GB/T 38343-2019Technical specification for flange joints installation (English PDF)

4.1 General

The strength and rigidity of flange joints under the design conditions and installation conditions shall be respectively evaluated in accordance with 4.2 and 4.3, and the sealing performance under the operating conditions shall be evaluated in accordance with 4.4, and the bolt installation load shall be determined accordingly.

4.3 Strength and Rigidity Evaluation of Flange Joints under Installation

Conditions

4.3.1 Bolts

4.3.1.1 Under installation conditions, the bolt installation stress SB shall not exceed 70% of the bolt material yield strength (at installation temperature). The actual bolt installation stress (including installation load deviation) shall not exceed 90% of the bolt material yield strength (at installation temperature).

4.3.2 Gaskets

4.3.2.1 Under installation conditions, the total bolt installation load (WA) is equal to the compressive load on the gasket contact surface (Aa). The compressive stress (QA) on the gasket contact surface shall not be greater than the maximum crushing stress (Qmax) of the gasket, see Formula (1).

4.3.2.2 The maximum crushing stress Qmax of non-metallic flat gaskets shall comply with the following provisions.

4.3.3 Flanges

4.3.3.1 Under installation conditions, the flange shall not produce deformation that affects the seal, and a comprehensive evaluation shall be carried out in accordance with the provisions of 4.3.3.2, 4.3.3.3 and 4.3.3.4.

4.4 Evaluation of Sealing Performance of Flange Joints under Operating

Conditions

4.4.1 Under installation conditions, the bolt installation load is the basis for the flange joint to have pressure-bearing - sealing capabilities. As the operating temperature increases and time goes by, due to the combined effects of stress relaxation of the bolt material, gasket creep and flange sealing surface deflection, etc., the bolt installation load will relax and attenuate.

4.4.5 When the user or design has other leakage control requirements or reliable performance parameters (such as. Qmax, Qsmin, RJ, etc.), the corresponding minimum bolt installation stress SBmin can be calculated in accordance with Formula (3), but it shall be indicated in the design documents and installation procedure documents.

4.5 Bolt Installation Load

4.5.1 The maximum bolt installation load is determined as follows. 4.3.1.2, set the bolt installation target stress.

4.5.3 When using different tightening tools and tightening methods, the actual bolt installation load will have certain deviations.

5.1 General

The use of maximum bolt installation load control technology can improve the bearing capacity of flange joints, increase the anti-relaxation margin of flange joints, and reduce the leakage rate of flange joints.

5.2 Fasteners

5.2.1 In addition to the selection of fasteners for standard pipe flange joints, which shall comply with the corresponding provisions of HG/T 20592~20635, flange joints assembled using the maximum bolt installation load control technology shall preferentially use high-strength bolts (studs) in accordance with the provisions of 4.3.1. Except for cast iron, non-metallic flanges or rubber gaskets, low-strength bolts (studs) shall not be used.

5.3 Gaskets

5.3.1 In addition to the gasket selection for standard pipe flange joints, which shall comply with the corresponding provisions of HG/T 20592~20635, flange joints assembled using the maximum bolt installation load control technology shall also comply with the additional requirements of 5.3.2~5.3.5.

5.3.2 The stress relaxation coefficient PQR of non-metallic flat gaskets or semi-metallic gaskets at the maximum operating temperature shall be greater than or equal to 0.7. The maximum operating temperature of the gaskets shall comply with the following requirements.

5.3.3 The maximum crushing stress of non-metallic flat gaskets shall comply with the provisions of 4.3.2.

5.3.4 Metal spiral wound gaskets shall comply with the following additional requirements.

5.3.5 Octagonal gaskets shall comply with the following additional requirements.

5.4 Flanges

5.4.1 In addition to the standard pipe flanges, which shall comply with the corresponding provisions of HG/T 20592~20635, the selection of flanges shall also comply with the provisions of 5.4.2 ~ 5.4.4.

5.4.2 The rigidity of the flanges shall be improved, and necked butt-weld flanges, necked slip- on flanges, integral flanges and socket-weld flanges with greater rigidity shall be selected.

When using the maximum bolt installation load control technology for assembly, threaded flanges and plate-type flat-weld flanges shall not be used.

5.4.3 The nominal size of socket-weld flanges shall not be greater than DN50.

6.1 General

6.1.1 This Chapter specifies the basic content of the installation process of flange joints of pressure-bearing equipment. Before installation, an installation procedure document shall be compiled in accordance with the specific operation conditions, and the installation personnel shall rigorously install the corresponding flange joints in accordance with the provisions of the installation procedure document.

6.1.3 When the assembled flange has deviations exceeding the limits, forceful assembly is not allowed.

6.1.4 The bolt tightening tools used for installation shall be regularly verified or calibrated, and used within the validity period.

6.1.5 The calibration of bolt installation load and bolt elongation shall comply with the following provisions.

6.1.6 The exposed bolt thread parts on the flange joint shall be protected with a suitable lubricant to facilitate the subsequent removal of the flange joint.

6.1.7 After installation is completed, installation records, inspection and maintenance records shall be kept in a timely manner.

6.2 Installation Preparation

6.2.2.4 The contact surface between the flange and the nut or gasket shall be flat, and without visible uneven wear, severe dents and scratches, etc.

6.2.1 Cleanup

6.2.1.1 Use tools or suitable solvents to clean various marks, paint, grease, protective coatings, dirt, etc. remaining on the flange sealing surface to prevent soils from damaging the surface roughness of the flange sealing surface. Do not use carbon steel brushes to clean stainless steel flange sealing surfaces.

7.1 Inspection of Flange Joint after Installation

After the flange joint is installed, the following inspections shall be performed.

7.2 Pressure Test and Sensitivity Leakage Test of Flange Joints

7.2.1 After installation, each flange joint shall be checked for leakage during the pressure test of the pressure equipment.

7.2.2 When required by the user or designer, sensitivity leakage test shall be carried out. The test methods and requirements shall comply with the provisions of GB/T 20801.5.