Carbon steel threaded fittings combines high strength and good ductility with outstanding corrosion resistance qualities. They have excellent resistance to stress corrosion cracking and corrosion fatigue, providing permanent leak proof while adding strength and power to the piping structure. The output of these products occupies a large part of the steel pipe fittings.
Types of Forged Fittings with Thread End
According to the usage, Forged Threaded Fittings mainly have four types.
1. Threaded fittings for connecting pipes. These fittings mainly are Screwed Union, Half Coupling and Full Coupling.
2. Direction Change Fittings. They are 45 degree Elbow, 90 degree Elbow and so on.
3. Branch Threaded Fittings: Reducing Tee, Equal Tee, Pipe Cross and Threadolet. Threadolet also can be used only to change the diameter of pipe line.
4. Threaded Fittings to seal the pipe end. They are Hex Head Bushing & Plug and Screwed Cap.
All of these are manufactured in accordance with ASME standards, one of the major international standards systems.
Carbon Steel Threaded Fittings Dimensions
ASME B16.11 is a specification standard for forged pipe fittings with thread end and socket weld end. It covers the diameter, pressure, tolerance, finish and testing of threaded fittings. Thread length and type are also indicated in this standard. The pressure rating is 2000LB, 3000LB & 6000LB.
Threaded Union also specified in MSS-SP-83, its dimensions are 1/8 inch to 3 inch in this standard.
Threadolet uses standard MSS-SP-97 more often. The diameter is from 1/8 inch to 4 inch.
Material & Grades
ASTM A105N, A350 LF2/LF3,A694 F52, F56, F60, F65, F70
Chemical Properties
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni |
| A105 | 0.035 | 0.6 – 1.05 | 0.1 – 0.35 | 0.035 | 0.04 | 0.3 | 0.12 | 0.4 |
| A350 LF2 | 0.3 | 0.6 – 1.35 | 0.15 – 0.3 | 0.035 | 0.04 | 0.3 | 0.12 | 0.4 |
| A350 LF3 | 0.2 | 0.9 | 0.20-0.35 | 0.035 | 0.04 | 0.3 | 0.12 | 3.3 – 3.7 |
| A694 F52 | 0.26-0.265 | 1.60-1.64 | 0.15-0.35 | 0.025-0.030 | 0.025-0.030 | |||
| A694 F56 | 0.26-0.265 | 1.60-1.64 | 0.15-0.35 | 0.025-0.030 | 0.025-0.030 | |||
| A694 F60 | 0.26-0.265 | 1.60-1.64 | 0.15-0.35 | 0.025-0.030 | 0.025-0.030 | |||
| A694 F65 | 0.26-0.265 | 1.60-1.64 | 0.15-0.35 | 0.025-0.030 | 0.025-0.030 | |||
| A694 F70 | 0.26-0.265 | 1.60-1.64 | 0.15-0.35 | 0.025-0.030 | 0.025-0.030 |
Mechanical Properties
| Grade | Tensile Strength (Mpa) | Yield Strength (Mpa) | Elongation (%) |
| A105 | 485 | 250 | 22 |
| A350 LF2 | 485 – 655 | 250 | 22 |
| A350 LF3 | 485 – 655 | 260 | 22 |
| A694 F52 | 455 | 360 | 20 |
| A694 F56 | 470 | 385 | 20 |
| A694 F60 | 515 | 415 | 20 |
| A694 F65 | 530 | 450 | 20 |
| A694 F70 | 565 | 485 | 18 |
Threaded End Connection
There are three types of threads that common used in carbon steel threaded fittings.
The standard threads of ASME B16.11 Fittings are NPT, The American National Pipe Thread Tapered. It is the best known and most widely used connection type specified by ANSI B1.20.1. The thread angle is 60 degree.
BSPP (Parrallel) and BSPT (Tapered) threads also required by a lot customers. They are British standard threads which is common in Australia and the commonwealth countries. The thread angle is 55 degree.
ASTM Carbon Steel Threaded Forged Fittings
ASTM A105 is most common material for carbon steel threaded fittings. It is a low carbon, manganese and silicon containing steel.
A350 LF2 and LF3 are low temperature carbon steels, chiefly used in low temperature pipe system. It is covers carbon and low alloy steel forgings that requiring notch toughness testing for piping components.
ASTM A694 carbon steel is suitable for use with high strength transmission service pipe. Included are flanges, fittings, and similar parts ordered either to dimensions specified by the purchaser or to ASME or MSS dimensional standards.