:::FLANGES:::

          After welding, flange is the second most commonly utilized joining technique. Flanges are utilized when the joints are needed dismantling. It provides easy access for maintenance like cleaning, inspection and modifications. Flange connects the pipe with numerous equipment, pumps and valves to form piping. Breakup flanges are added in the pipeline system if regular maintenance is needed or necessary during plant operation.

          A flanged joint consists of three distinct and independent although interrelated segments; the flanges, the gaskets, and also the bolting; that are assembled by yet another influence, the fitter. Sometimes flanges are welded to the pipe lines too. Exceptional controls are needed in the selection and application of all these components to accomplish a joint. A gasket is placed between the two mating flanges which provide acceptable leak tightness.
          However, it is not recommended to used flanged connection in underground piping when it is yo be buried. There are a variety of flanges are available. Flanges are classified as following below:
          1. On the basis of type of connection
          2. Based on flange facing type
          3. Material type
          4. On the basis of Temperature and pressure Ratings

TYPES OF FLANGES

Flanges can be classified in different ways as follows:

1. Based on Type of Connection:

a) Threaded Flanges:

         These types of flanges also called as "Screwed flanges", because these flanges having a thread inside the flange bore. The thread inside the flange bore which fits on the pipe which is having a matching male thread on the pipe. The main advantage of this flanges is that they can be attached to the pipe without any welding. In some cases a seal weld is also used in combination with a threaded connection. This type of joint connection and dismantling is speedy and also simple but for high pressure and temperature applications these are not suitable. It is also not suitable for a pipe system with thin wall thickness because thread cutting on a pipe of thin wall thickness is not possible so we have to choose pipe with thicker wall thickness.

b) Socket-weld Flanges:

          Socket-Weld Flanges features a female socket in which pipe is fitted. Generally Socket-weld flanges are used for small size (NPS 2 and smaller) and high pressure piping systems. These flanges static strength is equal to slip on flanges.

          The connection is done by inserting pipe into the recess area and 1 fillet weld is done from outside on the pipe. Before creating the welding, we need to create some space between the flange and pipe.

          To reduce the residual stress at the root of the weld that could occur during solidification of weld metal bottom clearance is given in the socket weld. In the bottom image X measures the expansion gap. 

Disadvantages: 

1. Maintain specific gap.

2. Cracking problems between the flange and pipe by corrosive  products can cause problems.

c) Slip on Flanges: