Lap Joint Flange

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Size Range: 1/2" - 24" / DN15 - DN600 Pressure Rating: Class 150, 300, 600, 900, 1500, 2500 Standard : ASME B16.5

SKU: ZZ106 Category:

What are Lap Joint Flanges?

A lap joint flange is a type of flange that is designed for easy assembly and disassembly. It consists of two parts: the flange itself and a backing flange (or stub end). The key feature of a lap joint flange is that it doesn’t actually weld directly to the pipe; instead, it mounts over a stub end that someone welds to the pipe. The flange then “laps” over this stub end, and users make a loose connection using bolts and nuts.

Lap Joint Flange

The flange part and the stub end part are usually purchase respectively. So if you need them all in one together, please mention it in your description and unit of the items.

Key Features of a Lap Joint Flange:

Two-Part Design: A lap joint flange consists of a flange and a backing stub end, where the flange does not weld directly to the pipe.

Ease of Disassembly: The design allows for easier disassembly and maintenance since one can remove the flange from the stub end without disturbing the pipe.

Alignment Flexibility: It offers better alignment flexibility, especially for applications where users need to rotate the flanges to fit.

No Need for Pipe Preparation: The pipe doesn’t require beveling for the lap joint flange, which makes it easier to install in certain applications.

Corrosion Resistance: Manufacturers often make the backing flange (stub end) from a different material or alloy to enhance corrosion resistance, and one can make the lap joint flange from stainless steel or other materials depending on the system’s needs.

Stub End Types:

While the backing flange itself doesn’t have distinct “types” in the same way as other flanges (like weld neck or slip-on), the stub end used with it comes in different types, which can indirectly influence the lap joint assembly:

1. Type A (Long Pattern): This type has a longer lap and users typically use it with standard lap joint flanges.

2. Type B (Short Pattern): This type has a shorter lap, and designers design it for use with standard slip-on flanges as backing flanges in some cases.

3. Type C: Manufacturers machine the lap from a pipe section to a specific length.

 Lap Joint Flange Standards

1. ASME B16.5

This standard covers the design, materials, dimensions, pressure-temperature ratings, testing, and marking of flanges and flanged fittings for use in piping systems. It applies to sizes from ½ inch to 24 inches.

Pressure : 150#, 300#, 600#, 900#, 1500#, 2500#

2. ASME B16.47

This standard covers large diameter flanges with sizes ranging from 26 inches to 60 inches. It is specifically used in industries with large piping systems, such as oil, gas, and power generation.

Pressure : 150#, 300#, 400#, 600#, 900#

3. EN 1092-1

This European standard specifies requirements for steel flanges, including lap joint flanges, for nominal sizes up to DN 4000 and pressure designations up to PN 400. It covers various types of flanges and their dimensions, tolerances, materials, and testing.

Pressure : PN 2.5, 6, 10, 16, 25, 40, 63, 100, 160, 250, 400

4. API 6A

This standard applies to flanges used in wellhead and Christmas tree equipment in the oil and gas industry. It is specifically designed for systems that involve high-pressure wellhead and blowout preventer (BOP) systems.

Pressure：

2,000 psi (13.8 MPa) – Often referred to as 2M  

3,000 psi (20.7 MPa) – Often referred to as 3M  

5,000 psi (34.5 MPa) – Often referred to as 5M  

10,000 psi (69.0 MPa) – Often referred to as 10M  

15,000 psi (103.5 MPa) – Often referred to as 15M  

20,000 psi (138.0 MPa) – Often referred to as 20M

5. JIS B2220:

This Japanese Industrial Standard covers steel pipe flanges, including lap joint flanges, for general use.

Pressure：5K, 10K, 16K, 20K, 30K, 40K

Material & Grades of Lap Joint Flanges :

Carbon Steel Threaded Flanges :
Carcon Steel: ASTM A105 / A105N,ASTM A350 LF2 / LF3, A694 F42 / 46 / 52 / 56 / 65 / 70

Alloy Steel Threaded / Screwed Flanges :
ASTM / ASME A/SA 182 & A 387 F1, F5, F9, F11, F12, F22, F91

Stainless Steel Threaded Flanges :
ASTM A 182, A 240 F 304, 304L, 304H, 316, 316L, 316Ti, 310, 310S, 321, 321H, 317, 347, 347H, 904L

Duplex & Super Duplex Steel Threaded Flanges :
ASTM / ASME A/SA 182 F 44, F 45, F51, F 53, F 55, F 60, F 61

Copper Alloy Steel Threaded Flanges :

 ASTM SB 61 , SB62 , SB151 , SB152 UNS No. C 70600 (Cu-Ni 90/10), C 71500 (Cu-Ni 70/30), UNS No. C 10100, 10200, 10300, 10800, 12000, 12200

Nickel Alloy Threaded Flanges :
ASTM SB564, SB160, SB472, SB162 Nickel 200 (UNS No. N02200), Nickel 201 (UNS No. N02201), Monel 400 (UNS No. N04400), Monel 500 (UNS No. N05500), Inconel 800 (UNS No. N08800), Inconel 825 (UNS No. N08825), Inconel 600 (UNS No. N06600), Inconel 625 (UNS No. N06625), Inconel 601 (UNS No. N06601), Hastelloy C 276 (UNS No.N10276), Alloy 20 (UNS No. N08020)

Considerations During Installation:

Welding Procedure

Ensure that the welding procedure used for attaching the stub end is appropriate for the materials involved and complies with relevant codes and standards. Qualified welders should perform the welding.

Gasket Selection 

Choosing the correct gasket material and type is crucial for achieving a proper seal and ensuring compatibility with the process fluid and operating conditions.

Bolt Torque

Applying the correct bolt torque is essential to compress the gasket adequately without damaging it or the flanges. Use a calibrated torque wrench and follow a proper tightening sequence.

Alignment

While lap joint flanges offer more flexibility in alignment compared to welded flanges, it is still important to ensure the pipes and flanges reasonably align before final bolting.

Inspection

After installation, inspectors check the welds for any defects and ensure the bolts are tightened correctly. The system may require pressure testing to verify the integrity of the flanged connection.

Lap Joint Flange Advantages:

Ease of Alignment

The flange rotates to align easily with the bolt holes on another flange, which helps in situations where accurate alignment is challenging.

Quick Disassembly

Because the flange isn’t welded directly to the pipe, you can quickly remove and replace lap joint flanges, which makes them ideal for industries with frequent maintenance or inspection needs.

Corrosion Resistance

Manufacturers make lap joint flanges from various materials, including stainless steel, carbon steel, and other alloys, ensuring good resistance to corrosion in harsh environments.

Cost-Effective

The lap joint flange is often less expensive than fully welded flanges due to its simpler design and ease of installation.

Applications

Piping Systems in Harsh Environments

The chemical, oil and gas, food processing, and pharmaceutical industries extensively use them where the piping needs to be disassembled for cleaning, maintenance, or inspection.

Systems with Frequent Maintenance

 Ideal for systems where pipes need to be opened up regularly for inspection, testing, or modification.

Systems with Misalignment

Used in cases where the alignment of the bolt holes may be problematic or where the system needs to be flexible in terms of alignment during installation.

Pressure Vessel Connections

Common in pressure vessels and heat exchangers where ease of installation and maintenance is important.

Frequently Asked Questions (FAQs)

1.What is the difference between lap joint and slip on flanges?

A lap joint flange assembly consists of two main components: a stub end and a backing flange . Bolting the backing flanges together compresses the assembly, and the sealing occurs between the flat faces of the two mated stub ends with a gasket in between.

A slip-on flange is a single piece of metal with a bore slightly larger than the outer diameter of the pipe. It is easier to align than a weld neck flange. However, it offers lower pressure ratings and strength compared to weld neck and lap joint assemblies.

2.Is a lap joint flange raised face?

The standard and overwhelmingly common facing type for lap joint flanges is flat face (FF), not typically raised face. In essence, in a lap joint assembly, the sealing occurs between the flat, lapped faces of the two stub ends welded to the pipes being joined, with a gasket positioned between them. Consequently, the bolting force, applied to the backing flanges, compresses this gasket to create the seal. The backing flanges themselves are loose and do not directly participate in creating the seal.

Dimension of ASME B16.5 Lap Joint Flange

Class 150 lb
Nominal
Pipe Size		 A B C D R F H I J Weight
mm mm mm mm mm mm mm Holes mm mm kg/
piece
1/2 21.30 88.90 22.90 11.20 15.70 3.000 30.20 4 15.70 60.45 0.38
3/4 26.70 98.60 28.2 12.70 15.70 3.000 38.10 4 15.70 69.85 0.55
1 33.40 108.0 35. 10 14.20 17.50 3.000 49.30 4 15.70 79.25 0.76
11/4 42.20 117.3 43.70 15.70 20.60 4.800 58.70 4 15.70 88.90 1.01
11/2 48.30 127.0 50.00 17.50 22.40 6.400 65.00 4 15.70 98.60 1.30
2 60.30 152.4 62.50 19. 10 25.40 7.900 77.70 4 19.10 120.7 2.03
21/2 73.00 177.8 75.40 22.40 28.40 7.900 90.40 4 19.10 139.7 3.25
3 88.90 190.5 91.40 23.90 30.20 9.700 108.0 4 19.10 152.4 3.81
31/2 101.6 215.9 104.1 23.90 31.75 9.700 122.2 8 19.10 177.8 4.76
4 114.3 228.6 116.8 23.90 33.30 11.20 134.9 8 19.10 190.5 5.25
5 141.3 254.0 114.5 23.90 36.60 11.20 163.6 8 22.40 215.9 6.02
6 168.3 279.4 171.5 25.40 39.6 12.70 192.0 8 22.40 241.3 7.40
8 219. 1 342.9 222.3 28.40 44.50 12.70 246. 1 8 22.40 298.5 12.1
10 273.0 406.4 277.4 30.20 49.30 12.70 304.8 12 25.40 362.0 16.4
12 323.8 482.6 328.2 31.75 55.60 12.70 365.3 12 25.40 431.8 26.1
14 355.6 533.4 360.2 35. 10 79.25 12.70 400. 1 12 28.40 476.3 34.5
16 406.4 596.9 411.2 36.60 87.40 12.70 457.2 16 28.4 539.8 44.6
18 457.2 635.0 462.3 39.60 96.80 12.70 505.0 16 31.75 577.9 48.7
20 508.0 698.5 514.4 42.90 103.1 12.70 558.8 20 31.75 635.0 61.6
24 609.6 812.8 616.0 47.80 111.3 12.70 663.4 20 35.10 749.3 86.6

 

Class 300 lb
Nominal
Pipe Size		 A B C D R F H I J Weight
mm mm mm mm mm mm mm Holes mm mm kg/
piece
1/2 21.30 95.20 22.90 14.20 22.30 3.000 38.10 4 15.70 66.55 0.62
3/4 26.70 117.3 28.20 15.70 25.40 3.000 47.70 4 19.00 82.50 1.10
1 33.40 123.9 35.10 17.50 26.90 3.000 53.80 4 19.0 88.90 1.33
11/4 42.20 133.3 43.70 19.00 26.90 4.800 63.50 4 19.00 98.50 1.65
11/2 48.30 155.4 50.00 20.60 30.20 6.400 69.85 4 22.30 114.3 2.44
2 60.30 165.1 62.50 22.30 33.20 7.900 84.00 8 19.10 127.0 2.83
21/2 73.00 190.5 75.40 25.40 38.10 7.900 100.0 8 22.3 149.3 4.25
3 88.90 209.5 91.40 28.40 42.90 9.700 117.3 8 22.30 168.1 5.78
31/2 101.6 228.6 104.1 30.20 44.40 9.700 133.3 8 22.30 184.1 7.27
4 114.3 254.0 116.8 31.70 47.70 11.20 146.0 8 22.30 200.1 9.55
5 141.3 279.4 114.5 35.0 50.80 11.20 177.8 8 22.30 234.9 12.2
6 168.3 317.5 171.5 36.50 52.30 12.70 206.2 12 22.30 269.7 15.5
8 219.1 381.0 222.3 41. 10 61.90 12.70 260.3 12 25.40 330.2 24.1
10 273.0 444.5 277.4 47.70 95.20 12.70 320.5 16 28.40 387.3 34.4
12 323.8 520.7 328.2 50.80 101.6 12.70 374.6 16 31.70 450.8 50.4
14 355.6 584.2 360.2 53.80 111.2 12.70 425.4 20 31.70 514.3 70.9
16 406.4 647.7 411.2 57. 15 120.6 12.70 482.6 20 35.00 571.5 89.5
18 457.2 711.2 462.3 60.45 130.0 12.70 533.4 24 35.00 628.6 111
20 508.0 774.7 514.4 63.50 139.7 12.70 587.2 24 35.0 685.8 137
24 609.6 914.4 616.0 69.8 152.4 12.70 701.5 24 41.10 812.8 204

 

Class 400 lb
Nominal
Pipe Size		 A B C D R F H I J Weight
mm mm mm mm mm mm mm Holes mm mm kg/
piece
1/2 21.30 95.30 22.90 14.20 22.40 3.000 38.10 4 15.70 66.55 0.72
3/4 26.70 117.3 28.20 15.70 25.40 3.000 47.80 4 19. 10 82.60 1.25
1 33.40 124.0 35.10 17.50 26.90 3.000 53.80 4 19. 10 88.90 1.50
11/4 42.20 133.4 43.70 20.60 28.40 4.800 63.50 4 19. 10 98.60 2.00
11/2 48.30 155.4 50.00 22.40 31.75 6.400 69.85 4 22.40 114.3 2.92
2 60.30 165.1 62.50 25.40 36.60 7.900 84.10 8 19. 10 127.0 3.55
21/2 73.00 190.5 75.40 28.40 41.10 7.900 100.1 8 22.40 149.4 5.23
3 88.90 209.6 91.4 31.75 46.00 9.700 117.3 8 22.40 168. 1 6.95
31/2 101.6 228.6 104.1 35.10 49.30 9.700 133.4 8 25.40 184.2 8.78
4 114.3 254.0 116.8 35.10 50.80 11.20 146.1 8 25.40 200.2 10.9
5 141.3 279.4 114.5 38.10 53.80 11.20 177.8 8 25.40 235.0 13.7
6 168.3 317.5 171.5 41.10 57.15 12.70 206.2 12 25.40 269.7 18.0
8 219.1 381.0 222.3 47.80 68.30 12.70 260.4 12 28.40 330.2 28.3
10 273.0 444.5 277.4 53.80 101.6 12.70 320.5 16 31.75 387.4 38.8
12 323.8 520.7 328.2 57.15 108.0 12.70 374.7 16 35. 10 450.9 56.6
14 355.6 584.2 360.2 60.45 117.3 12.70 425.5 20 35. 10 514.4 78.6
16 406.4 647.7 411.2 63.50 127.0 12.70 482.6 20 38. 10 571.5 100
18 457.2 711.2 462.3 66.55 136.7 12.70 533.4 24 38. 10 628.7 122
20 508.0 774.7 514.4 69.85 146.1 12.70 587.2 24 41. 10 685.8 145
24 609.6 914.4 616.0 76.20 158.8 12.70 701.5 24 47.80 812.8 217

 

Class 600 lb
Nominal
Pipe Size		 A B C D R F H I J Weight
mm mm mm mm mm mm mm Holes mm mm kg/
piece
1/2 21.30 95.30 22.90 14.20 22.40 3.000 38.10 4 15.70 66.55 0.72
3/4 26.70 117.3 28.20 15.70 25.40 3.000 47.80 4 19. 10 82.60 1.25
1 33.40 124.0 35.10 17.50 26.90 3.000 53.8 4 19. 10 88.90 1.50
11/4 42.20 133.4 43.70 20.60 28.40 4.800 63.50 4 19. 10 98.60 2.00
11/2 48.30 155.4 50.00 22.40 31.75 6.400 69.85 4 22.40 114.3 2.92
2 60.30 165.1 62.50 25.40 36.60 7.900 84.1 8 19. 10 127.0 3.55
21/2 73.00 190.5 75.40 28.40 41. 10 7.900 100.1 8 22.40 149.4 5.23
3 88.90 209.6 91.40 31.75 46.00 9.700 117.3 8 22.40 168.1 6.95
31/2 101.6 228.6 104.1 35.10 49.30 9.700 133.4 8 25.40 184.2 8.78
4 114.3 273.1 116.8 38.10 53.80 11.20 152.4 8 25.40 215.9 14.4
5 141.3 330.2 114.5 44.50 60.45 11.20 189.0 8 28.40 266.7 24.3
6 168.3 355.6 171.5 47.80 66.55 12.70 222.3 12 28.40 292.1 28.5
8 219.1 419.1 222.3 55.60 76.20 12.70 273.1 12 31.75 349.3 43.1
10 273.0 508.0 277.4 63.50 111.3 12.70 342.9 16 35. 10 431.8 70.5
12 323.8 558.8 328.2 66.55 117.3 12.70 400.1 20 35. 10 489.0 86.1
14 355.6 603.3 360.2 69.85 127.0 12.70 431.8 20 38. 10 527.1 100
16 406.4 685.8 411.2 76.20 139.7 12.70 495.3 20 41. 10 603.3 145
18 457.2 743.0 462.3 82.60 152.4 12.70 546.1 20 44.50 654.1 177
20 508.0 812.8 514.4 88.90 165.1 12.70 609.6 24 44.50 723.9 225
24 609.6 939.8 616.0 101.6 184.2 12.70 717.6 24 50.80 838.2 318

 

Class 900 lb
Nominal
Pipe Size		 A B C D R F H I J Weight
mm mm mm mm mm mm mm Holes mm mm kg/
piece
1/2 21.30 120.6 22.90 22.30 31.70 3.000 38.10 4 22.30 82.50 1.71
3/4 26.70 130.0 28.20 25.40 35.00 3.000 44.40 4 22.30 88.90 2.30
1 33.40 149.3 35.10 28.40 41.10 3.000 52.30 4 25.40 101.6 3.40
11/4 42.20 158.7 43.70 28.40 41.10 4.800 63.50 4 25.40 111.2 3.85
11/2 48.30 177.8 50.00 31.70 44.40 6.400 69.85 4 28.40 123.9 5.28
2 60.30 215.9 62.50 38.10 57.15 7.900 104.6 8 25.40 165. 1 9.78
21/2 73.00 244.3 75.40 41.10 63.50 7.900 123.9 8 28.40 190.5 13.6
3 88.90 241.3 91.40 38.10 53.80 9.700 127.0 8 25.40 190.5 11.3
4 114.3 292.1 116.8 44.40 69.85 11.20 158.7 8 31.70 234.9 19.2
5 141.3 349.2 114.5 50.80 79.25 11.20 190.5 8 35.00 279.4 31.20
6 168.3 381.0 171.5 55.60 85.80 12.70 234.9 12 31.70 317.5 40.50
8 219.1 469.9 222.3 63.50 114.3 12.70 298.4 12 38.10 393.7 71.5
10 273.0 546.1 277.4 69.85 127.0 12.70 368.3 16 38.10 469.9 104
12 323.8 609.6 328.2 79.25 142.7 12.70 419.1 20 38.10 533.4 139
14 355.6 641.3 360.2 85.80 155.4 12.70 450.8 20 41.10 558.8 161
16 406.4 704.8 411.2 88.90 165.1 12.70 508.0 20 44.40 615.9 194
18 457.2 787.4 462.3 101.6 190.5 12.70 565.1 20 50.80 685.8 267
20 508.0 857.2 514.4 107.9 209.5 12.70 622.3 20 53.80 749.3 334
24 609.6 1041.4 616.0 139.7 266.7 12.70 749.3 20 66.55 901.7 618

 

Class 1500 lb
Nominal
Pipe Size		 A B C D R F H I J Weight
mm mm mm mm mm mm mm Holes mm mm kg/
piece
1/2 21.30 120.6 22.90 22.30 31.70 3.000 38.10 4 22.30 82.50 1.71
3/4 26.70 130.0 28.20 25.40 35.00 3.000 44.40 4 22.30 88.90 2.30
1 33.40 149.3 35. 10 28.40 41.10 3.000 52.30 4 25.40 101.6 3.40
11/4 42.20 158.7 43.70 28.40 41.10 4.800 63.50 4 25.40 111.2 3.85
11/2 48.30 177.8 50.00 31.70 44.40 6.400 69.85 4 28.40 123.9 5.28
2 60.30 215.9 62.50 38.10 57.15 7.900 104.6 8 25.40 165.1 9.78
21/2 73.00 244.3 75.40 41.10 63.50 7.900 123.9 8 28.40 190.5 13.6
3 88.90 266.7 91.40 47.70 73.15 9.700 133.3 8 31.70 203.2 17.8
4 114.3 311.1 116.8 53.80 90.40 11.20 162.0 8 35.00 241.3 27.5
5 141.3 374.6 114.5 73.15 104.60 11.20 196.8 8 41.10 292.1 51.5
6 168.3 399.7 171.5 82.50 119. 1 12.70 228.6 12 38.10 317.5 62.0
8 219. 1 482.6 222.3 91.90 142.7 12.70 292.1 12 44.40 393.7 105
10 273.0 584.2 277.4 107.9 177.8 12.70 368.3 12 50.80 482.6 179
12 323.8 673.1 328.2 123.9 218.9 12.70 450.8 16 53.80 571.5 269
14 355.6 749.3 360.2 133.3 241.3 12.70 495.3 16 60.45 635.0 365
16 406.4 825.5 411.2 146.0 260.3 12.70 552.4 16 66.55 704.8 459
18 457.2 914.4 462.3 162.0 276.3 12.70 596.9 16 73.15 774.7 598
20 508.0 984.2 514.4 177.8 292.1 12.70 641.3 16 79.25 831.8 712
24 609.6 1168.4 616.0 203.2 330.2 12.70 762.0 16 91.90 990.6 1090

 

Class 2500 lb
Nominal
Pipe Size		 A B C D R F H I J Weight
mm mm mm mm mm mm mm Holes mm mm kg/
piece
1/2 21.30 133.4 22.90 30.20 39.60 3.000 42.90 4 22.40 88.90 2.92
3/4 26.70 139.7 28.20 31.75 42.90 3.000 50.80 4 22.40 95.30 3.40
1 33.40 158.8 35. 10 35.10 47.80 3.000 57. 15 4 25.40 108.0 4.77
11/4 42.20 184.2 43.70 38.10 52.30 4.800 73. 15 4 28.40 130.0 7.08
11/2 48.30 203.2 50.00 44.50 60.45 6.400 79.25 4 31.75 146.1 9.93
2 60.30 235.0 62.50 50.80 69.85 7.900 95.30 8 28.40 171.5 14.7
21/2 73.00 266.7 75.40 57.15 79.25 7.900 114.3 8 31.75 196.9 21.3
3 88.90 304.8 91.40 66.55 91.90 9.700 133.4 8 35.10 228.6 32.3
4 114.3 355.6 116.8 76.20 108.0 11.20 165.1 8 41.10 273.1 52.5
5 141.3 419.1 114.5 91.90 130.0 11.20 203.2 8 47.80 323.9 82.6
6 168.3 482.6 171.5 108.0 152.4 12.70 235.0 8 53.80 368.3 127
8 219. 1 552.5 222.3 127.0 177.8 12.70 304.8 12 53.80 438.2 186
10 273.0 673.1 277.4 165.1 228.6 12.70 374.7 12 66.55 539.8 352
12 323.8 762.0 328.2 184.2 254.0 12.70 441.5 12 73.15 619.3 501

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