Pipe fittings are one of the most important components of fluid handling systems, installed at critical connection points, and must provide sealing performance to improve operational safety and efficiency. There are many different accessories to choose from for pipe joints, each type suitable for different needs. How should we make the right choice? Let's take a look at the common available options and their advantages.
Part one
Threaded pipe joint
Threaded pipe fittings are one of the most common options used to secure two threaded connections, one with an external thread that protrudes outside the pipe fitting; The other is an internal thread with threads inside the accessory. When the external thread is screwed into the internal thread and fixed by tightening, a connection is formed. There are two types of threaded joints.
●Conical thread
When the external and internal threads are pulled together, the tapered threads seal, and these fittings are at an angle to the centerline (in contrast, the straight threads are parallel to the centerline). It is necessary to use thread sealant or thread tape to fill the gap between the top (peak) and root (valley) of the thread to prevent leakage. Conical threads are typically suitable for system pressures up to 15000psi.
Conical thread
●Parallel thread
Also known as straight thread, it seals by pulling the sides of the thread together. There is no interference between the sides, crowns, and roots of parallel threads. Installing them requires additional items, including gaskets, O-rings, or metal to metal contacts, to form a leak proof seal. Parallel threads are typically used in applications with system pressures of 5000 psi or lower.
straight thread
The selection of threaded pipe joints first depends on the system pressure to choose tapered or parallel threads. When the system pressure does not exceed 5000psi, straight threads are usually used. The tapered thread is effective when the system pressure reaches 15000psi.
When not constrained by pressure requirements, the choice between parallel and tapered threaded connections often boils down to simple user preferences.
Part two
Compression pipe joint
Compression tube fittings are another common option, using gaskets to form leak proof seals. When the nut of the joint is tightened, the collar is compressed between the nut and the receiving joint. Due to this compression, the collar effectively bites into the tube, forming a firm grip and tight seal. The compression fittings of the compression pipe joint are also easy to assemble and disassemble.
There are two main types of compression joints: single ring and double ring.
●Single ring compression joint: includes a ring to form a seal. When tightening the nut, the collar is compressed between the nut and the receiving joint. Then the collar bites into the tube, forming a pipe clamp and main body sealing effect.
●Double ring compression joint: including front ring and rear ring. Each has its own function, but can work together with another. The front collar forms a seal between the valve body and the pipe, while the rear collar clamps the pipe.
It is important to understand how the back ring bites into the pipe, as not all pipe joint designs are similar. The reliability of the compression joint clamp is related to the degree to which the rear collar bites into the pipe.
There are some design differences between compression tube joints that may affect performance. For example, bite type collars, whether designed as single or double collars, will bend during assembly. Bending drives the leading edge of the collar into the tube to retract the surface of the tube, thereby forming its grip.
However, any vibration, pulsation, thermal shock, or lateral load on the accessory may damage the minimum contact of a single clamping ring. In dynamic fluid systems, there may be a possibility of damaging pipes or pulling them out. The accessory with a mechanical grip design with two rings provides stronger grip and sealing.
Part three
Conical threaded joint
Cone thread joint is another widely used type of joint, suitable for medium and high pressure applications. For many years, tapered threaded joints have been the standard choice for demanding high-pressure applications.
Conical and threaded joints will have glands, collars, female ports, and drain holes, allowing technicians to detect leaks and verify proper installation.
Installing conical and threaded joints is complex, requiring conical and threaded tools to establish the connection, as well as lubricants to reduce friction during the cutting process. Before connecting with the fittings, the pipes must be correctly tapered and threaded. It is crucial to ensure that there are no burrs, chisels, or scratches during this process. After the pipeline preparation is completed, tighten the collar onto the pipeline and insert the gland nut into the joint body for final tightening. For systems that are frequently subjected to impact or vibration, it is recommended to use anti vibration components to help extend the service life of oil pipe connections. If operated correctly, it can bring long-term reliability.
Part four
Material selection for pipe joints
Pipe joints can be made of various materials, including stainless steel such as 316 SS, 6-Moly alloy, and 2507 Super Duplex, as well as other alloys, with 316 SS being the most common choice.
However, components made of higher alloy materials with at least 12% nickel and 17% chromium have better corrosion resistance. Nickel can stabilize the austenitic structure of stainless steel and help provide more ductile or non brittle materials for a wider temperature range and system media. Chromium forms a passive oxide surface layer for manufacturing stainless steel, providing corrosion resistance, while higher levels of chromium can increase resistance to localized corrosion.
