Pipe Connections2 min read
Threaded Flange vs Weld-Neck Flange: A Practical Selection Guide
Both create a bolted flange joint. The difference is how the flange is attached to the pipe — and that changes where each one belongs.
At a glance
4 key points- 01
Threaded flanges screw onto threaded pipe and need no welding.
- 02
Weld-neck flanges are butt-welded and suit more demanding service.
- 03
Threaded joints suit smaller bores and moderate conditions.
- 04
Flange standard, class, facing and thread form must all be specified.
01How each flange attaches to the pipe
A threaded flange has an internally threaded bore that screws onto a threaded pipe end. A weld-neck flange has a tapered hub that is butt-welded to the pipe. Both then bolt to a mating flange with a gasket between the faces.
That single difference — thread or weld — drives where each type is used.
02Comparison at a glance
| Criteria | Threaded flange | Weld-neck flange |
|---|---|---|
| Pipe attachment | Screwed onto threaded pipe | Butt-welded to the pipe |
| Welding required | No | Yes |
| Typical service | Moderate pressure, smaller bores | Higher pressure, temperature or cyclic service |
| Installation | Fast, no hot work | Qualified welding and inspection |
| Leak path | Thread must be sealed | Welded joint, no thread |
03Where threaded flanges make sense
- Utility services such as water and air lines.
- Areas where hot work is restricted or hazardous.
- Smaller-bore lines operating at moderate pressure and temperature.
- Connections that may need to be dismantled without cutting pipe.
04Getting the specification right
- Nominal pipe size.
- Flange standard and pressure class.
- Facing — raised face or flat face — to match the mating flange.
- Bore thread form, for example NPT or BSP, matching the pipe thread exactly.
- Material, aligned with the piping specification and process fluid.
Mixing taper and parallel threads, or mismatching the mating flange drilling, are the most common causes of problems with threaded flange joints. Matching pipe fittings should follow the same thread standard.
Questions & answers
Frequently Asked Questions
Can a threaded flange be used for high-pressure service?
Threaded flanges are generally used for moderate pressure and temperature on smaller bores. For demanding pressure, temperature or cyclic service, welded flange types are usually specified. Follow your piping specification.
Do threaded flanges need a gasket?
Yes. The flange faces are sealed with a gasket like any other flange joint, and the thread connection to the pipe is sealed separately with a compatible thread sealant.
What is the difference between a slip-on and a threaded flange?
A slip-on flange slides over the pipe and is fillet-welded, while a threaded flange screws onto the pipe without welding.
What information is needed to quote a threaded flange?
Provide the pipe size, flange standard, pressure class, facing, bore thread form, material, quantity and any marking or drawing requirement.
