Ball Valve Leakage Mechanisms and Detection Technologies in Long-Distance Hydrogen Pipelines

Abstract: The booming hydrogen energy industry has spurred widespread construction of long-distance hydrogen pipelines. Within these systems, ball valves serve as critical control devices. However, their susceptibility to leakage presents significant challenges to both safe energy delivery and environmental conservation. This paper critically reviews the latest progress on leakage mechanisms and detection technologies for ball valves in long-distance hydrogen pipelines. It covers the dominant causes and influencing parameters of leakage, compares the working principles, capabilities, and real-world performance of current detection approaches, and outlines key directions for future research. Research indicates that leakage in these ball valves is primarily attributable to factors such as hydrogen embrittlement of materials, seal degradation, and structural design deficiencies. Technologies such as acoustic emission testing, pressure monitoring, and optical detection have demonstrated effective performance in practical applications. This review provides a theoretical reference for the safe operation and fault diagnosis of ball valves in long-distance hydrogen pipelines.

Hydrogen energy is pivotal to the global transition toward cleaner energy sources. As the hydrogen industry expands rapidly, the construction of long-distance hydrogen pipelines is growing accordingly. As key control components in pipeline systems, ball valves underpin both the safe and reliable transport of hydrogen and the stability of energy supply. However, due to hydrogen's small molecular size, high permeability, and flammability/explosivity, ball valves in long-distance hydrogen pipelines pose severe leakage risks.

However, given hydrogen's small molecular size, high permeability, and flammability/explosivity, ball valves in long-distance hydrogen pipelines pose significant leakage risks. Zi-ang Li et al. developed a thermal-fluid-solid-dynamic coupled numerical model for ball valves in natural gas and hydrogen-blended natural gas pipelines. They systematically evaluated flow capacity, seat contact characteristics, and opening and closing stability, thereby identifying the key factors that limit the suitability of conventional natural gas pipeline ball valves for hydrogen-blended service. Bin Jiang et al. experimentally showed that vibration sensors are effective for hydrogen leakage monitoring at refueling stations, whereas concentration sensors are vulnerable to environmental interference such as wind direction. This paper reviews recent advances in leakage mechanisms and detection technologies for ball valves in long-distance hydrogen pipelines. This paper identifies the key causes and contributing factors of leakage, assesses the principles and performance of various detection technologies, and offers a theoretical basis for the safe operation and fault diagnosis of these valves.

Hydrogen embrittlement is a primary cause of leakage in ball valves used in long-distance hydrogen pipelines. Given their small molecular size and high permeability, hydrogen molecules readily penetrate metal materials and react with the metal, degrading mechanical properties and leading to cracks and perforations. Zhen Yang analyzed a fractured fastening stud from a hydrogen pipeline valve and identified the failure mode as stress corrosion cracking, concluding that improper material selection was the root cause. Additionally, Anqing Fu et al. investigated a case of leakage and cracking in a natural gas pipeline ball valve at a gas field in western China. Cracks originated on the inner surface of the valve body and propagated along grain boundaries (Figure 1). They systematically evaluated flow capacity, seat contact characteristics, and opening and closing stability, identifying the key factors that limit the suitability of conventional natural gas pipeline ball valves for hydrogen-blended service. Under operational pressure, these micro-cracks propagated further along grain boundaries, ultimately causing brittle inter-granular fracture of the valve body.

Figure 1 Morphology of the inter-granular fracture surface

Seal failure is another major cause of ball valve leakage. The sealing function relies primarily on the contact pressure between the valve seat and the ball to form a sealing band. However, sealing performance gradually deteriorates during long-term operation due to wear, corrosion, and temperature fluctuations. Renshe Peng et al. noted that sealing surface damage and gas leakage frequently occur in gas pipeline ball valves during operation, largely attributable to improper handling during installation. In a comparative study of design standards for hydrogen and natural gas pipelines, Cuicui Chen et al. found that the unique properties of hydrogen impose strict limitations on material selection. Relevant standards specify not only upper limits for chemical constituents (e.g., carbon, sulfur, and phosphorus) in steel pipes and pipeline fittings but also material requirements for valve stems, sealing packing, flanges, and gaskets.

Structural design is another critical factor in ball valve leakage. Demiao Wang et al. reviewed sealing standards and material technologies through theoretical analysis and technical synthesis. Their analysis addressed failure mechanisms stemming from a combination of factors, including design flaws, machining inaccuracies, installation errors, and material degradation. The study indicates that developing highly elastic non- composites to enhance sealing interface adaptability is key to controlling valve leakage rates. Simultaneously, structural reliability can be further improved, and leakage risk significantly reduced, through the use of dual-sealing structures and bellows technology. They systematically evaluated flow capacity, seat contact characteristics, and opening and closing stability, identifying the key factors that limit the suitability of conventional natural gas pipeline ball valves for hydrogen-blended service. The integrity of the internal sealing surface is crucial for preventing hydrogen leakage.

Figure 2 Schematic of the structure, cross-section, and elevation of a ball valve for long-distance hydrogen pipelines

High-pressure hydrogen leakage carries a potential risk of inducing spontaneous ignition. Zongcheng Wang investigated this mechanism using numerical simulation, the results are presented in Figure 3. When high-pressure hydrogen leaks through the valve, the valve's complex internal geometry induces shock wave reflection and diffraction effects. This physical process significantly increases the air temperature downstream of the shock wave, triggering spontaneous ignition of the high-pressure hydrogen within the valve. Simulation data further reveal that when the leakage pressure reaches 6 M Pa, spontaneous ignition first occurs along the central axis of the pipeline. As the leakage pressure increases from 6 M Pa to 10 M Pa, the induction time required for spontaneous ignition drops sharply from 26 µs to 10 µs, and the onset distance for ignition decreases significantly from 24 mm to 10 mm; this implies that the probability of spontaneous hydrogen ignition rises substantially with increasing pressure.

Figure 3  Effect of leakage pressure on spontaneous ignition characteristics

Acoustic emission (AE) testing is a widely used method for detecting ball valve leakage. It works by capturing the elastic waves generated by leaking fluid and using these signals to evaluate the severity of the leak. Bo Deng et al. built an experimental setup at an integrated hydrogen production and refueling station to explore AE-based detection of internal leakage in hydrogen transmission pipeline valves. Their results demonstrated that the root mean square (RMS) voltage and average signal level (ASL), two key acoustic emission parameters, are highly effective and reliable indicators for detecting internal valve leakage. In the event of a leak, both ASL and RMS values display a pronounced upward response. Notably, RMS shows greater sensitivity, increasing by one to two orders of magnitude relative to its baseline level (Figure 4).

Figure 4 Comparison of changes in ASL and RMS parameters before and after leakage

Zhenlin Li and colleagues conducted an in-depth analysis of the acoustic characteristics and leakage behavior associated with damaged ball valve seals. Through theoretical derivation, they successfully developed a mathematical model that describes the relationship between the internal leakage rate and the Root Mean Square value of the AE signal (AERMS). As shown in Figures 5 and 6, the AE signal energy is predominantly concentrated in the 12.5–62.5 kHz frequency range, and a log-log linear relationship exists between the AERMS parameter and the internal gas leakage rate (by volume) of the ball valve. This result demonstrates that AE technology can both effectively detect internal leaks in natural gas pipeline valves and enable quantitative estimation of leak rates. Additionally, Haifeng Zhang et al. provided a systematic overview of AE testing methods, highlighting the key technical challenges involved in applying this technology to detect internal leakage in gas transmission pipeline valves. They concentrated on AE generation mechanisms and signal characteristics for ball valve internal leakage, noise reduction and feature extraction methods for signal purification, and AE-based approaches for leakage flow rate prediction.

Pressure detection technology detects internal leakage in ball valves by monitoring pressure changes within the valve cavity. To address the issue of detecting internal leakage in ball valves on buried oil and gas pipelines, Bo Zhou developed a system that identifies leakage and estimates the leakage aperture size by monitoring pressure changes inside the valve cavity. This study theoretically established the pressure variation patterns associated with internal leakage, analyzed experimental data via simulation, and developed a detection system tailored for ball valves on oil and gas pipelines.

Figure 5 Energy distribution of acoustic emission signals across different frequency bands

Figure 6 Log-log relationship between AERMS and internal leakage rate

A simple method for identifying internal leakage and corresponding countermeasures were proposed for ball valves in isolation valve stations of long-distance gas pipelines.The study suggests a multi-step approach: first, use the valve cavity's vent system to make a preliminary assessment of whether internal leakage exists. next, employ a lowpressure internal leakage detector to precisely measure the pressure rise in the cavity caused by internal leakage following the venting operation; and finally, calculate the specific leakage volume based on the measured pressure data and the actual volume of the valve cavity.

Optical detection technology utilizes optical principles to detect hydrogen leaks, with key methods including laser interferometry and fiber-optic sensing. Han Yun et al. investigated the application of acoustic emission and fiber-optic sensing technologies for inspecting hydrogen pipelines and valves at high-pressure hydrogen refueling stations.They noted that hydrogen is characterized by low density, rapid diffusion, flammability, explosiveness, and a high propensity for leakage. Rapid hydrogen leakage leads to mixing with air, and within certain concentration ranges, exposure to ignition sources such as open flames or static electricity can easily trigger serious accidents, including explosions and fires.Researchers at the Henan Institute of Boiler and Pressure Vessel Inspection Technology and Science developed a hydrogen leak detection device for refueling stations that monitors optical interference signal changes to detect minute leaks in real time, thereby enhancing station safety.

Flow-based detection technology assesses leakage by monitoring changes in pipeline flow rates. Zhejiang Zheneng Aerospace Hydrogen Energy Technology Co. Ltd. has developed a method and system for detecting hydrogen pipeline leaks at hydrogen refueling stations. This method determines whether a leak exists within a specific pipeline group by monitoring changes in mass flow rate.If leakage is detected, the lengths of the connected and associated pipelines are measured to calculate the gas mass, which, together with the change in mass flow rate, is used to quantify the leakage volume.

With the advancement of artificial intelligence, intelligent detection technology has found widespread application in ball valve leak detection. Zhejiang Lianda Valve Co. Ltd. developed a method and device for ball valve leak detection that acquires detection signals, generates detection data, identifies the locations of potential risk points on the ball valve, and issues data acquisition commands corresponding to those locations. This process enhances detection accuracy in complex scenarios and enables the identification of potential leakage hazards.

Table 1 provides a comparison of the various detection technologies, each with its own strengths and limitations. Acoustic emission technology offers high sensitivity and real-time online monitoring capabilities but is susceptible to external environmental factors, particularly ambient noise. Pressurebased detection is simple and reliable, yet offers relatively low precision. Optical detection technology offers high precision, though equipment costs are substantial. Flow-based detection enables direct leakage volume measurement, but installation is complex. Intelligent detection technology features a high degree of integration, yet depends on sophisticated algorithms.

Table 2 compares the application scenarios of various detection technologies. Acoustic emission detection is applicable to internal leakage detection in valves at hydrogen refueling stations and in hydrogen pipelines; while the technology is mature, it is susceptible to noise interference. Pressure detection is used for ball valves in buried pipelines, offering strong environmental adaptability and simple maintenance.Optical detection is suitable for monitoring micro-leaks at hydrogen refueling stations; it offers high accuracy but requires specialized maintenance. Flow detection is used to quantify pipeline leakage and is a mature technology. Intelligent detection is suitable for complex scenarios and is evolving towards deep learning and edge computing.

The future development trends for leak detection technology applied to ball valves in longdistance hydrogen pipelines mainly encompass the following aspects:

(1) Multi-technology integration: combining various detection technologies to improve the accuracy and reliability of detection results.

(2) Intelligent development: Utilizing technologies such as artificial intelligence and big data to achieve intelligent identification and prediction of leaks.

(3) Online monitoring: Developing real-time online monitoring systems to enable continuous surveillance and early warning of ball valve leaks.

(4) Standardization: Establishing comprehensive detection standards and specifications to promote the standardized application of detection technologies.

This paper systematically reviews the latest research on leakage mechanisms and detection technologies for ball valves in longdistance hydrogen pipelines, with the main conclusions drawn as follows:

(1) Ball valve leakage in longdistance hydrogen pipelines is mainly attributed to hydrogen embrittlement, seal failure, and structural design, with hydrogen embrittlement being the primary cause.

(2) Owing to its high sensitivity and realtime monitoring capability, acoustic emission testing has become the most widely adopted method. It performs best in the 12.5–62.5 kHz frequency band, where it can effectively identify leakage signals.

(3) Pressure, optical, and flow detection technologies each exhibit unique performance characteristics; practical applications must be tailored to specific scenarios to select the optimal detection solution.

(4) Future leak detection technologies will evolve towards the integration of multiple technologies, intelligent systems, online monitoring, and standardization.

Despite considerable progress, challenges remain in ensuring detection accuracy in complex environments, maintaining realtime monitoring reliability, and controlling costs for longdistance hydrogen pipeline ball valves. Looking ahead, it is essential to strengthen fundamental theoretical research, accelerate the development of advanced detection technologies, and improve the standardization framework to establish a solid technical foundation for the safe and sustainable development of the hydrogen energy sector.