The Comprehensive Knowledge of Flanges

This article talks about the comprehensive knowledge of flanges.

Flange is an important part of connecting pipe and pipe. It is connected to the pipe end. There are holes on the flange. The two flanges are connected tightly with wear-resistant bolts, and the flange is sealed with gasket.

There are two connection modes between container parts: non detachable (welding) way and detachable way. Due to the needs of production process. In order to facilitate manufacturing, transportation, installation and maintenance, detachable flange connection is often used between cylinders and cylinder heads, pipelines and valves. Removable structure includes flange connection, thread connection, socket connection, etc. But flange connection has the unique advantages of reliable sealing, high strength and wide application range, which is widely used in chemical and pharmaceutical equipment and pipelines.

Flange connection structure and flange seal:
Working mechanism: the gasket between the flange sealing surfaces is compressed and reinforced by pre tightening bolts to fill the uneven gap on the flange sealing surface. It can prevent the medium from leaking through the pores on the gasket and the interface between the gasket and the sealing surface, so as to realize the sealing.

The conditions to ensure the sealing of flange connection are as follows: when preloading, the preload specific pressure acting on the gasket shall not be lower than the preloading specific pressure. When operation, the residual specific pressure acting on the gasket shall not be lower than the specific pressure of working seal.

Flange types:
1. Slip on flange: it is suitable for low temperature and low pressure. (specific temperature and pressure values are included in the standard)
2. Welding neck flange: it is suitable for high pressure, high temperature, toxic, flammable, explosive and other important occasions. Its cost is high.

Difference between slip on flange and welding neck flange:
Different welding forms: radiography is not allowed for flat welding seam, but butt weld can be used. Flat welding seam is composed of two fillet girth welds, and butt weld is one butt girth weld.
Different nominal pressure: the nominal pressure of welding neck flange is 0.6-4.0mpa, and the nominal pressure of welding neck flange is 1-25mpa.
Features: flange is connected with pipe or vessel, which is suitable for low pressure occasions. There is no additional bending stress on non-ferrous metal, stainless steel equipment and pipe shell; carbon steel manufacturing can save precious metal consumption, but the rigidity of loose flange is poor.

1. Threaded flange
It is widely used in small diameter high pressure pipeline, and the additional stress of flange to pipe wall is small.

2. Flange shape
Generally speaking, the shape of the flange has the disk shape or the disk shape with the neck. There are also some square or oval (waist). Other shapes also have square flange, elliptical flange, round flange.

Factors affecting flange sealing:
The main factors affecting flange sealing are bolt preload, sealing surface form, gasket performance, flange stiffness and working conditions.

Sealing surface forms:
Plane type: simple structure, convenient processing, easy anti-corrosion or lining. But the gasket is easy to squeeze and not easy to compress. It is suitable for low pressure and in a small volume. It is non-toxic, and it has low sealing requirements.
Concave convex type: good neutral and good sealing performance. It is suitable for medium and high temperature occasions.
Tenon and groove type: reliable sealing, small gasket width and small pressure. It is suitable for inflammable, explosive, toxic, high pressure occasions. And it is difficult to handle and repair.