What Is A Casing Coupling?

A casing coupling is a connecting pipe fitting that puts two pipes of different diameters together. Casing couplings are usually used to connect pipelines, pumps, valves and other equipment to facilitate the installation and maintenance of pipelines.

Structure and Types of Casing Couplings

1. Structure

The structure of a casing coupling mainly consists of two parts, namely the casing of the pipe and the connecting pipe. The casing is generally cylindrical with a larger inner diameter and a smaller outer diameter, which is convenient for fitting on a pipe with a smaller outer diameter; the connecting pipe is generally a flat ring, which is used to connect the casing and the pipe with a larger outer diameter.

2. Types

There are many types of casing couplings, mainly including cast iron casing couplings, steel casing couplings, stainless steel casing couplings, etc. According to the different connecting pipes, casing couplings are also divided into bayonet casing couplings and flange casing couplings.

Casing Coupling Steel Grades

Casing couplings can be categorized into various types based on steel grade, including but not limited to J55, K55, N801, N80Q, L80 1, L80 9Cr, L80 13Cr, C90, T95, P110, and Q125.

Casing Coupling Specifications

Casing couplings come in a variety of sizes, with common specifications including 4.5, 5.5, 6.5/8, 7.5, 7.5, 8.5, 9.5, 10.3, 11.3, 13.3, 16.5, 18.5, and 20. Commonly used sizes include 5.5, 7.5, 9.5, and 13.3.

Casing Coupling Threads

Casing coupling thread types include long round threads, short round threads, trapezoidal threads, and special threads. It's important to note that not all sizes of casing couplings have long round threads. For example, sizes like 103/4, 113/4, 133/8, 16, and 185/8 only have short round and trapezoidal threads.

Advantages of Casing Couplings

1. No Welding Required

Casing couplings eliminate the need for welding pipes, saving time and money.

2. Convenient Maintenance

Casing couplings allow for quick and easy pipe removal and repair.

3. Easier Pipe Replacement

Casing couplings allow pipes to be replaced with different diameters and shapes, facilitating modifications and repairs.

Functions of Casing Couplings

1. Mechanical Connection

Through threads, they connect individual casing pipes into a continuous column, capable of withstanding axial loads.

2. Sealing Assurance

A metal/elastomeric seal structure prevents wellbore fluid leakage.

3. Strength Compensation

The wall thickness of the coupling area is increased by 20-30% to compensate for the strength loss at the threaded connection.

4. Centering Guidance

A special chamfered design facilitates casing pipe running operations.

Casing Coupling Installation Method

1.The following points should be noted when installing the casing coupling:

2.The butt-jointed pipes must be clean, flat and free of burrs;

3.A special sealant should be applied to the casing connection to ensure the sealing of the joint;

4.Use a wrench to tighten the casing coupling. The tightening force should not be too tight or too loose;

5.After the installation is completed, a pressure test should be carried out to check for water leakage.

Precautions for Using Casing Couplings

1. When using casing couplings, the length of the connecting pipe should be controlled within the specified range and should not exceed the standard requirements;

2.The temperature range and medium property requirements of the casing coupling must match those of the pipeline;

3.When using casing couplings, the material, diameter, wall thickness, etc. of the butt-jointed pipes should be checked to ensure a reliable connection;

4. Do not weld or apply external force around the casing coupling to avoid damage to the connection.

FAQ

1.Can casing couplings be used on high-pressure pipelines?

Answer: Casing couplings can be used on low-pressure, medium-pressure and high-pressure pipelines, but the conditions and requirements for use are different. When used on high-pressure pipelines, it is necessary to select the corresponding model and perform pressure tests to ensure that the connection is sealed reliably. 

2.How to determine whether the connection of the casing coupling is effective? 

Answer: The connection of the casing coupling can be tested by pipeline pressure test or mechanical testing. 

Conclusion

This article introduces the definition, structure, type, advantages etc. of the casing coupling, and provides help for correct operation and use. In actual use, you should also read the product manual carefully and install and use the casing coupling correctly as required.