GB/T 38810-2020Seamless stainless steel pipes for liquefied natural gas (English PDF)

4.1 Outer diameter and wall thickness

4.1.1 The nominal outer diameter (D) and nominal wall thickness (S) of steel

pipes shall meet the requirements of GB/T 17395. Required by the purchaser and agreed by the supplier and the purchaser, steel pipes of other sizes beyond those specified in GB/T 17395 can be supplied.

4.1.2 The allowable deviation of the nominal outer diameter and the nominal

wall thickness of steel pipes shall meet the requirements of Table 1.

4.1.3 When the purchaser does not specify the allowable deviation level of the

steel pipe size in the contract, the allowable deviation of the outer diameter and the wall thickness of steel pipes shall meet the requirements of ordinary a) The wall thickness is not more than 15mm, 1.5mm/m;

b) The wall thickness is greater than 15mm, 2.0mm/m.

4.4 End shape

4.4.1 The ends of steel pipe shall be cut flat. It shall remove the incision burrs.

4.4.2 Required by the purchaser, agreed by the supplier and the purchaser and

indicated in the contract, groove can be processed at both ends of steel pipe.

The groove type is determined by the supplier and the purchaser through negotiation.

4.5 Out-of-roundness and unevenness of wall thickness

Required by the purchaser, agreed by the supplier and the purchaser and indicated in the contract, the out-of-roundness of steel pipes shall not exceed 80% of the outer diameter tolerance. The unevenness of wall thickness of steel pipes shall not exceed 80% of the wall thickness tolerance.

4.6 Weight

4.6.1 Steel pipes are delivered according to actual weight. Required by the

purchaser, agreed by the supplier and the purchaser and indicated in the contract, steel pipes can also be delivered according to theoretical weight.

4.6.2 The theoretical weight per meter of steel pipes is calculated according to

formula (1):

Where, W - Theoretical weight of steel pipe, in kilograms per meter (kg/m);

pi - 3.1416;

rho - Density of steel, in kilograms per cubic decimeter (kg/dm3), see Table 3;

D - Nominal outer diameter of steel pipe, in millimeters (mm);

S - Nominal wall thickness of steel pipe, in millimeters (mm).

5.1 Designation and chemical composition

pressure test.

5.5.4 The supplier can use eddy current testing to replace hydraulic pressure

test. The artificial defects of the eddy current testing’s comparison sample tube shall meet the requirements of the acceptance level E4H or E4 in GB/T 7735-2016.

5.6 Process performance

5.6.1 Flattening

Steel pipes shall be subjected to flattening test. During the flattening test, the sample shall be pressed until the distance between the two plates is H. H is calculated according to formula (3). After flattening, there shall be no cracks or breaks on the outside of the sample bend.

Where, H - Distance between two plates, in millimeters (mm);

alpha - Deformation coefficient per unit length, taking 0.09;

S - Nominal wall thickness of steel pipe, in millimeters (mm);

D - Nominal outer diameter of steel pipe, in millimeters (mm).

5.6.2 Flaring

Required by the purchaser, agreed by the supplier and the purchaser and indicated in the contract, steel pipes of which the outer diameter is not greater than 168.3mm and the wall thickness is not greater than 10mm may be subjected to flaring test. The top core taper of the flaring test is 60°. The flaring rate of the outer diameter is 10%. After flaring, the sample shall not have visible cracks.

5.7 Intergranular corrosion

Required by the purchaser, agreed by the supplier and the purchaser and indicated in the contract, steel pipes can be tested for intergranular corrosion.

The intergranular corrosion test method shall meet the requirements of method E in GB/T 4334-2020. After the test, the sample shall not have the tendency of intergranular corrosion.

5.8 Surface quality

5.8.1 There shall be no cracks, folds, folds, delamination and scars on the inner

and outer surfaces of steel pipe. These defects shall be completely removed.

The removal depth shall not exceed 10% of the wall thickness. The actual wall thickness where the defect is removed shall not be less than the minimum allowable wall thickness.

5.8.2 The allowable depth of the straightway on the inner and outer surfaces of

steel pipe shall not be greater than 4% of the wall thickness, not greater than 0.3mm.

5.8.3 Other local defects that do not exceed the deviation of the wall thickness

are allowed to exist.

5.9 Ultrasonic testing

Steel pipes shall be ultrasonically tested. The artificial defects of the ultrasonic testing’s comparison sample tube shall meet the requirements of the acceptance level U3 in GB/T 5777-2019.

6.1 The sampling for chemical composition analysis of steel pipes shall be

carried out according to the rules of GB/T 20066. Chemical composition analysis is usually carried out according to GB/T 11170, GB/T 20123 or other general methods. During arbitration, it shall be conducted in accordance with

GB/T 223.11, GB/T 223.25, GB/T 223.28, GB/T 223.40, GB/T 223.59, GB/T 223.60, GB/T 223.63, GB/T 223. 84, GB/T 223.85, GB/T 223.86.

6.2 The size and shape of steel pipe shall be measured one by one with a

measuring tool that meets the accuracy requirements.

6.3 The inner and outer surfaces of steel pipe shall be visually inspected or

endoscopically inspected one by one under sufficient lighting conditions.

6.4 The test methods and sampling methods for other inspection items of steel

pipes shall meet the requirements of Table 5.

Table 5 -- Inspection items, sampling quantity, sampling methods and

test methods of steel pipes No. Inspection item Sampling quantity Sampling method Test method

1 Chemical composition Take 1 sample per furnace GB/T 20066 See 6.1