Pipeline pressure testing and opening holes using pressure sealing: Technical analysis and practical application of non-stop production operations

In modern pipeline transportation systems, whether it is for petroleum, natural gas, chemical media, or urban water supply and heating pipelines, as the operating years increase and the needs of urban development arise, there are often demands for pipeline renovation, branch line connection, leakage repair, valve replacement, etc. The traditional approach is to stop the transportation, empty the medium, conduct purging and replacement before implementing the operation. However, this not only causes huge economic losses and resource waste, but also may affect residents' lives and industrial production. The pipeline pressure testing and hole opening technology using the pressure sealing technology emerged as a result. It can complete the pipeline hole opening and sealing operations safely and efficiently under the condition that the pipeline does not stop transporting or reduce pressure, and has become a core technology in the modern pipeline maintenance and emergency repair field. This article will start from the basic concepts of pipeline pressure testing hole opening and pressure-sealing sealing, systematically elaborate on the collaborative relationship, technical process, equipment configuration, safety control, and typical application scenarios of the two, providing a comprehensive and professional technical reference for pipeline operation units and engineering technicians. I. Basic Concepts of Pipeline Pressure Testing, Opening Holes, and Pressure-Resistant Sealing 1.1 What is Pipeline Pressure Testing and Opening Hole? "Piping pressure test" usually refers to a pressure test conducted on a piping system to verify its pressure-bearing capacity and sealing performance. However, in the compound term "piping pressure test with hole opening", "pressure test" more specifically refers to the process of conducting a sealing pressure test on temporarily installed valves, flange short pipes, hole opening machines, etc. before the hole opening operation, to ensure a reliable pressure boundary between the hole opening equipment and the main pipeline. While "hole opening" refers to using specialized mechanical cutting equipment to drill the required diameter holes in the pipeline wall during the operation of a pressurized pipeline, for the installation of branch pipes or for subsequent sealing operations. Therefore, the pipe pressure testing and hole drilling can be understood as follows: Before conducting the hole drilling operation on a pressurized pipeline, the connection parts and sealing system need to undergo a pressure test (pressure holding) to verify their ability to withstand the internal medium pressure of the pipeline. After confirming there is no leakage, the hole drilling and cutting process can be carried out. This "pressure holding first, then hole drilling" principle is the core prerequisite for ensuring the safety of the operation. 1.2 What is Pressure-Resistant Sealing? Pressure-sealing operation refers to the process of establishing a temporary seal inside the pipeline using specialized sealing equipment while the pipeline is in operation without interruption. This is done to block the flow of the medium, allowing for pipeline cutting, replacement, or rerouting operations downstream. After the sealing is completed, once the downstream operations are finished, the seal will be removed to restore the normal operation of the pipeline. Pressure-sealing is usually used in conjunction with pressure-opening: First, a hole is drilled in the pipeline to create two (or more) sealing holes. Then, a sealing head (such as a disc-type sealing device or a cylindrical sealing device) is inserted through these holes to form a seal inside the pipeline and cut off the medium. Thus, the section of the pipeline that is sealed can undergo non-pressure operations safely. 1.3 The overall meaning of "Pipe pressure testing and opening with in-service pressure sealing" Combining the two methods, "pipe pressure testing and opening for pressure sealing" describes a complete pipeline maintenance and renovation process without interrupting the flow: First, weld a flange short pipe at the appropriate position of the pipeline to be worked on and install a valve. Verify the sealing performance through a pressure test; then use an opening machine to perform pressure opening below the valve; next, lower the sealing device from the opening point, establish a seal inside the pipeline; finally, carry out maintenance, replacement or addition of branch pipes on the target pipeline section under the sealing protection. After the operation is completed, remove the sealing device, close the valve, and restore the pipeline transportation. This technology is widely applied in long-distance pipeline systems, urban pipeline networks, station process pipelines and other fields, and it is an important supporting technology for pipeline integrity management. The core advantages of using a pressure-sealing core for pipe pressure testing and hole drilling Compared with the traditional pipeline shutdown operation method, the use of pressure-sealing technology for pipeline pressure testing and opening holes has the following significant advantages: 2.1 Continuous Supply, Ensuring Continuity For gas pipelines, refined oil pipelines, and main urban water supply pipelines, a one-day pipeline shutdown could result in millions or even hundreds of millions of yuan in economic losses, and may also cause social problems. The pressure-sealing technology enables the operation to be completed without shutting down the pipeline, and the users hardly feel any impact. 2.2 No need for medium discharge, environmentally friendly and safe Traditional operations require the complete removal of the medium in the pipeline. The large-scale discharge of oil, gas or chemicals can cause environmental pollution and waste of resources, and also poses a risk of fire and explosion. In contrast, the pressure-sealing operation is completely emission-free throughout the process, resulting in significant environmental benefits. 2.3 Reduce the time spent on homework and enhance efficiency By eliminating time-consuming steps such as shutdown, emptying, replacement, and re-starting production, the overall operation cycle can be shortened by more than 50%. In emergency repair scenarios, the time advantage is even more significant. 2.4 Reducing Construction Risks Avoiding hot work operations (both opening and sealing are mechanical processes without generating open flames), this method reduces the risk of fire and explosion in flammable and explosive environments. At the same time, since the pipeline remains under pressure, external impurities cannot enter, thus avoiding pipeline contamination. III. Technical process for pipe pressure testing and hole drilling using the pressure-sealing technology A complete set of pipeline pressure testing, opening holes and pressure-sealing operations usually involves the following ten main steps: 3.1 On-site Investigation and Scheme Design The technicians conducted a detailed inspection of the operation pipeline, confirming parameters such as the material, diameter, wall thickness, operating pressure, medium characteristics, and operating temperature of the pipeline. Based on the operation purpose (such as replacing pipe sections, installing valves, sealing abandoned sections, etc.), they designed the location, quantity of the opening, and the sealing method (single sealing, double sealing, opening without stopping the flow, etc.). They compiled the construction plan and safety emergency response plan, and could only implement them after obtaining approval. 3.2 Welded Flange Short Pipe and Gate Valve At the preset opening position, the special flange short pipe (also known as pipe fitting, saddle seat, or connection piece) is welded onto the main pipeline. The material and welding process of the flange short pipe must be compatible with that of the main pipeline. After welding, an appearance inspection and magnetic particle testing are conducted to ensure there are no cracks, incomplete fusion, or other defects. The upper end of the flange short pipe is equipped with a full-bore gate valve, and the valve pressure rating must be no less than the design pressure of the pipeline. Before installation, the valve needs to undergo pressure testing and flexibility checks for opening and closing.