In this article, the following types of flanges are covered.
The pipe flanges are the second most used joining method after welding. They are used when joints need dismantling. It provides flexibility for maintenance. Flange Connects the pipe with various equipment and valves. Breakup flanges are added to the pipeline system if regular maintenance is required during plant operation.
A flanged joint comprises three components; flanges, gaskets, and bolting and assembled by a pipefitter. Special controls are required to select and apply all these elements to attain a joint that has acceptable leak tightness.
However, using a flange connection in underground piping is not advisable when it is supposed to be buried. The flange is also the most common source of leaks and fire in a process plant. There are a variety of flanges available to suit the requirements. A flange can be classified in several alternate ways based on the following:
A threaded Flange is also known as a screwed flange, and it has a thread inside the flange bore which fits on the pipe with a matching male thread on the pipe. This type of joint connection is speedy and simple but not suitable for high pressure and temperature applications. Threaded Flanges are mostly used in utility services such as air and water.
Socket-Weld Flanges have a female socket in which the pipe is fitted. Fillet welding is done from outside on the pipe. Generally, it is used in small bore piping and is only suitable for low pressure and temperature application.
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Slip-On flange has a hole with a matching outside diameter of pipe from which pipe can pass. The flange is placed on pipe and fillet welded from both inside and outside. Slip-On Flange is suitable for low pressure and temperature application.
The lap flange has two components: a stub end and a loose backing flange. The stub end is butt-welded to the pipe, and the backing flange freely moves over the pipe. The backing flange can be of a different material than stub material and normally of carbon steel to save the cost. A lap flange is used where frequent dismantling is required, and space is constrained.
Weld neck flange is the most widely used type in process piping. It gives the highest level of joint integrity as it is butt-welded with a pipe. These types of flanges are used in high pressure and temperature application. Weld neck flanges are Bulky & costly with respect to other types of flanges.
The blind flange is a blank disc with a bolt hole. These flanges are used with another type of flange to isolate the piping system or terminate the piping as an end. Blind flanges are also used as a manhole cover in the vessel.
A reducing flange is used in place of a standard flange to allow for a change in pipe size. This flange eliminates the need for a standard reducer in piping. The flange consists of one specified diameter with a smaller diameter bore size.
Except for the bore and hub dimensions, a reducing flange has dimensions of the standard pipe flange size and is considered economical to make a pipe size transition.
These flanges are available in weld neck, slip-on, and threaded end types. Reducing flanges are an economical way to make transitions between pipes of different sizes, however, due to high-pressure loss, they are rarely used in piping. ASME B16.5 covers the dimensions of reducing flanges.
Image source: www.msmmfg.com
It is similar to a weld neck flange but increases the size of the pipe to the first or second larger size. It is an alternative to using a reducer and weld neck flange. Useful for connecting to valves, compressors, and pumps.
These flanges are specially designed. Dimensions of the weld neck are in line with the connecting pipe, other dimensions are in accord with standard ASME B16.5 flanges.
Expander flangeImage source: www.msmmfg.com
Flangeolet is a combination of two olets (mainly weldolet or nipple) and a flange as you can see in the image that the hub length is longer, like a long neck weld flange. It is a 90 Degree branch connection used for high-pressure piping.
It reduces the two weld joints more than the traditional Olet + Pipe + Flange connection and one weld joint in the case of the Olet + Flange connection. You can see the image of the flangeolet branch.
FlangeoletDepending on the flange facing Types, it can be further classified as
As the name suggests, the flat face flange has a flat face. Flat face flanges are used when the counter-flanges are flat faces. This condition occurs mainly in connection to Cast Iron equipment, valves, and specialties. A full-face gasket is used when a flat face flange is used.
Raised face flange has a small portion around the bore raised from the face. The gasket seat on this raised face. The height of the raised face depends on the flange pressure-temperature rating, known as a flange class. For 150# & 300# height of the raised face is 1/16”, and above 300#, it is 1/4”. The inside bore circle type of gasket is used with a raised face flange.
Ring joint type face flange has a specially designed grove in which metal gasket seats. This type of flange is used in high pressure and temperature services.
RTJ, Raised and flat faceFlanges are welded to pipe and equipment nozzle. Accordingly, it is manufactured from the following materials;
The list of materials used in manufacturing is covered in ASME B16.5 & B16.47.
Commonly used Forged material grads are
Before dispatching from the manufacturer, each flange is inspected to ensure quality. During an inspection, you have to check the following;
ASME B16.5 and B16.47 standards cover permissible tolerances for inspection.
Flange InspectionEach piping component is marked for proper identification. Marking of flanges must include the following so that during fabrication and post-fabrication, it can be easily traced;
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