Flanges

FLANGES

Introduction
Flanges are normally used to connect sections of pipe, valves, vessels or other fittings by forming a seal with either a ring or flat type gasket. They are assembled with stud bolts, which when tightened, force the two flange faces towards each other on the gasket to form a pressure tight seal. Flanges in the oil industry are classified according to their construction, pressure rating and diameter.

The two classifications of flanges are:
1. ASA (ANSI) American Nation Standards Institute.
2. API American Petroleum Institute
4.3.2 API Classification of Flanges

There are three common types of API flanges: API 2000,3000,5000 and there are two high pressure series, API 10,000 and 15,000. The number of the series indicated corresponds to the maximum working pressure expressed in psi at a temperature of l00ºF.

This maximum working pressure is affected by temperature। The maximum working pressure of the flange will be reduced by a factor of 1.8% for each 50ºF increase in temperature above 100ºF to a maximum of 450’F. The following table gives the maximum working pressure as a function of temperature.

Pressure Ratings

1. Test And Working Pressures
The hydrostatic test pressure is equal to twice the maximum working pressures for flanges of diameter below or equal to 14 inches. The test pressure is equal to 1.5 times the maximum working pressure for flanges of diameter equal to or greater than 16 inches.

2. ASA Flanges
With the exception of the ASA 150 series, the number corresponds to the maximum working pressure of the flange in psi at a temperature of 85OºF for carbon steel flanges.
To obtain the working pressure of the flange at temperature from –20 to+ 100ºF, the number is multiplied by 2.4.

For example:
ASA 300 Max WP = 2.4 x 300 = 720psi
ASA 900 Max WP = 2.24 x 900 =2160psi

The following table gives the working pressures of all flanges in this classification. The hydrostatic test pressure is equal to 1.5 times the working pressure at 100ºF.

4. Flange Physical Characteristics
To avoid any confusion when describing or ordering flanges, the following information should be given:
1. Type ASA or API;
2. Description of connection:
a) Weld neck flange
b) Slip on welding flange
c) Threaded flange
d) Blind flange.
3. Nominal diameter;
4. Number in ASA or API classification;
5. Type of face and gasket;
6. Bore if necessary;
7. Type of steel used for manufacture.

5. Flange Make-Up
To ensure that the flange will form a good seal, care should be taken when making them up. The studs should first be made hand tight with the faces of the flanges parallel to each other. The studs should then be gradually tightened in the sequence shown in the diagram below.

6. Line Pipe
Line pipe is required by the oil and gas industry to convey oil, gas, water, chemicals, etc. in its operations.

The API with cooperation of the American Gas Association has developed specifications meeting the needs of the oil and gas industry for steel and wrought-iron line pipe and published these in API standards 5L and 5LX. These provide standard dimensions, strengths and performance properties and the required thread gauging practice to ensure complete interchangeability.