Flat welding flange

Flat welding flange is commonly referred to as the flat plate, also called lap welding flange. The connection between the flat welding flange and the pipe is to insert the tube into the flange hole to the proper position and then weld it again.

Flat welding flange is suitable for low pressure level, pressure fluctuation, vibration and concussion are not serious pipe system. The advantages of flat welding flange are easy to be used in welding and assembly of welding flange, and the price is cheaper, so it is widely used.

The characteristics of flat welding flange: the flat welding flange not only saves the space, reduces the weight, but more importantly ensures that the joint area does not leak and has good sealing performance. The compact flange size is reduced by reducing the diameter of the sealing part, which will reduce the cross-section of the sealing surface. Second, the flange gasket has been replaced by the sealing ring to ensure that the seal faces the sealing surface match. In this way, it only takes a little pressure to compress the cover. As the pressure required to reduce, the size of the bolt and the required quantity can be reduced accordingly, so the final design out a small volume and light weight (70% ~ 80% reduction in weight than traditional flange) of new products. Therefore, the flat welding flange is a kind of high quality flanged product, which reduces the quality and space and plays an important role in industrial use.

The sealing principle of flat welding flange: the two sealing surface of the bolt extrude flange gasket and form seal, but it also causes sealing damage. To keep the seal tight, it must maintain a large bolt force. For this purpose, the bolt must be larger. Larger bolts match larger nuts, which means larger bolts are needed to create conditions for tightening nuts. However, the larger the diameter of the bolt, the suitable flange will become bent. The good method is to increase the wall thickness of the flange. The whole device will require a great deal of size and weight, which becomes a special issue in the offshore environment, because in this case the weight is always the main concern. And, fundamentally, flat welding flanges are an ineffective seal that requires 50 percent of the bolt load to be used to squeeze the gaskets, while the load that is used to keep the pressure is 50 percent.

Flat welding flange and pipe connection way of welding, the flat welding flange welding with one-side welding does not need to welded pipe and flange connection inside the mouth, the welding of butt welding flange installation requires flange welding by both sides. So flat welding flange is generally used in low and medium pressure piping, used for medium and high pressure pipe butt welding flanges, butt welding of flange is usually at least PN2.5 MPa, the butt welding is to reduce the stress concentration, generally the butt welding of flange with flange neck flange is also called the nipple. Therefore, the installation charge of welding flange, the cost of labor and auxiliary materials is high, because of many processes.

Precautions for use of flat welding flange products:

1, in order to prevent the result of the flange cover heat corrosion between eyes, welding current should keep shoulds not be too big, than carbon steel electrode is less than 20%, the arc shoulds not be too long, the interlayer cold quickly, with narrow bead advisable.

2, electrode should maintain its dry, when using titanium calcium type should be maintain 150 ℃ dry for 1 hour, low hydrogen type a should keep 200-250 ℃ dry for 1 hour, to prevent the covering viscous oil and other dirt, so as not to cause weld increased carbon content and affects the quality of weldment.

3. When welding of flanged flange pipe, it is repeatedly heated and precipitated out of carbide, reducing corrosion resistance and mechanical properties of products.

4. The flanged flanged flange of chrome-flat welding flange is larger and prone to cracks. If using the same type of chromium stainless steel electrode (G202, G207) welding, must be above 300 ℃ preheat and 700 ℃ or so slow cooling after welding. If the welding piece cannot be done after welding, the welding rod (A107 and A207) of the flanged flange shall be used.

5. Flat welding flange, to improve the corrosion resistance and welding property, the appropriate amount of stable element Ti, Nb, Mo and so on, welding property is better than chrome plain welding flange. Based on the same type of chromium flat welding flange electrode (G302, G307), should be above 200 ℃ preheat and around 800 ℃ tempering treatment after welding. If the welding part cannot be treated, the welding rod of the flanged flange shall be used (A107, A207).

Main functions of flat welding flange:

1. Connect the pipeline and maintain the sealing performance of the pipeline;

2. Facilitate the replacement of a certain pipeline;

3. Easy to disassemble the inspection pipeline;

4. Facilitate the closure of a certain section of the pipeline.