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Piping Flange Fundamentals
Contents
Introduction .................................................................... 1
Flange Terminology .............................................................. 1
Bolted, Threaded and Welded Joints ................................. 2
Expansion Joints ................................................................... 3
Flange Construction ............................................................. 3
How Flanges Work ................................................................ 4
Basic Flange Math ................................................................ 5
Flange Defining Factors ................................................. 7
The Need for Standardisation ....................................... 8
Regulatory Organisations .................................................... 8
Insurance ............................................................................... 8
Codes, Standards and Specifications ................................. 9
Pipes and Piping ............................................................ 11
Piping Systems .................................................................... 11
Pipe Types ........................................................................... 12
Pipe Ends ............................................................................. 13
Pipe Sizing History .............................................................. 15
Nominal Pipe Size (NPS) .................................................... 15
Diameter Nominal (DN) ..................................................... 16
Larger Pipe Sizes ................................................................ 16
Pipe Wall Thickness ............................................................ 17
Schedule (SCH) .................................................................... 18
Flange Schedule .................................................................. 19
Defining A Flange .......................................................... 20
Flange Pressure Class ........................................................ 20
Flange Pressure Class Examples ...................................... 20
Determining Pressure Class .............................................. 21
Pressure Class Tables ........................................................ 22
Pressure Class Table Examples ........................................ 23
Flange Pressure Class Effects ............................................ 25
Flange Dimensions ............................................................. 25
Flange Material Selection .................................................. 26
Flange Materials ................................................................. 27
Flange Faces ................................................................... 28
Plain Face/Flat Face (FF) .................................................... 28
Raised Face (RF) ................................................................. 29
Ring-Type Joint (RTJ) ........................................................... 29
Flange Face Summary ....................................................... 30
Flange Face Surfaces .................................................... 31
Surface Finish ..................................................................... 31
Smooth Flange Surface Finish .......................................... 31
Serrated Flange Surfaces .................................................. 32
Concentric Circular Groove Surfaces .............................. 33
Spiral Groove Surfaces ...................................................... 33
Roughness and Surface Finish .................................... 34
Roughness Average (Ra) ................................................... 34
Gaskets and Sealing Agents ........................................ 35
Gaskets ............................................................................... 35
Soft Gaskets........................................................................ 35
Hard Gaskets ...................................................................... 36
Composite Gaskets ............................................................ 37
Screw Thread Sealing Agents ........................................... 37
Nuts and Bolts............................................................... 39
Bolting Criteria ................................................................... 39
Bolts .................................................................................... 39
Nuts ..................................................................................... 40
Washers .............................................................................. 41
Bolting Procedure .............................................................. 41
Alignment ........................................................................... 42
Flange Types .................................................................. 43
Welds ................................................................................... 43
Non-Destructive Testing (NDT) ........................................ 44
Welding Neck Flange ......................................................... 45
Slip-on Flange ..................................................................... 46
Socket Weld Flange............................................................ 47
Lap Joint Flange (LJF) .......................................................... 48
Threaded Flange ................................................................ 50
Blind Flange ........................................................................ 51
Flange Types Summary ..................................................... 52
Special Flange Types ......................................................... 52
Final Thoughts............................................................... 53