A flange is a forged or cast ring of steel designed to connect mechanically sections of pipe or join pipe to a pressure vessel, pump, valve or any other piece of equipment.
The Basics Of Steel Flanges
Steel flanges provide an easy access for cleaning, inspection or modification. They usually come in round shapes but they can also come in square and rectangular forms. The flanges are joined to each other by bolting and joined to the piping system by welding or threading and are designed to the specific pressure ratings; 150lb, 300lb, 400lb, 600lb, 900lb, 1500lb and 2500lb.
A flange can be a plate for covering or closing the end of a pipe. This is called a blind flange. Thus, flanges are considered to be internal components which are used to support mechanical parts.
Each flange material is to be considered for its application prior to ordering, this is due to the structural integrity of the application that the flange will be used on.
Copper Nickel Flanges
Currently, the most common materials for flanges are:
• ASTM A105/A266 Gr.2 (high temperature carbon steel flanges)
• ASTM A350 LF1 to LF3 (low temperature carbon steel flanges)
• ASTM A694 Gr. F42/F52/F56/F60/F65 (high yield carbon steel flanges to match API 5L linepipes)
• ASTM A182 Gr. F1/F2/F5/F9/F11 Cl.2/F12 Cl.2/F22 Cl.3/F91 (alloy steel flanges)
Stainless / Duplex Steel
• ASTM A182 F304/304L, 316/316L, 321, 347, 348 (stainless steel flanges), 904/904L
• ASTM A182 F51 (duplex flanges)/F53-F55 (superduplex flanges)
Nickel Alloys / Superalloys
• ASTM B166 UNS NO6600 (Inconel 600)
• ASTM B564 UNS N06625 (Inconel 625)
• ASTM B425 UNS-NO8800 (Incoloy 800)
• ASTM B564 UNS N08825 (Incoloy 825)
• ASTM B160 UNS N0200 (Nickel 200)
• ASTM B564 UNS N04400 (Monel 400)
• ASTM B564 UNS N10276 (Hastelloy C-276)
• ASTM B381 Gr.2 (Titanium)
But there are also flanges in:
Flanges within the same standard can either be flat (commonly cast iron, ductile iron) or raised face (commonly cast steel and stainless steel). These flange tables cover the critical flange dimensions to help identify what standard you have.
Critical flange dimensions help to identify the standard
Pipe Size – Pipe flanges also have a corresponding pipe size, generally according to accepted standards.
Outside Diameter of Flange (OD) – this is measured from outer edge to opposing outer edge.
Pitch Circle Diameter (PCD) – this is a diameter that measures from the center of bolt hole to opposing bolt hole.
Flange Thickness – this measures only the thickness of the attaching outer rim, and does not include the part of the flange that holds the pipe.
Manufacturers are able to custom design flanges to suit the desired requirement, they can include but are not limited to:
• Weld neck
• Socket Weld
• Lap Joint
Most common flange types
Custom shapes and sizes are manufactured by a large range of manufacturers, not only the popular ranges. Various flanges can include machining details such as gasket surfaces, facing details, non-standard drilling, bevel and radius edges, o-ring grooves and raised or recessed faces.
Several organizations and associations have published specifications that provide dimensional information as well as pressure specifications at different temperatures.
DIN EN 1092-1
Many countries in the European Union (EU) mainly install flanges to the DIN EN 1092-1 (forged stainless or steel flanges).
This standard is very similar to the ASME flange standard. The EN 1092-1 standard incorporates a threaded flange to IOS7.1 instead of NPT. The different forms of flanges within the EN 1092-1 (European Norm Euro norm) is indicated within the flange name through the type. Different types of flanges have different standards, some are as follow:
Type of Flange
|Blind Flange||Type 5||DIN 2527|
|Threaded Flange||Type 12||DIN 2558, 2565 – 2569|
|Weld Neck Flange||Type 11||DIN 2627 – 2638|
|Flat Flange||Type 1||DIN 2573, 2578|
|Lapped Flange||Type 2, 4||DIN 2641, 2622, 2655, 2656|
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)
ANSI B16.5 / ASME B16.47 Flanges
The ASME Code is not a standard as such but section VIII provides the procedure for calculating dimensions for all pressurized 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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