GB/T 24925-2019Low temperature valve—Technical specifications (English PDF)

3.1 Bonnet extension

The part from the uppermost end of the bonnet support to the bottom of the bonnet stuffing box.

3.2 Cryogenic treatment

The treatment process in which the parts are immersed in liquid nitrogen for cooling, and when the temperature of the parts is stable at -196 °C, the heat is kept for 2 h~4 h according to the thickness of the parts, and then taken out of the box to naturally return to room temperature.

3.3 Drip plate

The disc set at the bonnet extension to prevent condensate from entering the insulating layer of the extended bonnet.

3.4 Cold working pressure; CWP

The maximum allowable working pressure of the valve when the medium temperature is -20 °C~38 °C.

3.5 Internal cooling cycle

The method to make the low temperature medium flow through the inside of the test valve to reduce the temperature of the test valve.

5.1 General requirements

5.1.1 In addition to meeting the requirements of this Standard, the valve shall also comply with the corresponding valve product standards, such as GB/T 12234, GB/T 12235, GB/T 12236, GB/T 12237, GB/T 21387, JB/T 8527, JB/T 7746.

5.1.2 The pressure-temperature rating of the valve shall comply with the provisions of GB/T 12224 and JB/T 7746.

5.1.3 According to the contract requirements, the valve shall be provided with a drip plate.

5.1.4 The end connection of the valve can be flanged or welded. The flange shall comply with the provisions of GB/T 9113 and GB/T 13402. The welded connection shall comply with the provisions of GB/T 12224, or as required by the order contract. The structural length of the flange connection and welded connection valve shall comply with the provisions of GB/T 12221, or as specified in the order contract.

5.1.9 When using welded structure to design the pressure parts, it shall consider the welding performance of the material and the reliability of the weld at low temperature. The form of butt welded joint should be adopted.

5.1.11 Non-metallic seat valves for flammable and explosive media shall have anti-static structure. The design shall ensure that, the valve, opening-closing parts, and valve stem have electrical conductivity.

5.2 Performance

5.2.1 The normal temperature performance requirements and tests of the valve shall comply with the provisions of GB/T 26480.

5.2.2 The low temperature performance test of the valve shall be completed on a special rig. The test rig shall meet the requirements of JB/T 12003.

5.2.3 When required in the order contract, the flange and stem seal in the valve shall be tested for fugitiveness. The results shall comply with the requirements of Table 1.

5.3 Valve

5.3.1 Under the total load of the stress generated by the alternating pressure and temperature of the medium and the additional stress caused by the pipeline installation, the valve shall be able to maintain sufficient strength.

5.3.2 The minimum wall thickness of the valve shall not be less than that specified in GB/T 26640.

5.3.3 The cast flanged end valve shall be integrally cast; no flange shall be welded.

5.3.4 For the cast welded end valve, the flanged end valve shall not be used to become the welded end valve after removing the flange.

5.4 Bonnet

5.5 Stem

5.5.1 The diameter of the valve stem shall be determined by calculation. Under the conditions of meeting the operating strength, it shall also meet the stability requirements. Its dangerous section shall be set outside the pressure boundary above the stuffing box.

5.5.2 The surface roughness Ra value of the contact surface between the stem and the packing shall be no more than 0.4 µm.

5.5.3 The stem shall be able to transmit the necessary operating force to the valve closing member; be able to withstand the additional stress of the operating load.

5.9 Operation

5.9.1 Manual operation

5.9.1.1 When the manually-operated valve is operated and subjected to the performance test under low temperature conditions, the maximum operating force on the edge of handle or handwheel shall not exceed 360 N. When equipped with deceleration mechanism and actuator, it shall be adapted to the requirements of ambient temperature and working conditions.

5.10 Material

5.10.1 According to the working temperature and material properties, select the valve material. It shall meet the following requirements. […]

5.13 Nondestructive testing

5.13.3 Ultrasonic testing

Forged valve body, bonnet, and stem, etc. shall be subjected to ultrasonic testing. The inspection result shall not be lower than the requirements of level 2 in JB/T 6903-2008.

5.13.4 Magnetic particle testing

5.13.5 Degreasing treatment

When required in the order contract, the valve shall be degreased.

6.1 Marking inspection

The contents of the visual examination are as follows. […]

6.2 Visual quality of steel castings

Visual examination. Compare the drawing in JB/T 7927 with any surface of the casting. The comparison area of the casting surface shall be the same as the size of the picture. The comparison result shall meet the requirements of 5.11.

6.3 Dimensional check

6.4 Chemical composition

The material of the main pressure parts shall be analyzed for chemical composition. Each lot of materials with the same heat number shall be inspected at least once. The inspection results shall comply with the provisions of 5.10.3.

6.5 Mechanical properties

6.5.1 For each lot of materials of main pressure parts (the same heat number, the same manufacturing process, and the same heat treatment conditions), the mechanical properties shall be inspected at least once.

6.5.2 For the test methods and results of mechanical properties, refer to the corresponding material standards listed in Appendix A. It shall comply with the provisions of 5.10.3.

6.6 Normal temperature test

It shall be carried out in accordance with the provisions of GB/T 26480. It shall meet the requirements of 5.2.1. The chloride ion content of the hydraulic test medium for stainless steel valves shall not exceed 25 µg/g.

6.7 Low temperature test

6.7.1 Test requirements

The low temperature test shall be carried out after passing the normal temperature test.

6.7.2 Test conditions

6.7.2.1 Test medium

The test medium is shown in Table 7.

6.7.2.2 Cooling medium

The cooling medium is shown in Table 8 or as specified in the order contract.

6.7.2.5 Test preparation

Before the test, the valve parts shall be degreased and dried. The valve shall be installed in a clean and dustproof environment. Except for the primer, the valve shall not be painted.

6.7.3 Test procedure

6.7.3.1 The normal temperature test uses nitrogen or air as the initial detection test, to ensure that the valve is tested under appropriate conditions.

6.7.3.2 The typical test device of low temperature valve is shown in Figure 13.

Install the valve in the test container; connect all the joints, to ensure that the valve packing gland is located above the lid of the incubator.

6.7.3.3 Before the valve starts to cool, use 0.2 MPa helium medium to continuously purge the valve cavity, to replace the air in the valve cavity.

6.7.4 Test procedure of check valve

6.7.4.1 The valve test device is shown in Figure 13. The test device shall be able to reverse the gas source and the measurement system. According to the opening direction, the check valve is installed in the test container. All joints are connected.

6.7.4.2 In accordance with 6.7.3.1, perform the initial system verification test on the marked flow direction of the check valve.

6.9 Nondestructive testing

6.9.1 Radiographic testing

Radiographic testing is carried out in accordance with the provisions of JB/T 6440-2008 and NB/T 47013.2-2015. The inspection result shall meet the requirements of 5.13.1.2.

6.9.2 Penetrant testing

Penetrant testing of the overlaying-welding surface is carried out in accordance with the provisions of GB/T 22652. The others are carried out in accordance with the provisions of NB/T 47013.5-2015. The inspection result shall meet the requirements of 5.13.2.

6.9.3 Ultrasonic testing

Valves with a nominal size greater than DN25 are tested in accordance with the provisions of JB/T 6903-2008. The forged valve body, bonnet, and stem, etc. are subjected to ultrasonic testing piece by piece. The testing results shall meet the requirements of 5.13.3.

6.9.4 Magnetic particle testing

6.9.4.1 The parts of ferromagnetic materials such as valve body and bonnet shall be subjected to magnetic particle testing.

6.9.4.2 The magnetic particle testing method of steel castings is in accordance with the provisions of JB/T 6439-2008. The magnetic particle testing method of forgings is in accordance with the provisions of NB/T 47013.4. The inspection results shall meet the requirements of 5.13.4.2.

6.10 Anti-static test

A new and dry valve shall be subjected to no less than 5 cycles of opening and closing operation. It shall use a DC power supply not exceeding 12 V for resistance measurement. The measurement result shall meet the requirements of 5.1.11.

7.1 Inspection items

7.1.1 The inspection of low temperature valves is divided into exit-factory inspection and type test.

7.1.2 The inspection items, technical requirements, and test methods shall be in accordance with Table 10.

7.2 Exit-factory inspection

Valves shall be subjected to exit-factory inspection one by one. Only after passing the inspection, can it leave the factory.

7.3 Type test

7.3.1 In one of the following situations, the prototype shall be type tested. The mass production can only be carried out after the test is passed.

7.3.2 When the type test is required by the technical agreement, the type test shall be conducted by sampling. Samples can be randomly selected from the products, which pass the inspection, at the end of the production line; or randomly selected from the finished product warehouse. Or 1 piece is randomly selected from products, which have been supplied to users but have not been used and remain in the exit-factory state. During the quality assessment of the entire series of products, according to the range of this series, 2 or 3 typical specifications are selected therefrom for testing.

7.3.3 All test items of the type test shall meet the requirements of Table 10.