When the purchaser has the following special requirements, the supplier and the purchaser shall negotiate and indicate in the contract:

a) Adjust the chemical composition range specified in Table 2;

b) Provide modulus of elasticity and thermal expansion coefficient data;

c) Test of harmful precipitating phase;

d) Provide the measured data of high-temperature mechanical properties.

For recommended high-temperature mechanical property values of some designations, see Appendix A;

e) Specify the content of austenite or ferrite different from the requirements of 5.8;

f) Other requirements.