What is Blind Flange?
A blind flange has no hole in its center, resulting in there is no fluid or gas through it. It is usually installed at the end of a piping system to terminate a pipe, as well as used for isolating a pipe, valve or pressure vessel. In addition, it is available in all sizes and classes, and has several sealing faces including raised face (RF), flat face (FF) and ring-type joint face (RTJ). RF and FF are more common in basic sealing applications, with RTJ being the preferred choice for high pressure applications.
A blind flange is bolted, rather than welded in place, which makes piping systems more accessible when maintaining, inspecting or future expansion. It paired with a gasket can create a tight seal, that is, the gasket fills the space between the flange faces, which can effectively prevent liquid or gas leakage.
The most important consideration when selecting blind flanges is the thickness. They are available in the same pressure classes and bolt hole patterns as other flange types, but they tend to be thicker. Blind flanges can be made of carbon steel , stainless steel, alloy steel , etc. Carbon steel and alloy steel are preferred for high strength. Stainless steel flanges are often preferred for corrosion resistance.
Applications
Blind flanges are widely used for the pipeline connections of petroleum & gas, petrochemical, water engineering, ship building, seawater cleaning, construction etc.
Technical Specifications
Blind flange has many sizes no matter for carbon steel or stainless steel. The following information is just about their sizes and tolerances.
Blind Flange type According to sealing face
Blind Flange materials
Carbon steel blind flange
Carbon steel blind flange is made of carbon steel, which is usually stronger than stainless steel flanges. However, it is easy to rust when it encounters water or humid air, thus reducing its service life. The common materials refer to ASTM /ASME A105, A350 LF1, LF2, A694, F46 to F70.
Stainless steel blind flange
Stainless steel blind flange is made of stainless steel, which is better than carbon steel flanges in acid and alkali resistance and corrosion resistance, but its price is more expensive. The common materials refer to ASTM / ASME A182 F304/L, F316/L, 310/S, 327/H,904L, etc.
Alloy steel blind flange
Alloy steel blind flange is mainly made of alloy steel, carbon steel and stainless steel. It combines the advantages of carbon steel and stainless steel, with higher strength and corrosion resistance. The common materials refer to ASTM / ASME A/SA 182 & A 387 F1, F5, F9, F11, F12, F22, F91.
Blind Flange manufacturing technique
Casting blind flange
The shape of the casting blind flange is accurate, has a small processing capacity, and the cost is low. However, there are casting defects, such as air holes, cracks, inclusions, and the flow line of the inner casting part is bad, even the streamline is worse if it is a cutting part.
Forging blind flange
Forging blind flange generally has lower carbon content than casting blind flange, which is not easy to rust, and has better streamlined shape, denser structure and better mechanical properties. However, if the forging process is improper, the grain will be large or uneven, and there will be hardening cracks.
Quality Assurance
1) Raw material testing: Conduct chemical analysis and inspection of flange raw materials and retain the certificate
2) After cutting the material, inspect the cut surface and detect the weight.
3) Strictly control the forging temperature during the blind flange forging process
4) Perform heat treatment such as normalizing and tempering on the blind flange
5) After production is completed, perform dimensional and non-destructive testing on the flange.
6) Anti-rust treatment before packaging