valve connection pipe flange precautions
The flange surface of the valve and piping should be free of damage, scratches, etc. and kept clean. In particular, when using metal gaskets, the flange groove should match the gasket, and be coated with red tannin for research, to ensure that its sealing state is good.
The verticality of the flange surface and the centre line of the pipeline and the error of the flange bolt hole should be within the allowed value. The centre line of the valve and the pipeline should be consistent before installation.
When connecting two flanges, first of all, the flange sealing surface and gasket should be evenly compressed, thus ensuring that the flange is connected by the same bolt stress.
When tightening the bolts, use the spanner that matches the nut, when using hydraulic and wind tools for tightening, take care not to exceed the specified torque.
The tightening of the flange should avoid uneven force, and should be tightened in a symmetrical, cross direction sequence.
After installation of the flange, confirm that all the bolts and nuts are fastened evenly.
The material of the bolts and nuts should be in accordance with the regulations. After tightening, the bolt head should be exposed from the nut in two pitches as appropriate.
To prevent loosening due to vibration, use washers for fastening of bolts and nuts. In order to avoid adhesion between threads at high temperatures, the threaded parts should be coated with anti-adhesive during installation.
For high temperature valves above 300°C, tighten the flange connection bolts, bonnet fastening bolts, pressure seal and packing gland bolts again after the temperature rises.
When the valve is installed at low temperature, it is in the state of atmospheric temperature, due to the formation of temperature differences, flanges, gaskets, bolts and nuts, etc. shrinkage, and because the material of these parts is different, their respective coefficients of linear expansion are also different, forming a very easy to leak environmental conditions. From this objective point of view, when tightening bolts at atmospheric temperature, a torque that takes into account the shrinkage of each component at low temperatures is used.