Flat welding flange and butt welding flange are common integral flanges of large flanges. Flat-welded flange has poor rigidity, which is suitable for pressure P < 4 MPa. Butt-welded flange is also called high neck flange, which has high rigidity and is suitable for high pressure and temperature occasions. There are three types of flange sealing surface: flat sealing surface, which is suitable for situations with low pressure and non-toxic medium; concave and convex sealing surface, which is suitable for situations with slightly higher pressure; mortise sealing surface, which is suitable for situations with flammable, explosive, toxic medium and high pressure. Flanges & pipe fittings of different properties have good product performance in different fields, and the effect will be different when the occasion and space are different.
The gasket of large flange is a ring made of material which can produce plastic deformation and has certain strength. Most gaskets are cut from non-metallic sheets or made by specialized factories according to specified sizes. The materials are asbestos rubber sheets, asbestos sheets, polyethylene sheets, etc. There are also metal-clad gaskets made by wrapping asbestos and other non-metallic materials with thin metal sheets (white iron sheets, stainless steel); and there are winding gaskets made of thin steel strips and asbestos strips.
The selection of stainless steel flange must meet the design requirements. When the design is not required, the appropriate form and specification of the flange should be selected according to the system’s maximum working pressure, maximum working temperature, working medium, material grade of flange and other factors.
Flanges must be inspected before installation. The surface should be smooth. There should be no defects such as sand holes, cracks, spots and burrs to reduce the strength of flanges. There should be no defects such as penetrating scratches on the sealing surface that affect the sealing performance.
When assembling flange and pipeline, the verticality of flange is checked by flange ruler. When the design of parallel deviation dimension of flange connection is not specified, it should not be greater than 1 or 5% of the flange outer diameter, and not more than 2 mm. When the two flanges are not parallel and exceed the specified requirements, it must be trimmed and not be corrected by using multiple gaskets.
When the flange is welded to the pipeline, it should be welded on both sides according to the standard, and the height of the welding foot should be in accordance with the regulation.
With the rapid development of long distance pipeline construction at home and abroad, pipeline pressure testing has become an indispensable important link. Before and after pressure testing, it is necessary to sweep each pipeline globally, the number of times is generally 4–5. Especially after pressure test, it is difficult to clean the water stored in the pipeline, and the times of cleaning will be more. There are some problems in the construction method of repeated welding head at ball receiving place: firstly, to increase the labor intensity of workers; secondly, the method of repeated welding head has high consumables, many times of large-scale equipment and high cost.
In order to solve the problems of high labor intensity, high consumables, many times of large-scale equipment and high cost when the long-distance pipeline is swept through the ball after pressure test, a new construction method of quick opening large-scale flange blind plate is proposed. The construction method introduces the structure, working steps and strength checking of the fast opening blind plate.
Through the application in Shining-Lan gas pipeline project, it is proved that the construction method of quick opening blind plate is three times more efficient than the construction method of repeated welding head, which not only reduces the labor intensity of workers, but also reduces the cost. Carbon steel flange needs to do some preparatory work before measurement, according to a certain way and method of measurement, according to the specific situation to determine different measurement methods, to ensure the accuracy of measurement.
1. According to the position of large flange before measurement, first of all, we should draw the sketch of connecting large flange of equipment, and serial number, so that fixture can be installed in accordance with a certain way and principle to ensure normal use.
2. Because the outer diameter of carbon steel flange may be different, the wrong orifices (different centers) and the thickness of gaskets are different, the fixture processed should not be interchangeable with the side carbon steel flange, so measuring the size and number of each part is the key to fixture processing and installation.
3. When measuring, it is best to arrange three persons, two of whom should check and fill in the form, and vernier calipers should be used for measuring tools. If there is no condition to use external calipers and steel plate calipers, measurement is a meticulous work and a prerequisite for fixture installation. Measurement and record must be prepared correctly and carefully when filling in the form. In actual measuring work, they should cooperate with each other and be able to proceed according to the correct principle. Line coordination and use.
