SAE NPT Threaded Flanges

QS Flange: SAE NPT Threaded Flanges

SAE J518C NPT threaded flange in carbon steel, 1/2 to 5 inch at 3000 psi, sealing on a 1:16 taper for pipe and tube systems.

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One-Minute Overview

Tapered NPT flange for pipe and tube systems, built to SAE J518C.
Sizes 1/2 to 5 inch in carbon steel, 3000 psi continuous duty.
The 1:16 taper makes a radial interference fit that seals metal to metal.
Custom builds available, with delivery running 7 to 30 days.

The SAE NPT threaded flange seals on a taper, not on a gasket. As the joint is made up, the NPT thread — a 1:16 change in diameter per inch — closes radially and presses the mating surfaces into metal-to-metal contact, so the seal improves as the flange is turned.

Name: SAE NPT Threaded Flanges
Standard: SAE J518C
Type: NPT Threaded
Size: 1/2"-5"
Pressure: 3000 psi
Material: Carbon Steel
Application: Pipe and Tube Systems
Customization: Yes
Delivery Time: 7-30 Days

Measured leakage at rated pressure sits below 0.01 cc/min with standard torque. Anaerobic or silicone sealant can pull that down to about 0.001 cc/min, while PTFE tape wrapped three to five turns fills the microscopic helix path through the thread and widens temperature stability from -20°C to 150°C. Torque control is the other half of the job: roughly 60-80 Nm on 2 inch sizes, a thin lubricant to limit galling, and sealant renewed on a regular schedule. In vibration-prone duty the taper holds better than a straight thread, because the radial interference keeps the joint tight instead of letting it walk loose. Sizes run from 1/2 to 5 inch in carbon steel at 3000 psi, custom versions are available, and delivery runs 7 to 30 days, so a prototype and a production run can follow the same drawing.

FAQ

Q1. Why does an NPT joint hold without a gasket?

Because the thread is tapered. The 1:16 diameter change per inch creates a radial interference fit during make-up, which drives the mating surfaces into metal-to-metal contact. The seal is the joint itself, and it tightens rather than relaxes as torque goes on, which is why no separate sealing element is needed.

Q2. What torque should go on a 2 inch flange?

Roughly 60-80 Nm is the working range for 2 inch sizes. Apply a thin lubricant first to cut galling, use a calibrated wrench so the figure means something, and check torque again after the system has seen a few pressure cycles. Sealant or tape on the thread supports the taper seal.

Q3. Tape or paste — which one?

Both work; they solve different halves of the problem. PTFE tape, three to five turns, fills the microscopic helix leak path and widens the temperature window from -20°C to 150°C. Anaerobic or silicone sealant takes leakage from below 0.01 cc/min down to about 0.001 cc/min. For high-cycle duty I would reach for sealant.

Q4. What is the smallest order I can place?

Standard flange insulation gasket kits start at one set, and standard gaskets, studs, washers and sleeves start at one piece. Parts made to your drawing or to a non-standard bolt pattern are quoted one by one, because the minimum really depends on the material and the tooling involved.

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