Which Threads Are Sealing Threads?

Which threads are sealing threads?

Which type of connection will be used in situations where tightness is required? Many people just do it for convenience when tightening bolts, which eventually leads to liquid leakage and air leakage, which in turn requires rework and repair in situations where sealing is required . This is really not worth the gain.

Sealing characteristics of cylindrical threads

Cylindrical thread is a very common thread style. Its tooth profile is arranged in a straight line. It mainly relies on high-precision processing to ensure tight fit. This thread itself does not have the ability to self-sealing. Generally speaking, it requires a sealing ring, gasket or sealant to effectively prevent fluid leakage.

Cylindrical threads are widely used in flange connections of low-pressure plumbing pipes and mechanical equipment. Its tooth profile is straight-cylindrical. When tightening, no axial extrusion force is generated. The sealing effect relies entirely on the compression deformation of the external seal to fill the fitting gap.

How taper threads work

In a tapered thread, the tooth profile is tapered. When the internal and external threads are matched together, radial extrusion will occur, forming a self-tightening sealing effect based on the extrusion. As the tapered thread is tightened step by step, the contact pressure generated between the tapered surfaces becomes larger and larger, and in the process the sealing property of the tapered thread is also improved.

In extremely harsh working conditions such as high-pressure hydraulic pipelines and natural gas transmission pipelines, the advantages of tapered threads are extremely obvious. The NPT tapered thread, which is often used in German industrial standards, has a sealing level of up to level 4. It can effectively withstand pressures exceeding 10 MPa when the system is working.

Special advantages of pipe threads

The type of thread designed specifically for pipe connections is pipe thread. It is specifically divided into two categories: non-threaded seals and threaded seals. The former type needs to be used in conjunction with washers. The latter type relies on the geometry of the thread itself to achieve sealing and does not require the addition of additional sealing material.

In the field of domestic water pipes and oil pipes, the British 55-degree pipe thread is most frequently used. Its crest and bottom are specially processed, and the matching accuracy is extremely high. There will be almost no leakage after the connection is completed. It is especially suitable for drinking water pipelines and fuel transportation pipelines.

Comparative analysis of three types of threads

Cylindrical thread with simple processing characteristics and lowest cost, suitable for static connection situations under low pressure and low vibration conditions. The tapered thread has the best sealing performance and can withstand dimensional fluctuations caused by high pressure and temperature changes, but its processing is relatively difficult.

In terms of pipeline installation and maintenance, pipe threads are the most convenient, and standardized thread specifications make on-site connections faster. However, pipe threads are not as reliable as tapered threads in high-pressure large-diameter pipelines, so reasonable selection must be based on actual working conditions.

Actual application scenario selection

Usually, in chemical plant high-pressure reactor piping systems that are filled with extremely high working pressures and are accompanied by dangerous media, which have extraordinary requirements for sealing reliability, engineers often choose tapered thread connections. In ordinary civil building waterway systems that are easy to install and cost-controllable, pipe threads are mostly used.

In terms of automobile engines, key parts such as oil lines and brake systems basically use tapered threads, which threads are sealing threads, to ensure no oil or air leakage. As for general mechanical casing connections and low-pressure gas lines, the use of cylindrical threads and O-rings for occasions with high sealing requirements can meet the requirements.

Summary of selection suggestions

In occasions with high sealing requirements, tapered threads will be the first choice for connection. Its self-tightening characteristics can make the sealing more reliable. If the cost is more sensitive and the pressure is not very high, pipe threads are the most cost-effective solution. Cylindrical threads are suitable for connection of mechanical structures that do not require strict sealing.

When selecting, you must also consider factors such as the corrosiveness of the medium, the range of temperature changes, and whether frequent disassembly is required. In actual projects, it is recommended to refer to relevant national standards and industry specifications to ensure safe and reliable connections. In which industry do you work now? Have you ever encountered leakage caused by loose thread sealing? Feel free to share your experience in the comment area.