Threaded Flange

Threaded flange, abbreviated as TRHF,, also called a screwed flange, is a type of pipe flange that has internal threads (female threads) machined into its bore so it can be screwed directly onto a pipe with matching external threads.  Unlike weld neck, slip-on, or socket weld flanges, a threaded flange is installed without welding under normal conditions.  Once the pipe is threaded into the flange, the flange can be bolted to a mating flange using bolts, nuts, and a gasket to create a pressure-tight joint.

Threaded flanges are primarily used in piping systems where welding is undesirable, impractical, or prohibited.  Because installation only requires threading the pipe into the flange, assembly and disassembly can often be completed more quickly than with welded flanges.

These flanges are generally intended for small-diameter piping systems, typically in nominal pipe sizes where threaded pipe is commonly used.  They are most often found in low pressure and moderate temperature services, although the specific pressure and temperature limits depend on the applicable flange pressure class, material, thread design, and the governing engineering code.  In many industrial applications, threaded flanges are not recommended for severe cyclic loading, vibration, or large temperature fluctuations because the threaded connection can be more susceptible to loosening or fatigue than a properly welded joint.

The principal advantages of threaded flanges include the elimination of welding, ease of installation, suitability for hazardous locations where welding is restricted, and the ability to disconnect the piping without cutting the pipe.  Their disadvantages include lower resistance to vibration and fatigue than welded connections, potential leakage if threads are improperly assembled or damaged, and practical limitations for larger pipe sizes and more demanding pressure or temperature conditions.