TYPES OF FLANGES (PART - 2)

 TYPES OF FLANGES BASED ON THE FACE

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Depending on the flange facing Types, it can be further classified as

1. Flat Face (FF)
2. Raised Face (RF)
3. Ring Joint (RTJ)
4. Tongue and groove (T&G)
5. And Male and Female type

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Flat Face

As the name suggests, the flat face flange has a flat face. Flat face flanges are used when the counter-flanges are flat face. This condition occurs mainly in connection to Cast Iron equipment, valves, and specialties. Full face gasket is used when a flat face flange is used.

Raised Face

Raised face flange has a small portion around the bore is raised from the face. The gasket seat on this raised face. The height of the raised face depends on the flange pressure-temperature rating that is known as a class of the flange. For 150# & 300# height of the raised face is 1/6” and above 300# it is 1/4”. The inside bore circle type of gasket is used with a raised face flange.

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RTJ Face

Ring joint type face flange has a specially designed grove in which metal gasket seat. This type of flange is used in high pressure and temperature services.

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Flange Materials

Flanges are manufactured from following materials

• Carbon steel
• Low alloy steel
• Stainless steel
• Combination of Exotic materials (Stub) and other backing materials

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The list of materials used in manufacturing are covered in ASME B16.5 & B16.47.

• ASME B16.5 -Pipe Flanges and Flanged Fittings NPS ½” to 24”
• ASME B16.47 -Large Diameter Steel Flanges NPS 26” to 60”

Commonly used Forged material grads are

• Carbon Steel: – ASTM A105, ASTM A350 LF1/2, ASTM A181
• Alloy Steel: – ASTM A182F1 /F2 /F5 /F7 /F9 /F11 /F12 /F22
• Stainless Steel: – ASTM A182F6 /F304 /F304L /F316 /F316L/ F321/F347/F348

Flange Inspection

During an inspection you have to check the following;

• Outer & Inner Diameter of body
• Bolt Circle & Bolt hole Diameter
• Hub Diameter & thickness of weld end
• Length of the Hub
• Straightness and alignment of the bolt hole

ASME B16.5 and B16.47 standards covers permissible tolerances for inspection.

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Marking on the Flange Body

Marking of flange must includes the following;

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• Manufacturer logo
• ASTM material code
• Material Grade
• Service rating (Pressure-temperature Class))
• Size
• Thickness (Schedule)
• Heat No
• Special marking if any QT (Quenched and tempered) or W (Repair by welding)

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