Pipe End Connections
Bevelled, plain, threaded and grooved — how each end preparation is made, what it joins to, and the wall-mismatch rule that catches schedule changes mid-run.
- Bevelled end
- 37.5° ± 2.5°, for butt welding
- Plain end
- Square cut, for socket or slip-on
- Threaded end
- NPT taper, ASME B1.20.1
- Root face
- 1/16 in ± 1/32 in typical
Short answer. Pipe ships with one of three end preparations. A bevelled end is machined to 37.5° for butt welding and is the default for process piping. A plain end is cut square, for socket welding, slip-on flanges and grooved couplings. A threaded end carries an NPT taper thread for screwed joints. The end preparation has to be stated on the purchase order — it is not implied by the schedule.
The three preparations
| End type | Preparation | Joined by | Typical use |
|---|---|---|---|
| Bevelled (BE) | 37.5° ± 2.5° bevel with a 1/16 in root face | Butt weld, usually with a root gap of about 1/16 in | Process piping, all sizes. The default above NPS 2. |
| Plain (PE) | Cut square, deburred | Socket weld, slip-on flange, or grooved coupling | Small bore socket weld systems and slip-on flanged work. |
| Threaded (TE / TOE) | NPT taper thread to ASME B1.20.1 | Screwed joint, usually with PTFE tape or pipe dope | Utility piping, hazardous areas, instrument connections. |
| Grooved | Rolled or cut groove near the end | Mechanical coupling clamped over the groove | Fire protection, HVAC, and thin-wall systems. |
| Belled / spigot | One end expanded to receive the next | Solvent weld, gasket, or caulked joint | Cast iron and plastic pipe; not standard for steel. |
The butt weld bevel
ASME B16.25 governs the welding end preparation for buttwelding fittings and pipe. The standard preparation is a single V bevel at 37.5° from the pipe axis — giving a 75° included angle when two ends meet — with a root face, or land, of about 1/16 in.
Bevel angle 37.5° ± 2.5° · root face 1/16 in ± 1/32 in · root gap ≈ 1/16 in
Heavier walls change this. Above about 3/4 in wall thickness B16.25 provides compound bevels — a steeper angle near the root and a shallower one further out — to reduce the volume of weld metal required. The root face and gap exist so the root pass achieves full penetration without burning through.
Matching mismatched walls
When two components of different wall thickness are butt welded, the bores do not line up and the transition has to be handled. ASME B31.3 limits the permissible internal misalignment and requires the thicker component to be tapered — no steeper than 30° — down to the thinner bore. In practice that means the heavier part is counterbored and back-bevelled before fit-up.
This is exactly the situation created by welding Schedule 40 to Schedule 80 pipe, and it is why a schedule change should happen at a fitting or a flange rather than mid-run wherever possible.
Threaded ends in practice
NPT threads seal on interference between the tapered flanks, not on the sealant — the tape or dope is a lubricant and a gap filler, not the seal. Three consequences follow:
- Wall thickness matters. The thread root cuts into the wall, so threaded pipe needs a heavier schedule — Schedule 80 as a practical minimum in most specifications.
- Vibration loosens threads. Threaded joints are excluded from severe cyclic service by ASME B31.3 and are a poor choice on anything that shakes.
- Seal welding is sometimes required. B31.3 requires threaded joints in Category M fluid service to be seal welded, which makes them permanent.
Specifying an end on a purchase order
| Abbreviation | Means |
|---|---|
| BE | Bevelled end, both ends |
| PE | Plain end, both ends |
| TBE | Threaded both ends |
| TOE | Threaded one end |
| T&C | Threaded and coupled — threaded both ends with a coupling fitted to one |
| POE | Plain one end |
Always state the end preparation explicitly. Mill stock defaults vary by size and supplier.
See also: B16.9 buttweld fittings · socket weld vs threaded · slip-on vs threaded · material selection.
Common questions
What angle is a standard pipe bevel?
37.5° ± 2.5° from the pipe axis, giving a 75° included angle when two ends meet, with a root face of about 1/16 in. ASME B16.25 governs the preparation.
What does BE mean on a pipe purchase order?
Bevelled end — the pipe is supplied with a butt welding bevel on both ends. PE is plain end, TBE is threaded both ends, and TOE is threaded one end.
Why is a root face needed on a weld bevel?
To give the root pass something to fuse into without burning through. A knife-edge root melts away and leaves a concave or burned-through root.
Can I butt weld Schedule 40 to Schedule 80 pipe?
Yes, but the internal misalignment must be handled. ASME B31.3 requires the thicker component to be tapered at no more than 30° down to the thinner bore, which means counterboring and back-bevelling the heavier part.
What schedule is needed for threaded pipe?
Heavy enough that the thread root leaves adequate wall — Schedule 80 is the practical minimum in most specifications. Thin-wall pipe such as Schedule 10 cannot be threaded.