Reducing pipe fitting is a kind of pipe fitting used to connect two pipes with different outer diameter or specification, which can be divided into concentric reducer and eccentric reducer according to the concentricity of ends. They usually use a hot/cold stamping or forging process to enlarge or reduce the outer diameter of one end of the fitting. Reducing pipes fitting with the same specification have the same end sizes, wall thickness, and length, except that the centers of the two ends of the concentric reducer are on a vertical line while the eccentric reducer tubes are not.
Reducing forming is a process which made the pipe ends of which diameter equal to the reducing pipe end into the forming mold and press along the tube blank axially to make the metal move along the mold chamber, which can be one or more times. Expanding forming is to enlarge the tube blank with the diameter smaller than the large end of reducing tube and use the inner mold to enlarge the diameter along the inner diameter of tube blank. The process of enlarging mainly solves the situation that the reducing pipe with larger diameter is not easy to be formed by reducing diameter. Sometimes, according to the needs of materials and products, the method of expanding and reducing can be used simultaneously. In the process of deformation pressing according to the material and actual conditions can be used cold pressing or hot pressing, of which cold pressing is usually used, but repeated diameter and cause serious work hardening, large wall thickness or alloy steel should be hot pressed.
They share the same specifications, materials and standard systems such as ANSI B16.5 and ANSI B 16.47, materials implement ASTM A106/A53 GRB, API 5L, APT5CT, ASTM A105, ASTM A234, ASTM A106, DIN and so on. ASTM/ASME A860 grade WPHY 42/46/52/60/65/70 reducing eccentric/concentric fitting is available for use in oil and gas pipe-line applications. Other standards can be divided into alloy elements:
Carbon steel: ASTM/ASME A234 WPB/WPC
Alloy steel: ASTM/ASME A234 WP 1/ WP 12/ WP 11/ WP 22/ WP 5/WP 91/ WP911/15Mo3 /15CrMoV/ 35CrMoV
Stainless steel: ASTM/ASME A403 WP 30/304L/304H/304LN/304N/ 316/ 316L/316H/316LN/316N/316Ti/ 321/ 321H/347/347H
Low temp steel: ASTM/ASME A402 WPL3/WPL 6
In general, they can be used in the following conditions:
Concentric reducer is generally used if no special requirements as well as diameter less than DN50 pipe；
Both concentric and eccentric reducer can be used in vertical pipes and more concentric reducer. Eccentric reducer are more used in horizontal pipes.
Most of the eccentric reducer are used pipeline for transporting liquid flow to prevent the accumulation, while concentric reducer are used the pipeline for transporting gas.
Some pumps inlet and outlet or the horizontal fitting that does not allow residual fluid used eccentric reducer more.