In pipeline engineering, connecting pipes of different diameters is a common requirement, and there are various ways to achieve this transition. Among them, swage nipples and reducers are two of the most commonly used types of pipe fittings. Their common feature is that they can connect pipes of different diameters, but they differ significantly in terms of structural design, connection methods, applicable conditions, and manufacturing processes. A thorough understanding of the characteristics of these two types of fittings not only facilitates proper selection but also enhances the safety and cost-effectiveness of pipeline systems.
What is Swage Nipples?
A swage nipple is a short length of pipe with a tapered transition in the middle, where one end has a larger diameter and the other end a smaller diameter. It is usually made with either a threaded end or a socket-welded end. This type of fitting is often used to connect small-diameter, high-pressure pipelines. Its main purpose is to join pipes of different sizes, enabling a quick change in diameter over a short distance. By doing so, it allows the pipeline system to adjust the pipe size to suit varying flow rates or pressure requirements in different sections.
Function and Types of Swage Nipples
Concentric swage nipple: The centerlines of the two connected pipes are aligned in a straight line. This type is primarily used in vertical pipelines. In some vertical water supply or gas supply pipeline systems, concentric reducers ensure stable fluid flow in the vertical direction, reducing resistance and turbulence caused by changes in pipe diameter.
Eccentric swage nipple: Primarily used in horizontal pipelines. For example, in horizontal oil transportation pipelines, eccentric reducers can be adjusted to accommodate height differences between pipes as needed to meet process requirements or avoid interference with other equipment. Additionally, in applications requiring control of fluid flow direction and velocity, eccentric reducers can play a unique role.
What is Reducers?
A reducer is a tapered pipe fitting used to connect pipes of different diameters. It typically consists of two pipe sections of different sizes or specifications, connected by a transitional shape. Reducers can be configured with various transitional shapes, such as tapered and flared, depending on the application. They are primarily used in piping systems where sizes or specifications vary significantly, solving the connection problem between pipes of varying sizes or specifications. They are available in concentric and eccentric versions. They are longer than reducing nipples and typically have butt-weld ends.
Function and Types of Reducers
Concentric Reducer：The centers of the two ends of the concentric reducer are aligned on the same axis, and its appearance is symmetrical in shape, typically used for connecting vertical pipes to ensure smooth fluid flow and prevent the formation of vortices or turbulence within the pipe.
Eccentric Reducers：eccentric reducers have pipe openings at both ends that are not aligned on the same axis, with an eccentric conical shape. This design makes them highly useful for horizontal pipe connections, typically maintaining a level bottom to prevent the accumulation of liquid or gas inside the pipe, thereby effectively avoiding issues such as cavitation.
Differences Between Swage Nipple and Reducer
Diameter Range:
the diameter range of reducer is relatively wide, and the current standard range is DN15-DN3400 (1 / 2 ’’ ~ 136”).
And the specification range of nipple is: DN6-DN300 (1 / 4 ’’- 12”) is generally the maximum DN100.
Pressure Rating Adaptability
Reducing elbows, which are manufactured using a forging process, have high overall strength and can withstand high-pressure environments. They are commonly used in high-pressure pipeline systems, such as high-pressure hydraulic pipelines and high-pressure steam pipelines.
While reducers also have a broad pressure rating adaptability range, their performance in ultra-high-pressure scenarios is slightly inferior to that of reducers. However, for medium-to-low-pressure large-scale pipeline systems, reducers leverage their structural characteristics to better distribute pressure and meet operational requirements.
Materials
Swage nipples
Because they are often used for small-diameter, high-pressure pipes, they are often made from high-strength, pressure-resistant forged materials. Such as ASTM A105 carbon steel, A182 series stainless steel, and nickel-based alloys.
Mostly forged, they offer high density and superior pressure-bearing capacity compared to castings or sheet metal parts of the same material.
ASTM A105: Standard specification for carbon steel forgings for piping applications
ASTM A350: Standard specification for carbon and low-alloy steel forgings requiring notch toughness testing for piping components
ASTM A182: Standard specification for forged or rolled alloy and stainless steel pipe flanges, forged fittings, and valves
Reducers
Commonly used for medium- and large-diameter pipes, they are often machined from pipe or sheet metal (seamless or welded).
When high corrosion and temperature resistance are required, stainless steel, duplex steel, or nickel-based alloys are often used.
Due to their long lengths, they are often manufactured using cold forming or hot pressing, making them suitable for large-scale processing.
ASTM A234: Standard specification for piping fittings of wrought carbon steel and alloy steel for moderate and high-temperature service
ASTM A403: Standard specification for wrought austenitic stainless steel piping fittings
Manufacturing processes
The manufacturing process for swage nipples (reducer fittings) typically involves forging. The raw materials are usually round bars or forged blanks, which are heated and forged into the desired shape. The ends are then machined to form different connection types, while the middle section is machined into a conical transition segment. Due to the dense internal structure and high strength of forged components, reducers are highly suitable for small-diameter, high-pressure, and high-strength pipeline connections.
The manufacturing process for reducers (size heads) is primarily divided into two categories: seamless forming and welded forming. Seamless reducers are typically made from steel pipes through cold pushing, hot pressing, or mold forming, while large-diameter or special-sized reducers are often produced by rolling and welding steel plates. During manufacturing, mold pressing is performed according to concentric or eccentric structural requirements, followed by heat treatment and dimensional finishing to ensure welding performance, corrosion resistance, and geometric accuracy.
Connection Ends
Beveled ends are basically adopted for reducers, and plain ends are hardly adopted for reducers. Although the plain end are allowed to be used for the stainless steel or the carbon steel reducer product whose wall thickness is lower than a certain amount. Swage nipples have more connection ends, and two ends of swage nipples can be the same or different based on the requirements of sites or designs. Connection ends of swage nipples can be divided into beveled ends, plain ends and threaded ends three kinds. The following is a good introduction to the connection end of the swage nipple.
Bevel of Both Ends ( BBE)
Plain of Both Ends ( PBE)
Thread of Both Ends ( TBE)
Bevel of Large End / Plain of Small End ( BLE/PSE)
Bevel of Large End / Thread of Small End ( BLE/TSE)
Plain of Large End / Thread of Small End ( PLE/TSE)
Plain of Large End / Bevel of Small End ( PLE/BSE)
Thread of Large End / Bevel of Small End ( TLE/BSE)
Bevel of Large End / Thread of Small End ( BLE/TSE)
Application Scenarios
Due to their smaller size and flexible connection end forms, swage nipples are commonly used in pipeline systems with smaller diameters, particularly in scenarios requiring threaded connections or flexible adjustment of connection methods. For example, they are commonly found in small-scale industrial installations and local pipe connections in building plumbing systems.
Reducers, with their wide range of sizes, are more widely used in large-scale industrial projects, such as pipeline systems in oil and gas, chemical, and petrochemical plants. In these large-scale systems, it is necessary to connect pipes of different diameters to meet process requirements, and steel reducers are well-suited for this task.