What is a Blind Flange?

by yane Yang Sales Manager

Blind flange is a kind of a solid round plate with no center holes but with uniformly distributed bolt holes along the periphery of the plate. It is used for covering or closing the end of a pipe or conveniently cleaning sundries in pipelines for pipeline maintenance. Blind flanges have the same function as shell covers and pipe caps except minor differences—shell covers cannot be disassembled if installed while blind flanges are fastened by bolts and easily dismantled. Sealing faces of blind flanges can be categorized into several kinds: flat face (FF), raised face (RF), male and female face (MFF), ring joint face (RTJ), tongue and groove face (TG), etc. Materials of blind flanges include carbon steel, alloy steel, stainless steel, plastic, copper, aluminum, etc. A blind flange is a solid disk used to block off a pipeline or to create a stop. It is machined in the same manner as a regular flange with the mounting holes around the perimeter and the gasket sealing rings machined into the mating surface. The difference is that a blind flange has no opening to allow fluid to pass through. The blind flange can be inserted between two open flanges and used to block off the flow of liquid through a pipeline.

Categories of blind flanges

From the perspective of appearance, blind flanges can be divided into blind plate flanges, figure 8 blind flanges (also called spectacle blind flanges) as well as paddle blanks and paddle spacers, among which paddle blanks are generally used in conjunction with paddle spacers.

Production processes of blind flanges

There are four production processes of blind flanges: striking & forged, cast-forged, medium plate cutting and casting.

Function of blind flanges

Blind flanges have the same block-off function as shell covers, pipe caps and welding pipe plugs. Due to good sealing performance, they provide an ideal and reliable solution for the systems requiring complete sealing. Among various kinds of blind flanges, figure 8 blind flanges are shaped like Arabic number 8, with blind plate at one end and restrictor ring at the other end. Restrictor rings have the same diameter as pipelines but has no throttling function. Figure 8 blind flanges are easy to use: when sealing is required, blind plate can be used, while when normal operation is needed, restrictor ring can be used. In addition, restrictor rings can be also used to fill the clearances after mounting blind plates. Blind flanges should not be galvanized when used in systems with oil as medium but should be hot-dip galvanized in systems with other media. The minimum hot dip galvanized coating weight is 610g/m2, based on CB*/Z343 standard.

The blind flange does not have a bore. It is used to blind off a flange or even a valve. When used at the end of a pipe or fitting, it provides an easy to open access for further extension of the pipe. The blind flange and its bolts are stressed more than any other flange. This flange has a raised face.

Often a blind flange is inserted into a pipeline when a repair is required further up the line. This allows the flanges down stream to be disconnected without fear of losing liquid. Many times this type of blockade is used when adding another line onto an existing pipeline or when a new valve is being added. This blockade is also used to shut down a line when it is no longer needed.

Without the blind flange it would be difficult to perform maintenance or repairs on a pipeline. The flow would need to be shut off at the nearest valve, which could be miles away from the repair area. Valves are also very expensive and are prone to sticking. The blind flange is a much more cost efficient way of sealing a pipe.

When a pipeline is being constructed, a blind flange is often incorporated into the final length of pipe. This design allows for expansion or continuation of the pipeline by simply adding onto the final flange. This holds true for the addition of tees in the pipeline as well. A tee can be installed and then blocked in order to leave the option of running a pipe at a later date.

The use of flanged pipe has allowed pipelines to be built in a much faster manner than traditional welded seam pipelines. Moreover, it has made the task of repair and sectional replacement a simpler job. Sections of pipe can now be assembled anywhere in the world and shipped to the job site. Once there, they can simply be bolted into place and the pipeline can resume transportation of its liquid cargo.

Source: China Flange Manufacturer: Yaang Pipe Industry Co., Limited (www.yaang.com)