Pipe Fitting End Connections: Buttweld, Threaded, and Flanged Explained

Three Ways to Connect a Fitting

How a fitting joins the pipe is just as important as its material and size. The three most common end connection types are buttweld, threaded, and flanged. Each offers different tradeoffs in strength, installation speed, and disassembly.

Buttweld Ends: Permanent and Strong

Buttweld ends are bevelled and welded directly to the pipe, creating a monolithic joint. This is the strongest and most leak-free option. It is preferred for high-pressure, high-temperature, and hazardous service. The downside is that the joint is permanent and requires cutting to disassemble.

Threaded Ends: Quick Assembly

Threaded fittings have male or female NPT threads that screw onto the pipe. They are fast to install and do not require welding. They are commonly used for small-bore instrumentation lines, water systems, and low-pressure utilities. The main limitation is thread leakage risk and lower pressure capacity compared to welding.

Flanged Ends: Bolted Disassembly

Flanged fittings have integrated flanges that bolt together with a gasket between them. This allows easy disassembly for maintenance, valve replacement, or equipment access. Flanges are standard on large piping, pump connections, and pressure vessels. They are heavier and more expensive but offer unmatched flexibility.

Which to Choose?

Use buttweld for permanent, high-integrity joints. Use threaded for small, low-pressure, no-weld locations. Use flanged where regular disassembly is needed. Many systems combine all three: buttweld for the main run, flanges at equipment, and threaded for instrument branches.