Pressure-assisted hole-making service includes pressure testing: a crucial step in ensuring the safe operation of pipelines.

In modern industrial pipeline systems, the pressure-bearing opening technology, as a non-stop-flow, non-flame operation method that is safe and efficient for pipeline renovation, is widely applied in various fields such as oil, chemical, natural gas, municipal water supply, and heating networks for branch line connections, sealing and rerouting, and valve installation. However, the pressure-bearing opening operation itself has certain technical complexity and safety risks. Any operational error or equipment defect may lead to medium leakage, pipeline damage, or even major safety accidents. Therefore, pressure testing is an indispensable core step in ensuring the safety of the operation and verifying the quality of the project. This article will start from the basic principles of pressure-bearing opening, systematically explain the significance, testing methods, operation procedures, standards and norms, and common problem handling of pressure testing in pressure-bearing opening services, to help practitioners and pipeline operation units fully understand this key process. I. Overview of Pressure-Resistant Hole Opening Technology Pressure-bearing hole drilling, also known as non-stop pipeline hole drilling or in-line hole drilling, refers to the technology of drilling holes on the pipeline wall and installing branch pipelines using specialized equipment while the pipeline is not stopped from transporting media and without reducing the system pressure. This technology avoids the cumbersome steps required by traditional operation methods such as stopping the pipeline, purging, blowing, and hot work, significantly reducing the impact on production and the environment. It is particularly suitable for long-distance pipeline systems, urban pipeline networks, refining and chemical plants, and other scenarios where it is not easy to stop the pipeline. The basic process of pressure-bearing hole opening includes: welding the flange short pipe and gate valve, installing the hole opening machine, pressure balancing, hole cutting, retracting the tool and closing the valve, and removing the hole opening machine. Throughout the entire operation, reliable sealing and pressure control are the core aspects of safety. And pressure testing is the most direct means to verify whether these key steps meet the requirements. II. Why must pressure testing be provided during pressure-opening services? Pressure-opening service includes pressure testing, which is not an optional add-on but rather a necessity based on the following multiple factors: 2.1 Verify the sealing performance of the welded joint The first step in pressure-bearing opening is to weld a flange short pipe (also known as a connector or saddle) on the main pipeline. The quality of this weld directly affects whether the medium leaks after the opening. Since the welding is carried out outside the pressurized pipeline, the inner wall of the pipe is subjected to the medium pressure, and the welding heat input may affect the material properties of the base metal, and the weld may also have defects such as pores, incomplete fusion, and cracks. The pressure test can effectively check whether there is a leakage channel in the weld by applying a test pressure higher than the operating pressure to the annular space between the flange short pipe and the main pipeline. 2.2 Test the sealing performance of the valve and the opening machine During the hole-making operation, the gate valve installed above the flange short pipe is the key to controlling the on-off of the medium after the hole is made. The hole-making machine cuts through the valve for the operation, and after completion, the valve needs to be closed and the hole-making machine removed. If the valve seal is not tight or the sealing components between the hole-making machine and the valve fail, the medium will spray out. Pressure testing can simulate the actual working conditions before the hole is made to verify the reliability of the valve and the sealing components. 2.3 Verify the tightness of the connection of the branch pipe after the opening is made After the holes are drilled, it is usually necessary to install branch pipes or sealing devices. The connection point between the branch pipe and the flange short pipe also needs to undergo a pressure test to ensure there is no leakage. For long-term operating pipeline systems, this test provides quality assurance for subsequent commissioning. 2.4 Meeting regulatory and standard requirements National and industry-related standards (such as GB/T 28055 "Technical Specifications for Pressure Sealing of Steel Pipelines", SY/T 6150 "Technical Specifications for Pressure Opening of Steel Pipelines", etc.) clearly stipulate that pressure tests should be conducted before, during, and after the pressure opening operation. Failure to conduct pressure tests or if the tests are不合格 (unqualified), and continuing the operation, constitutes a serious violation. In case of an accident, the operation party shall bear legal responsibility. 2.5 Ensure the safety of workers and the surrounding environment Pressure-bearing hole opening operations are often carried out on pipelines containing flammable, explosive, or toxic and harmful media. A small leakage point could lead to a fire, explosion or poisoning accident. Pressure testing is the final line of defense for detecting hidden dangers and eliminating risks, and it demonstrates a high level of responsibility towards the lives and safety of the operators and the surrounding population. III. Main Types of Pressure Testing in Pressure-Resistant Opening Services Depending on the different stages and purposes of the testing, the pressure tests in the pressure-opening operation services can be mainly classified into the following types: 3.1 Post-weld Sealing Test (also known as Chamber Pressure Test) After the flange short pipe is welded and cooled, through the preset test holes on the flange short pipe (or by using a hole-making machine to install the interface), the test medium (usually nitrogen, water or air) is injected into the annular space between the short pipe and the outer wall of the main pipe. A specified test pressure is applied, and the pressure is maintained for a certain period of time. The pressure drop and leakage conditions are checked. This test is aimed at verifying the tightness of the fillet welds. 3.2 Air tightness test after installation of valves and hole-making machine After the gate valve and the hole-making machine are installed in place, close the valve. Through the pressure test interface on the hole-making machine, inject the test pressure into the upper chamber of the valve and the interior of the hole-making machine to check for any leakage in the valve packing, flange gaskets, and sealing rings of the hole-making machine. This test is usually conducted before the hole cutting operation to ensure the reliable sealing system between the hole-making machine and the valve. 3.3 Pressure test for branch pipes after opening holes After making the holes and installing the branch pipes (or temporary plugs), a strength test and a tightness test need to be conducted on the entire newly installed pipe section. The test medium can be water (for water pressure test) or gas (for gas pressure test). The test pressure is determined according to the design pressure and standards, generally not less than 1.5 times the operating pressure. Only after the test is qualified can production be resumed. 3.4 Final Overall System Stress Test For projects involving multiple work sites or the entire pipeline renovation, after all the pressure-bearing hole openings and branch pipe connections have been completed, an overall pressure test needs to be conducted on the renovated part to confirm that there is no leakage or abnormal deformation in the entire system, and that it meets the requirements for long-term safe operation. IV. Standard Procedure for Pressure Testing of Openings under Pressure Standardized pressure testing for on-pressure opening services should follow the following standardized procedures: