Discussion on the Structure of Spiral Welded Pipe Socket Technology

1. Preface

Spiral welded pipe, as a multifunctional pipeline material, is widely used in the transportation systems of natural gas, petroleum, water, and steam. Its pressure bearing capacity covers a wide range of pressures up to 20 MPa, demonstrating its unique advantages in the fields of energy and fluid transmission. However, traditional spiral welded pipes rely on tedious welding processes during pipe mouth docking, which not only requires construction personnel to hold professional special equipment welding operation certificates, but also comes with the consumption of welding materials and the high cost of X-ray testing, resulting in a significant increase in on-site construction costs. For low-pressure water pipelines with a pressure not exceeding 1.6 MPa, in addition to spiral welded pipes, various options such as PCCP pipes, ductile iron pipes, and fiberglass pipes have emerged in the market. The common highlight of these pipes is the use of socket flexible interface design, which can effectively absorb small axial and angular displacements, and achieve tight connection through sealing materials such as rubber rings. This installation method greatly simplifies the on-site operation process, without the need for welding. Simply insert the sealing ring into the socket groove and use an oil cylinder or guide chain to easily connect the pipe fittings. The entire installation process can be quickly completed within 15 to 30 minutes, greatly improving construction efficiency. Based on current market feedback, users' preference for flexible connection methods is becoming increasingly evident, which has prompted the spiral welded pipe industry to explore and improve its on-site interface technology in order to enhance its competitiveness in the low-pressure pipeline market by increasing construction speed. In recent years, many spiral welded pipe production enterprises have actively engaged in the research and application of flexible interface technology, successfully introducing the socket process structure into the field of water pipelines and achieving significant results. This innovation not only simplifies the installation process, but also further enhances the overall performance and reliability of the pipeline system, thus winning the favor and recognition of more and more users.

2. Common spiral welded pipe socket process structure

There are three types of spiral welded pipe socket technology structures in China: (1) imitation ductile iron pipe form; (2) Imitation fiberglass pipe type; (3) Imitation of PCCP tube form, using rolled profiles in a three roll round and welded form.

2.1 Imitation of ductile iron pipe form

The structure of the imitation ductile iron socket process is based on spiral welded pipes, with one end of the steel pipe expanded and pressed as a socket using equipment, and the socket formed by shrinking. It is suitable for steel pipes of 10mm and below, and the sealing ring is the same as ductile iron pipes. Each ring has two different Shore hardness, and the larger the pipe diameter, the higher the cost. This type of socket steel pipe cannot be installed and pressed on site due to single groove sealing. It must be pressed in sections after installation, and problems cannot be detected in a timely manner. If there is water leakage, all pipes must be excavated, which is quite troublesome to handle.

2.2 Imitation of fiberglass pipe form

The structure of the imitation glass steel pipe socket process is based on spiral welded pipe as the base pipe, with specialized equipment to expand the socket, and the socket groove is pressed. The socket groove is higher than the inner wall of the steel pipe, and there is water resistance during actual use. The sealing ring is the same as the fiberglass pipe, using EPDM rubber, and each ring has a Shore hardness. This type of socket steel pipe can be installed and pressed on site due to its double groove sealing, which can detect installation or manufacturing quality problems in a timely manner. If there is water leakage, it can be replaced immediately.

2.3 Imitation of PCCP Tube Form

The middle of the PCCP pipe socket structure is a spiral welded pipe, with the socket strip steel rolled and expanded, welded onto the spiral welded pipe. The socket steel strip is made of formed steel strip, which is rolled and welded onto the socket steel pipe, with a relatively flat inner wall. Both the socket and the plug need to be sized and welded onto the steel pipe, which results in low production efficiency and is not suitable for mass production. The sealing ring is the same as the PCCP pipe, using EPDM rubber with one Shore hardness per ring. This type of socket steel pipe, due to its double groove sealing, can be installed and pressed on site, allowing for timely detection of installation or manufacturing quality issues. If there is water leakage, it can be replaced immediately.