What is ASME B16.25?
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What is ASME B16.25?
ASME B16.25 is an international standard covering the preparation of butt welding ends for pipes, valves, fittings, and flanges to be joined by welding. It defines bevel angles, tolerances, and wall thickness configurations (3 mm to 10 mm standard) for secure butt-weld joints. Common applications include industrial pipe fabrication and joining pressure-containing components.
ASME B16.25 Scope and Application
Components: It applies to any component joined by butt welding, including pipes, valves, flanges, and fittings.
Materials: It covers both metallic and non-metallic piping materials.
Preparation Methods: It includes requirements for machining, grinding, or thermal cutting to achieve the required shapes.
Technical Requirements of ASME B16.25
The ASME B16.25 standard specifies different types of end preparation (bevel design) based on pipe wall thickness:
Square End (Plain End):Typically used for very thin-walled pipes (generally ≤ 3 mm).
Single Bevel:The most common end preparation. For pipes with a wall thickness between 5 mm and 22 mm (0.19" to 0.88"), the standard requires a bevel angle of 37.5°, along with a small flat land at the root of the bevel, known as the root face.
Compound Bevel:Applied to thick-walled pipes (wall thickness > 22 mm / 0.88"). Unlike a single straight bevel, this design uses a variable angle (e.g., transitioning from 37.5° to 10°). This helps prevent excessive weld gap width, reduces filler metal consumption, and minimizes the heat-affected zone.
ASME B16.25 Relationship to Other Standards
ASME B16.5 / B16.47: For flange dimensions (which refer to B16.25 for the welding neck).
ASME B16.9: For factory-made wrought buttwelding fittings.
ASME B31.3 / B31.1: The overarching Process and Power Piping codes that mandate how these welds must be performed and inspected.
End Preparation Requirements Based on Wall Thickness
This table lists the basic end-finishing types determined by wall thickness.
| Wall Thickness (t) | End Preparation Type | Typical Geometry |
| t<3 mm (0.12 in.) | Cut Square (Plain End) | Ends shall be square or slightly chamfered. |
| 3 mm ≤t≤22 mm (0.12 in.≤t≤0.88 in.) | Single Bevel | 37.5° angle with root face. |
| t> 22 mm (0.88 in.) | Compound Bevel | Double angle (37.5° and 10°) or J-bevel. |
Standard Dimensions and Tolerances for Bevels
This table describes the specific parameters for a standard Single Bevel.
| Parameter (Symbol) | Technical Description | Standard Dimension | Tolerance |
| Bevel Angle (
θθ) |
Angle of bevel for t≤22mm | 37.5° | ±2.5° |
| Root Face (C) | The flat part at the bottom of the bevel |
1.6 mm1.6 mm (1/16 in) |
±0.8 mm±0.8 mm (1/32 in.) |
| Outer Bevel Angle | First angle for compound bevel (t>22mm) |
37.5° |
±2.5° |
| Inner Bevel Angle | Second angle for compound bevel (t>22mmt) |
10° |
±1° |
| Inside Diameter (d) | Internal diameter at the welding end | As per pipe schedule |
+2 mm/−1 mm |
Requirements for Unequal Wall Thickness (Transitions)
When the two connected components have unequal wall thicknesses, ASME B16.25 mandates the implementation of a tapered transition.
| Configuration | Requirement | Minimum Slope / Ratio |
| Internal Offset | For difference in internal diameters |
1:4 minimum taper |
| External Offset | For difference in external diameters |
1:3 maximum slope (preferred) |
| Combined Offset | When both ID and OD are different | Requires specific transition machining (Taper) |
Dimensions of Welding Ends (See Figures 2-1 Through 3.2-3)
| Nominal Pipe Size(NPS) | Schedule No.[Note(1)] | O.D. at Welding Ends, A | B | C[Note(3)] | t | |
| Wrought or Fabricated Components[Note(1),(2)] | Cast Components[Note(2)] | |||||
| 20 | 100 | 508.0(20.000) | 516(20.31) | 443.00(17.438) | 450.02(17.717) | 32.54(1.281) |
| 120 | 508.0(20.000) | 516(20.31) | 432.00(17.000) | 440.29(17.334) | 38.10(1.500) | |
| 140 | 508.0(20.000) | 516(20.31) | 419.00(16.500) | 429.17(16.896) | 44.45(1.500) | |
| 160 | 508.0(20.000) | 516(20.31) | 408.00(16.062) | 419.44(16.513) | 50.01(1.969) | |
| 22 | STD | 558.8(22.000) | 567(22.34) | 539.00(21.250) | 541.08(21.303) | 9.53(0.375) |
| XS | 558.8(22.000) | 567(22.34) | 533.00(21.000) | 535.54(21.084) | 12.70(0.500) | |
| 60 | 558.8(22.000) | 567(22.34) | 514.00(20.250) | 518.86(20.428) | 22.23(0.875) | |
| 80 | 558.8(22.000) | 567(22.34) | 501.00(19.750) | 507.75(19.990) | 28.58(1.125) | |
| 100 | 558.8(22.000) | 567(22.34) | 488.50(19.250) | 496.63(19.553) | 34.93(1.375) | |
| 120 | 558.8(22.000) | 567(22.34) | 476.00(18.750) | 485.52(19.115) | 41.28(1.625) | |
| 140 | 558.8(22.000) | 567(22.34) | 463.00(18.250) | 474.41(18.678) | 47.63(1.875) | |
| 160 | 558.8(22.000) | 567(22.34) | 450.50(17.750) | 463.30(18.240) | 53.98(2.125) | |
| 24 | STD,40S | 609.6(24.000) | 619(24.38) | 590.50(23.250) | 591.88(23.303) | 9.53(0.375) |
| XS,80S | 609.6(24.000) | 619(24.38) | 584.00(23.000) | 586.34(23.084) | 12.70(0.500) | |
| 30 | 609.6(24.000) | 619(24.38) | 581.00(22.876) | 583.59(22.975) | 14.27(0.562) | |
| 40 | 609.6(24.000) | 619(24.38) | 574.50(22.624) | 577.97(22.755) | 17.48(0.688) | |
| 60 | 609.6(24.000) | 619(24.38) | 560.50(22.062) | 565.49(22.263) | 24.61(0.969) | |
| 80 | 609.6(24.000) | 619(24.38) | 547.50(21.562) | 554.38(21.826) | 30.96(1.219) | |
| 100 | 609.6(24.000) | 619(24.38) | 532.00(20.938) | 540.49(21.280) | 38.89(1.531) | |
| 120 | 609.6(24.000) | 619(24.38) | 517.50(20.376) | 528.03(20.788) | 46.02(1.812) | |
| 140 | 609.6(24.000) | 619(24.38) | 505.00(19.876) | 516.91(20.350) | 52.37(2.062) | |
| 160 | 609.6(24.000) | 619(24.38) | 490.50(19.312) | 504.37(19.857) | 59.54(2.344) | |
| 26 | 10 | 660.4(26.000) | 670(26.38) | 645.50(25.376) | 645.50(25.413) | 7.92(0.312) |
| STD | 660.4(26.000) | 670(26.38) | 641.34(25.250) | 642.68(25.303) | 9.53(0.375) | |
| 20 | 660.4(26.000) | 670(26.38) | 635.00(25.000) | 637.14(25.084) | 12.70(0.500) | |
| 28 | 10 | 711.2(28.000) | 721(28.38) | 695.50(27.376) | 696.30(27.413) | 7.92(0.312) |
| STD | 711.2(28.000) | 721(28.38) | 692.14(27.250) | 693.48(27.303) | 9.53(0.375) | |
| 20 | 711.2(28.000) | 721(28.38) | 686.00(27.000) | 687.94(27.084) | 12.70(0.500) | |
| 30 | 711.2(28.000) | 721(28.38) | 679.50(26.750) | 682.37(26.865) | 15.88(0.625) | |
| 30 | 10 | 762.0(30.000) | 772(30.38) | 746.00(29.376) | 747.10(29.413) | 7.92(0.312) |
| STD | 762.0(30.000) | 772(30.38) | 742.94(29.250) | 744.28(29.303) | 9.53(0.375) | |
| 20 | 762.0(30.000) | 772(30.38) | 736.50(29.000) | 738.74(29.084) | 12.70(0.500) | |
| 30 | 762.0(30.000) | 772(30.38) | 730.00(28.750) | 733.17(28.865) | 15.88(0.625) | |
