What is a ring type joint flange?

What is a ring type joint flange?

A Ring Type Joint Flange is a type of flange that uses a metal ring that sits in a hexagonal groove as a gasket to seal the flange pair. The flanges seal when the bolts are tightened and the gasket is compressed into the groove making a metal to metal seal. An RTJ flange usually has a raised face with the groove machined into the face of the flange. The raised face doesn’t serve as a way to contain the pressure.

Specifications Benefit Standards & Dimensions
Material Characteristics Tolerances
Designs Disadvantages

Specifications of Ring Type Joint Flange:

Size: 1/2” to 60”, DN 12mm to DN 1500mm 
Pressure class: Class 150 to Class 2,500, PN 2.5 to PN 250
Facing: RF / RTJ

Material of Ring Type Joint Flange:

Cabon steel: A105, A350 LF2
Stainless steel: A182 F304/F304L/F316/F316L/F321
Alloy steel: F11, F12
An RTJ flange may have a raised face with a ring groove machined into it. This raised face does not serve as any part of the sealing means. For RTJ flanges that seal with BX ring gaskets, the raised faces of the connected and tightened flanges may contact each other. In this case the already coined gasket will not bear additional load beyond the bolt tension, vibration and movement cannot further crush the gasket and lessen the connecting tension.

rtj faces - What is a ring type joint flange?

RTJ joints are used for high pressures (Class 600 or over) and/or high temperatures (above 427°C (882°F) ). They feature machined grooves in which a metallic ring joint is fitted. When the bolts are tightened, the metal joint is compressed between the two flanges and is deformed so as to create a metal-to-metal contact. An RTJ type flange may have a raised face with a machined groove. But this face does not play any role in the sealing capacity of the unit.

Designs of RTJ flanges

There are two different types of RTJ flange designs, oval and octagonal cross sections. Despite both types having identical pitch diameters, octagonal cross sections are more widely used due to their higher sealing efficiency with pressures up to 10,000 PSI.
There are other ranges of RTJ flanges that have been adapted to cope with both a higher pressure (up to 15,000 PSI) and a lower pressure (up to 5,000 PSI). These are called RX and BX styles respectively.
The standardised designs of these sometimes includes a pressure passage hole which is created to equalise the pressure on the sealing faces. Sometimes, the internal pressure of flanges and gaskets means no hole is required as the seal pressure balance is maintained internally in the pipeline already.

rtj flanges banner - What is a ring type joint flange?

Benefit of RTJ flanges

The benefit of RTJ flange’s is that the gasket is confined in a groove and has two sealing surfaces.  It also tends to be self-actuating (i.e., the sealing pressure, at least on one side, tends to increase with increased service pressure). 

rtj wnf - What is a ring type joint flange?

Characteristics of RTJ Flanges

The effect of being used first in the petrochemicals industry means the flanges offer a superb metal-to-metal seal under high pressures and high temperatures too. The flanges typical characteristics include matching groove cuts on the face, and when the bolts are tightened, the gaskets compress into each other providing a strong and robust connection – which is also very easy to assemble and dis-assemble.

Disadvantages of RTJ Flanges

The potential for crack formation at the intersection of the sides and bottom of the groove in RTJ flanges.  These cracks can propagate into the base metal.  They can be prevented by properly contouring the groove intersections, but avoiding the “problem” geometry all together was preferred.
 Ring type joint grooves may also accumulate dirt, moisture, etc when the flange is open, i.e., they are more difficult to keep clean.  A small amount of damage (including corrosion) on the narrow sealing surface(s) may lead to a leak.  Also, as the use of RTJ’s declined, warehousing (and finding) the proper gasket(s) became a more important concern.  Another factor is that the grooves and gasket must align properly in order to assemble the flange and obtain a seal.  They must stay aligned throughout the operating cycle.  The latter point becomes an issue when mating flanges are made of different materials and not providing different hardness materials for flange and ring and also thermal expansion is a concern.  The first point is an issue at the initial assembly but can be more of a concern at reassembly after service.
Furthermore in those cases where dissimilar joint materials are in contact and where the piping is 10” nominal size or larger the use of RTJ Flange is strongly not reccomended. In fact, due to the different nature of the two materials, ring joint flanges would experience local stresses due to differential expansion that potentially could lead to ring groove cracking. There are known cases of ring joint flange failures that have led to loss of reactor containment.

Standards & Dimensions of RTJ Flanges

A great way to understand a flange in more detail requires engineers to understand the industry standards on designs giving information on Dimensions & Weight of each flange and gasket.

For RTJs, engineers should refer to the following industry standards:

20181030120508 20191 - What is a ring type joint flange?

Dimensions Ring Joint Facings B16.47

Nominal Size Groove Dimensions Diameter of Raised Portion, K
Class 150 NPS Class 300 NPS Class 400 NPS Class 600 NPS Class 900 NPS Class 1500 NPS Class 2500 NPS Groove Number Pitch Diameter, P Depth, E Width, F Radius at Bottom, R Class 150 NPS Class 300,  600 NPS Class 900 NPS Class 1500 NPS Class 2500 NPS
_  1/2 _  1/2 _ _ _ R11 34.14 5.54 7.14 0.8 51.0
_ _ _ _ _  1/2 _ R12 39.67 6.35 8.74 0.8 60.5
_  3/4 _  3/4 _ _  1/2 R13 42.88 6.35 8.74 0.8 63.5 65.0
_ _ _ _ _  3/4 _ R14 44.45 6.35 8.74 0.8 66.5
1 _ _ _ _ _ _ R15 47.63 6.35 8.74 0.8 63.5
1 _ 1 _ 1  3/4 R16 50.80 6.35 8.74 0.8 70.0 71.5 73.0
1 1/4 _ _ _ _ _ _ R17 57.15 6.35 8.74 0.8 73.0
1 1/4 _ 1 1/4 _ 1 1/4 1 R18 60.33 6.35 8.74 0.8 79.5 81.0 82.5
1 1/2 _ _ _ _ _ _ R19 65.07 6.35 8.74 0.8 82.5
_ 1 1/2 _ 1 1/2 _ 1 1/2 _ R20 68.27 6.35 8.74 0.8 90.5 92.0
_ _ _ _ _ _ 1 1/4 R21 72.23 7.92 11.91 0.8 102.0
2 _ _ _ _ _ _ R22 82.55 6.35 8.74 0.8 102.0
_ 2 _ 2 _ _ 1 1/2 R23 82.55 7.92 11.91 0.8 108.0 114.0
_ _ _ _ _ 2 _ R24 95.25 7.92 11.91 0.8 124.0
2 1/2 _ _ _ _ _ _ R25 101.60 6.35 8.74 0.8 121.0
_ 2 1/2 _ 2 1/2 _ _ 2 R26 101.60 7.92 11.91 0.8 127.0 133.0
_ _ _ _ _ 2 1/2 _ R27 107.95 7.92 11.91 0.8 137.0
_ _ _ _ _ _ 2 1/2 R28 111.13 9.53 13.49 0.8 149.0
3 _ _ _ _ _ _ R29 114.30 6.35 8.74 0.8 133.0
_ (2) _ (2) _ _ _ R30 117.48 7.92 11.91 0.8
_ 3 (2) _ 3 (2) 3 _ _ R31 123.83 7.92 11.91 0.8 146.0 156.0
_ _ _ _ _ _ 3 R32 127.00 9.53 13.49 1.5 168.0
3 1/2 _ _ _ _ _ _ R33 131.78 6.35 8.74 0.8 154.0
_ 3 1/2 _ 3 1/2 _ _ _ R34 131.78 7.92 11.91 0.8 159.0
_ _ _ _ _ 3 _ R35 136.53 7.92 11.91 0.8 168.0
4 _ _ _ _ _ _ R36 149.23 6.35 8.74 0.8 171.0
_ 4 4 4 4 _ _ R37 149.23 7.92 11.91 0.8 175.0 181.0
_ _ _ _ _ _ 4 R38 157.18 11.13 16.66 1.5 203.0
_ _ _ _ _ 4 _ R39 161.93 7.92 11.91 0.8 194.0
5 _ _ _ _ _ _ R40 171.45 6.35 8.74 0.8 194.0
_ 5 5 5 5 _ _ R41 180.98 7.92 11.91 0.8 210.0 216.0
_ _ _ _ _ _ 5 R42 190.50 12.70 19.84 1.5 241.0
6 _ _ _ _ _ _ R43 193.68 6.35 8.74 0.8 219.0
_ _ _ _ _ 5 _ R44 193.68 7.92 11.91 0.8 229.0
_ 6 6 6 6 _ _ R45 211.12 7.92 11.91 0.8 241.0 241.0
_ _ _ _ _ 6 _ R46 211.14 9.53 13.49 1.5 248.0
_ _ _ _ _ _ 6 R47 228.60 12.70 19.84 1.5 279.0
8 _ _ _ _ _ _ R48 247.65 6.35 8.74 0.8 273.0
_ 8 8 8 8 _ _ R49 269.88 7.92 11.91 0.8 302.0 308.0
_ _ _ _ _ 8 _ R50 269.88 11.13 16.66 1.5 _ _ 318.0 _
_ _ _ _ _ _ 8 R51 279.40 14.27 23.01 1.5 _ _ _ 340.0
10 _ _ _ _ _ _ R52 304.80 6.35 8.74 0.8 330.0 _ _ _ _
_ 10 10 10 10 _ _ R53 323.85 7.92 11.91 0.8 356.0 362.0 _ _
_ _ _ _ _ 10 _ R54 323.85 11.13 16.66 1.5 _ _ 371.0 _
_ _ _ _ _ _ 10 R55 342.90 17.48 30.18 2.4 _ _ _ 425.0
12 _ _ _ _ _ _ R56 381.00 6.35 8.74 0.8 406.0 _ _ _ _
_ 12 12 12 12 _ _ R57 381.00 7.92 11.91 0.8 413.0 429.0 _ _
_ _ _ _ _ 12 _ R58 381.00 14.27 23.01 1.5 _ _ 438.0 _
14 _ _ _ _ _ _ R59 396.88 6.35 8.74 0.8 425.0 _ _ _ _
_ _ _ _ _ _ 12 R60 406.40 17.48 33.32 2.4 _ _ _ 495.0
_ 14 14 14 _ _ _ R61 419.10 7.92 11.91 0.8 457.0 _ _ _
_ _ _ _ 14 _ _ R62 419.10 11.13 16.66 1.5 _ 467.0 _ _
_ _ _ _ _ 14 _ R63 419.10 15.88 26.97 2.4 _ _ 489.0 _
16 _ _ _ _ _ _ R64 454.03 6.35 8.74 0.8 483.0 _ _ _ _
_ 16 16 16 _ _ _ R65 469.90 7.92 11.19 0.8 508.0 _ _ _
_ _ _ _ 16 _ _ R66 469.90 11.13 16.66 1.5 _ 524.0 _ _
_ _ _ _ _ 16 _ R67 469.90 17.48 30.18 2.4 _ _ 546.0 _
18 _ _ _ _ _ _ R68 517.53 6.35 8.74 0.8 546.0 _ _ _ _
_ 18 18 18 _ _ _ R69 533.40 7.92 11.91 0.8 575.0 _ _ _
_ _ _ _ 18 _ _ R70 533.40 12.70 19.84 1.5 _ 594.0 _ _
_ _ _ _ _ 18 _ R71 533.40 17.48 30.18 2.4 _ _ 613.0 _
20 _ _ _ _ _ _ R72 558.80 6.35 8.74 0.8 597.0 _ _ _ _
_ 20 20 20 _ _ _ R73 584.20 9.53 13.49 1.5 635.0 _ _ _
_ _ _ _ 20 _ _ R74 584.20 12.70 19.84 1.5 _ 648.0 _ _
_ _ _ _ _ 20 _ R75 584.20 17.48 33.32 2.4 _ _ 673.0 _
24 _ _ _ _ _ _ R76 673.10 6.35 8.74 0.8 711.0 _ _ _ _
_ 24 24 24 _ _ _ R77 692.15 11.13 16.66 1.5 749.0 _ _ _
_ _ _ _ 24 _ _ R78 692.15 15.88 26.97 2.4 _ 772.0 _ _
_ _ _ _ _ 24 _ R79 692.15 20.62 36.53 2.4 _ _ 794.0 _
_ 26 26 26 _ _ _ R93 749.30 12.70 19.84 1.5 810.0
_ 28 28 28 _ _ _ R94 800.10 12.70 19.84 1.5 861.0
_ 30 30 30 _ _ _ R95 857.25 12.70 19.84 1.5 917.0
_ 32 32 32 _ _ _ R96 914.40 14.27 23.01 1.5 984.0
_ 34 34 34 _ _ _ R97 965.20 14.27 23.01 1.5 1035.0
_ 36 36 36 _ _ _ R98 1022.35 14.27 23.01 1.5 1092.0
_ _ _ _ 26 _ _ R100 749.30 17.48 30.18 2.3 832.0
_ _ _ _ 28 _ _ R101 800.10 17.48 33.32 2.3 889.0
_ _ _ _ 30 _ _ R102 857.25 17.48 33.32 2.3 946.0
_ _ _ _ 32 _ _ R103 914.40 17.48 33.32 2.3 1003.0
_ _ _ _ 34 _ _ R104 965.20 20.62 36.53 2.3 1067.0
_ _ _ _ 36 _ _ R105 1022.35 20.62 36.53 2.3 1124.0

Tolerances (inches):                         Tolerances (mm):
P   (pitch diameter) ±0.0005             P   (pitch diameter) ±0.13
E   (depth) +0.026, -0.000                E   (depth) +0.40, -0.00
F   (width) ±0.008                             F   (width) ±0.20
R   (radius at bottom) max.               R   (radius at bottom) max.
23 deg. (angle) ±1/2 deg.                23 deg. (angle) ±1/2 deg.

  • Ring joint gasket dimensions conform to ASME B16.20 (not covered in this summary).
  • Use Class 600 lb in sizes NPS 1/2 to NPS 31/2 for Class 400 lb.
  • Use Class 1500 lb in sizes NPS 1/2 to NPS 21/2 for Class 900 lb.- Tolerances are as shown in the table below.
  • Height of raised portion is equal to the depth of groove dimension E, but is not subjected to the tolerances for E. Full face contour may be used.
  • Ring joint gaskets are not  contemplated for NPS 38 and larger flanges.

Ring Type Joint gaskets

Ring Type Joint gaskets - What is a ring type joint flange?

Ring Type Joint gaskets are metallic sealing rings, suitable for high-pressure and high-temperature applications. They are always applied to special, accompanying flanges which ensure good, reliable sealing with the correct choice of profiles and material.

Source: China Pipe Flange Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@pipelinedubai.com

Please notice that you might be interested in the other technical articles we’ve published:

References:

  • https://www.yaang.com
  • https://www.steeljrv.com/how-to-get-high-quality-ring-type-joint-flanges.html

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