GB/T 40297-2021Seamless austenitic stainless steel pipes for high pressure hydrogen (English PDF)

6.6 Weight

6.6.1 Steel pipes shall be delivered by actual weight. After it is negotiated between the supplier and the buyer, and indicated in the contract, the steel pipes can also be delivered according to the theoretical weight. The theoretical weight of the steel pipe per meter is calculated according to Formula (1): Where: W - theoretical weight of the steel pipe, in kilograms per meter (kg/m); pi - pi, which shall be 3.141 6; rho - density of steel, in kilograms per cubic decimeter (kg/dm3), as shown in Table 4; S - wall thickness of the steel pipe, in millimeters (mm); D - nominal outside diameter of the steel pipe, in millimeters (mm).

6.6.2 For steel pipes delivered according to the nominal outside diameter and minimum wall thickness, the theoretical weight shall be calculated by the average wall thickness. The average wall thickness is the average value of the maximum and minimum wall thicknesses calculated according to the wall thickness and its permissible deviation.

6.6.3 When the steel pipes are delivered according to the theoretical weight, the supplier and the buyer can negotiate the weight permissible deviation and indicate it in the contract.

7.3 Delivery state

7.3.1 Steel pipes shall be delivered after heat treatment and pickling. All steel pipes that have been wholly ground, bored or heat-treated in protective atmosphere can be delivered without pickling. See Table 4 for the recommended heat treatment system for steel pipes. 7.3.2 06Cr18Ni11Ti, 07Cr19Ni11Ti, 06Cr18Ni11Nb and 07Cr18Ni11Nb steel pipes shall be subjected to stabilization heat treatment after solution heat treatment. The stabilization heat treatment system shall be determined through negotiation between the supplier and the buyer.

7.3.3 For hot-rolled (extruded, upset, forged) steel pipes, if direct water cooling or other rapid cooling is carried out within the heat treatment temperature range specified in Table 4 after hot deformation, it shall be deemed that the steel pipe solution heat treatment requirements have been met.

7.3.4 After it is negotiated between the supplier and the buyer, and indicated in the contract, other heat treatment systems other than those specified in Table 4 can be adopted for the steel pipe.

7.4.1 Mechanical properties

7.4.1 Room temperature mechanical properties The room temperature mechanical properties of the steel pipes in the delivery state shall comply with the requirements in Table 4. Where: p - test pressure, in megapascals (MPa), which shall be rounded off to the nearest

0.5 MPa when p< 7 MPa, and to the nearest 1 MPa when p>=7 MPa; S - wall thickness of the steel pipe, in millimeters (mm); R - allowable stress, which shall be 60% of the minimum plastic elongation strength specified in Table 4, in megapascals (MPa); D - nominal outside diameter of the steel pipe, in millimeters (mm).

7.5.2 The chloride ion (Cl-) content (mass fraction) in the water used for the hydraulic test shall not exceed 25×10-6.

7.5.3 With the consent of the buyer, the supplier may use eddy current testing instead of the hydraulic test. In eddy current testing, the acceptance grade shall meet the requirements of E4H or E4 in GB/T 7735-2016.

7.6.1 Flattening

7.6.1.1 The steel pipes shall be subjected to a flattening test. Flattening shall be performed in the following two steps.

a) The first step is the ductility test. The sample shall be pressed to H, the distance between the two plates, and shall not have cracks or breaches. H shall be calculated according to Formula (3). Where: H - the distance between the two plates, in millimeters (mm); alpha - deformation coefficient per unit length, which shall be 0.09; S - wall thickness of the steel pipe, in millimeters (mm); D - nominal outside diameter of the steel pipe, in millimeters (mm).

b) The second step is the integrity test (closed flattening). The flattening shall be continued until the sample ruptures or the sample collides with opposite walls; the sample shall not show any visible separation, white spots or inclusions during the entire flattening test.

7.6.1.2 The following conditions shall not be used as the basis for judging whether the flattening test is qualified or not:

a) cracks or breaches caused by defects on the inner surface of the sample;

b) cracks or breaches on the inner surface of the sample at the 6 o'clock (bottom) and 12 o'clock (top) positions, when S/D >0.1.

7.6.2 Bending test

7.6.2.1 For steel pipes with an outside diameter greater than 600 mm or a ratio of wall thickness to outside diameter greater than 15%, a bending test may be adopted instead of a flattening test. A set of bending tests shall include a forward bending (the surface of the sample near the outer surface of the steel pipe is deformed in tension) and a reverse bending (the sample near the inner surface of the steel pipe is deformed in tension).

7.6.2.2 The diameter of the bending core of the bending test is 25 mm; the sample shall be bent 180° at room temperature. After bending, there shall be no visible cracks or breaches on the tensile surface and sides of the sample.

7.6.2.3 The sample for the bending test shall be taken along the transverse direction of the steel pipe; the sample preparation shall comply with the provisions of GB/T 232. When the sample is taken, the forward bending sample shall be as close as possible to the outer surface, and the reverse bending sample shall be as close as possible to the inner surface. There shall be no obvious scars or other defects on the surface of the sample under bending and tension deformation. The sectional dimensions of the sample after processing shall be

12.5 mm or 25 mm ×

12.5 mm (width × thickness); the four corners on the section shall be rounded, the radius of the rounded corners shall not be greater than

1.6 mm, and the length of the sample shall not be greater than 150 mm.

7.6.3 Flaring Steel pipes whose outside diameter is not more than 150 mm and wall thickness is not more than 10 mm shall be subjected to a flaring test. The taper of the top core of the flaring test is 60°; the flaring rate of the outside diameter after flaring shall meet the requirements of Table 6; the sample shall not have cracks or breaches after flaring. groove depth shall be

0.2 mm; when the wall thickness is not greater than 40 mm, the maximum groove depth shall be

1.0 mm; when the wall thickness is greater than 40 mm, the maximum groove depth shall be

7.11.1.2 When the steel pipes are delivered as per the minimum wall thickness, the groove depth of the comparative sample pipe shall be calculated according to the average wall thickness of the steel pipe.

7.11.1.3 The ends of steel pipes that cannot be completely detected by automatic inspection shall be cut off or manually ultrasonically inspected. The sensitivity of the manual detection method shall be at least the same as that of the automatic detection method; the steel pipe used to correct the sensitivity shall be the steel pipe used for automatic detection.

7.11.1.4 As required by the buyer, negotiated between the supplier and the buyer, and indicated in the contract, the steel pipe can be ultrasonically tested by methods specified in other standards.

7.11.2 Lamination detection As required by the buyer, negotiated between the supplier and the buyer, and indicated in the contract, the steel pipe can be subjected to ultrasonic testing for lamination.

7.11.3 Penetrant testing The outer surface, ends and accessible inner surfaces of the steel pipe shall be tested for liquid penetration. The liquid penetration test shall comply with the provisions of NB/T 47013.5-2015, and shall be accepted according to the quality level I of other components.