Boss Fitting
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What Is a Boss Fitting
Pipe Boss Fitting
Boss fittings, also known as pipe boss fittings, are mechanical connection components for pressurized piping systems. Common types include American Socket Weld Boss and American Threaded Boss. These pipe fittings feature thickened metal material around the opening area, creating a raised point that reduces stress concentration. This design enhances the strength of both the base and the pipe, thereby improving the efficiency, safety, and stability of the piping system.
Boss Fitting Size Chart
Boss fittings span a wide range of sizes, from NPS 1/8 to NPS 2 (DN6-DN50). Common specifications include NPS 1/8 boss fitting, NPS 1/2 boss fitting, NPS 1/4 boss fitting, and NPS 2 boss fitting.
Boss fittings utilize SAE Straight Thread and NPT Tapered Thread. For example, a 1/2-inch pipe diameter corresponds to thread specifications of 3/4-16 (SAE straight thread) or 1/2-14 NPT (tapered thread).
Nominal Pipe Size (NPS) | SAE Straight Thread (UN/UNF) | NPT Tapered Thread | Socket Depth (J-Dimension, in) | Threads per Inch (TPI) |
1/8 | 5/16-24 UNF | 1/8-27 NPT | 0.25 | 24 |
1/4 | 7/16-20 UNF | 1/4-18 NPT | 0.31 | 20 |
3/8 | 9/16-18 UNF | 3/8-18 NPT | 0.38 | 18 |
1/2 | 3/4-16 UNF | 1/2-14 NPT | 0.43 | 16 |
3/4 | 1-1/16-12 UNF | 3/4-14 NPT | 0.56 | 12 |
1 | 1-5/16-12 UNF | 1-11.5 NPT | 0.69 | 12 |
1-1/4 | 1-7/8-12 UNF | 1-1/4-11.5 NPT | 0.81 | 12 |
2 | 2-1/2-12 UNF | 2-11.5 NPT | 1.06 | 12 |
How to Choose Boss Fittings Materials
How should pipe boss fittings materials be selected? Consideration must be balanced based on operating conditions, media, temperature, and other factors.
- Carbon steel: Carbon steel boss fittings conforming to ASME B16.11 and ASTM A105 standards are common and often used in applications involving humid environments.
- Stainless steel: Stainless steel boss fittings are suitable for applications requiring corrosion resistance, high-temperature tolerance, or stringent cleanliness standards. Austenitic stainless steels like 304/L and 316/L are most commonly used.
- Alloy steel: F91 (9Cr-1Mo) alloy steel is suitable for high-temperature steam systems up to 540°C, offering creep resistance five times superior to carbon steel.
- Special materials: Materials like Hastelloy are commonly used in marine engineering and other applications with high levels of corrosive media.
Boss Fitting Connection Methods
– Socket weld boss: ANSI socket weld Boss Fittings are the most commonly used. During installation, the pipe is inserted into the socket for a fillet weld. The socket bore diameter tolerance is +0.003/-0.000 inches.
– Threaded boss: ASME B16.11 standard American threaded Boss Fittings require a thread engagement length of 1.5 times the pipe diameter. For example, a 1-inch fitting must have a thread engagement length of at least 1.5 inches. Thread mean diameter tolerance is controlled at ±0.002 inches.
– O-Ring boss: Utilizes 90 Shore A fluorocarbon rubber O-rings with compression set controlled between 15%-25%, ensuring leakage rate below 0.1cc/min at 3000 PSI pressure.
– Butt welding boss: Butt welded joints are used for extremely large branch diameters or specific structural requirements.
FIREMINUS offers a wide range of pipe fittings beyond boss fittings, including Elbows, Returns, Tees, Crosses, Caps, Couplings, Bosses, Nipples, and Holes. Here you can find the right pipe fittings for your project and a customized solution tailored to your needs.
Contact us quickly to get a quote and solution!
