What is the reason of flange seal failure? How to prevent flange leakage?

Analysis of leakage of flange seal  and its Prevention 

Abstract: By analyzing the causes of leakage of flange seal, find out the prevention and solution.

Key words: flange  seal  leakage

Flange connection is widely used in the pipeline connection, such as  in gas, oil, water supply and drainage pipes. There many different types of flanges such as SAE flanges (code 61/62 flanges), Slip on flanges, Lapped flanges, Weld neck flanges, and so on.

As the leakage of flange seal can cause the transmission of materials, gas leakage, pollution, and even cause a major fire or personal injury accidents, it must pay attention to the flange seal. This paper analyzes the factors that cause leakage of flange  and puts forward the solution to the solution.

First, the flange

1,  Sealing surface of flange exists in several forms

(1) Flat sealing surface is a smooth plane, usually in the plane with 2-3 concentric groove, tighten the bolt, the gasket material is easy to both inside and outside the squeeze, not easy to compact, only for the pressure is not high , Non-toxic media, non-flammable and explosive occasions.

(2) The concave-convex sealing surface consists of a concave surface and a convex surface, this sealing surface gasket is easy to center, when compress it ,the gasket will not squeeze out.So it can be used for slightly higher pressure occasions.

(3) The tongue and groove sealing surface consists of a tenon and a groove surface, the gasket placed in the tank, will not be squeezed and moved, because the gasket is narrow, the gasket clamping force correspondingly smaller, its shortcomings is the complex of structure and manufacturing , replace the gasket is also more trouble. Generally used for flammable, explosive, toxic media and high pressure occasions.

2, The requirements for flange sealing surface

The requirements for flange sealing surfaces are primarily the roughness of surface. The use of metal gasket sealing surface, the roughness value of flange surface  is required to be smaller; and the use of soft gasket sealing surface, the roughness value of flange surface is too small but not good, because at this time the interface leakage resistance becomes smaller , Prone to leakage. Flange on the surface of a few laps to seal the line (or waterline), but also to prevent leakage.

3, The stiffness of the flange

Flange should reach a certain stiffness.If the stiffness of the flange is insufficient, it will cause warping deformation or wave deformation, resulting in sealing failure.

The quality of the flange is the most important factor for flange seal, so it is very important to get the flanges from good quality suppliers. Younglee Metal Products Co., Ltd is one of the best Chinese SAE flange manufacture and supplier.

Second, the gasket

1, The performance of the gasket

Gasket is an important part of the flange seal, the gasket directly affects the sealing performance, especially for hydraulic flanges. Gasket material should be dense, not easy to impregnate the media, while tolerating temperature and pressure fluctuations and media corrosion. To have the appropriate deformation resilience and smaller permanent deformation, when the general rebound ability is big, the gasket not easy to penetrate the leak or corrosion aging.

2, The difference of flange and gasket hardness

Flange seal is mainly through the gasket to produce elastic or plastic deformation, which filled the flange surface of the small rugged, to prevent the interface leakage. So the hardness of the gasket should be lower than the flange, within the allowable range, the greater the difference between the two, the  easier to achieve the sealing.


Third, the bolt preload

When the flange is sealed, it is sealed by tightening the bolts to tighten the gasket. When tightening the bolts, the gasket is pressed by the flange so that the gasket is elastically or plastically deformed to fill the flattery of the flange surface. seal.

In the operation of the time, we can make the gasket left a larger seal pressure, to maintain a good sealed state. Bolt preload must be evenly symmetrically applied to the gasket.The preload is too small, the gasket can not stop leakage because it’s not pressed  , but the preload is too large and often make the gasket too large compression deformation, so that gasket loss of resilience or even damage.


Fourth, the use of conditions

The conditions of use mainly refer to the system’s pressure, temperature and physical and chemical properties of the medium.

The effect of simple pressure or medium factors on the seal is not the main. Only in combination with temperature, especially at high temperatures, will seriously affect the performance of the seal.

At high temperatures, the dissolved and corrosive effect of media on the gasket  is increased, increasing the possibility of leakage, flanges, bolts, gaskets may produce creep and stress relaxation, so that the seal pressure drop. If the temperature and pressure are changed,  the gasket will be tired, the seal will fail.

At low temperatures, due to the cooling speed of the flange and the bolt is not the same, the gasket preload will be unevenly reduced, plus the gasket at low temperature shrinkage and elasticity will accelerate the generation of leakage. This requires the use of conditions to be smooth, try to avoid the pressure and temperature fluctuations, in the use of a period of time and then tightly bolts, which is particularly important for high temperature and the use of hot and cold cycle .

Of course, there are many factors that affect the sealing performance of the flange, such as the mechanical damage of the flange surface or radial notation, the installation of two flange surface is not parallel, the pipeline is not flexible and stress.


Fifth, The installation

The surface of flange should be kept clean and no mechanical damage and corrosion damage and residual old gaskets are not allowed.

Check the roughness of the flange surface is appropriate, the protruding table  of  flange can be aligned, the gap between the two flange surface can not be too large, the parallel degree of two sealed plane must meet the requirements of the use of gasket.

Bolt load only can be used to press the gasket, and can not be used to draw the flange. Check the shape, material, size and bolt of the gasket to meet the specified requirements.

Place the gasket in the correct position, tighten the bolts evenly, and check that the assembly is correct. Bolts must be tightened symmetrically, for a certain bolt stress, we should use a pointer torque wrench to get the correct bolt preload, in the large flange can also be used hydraulic bolt tension measuring the amount of bolt extension.

Gasket need a certain degree of compression of the occasion, with a feeler to check whether the pad is tight to the appropriate level.

According to the use of high temperature and the use of hot and cold cycle occasions, the use of gasket after a period of time need to tight again. Non-metallic gaskets must be stored in dry and cool places, do not directly exposed to the sun or ozone, should be flat and can not hang on the hook.

For the storage period of more than two years ,should check whether it has been bad.The box for storage gasket  must be marked gasket material, form, size, flange temperature, pressure level and other technical data, so as to avoid the use of errors.


Six, concluding remarks

There are many reasons for the leakage of the flange seal, the above is based on the use of the scene to do a simple analysis, through continuous technical improvements and reasonable installation and use, the leakage of flange seal  will be greatly reduced.

This article is created by Younglee Metal Products Co., Ltd, anyone who reprinted the article should indicate the source URL http://www.sino-alloy.com/blog/analysis-prevention-of-leakage-of-flange-seal.html

Younglee Metal Products Co., Ltd is one  of the best manufacture and supplier of hydraulic SAE flanges, products including SAE socket weld flanges, SAE BSPP/NPT threaded flanges, SAE butt weld flanges, SAE Split flange halves, SAE flange clamps, SAE blind flanges and so on.