ASME B16.25

Covers — weld end preparation for all buttweld components:

• Pipes, fittings (B16.9), valves (B16.34), and flanges (B16.5).
• Wall thicknesses from standard (thin) to extremely heavy walls.
• Specific contours for carbon steel, alloy steel, and stainless steel preparations.
• Transition requirements when joining components of unequal wall thickness.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Socket weld preparations and geometries → ASME B16.11.
• The actual welding procedure qualifications and welder performance tests → ASME Section IX.

B16.25 categorizes bevel geometry strictly based on the wall thickness (t) of the component:

• Standard Bevel (t ≤ 22 mm or 0.88 in) — Requires a 37.5° ± 2.5° angle with a 1.6 mm (1/16 in) ± 0.8 mm root face. This is the classic V-bevel seen on almost all standard commercial piping.
• Compound Bevel (t > 22 mm) — Uses a compound angle (37.5° near the root, abruptly changing to 10° further out towards the OD). This critical design minimizes the massive volume of weld metal and heat input that would otherwise be required to fill a standard 37.5° V-groove on very thick pipes.
• Internal Machining — Specifies how to machine the inside of components (counterboring) when mating two items of different wall thicknesses to ensure a smooth transition.

While often overlooked by junior engineers as just "the bevel standard," ASME B16.25 is highly critical for welding engineering. A proper B16.25 bevel ensures that the welder has the correct accessibility to strike an arc and achieve full penetration at the root of the weld, while maintaining a consistent weld puddle without excessive heat input.

Whenever you order a "Buttweld" valve or fitting, the manufacturer will machine the ends exactly to ASME B16.25 based on the specific pipe schedule you denote on the purchase order. This guarantees that when the valve arrives at the construction site, it lines up perfectly with the pipe it is being welded to.