GB/T 37792-2019General specification for welded corrosion resistant alloy pipes and tubes (English PDF)

3.1 Outer diameter and wall thickness

3.1.1 The nominal outer diameter (D) and nominal wall thickness (S) of the

welded pipes and tubes shall comply with the provisions of GB/T 21835.

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

4.1 Designation and chemical composition

4.1.1 The designation and chemical composition of the corrosion resistant alloy

shall comply with the requirements of the corresponding product standard.

4.1.2 The permissible tolerances for chemical composition of welded pipe and

tube products shall comply with the provisions of GB/T 15007.

4.2 Manufacture

4.2.1 Smelting method

The alloy shall be smelted by means of electric arc furnace plus external refining plus electroslag remelting, or other smelting methods which meet the requirements of this Standard. The smelting method shall be indicated in the quality certification.

4.2.2 Manufacturing method of welded pipes and tubes

4.2.2.1 The welded pipes and tubes shall be manufactured by single-sided or

double-sided automatic welding method without adding or adding filler metal.

4.2.2.2 When filler metal is added during the manufacturing process of the

welded pipes and tubes, a matching filler metal shall be selected, or a filler metal with a higher alloy content may be selected.

4.2.2.3 Through negotiation between the supplier and the purchaser, and

indicated in the contract, welded pipes and tubes with a nominal outer diameter of not less than 508 mm allow for double longitudinal welds or circumferential weld joints of the same quality as longitudinal welds.

4.2.2.4 Two-time repair welding is not allowed at the same position of the weld

of the welded pipes and tubes. The defect of the base metal does not allow for repair welding.

4.2.3 Delivery state

The welded pipes and tubes shall be delivered in a heat-treated plus pickled state. The recommended heat treatment system shall be specified in the corresponding product standard or contract. Welded pipes and tubes which are overall polished, buffed, or heat treated in protective atmosphere may be not subjected to pickling. If delivered in other states, it shall be determined by D - The nominal outer diameter of the welded pipe and tube, in millimeters (mm).

4.4.2 Drift-expanding

The drift-expanding test has a center taper of 60°. The drift-expanding rate of outer diameter is not less than 15%. After drift-expanding, the sample shall not have cracks or gaps.

4.4.3 Bend on welded joints

4.4.3.1 The bend sample shall be taken from the welded pipe and tube or

welded test plate. The welded test plate shall be the same designation, the same heat number, the same welding process, and the same heat treatment system as the welded pipe and tube. A set of bend tests shall include a positive bend and a back bend (i.e., the outer weld and the inner weld of the welded pipe and tube are respectively at the maximum curved surface). For welded pipes and tubes with a nominal wall thickness greater than 10 mm, a set of two side bends may be adopted instead of a positive bend and a back bend.

4.4.3.2 In the bend test, the bend core diameter is 4 times the sample thickness;

the bend angle is 180°. After bending, in the weld area, there shall be no cracks or gaps.

4.5 Grain size

The average grain size of base metal of the welded pipes and tubes shall be determined in accordance with product standards or contract requirements.

4.6 Intergranular corrosion

The intergranular corrosion test results of the welded pipes and tubes shall be judged according to product standards or contract requirements. The samples shall include the weld, the heat-affected zone, and the base metal.

4.7 Nonmetallic inclusions

Nonmetallic inclusions of base metal of the welded pipes and tubes shall comply with product standards or contract requirements.

4.8 Compactness

4.8.1 Hydrostatic pressure test

When the welded pipes and tubes are subjected to a hydrostatic pressure test, the test pressure is calculated according to formula (3). The maximum test pressure is 20 MPa. Under the test pressure, the pressure holding time shall be no less than 5 s. The welded pipe and tube shall not leak.

the minimum wall thickness are allowed.

4.11.2 After the surface defects of the welded pipes and tubes are repaired, it

shall carry out liquid penetrant inspection. The inspection results shall comply with the product standard or the contract.

5.1 The inspection items and test methods of welded pipes and tubes shall

comply with the requirements of Table 3.

5.2 The inner and outer surfaces of the welded pipes and tubes shall, under full

lighting conditions, be visually inspected one by one. The liquid penetrant inspection shall be carried out in accordance with the provisions of NB/T 47013.5-2015.

5.3 The dimensions and shape of the welded pipes and tubes shall be

measured one by one using the measuring tools which meet the accuracy requirements. For welded pipes and tubes with a nominal outer diameter of not less than 508 mm, the outer diameter shall be measured using a diameter tape measure.

Table 3 -- Inspection items, sampling quantities, sampling locations, and

test methods No. Inspection items Sampling quantities Sampling locations Test methods

1 Chemical composition 1/furnace GB/T 20066

GB/T 223 (all parts), GB/T 8647 (all parts), GB/T 11170,

GB/T 20123, GB/T 20125

2 Tensile test 1/lot On any welded pipe and tube, GB/T 2975 GB/T 228.1

3 Tensile test on welded joints 1/lot On any welded pipe and tube, GB/T 2651 GB/T 2651

4 Delivery hardness 1/lot On any welded pipe and tube

GB/T 230.1, GB/T 231.1,

GB/T 4340.1

5 Flattening test 1/lot On any welded pipe and tube GB/T 246