Product Name：NBT47021-2012
1.Scope
This standard specifies the structural type and series size of the A-type flat welded flange for steel pressure vessels.
This standard is applicable to steel pressure vessel A flat welding flange with nominal pressure of 0.25MPa~1.6MPa and working temperature higher than -20°C~300°C.
2. Normative references
The following documents are indispensable for the application of this document. For dated references, only the dated version applies to this document. For undated references, the latest edition (including all amendments) applies to this document.
NB/T 47020 Pressure vessel flange classification and technical conditions
NB/T 47024 non-metallic soft gasket
NB/T 47027 Pressure Vessel Flange Fasteners
3. Structure type and size
The structural type and series size of the A-type flat welding flange of various sealing surfaces shall comply with the requirements of Figure 1~4 and Table 1. The quality of the flange and the lining ring are listed in Table 2
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The flange pre-tightening bolt connects the gasket and the flange. For flange sealing occasions with octagonal gaskets or oval gaskets, in terms of technology, the general requirement for flange pre-tightening bolts is to load gradually around the circumference, so that the gasket is gradually and evenly embedded in the flange sealing groove to ensure that the gasket does not locally deform ; The pre-tightening force of each bolt reaches the specified value. For the tightening process of this kind of bolts, the current process is to use a torque wrench to achieve loading, and the torque value displayed by the torque wrench is indirectly converted into the pre-tightening force of the corresponding bolt.
This torque method can achieve the control goal intuitively, the measurement is easy, the operation process is simple, and the control program is simple, but it fails to consider the frictional resistance between the components and the frictional resistance in the bolt assembly is not completely consistent, so that the preload is dispersed. The process requirements of large, uniform preloading process cannot be reliably guaranteed. Therefore, the control accuracy is low, which has a greater impact on the sealing effect of the butt flange, and directly affects the long-term, reliable and stable operation of the equipment.
Precautions for the use of non-standard flanges:
1. Non-standard flange gas must be strictly dust removed and compressed air dry and purified. The operating pressure of the actuator is a calibrated torque of 0.5mpa, and the air pressure is >0.55mpa, otherwise the output torque will be reduced and small due to the operating pressure.
2. Valve leakage should be found to further tighten the cylinder head screws or seals, gaskets, or affect the output torque, which occurs in serious cases.
3. If the work of the non-standard flange is found to be invalid, it should be carefully checked and repaired. The main reason is that the gas is not clean, so the cylinder and piston are stuck. Some cleaning work can be done, but strong movement should be avoided. Expand the surface of the damaged cylinder, and it is necessary to replace the damaged parts when the surface of the meat swing arm cylinder is found to be severely scratched.
4. The best repair time for the valve to work for more than 6 months is to clean or replace the sealing ring, which will extend the service life.
5. If the filter is cut off, the non-standard flange valve must be opened, and the service life is guaranteed.
