Flanges

A flange is a forged or cast ring of steel designed to connect sections of pipe or join pipe to a pressure Vessel, pump or any other integral flanges assembly.

Flanges are joined to each other by bolting and joined to the piping system by welding or threading.

The basic types of flanges are; Slip on, Blind, Weld Neck, Threaded, Socket Weld, Lap Joint and Orifice.

Flanges are designed to the following pressure ratings; 150lb, 300lb, 400lb, 600lb, 900lb, 1500lb and 2500lb.

The most common facings machined on flanges are:
(a) Raised face, 1/16 inch for 150lb and 300lb, ¼ inch for 400lb and heavier.
(b) Flat face, for 150lb and 300lb only, other may be flat face on request.
(c) Ring type joint, may be applied to all pressure ratings.

TYPES & APPLICATIONS

Slip-On Flange

The flange is slipped over the pipe and then welded both inside and outside to provide sufficient Strength and prevent leakage. This flange is used in preference to weld necks by many users because of its lower cost and the fact that less accuracy is required when cutting pipe to length.

Blind Flanges

This is a flange without a bore and is used to shut off a piping system or vessel opening. It also permits Easy access to vessels or piping systems for inspection purposes. Blind flange can be supplied with or without hubs at the manufacturers option.

Weld-Neck flange

This is designed to be joined to a piping system by buttwelding. It is relatively expensive because of Its long neck, but is preferred for high stress applications. The neck, or hub transmits stresses to the the base of the hub to the wall thickness at the butt weld, provide important reinforcement of the flange. The bore of the flange matches the bore of the pipe, reducing turbulence and erosion.

Threaded Flange

This is similar to a slip-on flange in outline, but the bore is threaded, thus enabling assembly without welding. This obviously limits its application to relatively low pressure piping systems. The flange may be welded around the joint after assembly, but this is not considered a satisfactory method of increasing its applications.

Socket Weld Flanges

This is similar to a slip-on flange in outline, but the bore is counter-bored to accept pipe. The diameter of the remaining bore is the same as the inside diameter of the pipe. The flange is attached to the pipe by a fillet weld around the hub of the flange. An optional interval weld may be applied in high stress applications. It’s biggest use is in high pressure systems such as hydraulic and steam lines.

Spectacle Flanges

This is a pressure retaining plate with one solid end and one open end connected with a web or tie-bar. In normal operation, the open end forms the seal between two flanges and permits normal flow of fluid through pipe work. If the solid end is swung into position it effectively blanks of the pipe and halts the flow.

Lap-Joint Flanges

This is again similar to a slip-on flange, but it has a radius at the intersection of the bore and the flange face toaccommodate a lap stub end. The face on the stub end forms the gasket face on the flange. This type of flange is used in applications where section of piping systems need to be dismantle quickly and easily for inspection or replacement.

Orifice Flanges

The function of an orifice flange is to provide access to a line for metering of gases or liquids. An orifice plate is clamped between a pair of flanges when installed in a line and the whole assembly is refer to as an orifice flange union. Jack-screws within the assembly facilitate removal of the orifice plate. The orifice plate, the metering device, consists of a thin plate with a concentric, square edge, circular hole in the centre. Two pressure tap-holes are drilled in each flange to measure pressure difference through the orifice.

Groove & Tongue Flanges

The Groove and Tongue faces of this flanges must be matched. One flange face has a raised ring (Tongue) machined onto the flange face while the mating flange has a matching depression (Groove) machined into it's face.
Tongue-and-groove facings are standardized in both large and small types. They differ from male-and-female in that the inside diameters of the tongue-and-groove do not extend into the flange base, thus retaining the gasket on its inner and outer diameter. These are commonly found on pump covers and Valve Bonnets.
Tongue-and-groove joints also have an advantage in that they are self-aligning and act as a reservoir for the adhesive. The scarf joint keeps the axis of loading in line with the joint and does not require a major machining operation.

General flange faces such as the RTJ, T&G and the F&M shall never be bolted together. The reason for this is that the contact surfaces do not match and there is no gasket that has one type on one side and another type on the other side.

Long Neck Flanges

Owing to our rich industrial experience, we are offering a comprehensive range of Long Weld Neck Flanges. The professionals of our organization source these neck flanges from trusted vendors. These flanges are unique due to their simple connectivity with other pipes. Moreover, our products are extensively used in refining industries for linking purposes. Our esteemed patrons can avail these qualitative range of flanges from us at industry-leading prices.

Flat Face Flanges

The Flat Face (FF) flange has a gasket surface in the same plane as the bolting circle face. Applications using flat face flanges are frequently those in which the mating flange or flanged fitting is made from a casting.

Flat face flanges are never to be bolted to a raised face flange. ASME B31.1 says that when connecting flat face cast iron flanges to carbon steel flanges, the raised face on the carbon steel flange must be removed, and that a full face gasket is required. This is to keep the thin, bittle cast iron flange from being sprung into the gap caused by the raised face of the carbon steel flange.

Raised Face Flanges

The Raised Face (RF) type is the most applied flange face, and is easily to identify. It is referred to as a raised face because the gasket surfaces are raised above the bolting circle face.

Specifications covering the manufacture and dimensions of flanges:

ASTM SPECIFICATIONS

ASTM specifications regulate approved raw materials for which flanges can be made and specifications .

For stainless flanges are:
ASTM A.182 - Forged or Rolled Alloy Steel Pipe Flanges & Fittings for high temperature service.

ANSI AND MSS SPECIFICATIONS

The standards govern the dimensions and tolerances to which fitting are manufactured:
ANSI B. 16.5                       - Steel Pipe Flanges and Flanged Fittings (½ inch to 24 inch nominal diameter)
MSS SP.6                             - Flange Facings
MSS SP.25                           - Marking of flanges   
MSS SP.39                           - Bolts and Nuts for Flanges
MSS SP.44                           - Large Diameter Pipeline Flanges. (Over 24 inch dia)
API-605                                - Large Diameter Flanges for petroleum Usage. (Over 24 inch dia)

The ASME Code is not a standard as such but section VIII provides the procedure for calculating dimensions For all pressurised vessels flanges.
The following are not flange specifications but they influence the manufacture of forged steel flange
ANSI B. 31.10                     - Code for Pressure Piping
ANSI B. 31.3                        - Petroleum Refinery Piping
ANSI B. 31.4                        - Oil Transportation Piping
ANSI B. 31.5                        - Refrigeration Piping Systems
ANSI B. 31.7                        - Nuclear Power Piping
ANSI B. 31.8                        - Gas Transmission and Distribution Piping systems
ANSI B. 36.10                     - Standard for Wrought Steel pipe
ANSI B. 36.19                     - Standard for Stainless Steel Pipe
ANSI B. 16.10                     - Valve Dimensions Face & End
ANSI B. 16.11                     - Forged Fittings Socket Weld & Threaded

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