What Is a Pipe Nipple? A Guide to Types, Materials, and Machining

A pipe nipple is a short length of pipe with male threads on one or both ends. It’s a foundational component in plumbing and fluid transfer systems, used primarily to connect two other fittings or pipes. While their name might sound a bit quirky, their function is critically important for creating reliable and secure connections in a vast range of applications, from residential plumbing to complex industrial systems.

Pipe nipples are defined by their short length, typically under 12 inches, and the presence of external, or male, threads. The threads are usually tapered, which means they get slightly wider toward the end, a key feature for creating a watertight seal when the nipple is screwed into a female-threaded fitting. This simple but effective design makes them versatile connectors for extending pipe runs, changing directions, or adapting to different pipe sizes.

Types of Pipe Nipples

Pipe nipples are not one-size-fits-all; they come in several common types, each designed for a specific purpose.

The Close Nipple is the shortest type. It is threaded for its entire length, with no unthreaded portion in the middle. When two female fittings are screwed onto either end, they sit as close together as possible, leaving very little of the nipple exposed. This type is used for making extremely tight connections in confined spaces.

A Shoulder Nipple is a slightly longer version of the close nipple. It has a short unthreaded space, or "shoulder," between the two threaded ends. This shoulder allows for a wrench to be used for tightening, offering a better mechanical advantage than a close nipple while still keeping the connection compact.

The Barrel Nipple is a common type with an unthreaded section in the middle, similar to a shoulder nipple but with a longer unthreaded space. This is a general-purpose nipple used for connecting two fittings that require a certain distance between them.

A Hexagonal Nipple, or Hex Nipple, is easily identified by a hexagonal section in the middle of the pipe. This hex shape provides a secure gripping surface for a wrench, making installation and removal easier, especially in high-pressure applications where a strong, tight seal is essential.

Reducing Nipples, also known as Swage Nipples or Unequal Nipples, are designed to connect pipes of different diameters. They have a smaller male thread on one end and a larger male thread on the other. These are crucial for creating a smooth transition in pipe size within a system, which can be necessary to adjust flow rates or connect different components.

A Welding Nipple has a male-threaded end on one side and a plain, unthreaded end on the other. As the name suggests, the plain end is designed to be welded directly to a pipe, fitting, or tank, creating a permanent, highly secure connection that is resistant to vibration, pressure surges, and temperature changes.

Finally, a Hose Nipple has a male-threaded end on one side and a hose barb on the other, allowing for a quick and easy connection to a flexible hose.

Materials Used for Pipe Nipples

The choice of material for a pipe nipple is critical and depends on the application, considering factors like the fluid or gas being transported, pressure, temperature, and environmental conditions.

Stainless Steel is a popular choice due to its exceptional corrosion resistance and high strength. Grades like 304 and 316 are common, with 316 offering superior resistance to pitting and corrosion, making it ideal for marine, chemical, and food processing industries.

Carbon Steel is a more economical and widely used material. It is strong and durable but susceptible to rust. To mitigate this, carbon steel nipples are often coated. Galvanized Steel nipples, for example, are coated with a layer of zinc, which provides a protective barrier against corrosion, making them suitable for water supply lines and outdoor applications. Black Steel nipples, coated with a black oxide finish, are commonly used for gas and fire sprinkler systems.

Brass is an excellent material for pipe nipples, offering great corrosion resistance, especially against rust. It's often used in water supply lines and exposed plumbing where its attractive appearance is a benefit. Brass also has a higher thermal conductivity than stainless steel, making it useful in HVAC systems.

PVC and other plastic materials are used for low-pressure applications, like drainage and irrigation systems. They are lightweight, highly resistant to chemicals, and do not corrode, but they cannot withstand high temperatures or pressures.

The Machining Process

The creation of a high-quality pipe nipple is a precise machining process that ensures the final product meets strict industry standards for reliability and a leak-free seal. The process typically involves several key steps.

It starts with the raw material, which is a long piece of pipe of the desired diameter and wall thickness. This pipe is then cut to the specified length, creating a blank.

The cut ends are then chamfered. This is a crucial step where the inside and outside edges of the pipe are beveled. This not only removes sharp edges and burrs but, more importantly, it makes it much easier to start the threading process and ensures the nipple screws smoothly into a fitting.

Next is the most critical step: threading. The blank is held securely in a threading machine, and specialized cutting dies are used to precisely cut the external male threads onto the ends of the pipe. The most common thread type is NPT (National Pipe Thread), which features a tapered design. The accuracy of this process is paramount, as the threads must be uniform and meet a specific pitch and taper to create a reliable seal.

After threading, the nipples are subjected to finishing and cleaning. They are cleaned to remove any metal shavings and cutting oil. For galvanized nipples, the part is hot-dipped in molten zinc at this stage.

Finally, a rigorous quality control and inspection process is performed. Each nipple is checked for thread quality, length, and overall finish using specialized gauges. This final check ensures that every nipple produced will provide a secure, leak-free connection, meeting the demanding requirements of various plumbing and industrial applications. This careful process guarantees that even the smallest component can be trusted for safety and performance.