Threaded pipe - Wikipedia
Pipes with helical threads
A threaded pipe is a pipe with screw-threaded ends for assembly.
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See also: Tapered thread
The threaded pipes used in some plumbing installations for the delivery of gases or liquids under pressure have a tapered thread that is slightly conical (in contrast to the parallel sided cylindrical section commonly found on bolts and leadscrews). The seal provided by a threaded pipe joint depends upon multiple factors: the labyrinth seal created by the threads; a positive seal between the threads created by thread deformation when they are tightened to the proper torque; and sometimes on the presence of a sealing coating, such as thread seal tape or a liquid or paste pipe sealant such as pipe dope. Tapered thread joints typically do not include a gasket.
Especially precise threads are known as "dry fit" or "dry seal" and require no sealant for a gas-tight seal. Such threads are needed where the sealant would contaminate or react with the media inside the piping, e.g., oxygen service.
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Tapered threaded fittings are sometimes used on plastic piping. Due to the wedging effect of the tapered thread, extreme care must be used to avoid overtightening the joint. The overstressed female fitting may split days, weeks, or even years after initial installation. Therefore many municipal plumbing codes restrict the use of threaded plastic pipe fittings.
Both British standard and National pipe thread standards specify a thread taper of 1:16; the change in diameter is one sixteenth the distance travelled along the thread. The nominal diameter is achieved some small distance (the "gauge length") from the end of the pipe.
Pipes may also be threaded with cylindrical threaded sections, in which case the threads do not themselves provide any sealing function other than some labyrinth seal effect, which may not be enough to satisfy either functional or code requirements. Instead, an O-ring seated between the shoulder of the male pipe section and an interior surface on the female, provides the seal.
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The Pros and Cons of Flanges
The Pros and Cons of Flanges
1. Slip on plate flange
Advantages: Convenient supply of raw materials, a simple manufacturing process, low costs and a wide range of applications.
Disadvantages: The slip on plate flange has poor rigidity, so it should not be used in chemical process piping systems with requirements of supply and demand, flammability, explosion and higher vacuum degree.
2. Slip on flange
Advantages: It is convenient to install on site.
Disadvantages: The slip on flange is shorter in length, which improves the stiffness and bearing capacity of the flange. Compared with weld neck flanges, slip-on flanges have heavy welding loads and can't withstand high temperatures and high pressures, repeated bending and temperature fluctuation.
3. Weld neck flange
Advantages: The weld neck flange is not easy to deform. And it has good sealing and a wide range of applications. The flange is suitable for pipelines with large fluctuations in temperature or pressure or pipelines with high temperature, high pressure or low temperature, and also used for pipelines transporting expensive media, flammable and explosive media and toxic gases.
Disadvantages: The weld neck flange is bulky and expensive, and it is difficult to install and locate, so the flange is easier to bump about during transportation.
4. Threaded flange
The threaded flange is a kind of non welded flange, whose inner hole is processed into a pipe thread and connected with the threaded pipe.
Advantages: Compared with slip on flanges and weld neck flanges, threaded flanges feature convenient installation and maintenance, and can be used for some pipelines that are not allowed to be welded.
Disadvantages: Under the condition that the pipeline temperature changes rapidly or the temperature is higher than 260 and lower than -45, it is recommended not to use threaded flanges to avoid leakage.
5. Welding-on collar lap joint flange
Advantages: The flange has convenient welding and processing, or requires high strength. Besides, it is convenient for construction.
Disadvantages: The flange has low strength at the welding-on collar especially when the thickness is less than 3 mm.