Technical Foundation
What Is a Pipe Fitting?
A pipe fitting joins, redirects, branches or terminates pipe runs — elbows change direction, tees branch a line, couplings join straight runs, and reducers step between pipe sizes. Fittings connect to pipe in one of three ways: threaded (NPT in the US, BSPT elsewhere — tapered threads that seal on interference, not interchangeable between standards), socket-weld (the pipe end inserts into a bored socket before welding, common on smaller high-pressure lines), or butt-weld (beveled ends welded directly to the pipe, used on larger diameters and high-purity or high-pressure service for its smooth uninterrupted bore).
A fitting's schedule (Sch 40, Sch 80, etc.) sets its wall thickness for a given nominal size, which must match the pipe it's joining or the bore and pressure capability won't align. Pressure-temperature ratings are set by ASME B16 standards — B16.3 for threaded and socket-weld fittings, B16.9 for butt-weld — based on material grade and wall thickness together, not size alone. Material selection (carbon steel, stainless steel, PVC/CPVC) is driven by the process fluid, temperature, and corrosion exposure, and dissimilar metals joined directly can suffer galvanic corrosion without a proper transition fitting.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Schedule Rating | Sch 40, Sch 80, etc. — wall thickness at nominal size | Must match the mating pipe's schedule or bore and pressure rating misalign |
| Connection Type | Threaded (NPT/BSPT), socket-weld, or butt-weld | Threaded standards aren't interchangeable; weld types suit different pressure/size ranges |
| Material | Carbon steel, stainless steel, PVC/CPVC | Driven by process fluid, temperature and corrosion exposure |
| Pressure-Temp Rating | Per ASME B16.3 (threaded/socket-weld) or B16.9 (butt-weld) | Set by material grade and wall thickness combined, must exceed operating conditions |
| Fitting Type | Elbow, tee, coupling, reducer, cap | Determines what the fitting does in the line — direction change, branch, or size transition |
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Applications
Where Pipe Fittings Get Used
Usage spans routine maintenance, new builds and facility upkeep — the right spec depends on the specific job.
Process piping & refineries
Butt-weld and socket-weld fittings rated to ASME B16.9/B16.3 for high-pressure, high-temperature process lines.
Chemical processing
Stainless and specialty-alloy fittings selected for corrosion resistance against aggressive process fluids.
HVAC & plumbing systems
Threaded and socket-weld carbon steel or copper fittings in building water and steam distribution.
Water & wastewater treatment
PVC and CPVC fittings for corrosion-resistant, lower-pressure fluid handling lines.
Compressed air & pneumatics
Threaded NPT fittings sized and rated for shop and plant compressed-air distribution.
Oil & gas gathering lines
Butt-weld fittings on larger-diameter carbon steel lines built to withstand sustained high pressure.
Brands
Pipe Fittings Brands in the Catalogue
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FAQ
Pipe Fittings Questions, Answered
What's the difference between NPT and BSPT threaded fittings?
Both are tapered thread standards that seal on thread interference, but NPT (National Pipe Taper, US) and BSPT (British Standard Pipe Taper) have different thread angles and pitch — they are not interchangeable even when the nominal size matches. Mixing them cross-threads or leaks; confirm which standard your mating fitting uses before ordering.
When should I use socket-weld versus butt-weld fittings?
Socket-weld fittings have a bored socket the pipe slips into before welding, which suits smaller pipe sizes and simpler alignment; butt-weld fittings are beveled and welded end-to-end with the pipe, used on larger diameters and higher-pressure or higher-purity lines where a smooth, uninterrupted bore matters.
How does schedule rating affect which fitting I need?
Schedule (e.g. Sch 40, Sch 80) describes wall thickness for a given nominal pipe size, which changes the fitting's actual bore and its pressure rating. A fitting must match the pipe's schedule, not just its nominal size, or the bore and pressure capability won't line up correctly.
What determines a fitting's pressure-temperature rating?
ASME B16 standards (B16.3 for threaded/socket-weld, B16.9 for butt-weld) set pressure-temperature ratings based on material grade and wall thickness — the same fitting shape in a higher material class or heavier schedule carries a higher rating. Always check the rating against your actual operating pressure and temperature, not just the fitting's nominal size.
Can I mix carbon steel, stainless steel and PVC fittings in one system?
Not without a transition fitting or flange rated for the interface — dissimilar metals in direct contact can cause galvanic corrosion, and metal-to-plastic joints need a proper transition fitting rather than a direct thread or weld. Match material to the process fluid, temperature and any galvanic compatibility concerns first.
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