Is there a specific diameter requirement for pressure-sealing operations? Comprehensive analysis of the size limitations and technical considerations for pipeline sealing. In the industrial fields such as oil and gas pipelines, urban pipelines, and chemical pipelines, the pressure-bearing sealing technology, as an important process for pipeline maintenance, renovation, or emergency repair without stopping the medium flow, has increasingly demonstrated its application value. However, in actual engineering applications, whether the pressure-bearing sealing technology has requirements for pipeline diameters, which diameters are suitable for which sealing methods, and what are the technical difficulties in sealing for different diameters - these issues directly affect the feasibility, safety, and economy of the construction plan. This article will start from the basic principle of pressure-bearing sealing, systematically analyze various requirements of pipeline diameters for sealing technology, deeply discuss the selection of sealing methods under different diameter conditions, technical difficulties, equipment requirements, and safety considerations, providing comprehensive reference for pipeline engineering technicians. I. Overview of Pressure-Resistant Sealing Technology Pressure-sealing technology, as the name suggests, refers to the operation technique of sealing a pipeline without interrupting the transportation process, by using specialized equipment and procedures when the medium inside the pipeline is under pressure. This technology is widely applied in pipeline emergency repairs, rerouting, and valve installation operations in industries such as petroleum, natural gas, chemical engineering, and thermal power. Its core value lies in avoiding economic losses and environmental impacts caused by pipeline shutdowns. The basic principle of pressure sealing is to establish temporary seals on both sides of the pipeline section to be worked on, creating an isolated section for the operation. Then, operations such as drilling holes, cutting, and welding can be carried out within the isolated section. The types of sealing methods mainly include the following: Tube-type sealing: Using a hole-making machine to drill holes on the pipeline, insert the sealing tube into the pipeline interior. By making the sealing elements at both ends of the sealing tube closely adhere to the inner wall of the pipeline, a seal is achieved. This method is suitable for medium to large diameter pipelines and provides reliable sealing. Foldable sealing: The sealing head adopts a foldable structure. It is inserted into the pipeline through an opening and then unfolds to form a seal. It is suitable for medium and small diameter pipelines, especially in situations with limited space. Capsule sealing: This method utilizes rubber capsules that expand through inflation or liquid filling to adhere to the inner wall of the pipeline, achieving sealing. It is suitable for temporary sealing or emergency repairs. Sealing block: A disc-shaped sealing element is used, which is mechanically pressed against the inner wall of the pipeline. It is suitable for medium and low pressure pipelines. Freeze plugging: By using liquid nitrogen or other refrigerants to form an ice plug in a specific area of the pipeline, a temporary seal is achieved. This method has specific requirements for the pipeline material and the medium. Different sealing methods have varying degrees of adaptability to the pipe diameter. Correctly selecting the sealing method that matches the pipe diameter is the key to ensuring successful and safe sealing. II. Requirements for the selection of sealing methods based on pipe diameter Small-diameter pipelines (typically referring to those with diameters ranging from DN50 to DN200) The pressure-sealing of small-diameter pipelines has its own unique technical features and requirements. Space limitation: The internal space of small-diameter pipes is very limited, and conventional cylindrical sealing devices may not be able to pass through the opening and expand. Therefore, folding-type sealing devices and capsule-type sealing devices are more widely used in small-diameter pipes. Advantages of folding-type sealing devices: The folding sealing head is in a folded state before entering the pipe. After being sent through the opening, it expands inside the pipe to form a seal. This design ingeniously resolves the contradiction between the opening size of small-diameter pipes and the size of the sealing head, making it possible to perform pressure-sealing on small-diameter pipes. The applicability of the capsule-type sealing method: The rubber capsule-type sealing method has good adaptability in small-diameter pipelines, especially for temporary sealing or emergency repair scenarios. The pressurized and expanded rubber capsule can adapt to the irregularity of the inner wall of the pipeline and form a reliable seal. Bore size limitation: After making a bore in a small-diameter pipeline, the remaining strength of the pipeline needs to be a key consideration. The ratio of the bore diameter to the outer diameter of the pipeline has strict limitations, and it should generally not exceed a certain proportion to ensure the structural safety of the pipeline after the bore is made. Medium-sized diameter pipelines (typically referring to DN200 - DN600) Medium-diameter pipelines are the field where the pressure-sealing technology is most widely applied, and various sealing methods have good adaptability. The applicability of the tube-type sealing method: For medium-sized pipelines, the tube-type sealing provides sufficient operational space. The sealing tube can be smoothly inserted through the opening, and the sealing elements at both ends can fit well with the inner wall of the pipeline. The tube-type sealing has the characteristics of reliable structure and good sealing performance, and is a commonly used method for sealing medium-sized pipelines. The supplementary function of the folding type plug: In medium-sized pipelines, the folding type plug is also applicable, especially in cases where a larger diameter is required or under special working conditions. The folding type plug can achieve a larger sealing diameter, which is suitable for situations where a larger flow rate needs to pass through or for special media. Application of disc-type plugging: For medium and low pressure, medium-sized diameter pipelines, disc-type plugging is an economical and practical choice. The disc-type plugging head comes into contact with the inner wall of the pipeline through mechanical compression. The structure is simple and the operation is relatively easy. Multi-diameter adaptability: Medium-sized pipeline sealing equipment usually has a certain range of diameter adaptability. By replacing the sealing head or sealing element, it can adapt to different specifications of pipelines within a certain range, thereby enhancing the universality of the equipment. 3. Large-diameter pipelines (typically referring to those with a diameter of 600mm or above) The pressure-sealing of large-diameter pipelines is a field with high technical difficulty, and it places even higher demands on equipment capabilities and process levels. Challenges of cylinder-type plugging: For large-diameter pipelines, larger-sized plugging cylinders are required, and the corresponding opening diameters are also larger, which means higher torque and stability requirements for the opening equipment. The weight and operating force of the plugging cylinder itself increase significantly, and it is necessary to be equipped with lifting and operating equipment with sufficient capabilities. The huge demand for sealing force: The area of the medium inside the large-diameter pipeline acting on the sealing element is large, resulting in a huge axial force. The sealing mechanism needs to provide sufficient clamping force to resist this axial force, which places higher requirements on the structural integrity of the equipment and the hydraulic system. Special requirements for sealing components: For large-diameter pipelines, the ellipticity and irregularity of the inner wall are more obvious, which means higher requirements for the adaptability and compensation ability of the sealing components. The size of the sealing components is large, and accordingly, the manufacturing accuracy and reliability requirements also increase. The amplification effect of safety risks: If the sealing of a large-diameter pipeline fails, the leakage volume will be extremely large and the consequences will be severe. Therefore, the sealing of large-diameter pipelines has higher requirements for the reliability of equipment, the safety redundancy design, and the skill level of operators.