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Learn about Flanges for Piping

In piping applications, a flange is used to join a pipe with other equipment (another pipe, a valve or a pump). Pipe flanges may be classified by shape (weld neck, blind, socket weld, threaded, etc), by facing type (RF, FF, RTJ), by material grade (cast and forged), and by specification (the ANSI/ASME B16.5 and B16.47 specifications cover US standard flanges for piping, the EN 1092-1 specification covers European pipe flanges).

WHAT IS A FLANGE?

A flange is a cast or forged steel product used to connect a pipe with another mechanical device. In the oil and gas industry, forged steel flanges are preferred due to their intrinsic strength and durability.

FLANGE SIZES

The key sizes for a pipe flange are:

  • the nominal size (i.e. the bore size of the flange, to match the bore size of the connecting pipe)
  • the flange rating (which designates the pressure/temperature performance of the flange, i.e. 150#, 300#, 400#, up to 2500#)
  • the schedule for welding neck flanges (that should match the pipe schedule)

FLANGES IN PIPING

Pipe flanges are available in multiple types, the standard ones are the welding neck, blind, socket weld, lap joint, threaded, etc.). There are also some special types of flanges, like the swivel flanges, the expander/reducer flanges, the “Nipoflange” / “Weldoflange”, and the orifice flanges.

As a general rule, welding neck, slip-on, and socket weld flanges are used for high-pressure applications that require long-lasting flanged joints. Threaded flanges can be used with a lower pressure piping system, and if vibrations are not present.

Lap joint flanges are used in connection with stub ends either to facilitate the alignment of the bolts of the two mating flanges, or to reduce the cost of noble materials in high-grade flanged joints (example, in an Inconel piping system, the stub end connected to the pipe may be in Inconel, whereas the lap joint flange can be of a lower grade, thus saving the overall weight of the expensive Inconel material).

MATERIAL GRADES

The key material grades for pipe flanges, examined in a separate article, are:

  • ASTM A105 (carbon steel flanges for high-temperature service)
  • ASTM A350 (CS flange for low temperature)
  • ASTM A694 (high yield carbon steel flange for line pipes)
  • ASTM A182 F1 to F91 (alloy steel flange)
  • ASTM A182 F304, F316, F321 (stainless steel flange)
  • ASTM A182 F51, ASTM A182 F53/55 (duplex and super duplex flange), and higher grades (Inconel, Hastelloy, Monel flange).

The pipe and the flange material shall, of course, match (according to the ASTM piping materials selection chart).

Flange Materials, General Requirements

  • Flanges and flanged fittings shall be castings, forgings, or plates
  • Bolting materials shall conform to ASME B16.5, Table 1B.
  • The material for flanges in pipeline service shall be suitable for welding. The carbon equivalents of the used flanges shall match with the pipe material

Cast Iron and Ductile Iron Flanges

  • Gray cast iron flanges shall not be used for process piping within the battery limits of any plant. The only exception shall be for fire systems applications. The material shall be ASTM A 126, Class B.
  • Ductile iron flanges may be used, in proprietary systems, for example plastic lined steel piping, as back-up for lapped joints flanges
  • ASME B16.1 Class 125 and class 250 cast iron flanges may be mated with ASME B 16.5 class 150 and 300 steel flanges respectively. However care shall be exercised to ensure that a flat-faced cast iron flange shall mate only with a flat faced steel flange, and vice versa.

Carbon Steel Flanges

  • Carbon steel flanges shall not be used in services above 425 °C
  • High-temperature service: Standard carbon steel material shall be ASTM A 105, a material that can be safely used for temperatures between minus 29 °C and 425 °C.
  • Low-temperature Service: Carbon steel flanges used for services below minus 29 °C, shall conform to the impact-testing requirements of ASME B 31.3. ASTM A 350-LF2 shall be the standard material for low temperature applications
  • High-Yield Service: High strength carbon steel flanges ASTM A694 should fit API Std. 5L pipe Grade X42 to X65.

Low-Alloy Flanges

Material for low-alloy steel flanges (11/4 Cr – 1/2 Mo) shall be ASTM A 182-F11. Material for intermediate alloy steel flanges (11/2 Cr – 5 Mo) shall be ASTM A 182-F5.

Stainless Steel and Non-ferrous Flanges

  • Usually, weld neck flanges shall match the metallurgy of the pipe in any material class. Austenitic stainless steels, however, may in certain cases be interchangeable. For example, type 347 and 321 stainless steels are compatible. Flanges that are double stamped, or double graded, and are so marked. For example, low carbon grades such as 304L, and 316L may be substituted, for the ‘straight’ grade, provided that the ‘L’ grade meets the physical requirements of the application.
  • When pipe material is forged, weld neck flanges shall be forged. When pipe material is not forged, material for weld neck flanges shall be subject to client approval.
  • Non-ferrous pipe flanges (copper, cupronickel, and aluminum) are used in marine and aeronautical applications.

Pipeline Service Flanges

Flanges for pipeline service shall match SMYS, and carbon equivalency specified in ASME B31.4 and B31.8.

NACE Service Flanges

When an in plant service has water and H2S concentrations above the limits specified in NACE MR0175, that service shall be considered as NACE service. Flanges for use in NACE service shall be in accordance with NACE MR0175 special requirements. Purchase description shall specify ‘NACE service’.

Coated, Painted and Lined Flanges

For specific applications, flanges may be coated, painted or internally lined (with Teflon, for example) to enhance the resistance of the metal to the aggression of corrosive or erosive fluids.

ASME/EN SPECIFICATIONS

The ASME B16.5 specification covers flanges for piping applications up to 24 inches in diameter, whereas the ASME B16.47 specification covers pipe flanges above 24 inches (series A and B are available).

More in detail, the following ASME standards apply to main and companion flanges in pipe works:

  • ASME B16.1: this standard applies to integral cast iron flanges and blind flanges
  • ASME B16.5, Classes 150, 300, 600, 900, 1500 up to NPS 24 and class 2500 up to NPS 12. Class 400 carbon steel flanges shall not be used
  • Flanges larger than NPS 24 to be specified in accordance with ASME B16.47. ASME B16.47 series A for NPS 26 to NPS 60 in class 150 to 900 replaces these flange sizes in MSS SP-44
  • Series B replaces API 605 in sizes NPS 26 to 60 (ASME B16.47 Series B is used for pipelines and is restricted to flanges used for joints)
  • MSS SP-44 shall be used for steel pipeline flanges for sizes smaller than ASME B16.47 where the material grade is not listed in ASME B16.5
  • Flanges of unlisted materials and flanges not covered by the above standards shall be designed in accordance with ASME Section VIII Div 1, Appendix 2, and for blind flanges, in accordance with ASME Section VIII Div 1, Section UG-34

Tolerances for flanges shall be in accordance with ASME B16.5, section 7 for flanges up to NPS 24, and ASME B16.47 for flanges over NPS.

Pipe flanges for European piping systems are covered by the EN 1092-1 specification  (weld neck flange type 11, plate flange type 01, blind flange type 05, threaded flange type 13).

FLANGES MARKING STANDARD

Flanges and flanged fittings shall be marked in accordance with MSS SP-25. The following shall be included in the marking:

  • Pressure rating class
  • ASME B16 designation
  • Nominal pipe size
  • The letter ‘R’ and the corresponding ring groove number for ring joint flanges
  • The letters ‘PL’ shall precede the grade symbol followed by the material grade of pipe
  • Type of flange facing
  • Schedule or wall thickness for weld-neck flanges
  • WHAT IS A FLANGED JOINT?

    A flanged joint is a connection between a pipe and another piping equipment (example, another length of pipe, a valve, or a pressure vessel). Hundreds, even thousands, of flanged joints are necessary for a piping system to function.

    The three main components of a flanged joint are:

    • two mating flanges (the “main” and the “companion” flange).
    • a number of stud bolts for flanges (flanges of different diameter, class, and face finish require different numbers and sizes of stud bolts and nuts for proper sealing);
    • two gaskets, which can be either metallic (spiral wound, ring joint, jacketed and Kammprofile), or non-metallic (non-asbestos gaskets).

    A steel pipe can be welded on the flange (this is the case of weld neck, socket weld, slip-on, and lap joint flange) or screwed onto it (threaded flange). Welded connections between pipes and flanges are used for high pressures and temperatures applications, and diameters above 2 inches. Threaded connections are used for small diameter piping systems that are not subject to mechanical forces as expansion, vibration, contraction, oscillation.

    A Flange insulation kits can also be used for a flanged connection, to protect the corrosion on flanges, bolts, and gaskets generated by the static currents running through the pipeline (this is called “cathodic protection”).

    To prevent dangerous leakages in the pipeline, flanged joints shall be executed by trained personnel only (the standard TSE – TS EN 1591 Part 1-4, “Flanges and their joints” is the reference norm).

    flanged joint connection

     

FLANGE BOLT CHART

Flanges for piping should be mated using proper stud bolts and nuts. It is absolutely critical to use the right number, diameter, length, and material to bolt flanges properly and ensure leak-free connections. Further, stud bolts shall be tightened with a proper sequence and by applying a proper torque.

The flange bolt chart shows the exact number, the diameter and the length of the stud bolts required by ASME flanges with different size, class and face finish.

Nominal Pipe Size (NPS)Class 150Class 300Class 400Class 600
# of BoltsBolt DiameterBolt Length# of BoltsBolt DiameterBolt Length# of BoltsBolt DiameterBolt Length# of BoltsBolt DiameterBolt Length
1/241/22 1/441/22 1/241/2341/23
3/441/22 1/245/8345/83 1/245/83 1/2
141/22 1/245/8345/83 1/245/83 1/2
1 1/441/22 3/445/83 1/445/83 3/445/83 3/4
1 1/241/22 3/443/43 1/243/44 1/443/44 1/4
245/83 1/485/83 1/285/84 1/485/84 1/4
2 1/245/83 1/283/4483/44 3/483/44 3/4
345/83 1/283/44 1/483/4583/45
3 1/285/83 1/283/44 1/487/85 1/287/85 1/2
485/83 1/283/44 1/287/85 1/287/85 3/4
583/43 3/483/44 3/487/85 3/4816 1/2
683/44123/44 3/4127/861216 3/4
883/44 1/4127/85 1/21216 3/4121 1/87 1/2
10127/84 1/21616 1/4161 1/87 1/2161 1/48 1/2
12127/84 3/4161 1/86 3/4161 1/48201 1/48 3/4
141215 1/4201 1/87201 1/48 1/4201 3/89 1/4
161615 1/4201 1/47 1/2201 3/88 3/4201 1/210
18161 1/85 3/4241 1/47 3/4241 3/89201 5/810 3/4
20201 1/86 1/4241 1/48241 1/29 1/2241 5/811 1/4
22201 1/46 1/2241 1/28 3/4241 5/810241 5/812
24201 1/46 3/4241 1/29241 3/410 1/2241 7/813

 

Nominal Pipe Size (NPS)Class 900Class 1500Class 2500
# of BoltsBolt DiameterBolt Length# of BoltsBolt DiameterBolt Length# of BoltsBolt DiameterBolt Length
1/243/44 1/443/44 1/443/44 3/4
3/443/44 1/243/44 1/243/45
147/8547/8547/85 1/2
1 1/447/8547/85416
1 1/2415 1/2415 1/241 1/86 3/4
287/85 3/487/85 3/4817
2 1/2816 1/4816 1/481 1/87 3/4
387/85 3/481 1/8781 1/48 3/4
3 1/2
481 1/86 3/481 1/47 3/481 1/210
581 1/47 1/281 1/29 3/481 3/411 3/4
6121 1/87 1/2121 3/810 1/48213 1/2
8121 3/88 3/4121 5/811 1/212215
10161 3/89 1/4121 7/813 1/4122 1/219 1/4
12201 3/81016214 3/4122 3/421 1/4
14201 1/210 3/4162 1/416
16201 5/811 1/4162 1/217 1/2
18201 7/812 3/4162 3/419 1/4
2020213 3/416321 1/4
22
24202 1/217 1/4163 1/224 1/4

PIPE FLANGE WEIGHT

CLASS 150 FLANGES WEIGHT

NPS

(Inches)

DN
(mm)
FLANGE OD
(mm)
THICKNESS
(mm)
SLIP ON
(KGS)
WELD NECK (KGS)BLIND FLANGE (KGS)
1/ 21588.911.20.40.50.4
3/ 42098.612.70.60.70.6
12510814.20.810.9
1 1/ 432117.315.711.31.2
1 1/ 24012717.51.31.71.5
250152.419.12.12.62.4
2 1/ 265177.822.43.34.13.9
380190.523.93.94.94.9
3 1/ 290215.923.94.86.16.2
4100228.623.95.36.87.0
512525423.96.18.68.6
6150279.425.47.510.611.3
8200342.928.412.117.619.6
10250406.430.216.52428.6
12300482.631.826.236.543.2
14350533.435.134.648.458.1
16400596.936.644.860.676.1
1845063539.648.968.393.7
20500698.542.961.984.5122.0
24600812.847.886.9115185.0

CLASS 300 FLANGES WEIGHT

NPS

(Inches)

DN
(mm)
FLANGE OD
(mm)
THICKNESS
(mm)
SLIP ON
(KGS)
WELD NECK (KGS)BLIND
(KGS)
1/ 21595.314.20.60.80.6
3/ 420117.315.71.11.31.1
12512417.51.41.51.4
1 1/ 432133.419.11.72.01.8
1 1/ 240155.520.62.52.92.7
250165.122.42.93.43.2
2 1/ 265190.525.44.35.24.9
380215.928.45.96.96.8
3 1/ 290228.630.27.38.78.7
410025431.89.611.211.5
5125279.435.112.315.115.6
6150317.536.615.619.120.9
820038141.124.229.934.3
10250444.547.634.142.753.3
12300520.750.849.861.878.8
14350584.253.869.985.8105.0
16400647.757.288.1106.0137.0
18450711.260.5109.0131.0175.0
20500774.763.5134.0158.0221.0
24600914.470.0201.0230.0339.0

CLASS 600 FLANGE WEIGHT

NPS

(Inches)

DN
(mm)
FLANGE OD
(mm)
THICKNESS
(mm)
SLIP ON
(KGS)
WELD NECK (KGS)BLIND
(KGS)
1/ 21595.314.20.70.90.8
3/ 420117.315.71.31.51.3
125124.017.51.51.81.6
1 1/ 432133.420.622.52.2
1 1/ 240155.422.433.53.3
250165.125.43.64.44.2
2 1/ 265190.528.45.36.46.1
380209.631.878.58.4
3 1/ 290228.635.18.810.711
4100273.138.114.517.417.3
5125330.244.524.429.229.4
6150355.647.828.734.936.1
8200419.155.643.453.958.9
1025050863.570.386.597.5
12300558.866.584.2103.0124
14350603.369.998.7122.0151
16400685.876.2142.0170.0214
1845074382.6173.0204.0272
20500812.888.9220.0254.0349.0
24600939.8101.6312.0358.0533.0

CLASS 900 FLANGE WEIGHT

NPS

(Inches)

DN
(mm)
FLANGE OD
(mm)
THICKNESS
(mm)
SLIP ON
(KGS)
WELD NECK (KGS)BLIND
(KGS)
1/ 215120.722.41.81.91.8
3/ 42013025.42.42.62.4
125149.428.43.63.73.6
1 1/ 432158.828.444.34.1
1 1/ 240177.831.85.55.95.8
250215.938.110.210.810
2 1/ 265244.341.113.91514
380241.338.111.613.713.1
4100292.144.519.722.526.9
5125349.350.831.937.436.5
615038155.641.147.747.4
8200469.963.570.781.382.5
10250546.169.9101.0119122.0
12300609.679.2133.0157.0173.0
14350641.485.6153.0180.0206.0
16400704.988.9185.0217.0259.0
18450787.4101.6258.0292.0367.0
20500857.3108.0317.0362.0463.0
246001041.4139.7606.0665.0876.0

CLASS 1500 FLANGE WEIGHT

NPS

(Inches)

DN
(mm)
FLANGE OD
(mm)
THICKNESS
(mm)
SLIP ON
(KGS)
WELD NECK (KGS)BLIND
(KGS)
1/ 215120.722.41.81.91.8
3/ 42013025.42.42.62.4
125149.428.43.63.73.6
1 1/ 432158.828.444.34.1
1 1/ 240177.831.85.55.95.8
250215.938.110.210.810.1
2 1/ 265244.341.113.91514
380266.747.819.919.1
4100311.253.829.929.9
5125374.773.255.458.4
6150393.782.668.471.8
8200482.691.9117122
10250584.2108194.0210.0
12300673.1124288.0316.0
14350749.3133.4380.0420
16400825.5146.1485.0558.0
18450914.4162.1644.0760.0
20500984.3177.8775.0965.0
246001168.4203.21232.01558.0

CLASS 2500 FLANGE WEIGHT

NPS

(Inches)

DN
(mm)
FLANGE OD
(mm)
THICKNESS
(mm)
SLIP ON
(KGS)
WELD NECK (KGS)
1/ 215133.430.23.13.0
3/ 420139.731.83.73.5
125158.835.15.25.0
1 1/ 432184.238.17.77.4
1 1/ 240203.244.510.910.4
25023550.816.215.6
2 1/ 265266.757.223.722.6
380304.866.536.234.8
4100355.676.255.353.9
5125419.191.992.590.8
6150482.6108143.0141
8200552.5127215.0214
10250673.1165.1406.0411.0
12300762184.2572.0592.0

HOW TO ORDER A FLANGE

The following data shall be communicated to the manufacturer when ordering flanges:

  • Flange type (welding neck, slip-on, threaded, lap joint flange)
  • Flange specification (example ASME B16.5, ASME B16.47 type A, EN 1092-1, JIS, UNI, DIN, etc.)
  • Nominal pipe size (NPS)
  • Flange rating (or class): flanges’ rating can range from 150 to 2500 for ASME flanges, from 5k to 30k for JIS B2220 flanges and KS1503 flanges; from PN 6 to PN 100 for European and Russian-standard flanges (DIN, UNI, EN 1092-1, GOST 12820 / 12821-80); Class 600/3, 1000/3, 1600/3, 2500/3, 4000/3 for SANS/SABS flanges (South African standard for flanges)
  • Pipe schedule (for welding neck and socket weld flanges)
  • Flange facing type (FF; RF, RTJ): according to ASME B16.5, the raised face is the standard facing for flanges (different facings, like RTJ or flat face FF, have to be ordered specifically)
  • Flange surface finish (smooth, stock, concentric serrated, etc)
  • Material grade (forged carbon, stainless, duplex, nickel-alloy steels or, non-ferrous materials as cupronickel, copper, aluminum, and bronze)

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