The Applications and Type of Piping Flanges

Used in many, different fields, such as the transport (pipelines, ships) of petroleum, gas, water, etc., their manufacturing facilities and those of power generation, chemicals, and chemical fertilizers, flanges are of various kinds in type and shape, and their material too is diversified (low carbon steel, low alloy steel, stainless steel, high alloy steel, non-ferrous steel, or such) in accordance with the type of fluid and service environment.
Flanges are classified in form as shown Figure 2 according to the method of linking with pipes, and their form of face is classified as shown in Figure 3 pursuant to the type of gaskets used. Like this, their forms are diverse under designated different conditions, and so it is necessary to indicate clearly the items shown in Figure 1 at the time of order placement. ( Both Figures 2 and 3 are quoted from JPI-7S-15 standards.)

Figure 1: Items requiring indication when an order is placed.
Figure 2: Form of flanges

Figure 3: Form of gaskets
(1) Applicable Material Standards & Material Codes
The material used most often for flanges includes low carbon steel, low alloy steel, and stainless steel (individual detailed material designation omitted), and applicable standards are roughly classified into JIS (Japan Industrial Standards) for domestic projects and ASME(American Society of Mechanical Engineers) and ASTM(American Society for Testing Materials) for foreign projects.
In addition laws and regulations, such as the High Pressure Gas Security Law, the Nuclear Power Notification, and the Electric Utility Industry Law, are applied depending on projects, and hence the requirements, such as manufacturing procedures, inspection items, and the necessity of qualification approval, differ depending on these applicable standards, laws and regulations.

(2) Applicable Form Standards
The form standards of the flanges manufactured by our company are classified into the following groups.

A. JIS-system
Typified by JIS2220, in which nominal pressure is expressed in k.
B. ASME-system Typified by ASME16.5, in which nominal pressure is expressed in Lbs.
(old ANSI standards)
B16.5(small & medium bore diameter) -> To JPI-7S-15
B16.47(large bore diameter)Series A <- MSS-SP-45 included
-> To JPI-7S-43
Series B <- API-605 included.
-> To JPI-7S-43
Flanges to which are applied the high pressure flange standards for oil drilling rigs in which API-6A and 6B get typified and nominal pressure is expressed in PSI.
Flanges with the form designed, developed by a user or manufacturer.
E. Not manufactured by our company and typified by DIN(German Industrial Standard) in which nominal pressure is expressed in PN(nominal pressure). Some flanges to which EN (European Union Standards) standards are applied.
 As stated above, there are various form standards, and since design philosophy, dimensions, and forms differ largely depending on standards, it is necessary to give an precise indication.
(3)Pressure class
Pressure class (nominal pressure) differs depending on standards pursuant to the difference in the design basis of each standard set forth in the preceding section. The pressure class of each standard is as follows:
  • JIS-system
  • ASME- and JPI-system
  • API-6A :2000 PIS、3000 PIS、5000 PIS、10000 PIS、15000 PIS、20000 PIS
  • EN standard-system : PN10、PN16、PN20、PN50、PN110、PN150、PN260、PN420
(4) Form Classification
As shown in Figure 2, the following fundamental forms are standardized according to the means of linking up with pipes.
  • Welding Neck: WN
  • Slip-on Welding: SO
  • Integral or Long Welding Neck: LWN
  • Socket Welding: SW
  • Threaded or Screwed
  • Lapped Joint: LAP
  • Blind: BL

Apart from the above forms, what is called a reducing flange is also standardized as their application version.
(5) Type of Face
It is a face called a gasket contact surface that is considered the most important portion of a flange. As shown in Figure 3 its forms are classified depending on the type of gaskets used. And not only forms but also the finish roughness accuracy of machined surfaces are specified meticulously. It is the portion which plays an important role in the sealability to prevent fluid from leaking. Heed must be paid to the fact that the thickness and total height of flanges differ depending upon FF(Flat Face), RF(Raised Face), and RTJ(Ring Joint) even if the pipe size, nominal pressure, or type (WN type for instance) is Identical.
(6) Applicable Pipe Diameter and Pipe Wall thickness (SCH.NO.)
For the pipe nominal diameter, Indication A is used in JIS and Indication B in ASME-system standards respectively, and 10A to 1500A (1/8B to 60B) is specified in each of these standards. And SCH. NO. (schedule No.) means the number showing the wall thickness classification of pipes. Here wall thickness increases with increasing SCH.NO. It is noted, however, that any size does not have the same wall thickness under the same SCH. NO., but all the wall thickness differs size by size depending on SCH. NO.
There is a range (5B, 6B, 8B, 10B, 12B) differing in outer diameter between JIS and ASME(ANSI) pipes even if the nominal diameter is identical, and the difference in outer diameter causes the inner diameter too to change each SCH. NO.
There occurs difference in the outer and inner diameter of groove portions for flanges, like SO type, welded by inserting a pipe into these, flanges, like WN type, butt-welded with a pipe, and flanges, like SW type, whose inner diameter coincides with that of a pipe.
In case of connecting a JIS pipe to an ASME flange, or in the reverse case, it is likely that unless the manufacturing side is informed in advance of such connection, there occurs trouble during welding at the field.

The contents carried here are from No.9, volume 42 of "Piping Technology" issued by Nippon Kogyo Publication Ltd. The writer: Masamitsu Kihara, general manager of Quality Assurance Dept of our company.

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