Flanges · ASME B16.5
Lap Joint Flange — ASME B16.5
Also written LJ
Lap joint flange — a loose flange that sits behind a stub end welded to the pipe. A lap joint flange rotates freely, making bolt alignment easy on lines that are dismantled often. In corrosive service the flange never touches the fluid, so it can be carbon steel while the stub end is the alloy — a big saving.
- ASME B16.5
- 23 grades
- EN 10204 3.1 / 3.2
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
Lap Joint Flange: What to Know Before Ordering
- Used with a stub end (MSS SP-43 or ASME B16.9)
- Flange can be a cheaper material than the stub end
- Lower pressure rating than a weld neck
Lap Joint Flange Materials & Grades
| Grade | Material standard | Best for |
|---|---|---|
| Inconel 825 lap joint flange | ASTM B564 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 904L lap joint flange | ASTM A182 F904L | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| SS 304 lap joint flange | ASTM A182 F304 | General corrosion resistance, food, water and architectural work |
| SS 304L lap joint flange | ASTM A182 F304L | Welded tanks, piping and vessels in general corrosive service |
| SS 310 / 310S lap joint flange | ASTM A182 F310 | Furnaces, burners and heat treatment at high temperature |
| SS 316 / 316L lap joint flange | ASTM A182 F316L | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 321 lap joint flange | ASTM A182 F321 | High-temperature service between 425 and 815 °C |
| SS 347 lap joint flange | ASTM A182 F347 | Welded high-temperature piping in refineries and power plants |
| Duplex 2205 lap joint flange | ASTM A182 F51 / F60 | Strength with chloride resistance at a stainless-steel budget |
| Super Duplex 2507 lap joint flange | ASTM A182 F53 | Seawater and high-chloride service where strength also matters |
| Inconel 600 lap joint flange | ASTM B564 | High-temperature oxidation, caustic and nuclear service |
| Inconel 625 lap joint flange | ASTM B564 | Seawater, high strength and high temperature in one alloy |
| Inconel 718 lap joint flange | ASTM B637 | Very high strength at temperatures up to about 650 °C |
| Incoloy 800 / 800H / 800HT lap joint flange | ASTM B564 | Furnaces, petrochemical heaters and high-temperature piping |
| Hastelloy C276 lap joint flange | ASTM B564 | The most aggressive mixed acids, wet chlorine and hypochlorite |
| Hastelloy C22 lap joint flange | ASTM B564 | Mixed oxidising and reducing acids, and weld overlays |
| Monel 400 lap joint flange | ASTM B564 | Seawater, hydrofluoric acid and marine service |
| Monel K500 lap joint flange | ASTM B865 | High-strength pump shafts, bolting and springs in seawater |
| Super Duplex S32760 lap joint flange | ASTM A182 F55 | Seawater firewater, injection and offshore piping |
| ASTM A106 Gr B lap joint flange | ASTM A105 | High-temperature process and steam piping in refineries and power plants |
| ASTM A333 Gr 6 lap joint flange | ASTM A350 LF2 | Cold-climate and refrigerated piping down to −45 °C |
| ASTM A335 P11 lap joint flange | ASTM A182 F11 | Steam and hot-oil piping up to about 550 °C |
| ASTM A335 P22 lap joint flange | ASTM A182 F22 | High-pressure steam and hydrogen service up to about 580 °C |
Other flanges
Weld neck flangeA flange with a long tapered hub that is butt-welded to the pipe.Slip-on flangeA flange that slides over the pipe and is fillet-welded inside and outside.Blind flangeA solid disc that closes the end of a pipe, valve or vessel nozzle.Socket weld flangeA flange with a counterbore socket into which the pipe is inserted and fillet-welded.Threaded flangeA flange with a tapered internal thread that screws onto threaded pipe.Long weld neck flangeA weld neck flange with an extended straight neck, used as a vessel nozzle.Orifice flangeA pair of weld neck or slip-on flanges with pressure taps that hold an orifice plate.Spectacle blindA figure-8 plate with one solid end and one open ring, fitted between two flanges.Reducing flangeA flange with a smaller bore than its outside dimensions, connecting to a smaller pipe.Ring type joint flangeA flange with a machined groove for a metal ring gasket.Expander flangeA weld neck flange whose hub increases the pipe size.Anchor flangeA forged ring welded into a pipeline to fix it to a structure.Swivel ring flangeA flange with a rotating ring that allows bolt holes to be aligned after welding.
Lap Joint Flange dimensions — ASME B16.5 Class 150 & 300
Outside diameter, thickness and bolting are set by size and class. Values in mm; thickness excludes the 1.6 mm raised face.
| NPS | Cl 150 OD | Cl 150 thickness | Cl 150 bolt circle | Cl 150 bolts | Cl 300 OD | Cl 300 thickness | Cl 300 bolt circle | Cl 300 bolts |
|---|---|---|---|---|---|---|---|---|
| ½" | 90 | 9.6 | 60.3 | 4 × ½" | 95 | 12.7 | 66.7 | 4 × ½" |
| 1" | 110 | 12.7 | 79.4 | 4 × ½" | 125 | 15.9 | 88.9 | 4 × ⅝" |
| 1½" | 125 | 15.9 | 98.4 | 4 × ½" | 155 | 19.1 | 114.3 | 4 × ¾" |
| 2" | 150 | 17.5 | 120.7 | 4 × ⅝" | 165 | 20.7 | 127.0 | 8 × ⅝" |
| 3" | 190 | 22.3 | 152.4 | 4 × ⅝" | 210 | 27.0 | 168.3 | 8 × ¾" |
| 4" | 230 | 22.3 | 190.5 | 8 × ⅝" | 255 | 30.2 | 200.0 | 8 × ¾" |
| 6" | 280 | 23.9 | 241.3 | 8 × ¾" | 320 | 35.0 | 269.9 | 12 × ¾" |
| 8" | 345 | 27.0 | 298.5 | 8 × ¾" | 380 | 39.7 | 330.2 | 12 × ⅞" |
| 10" | 405 | 28.6 | 362.0 | 12 × ⅞" | 445 | 46.1 | 387.4 | 16 × 1" |
| 12" | 485 | 30.2 | 431.8 | 12 × ⅞" | 520 | 49.3 | 450.8 | 16 × 1⅛" |
Full chart: ASME B16.5 flange dimensions.
Lap joint flange — questions buyers ask
Does a lap joint flange have to be the same alloy as the pipe?
No. Only the stub end touches the fluid, so the backing flange is often carbon steel, saving the cost of an alloy forging.
Which grades are lap joint flanges available in?
Inconel 825, SS 904L, SS 304, SS 304L, SS 310 / 310S, SS 316 / 316L, SS 321, SS 347, Duplex 2205, Super Duplex 2507, Inconel 600, Inconel 625, Inconel 718, Incoloy 800 / 800H / 800HT, Hastelloy C276, Hastelloy C22, Monel 400, Monel K500, Super Duplex S32760, ASTM A106 Gr B, ASTM A333 Gr 6, ASTM A335 P11, ASTM A335 P22.
Which standard covers lap joint flange dimensions?
ASME B16.5. The material standard depends on the grade.
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