2.1 Existing Materials and Testing Techniques are unable to meet the Requirements of Complex and Harsh Environments

With the increasing design process parameters, pipelines will face higher temperatures, pressures, and harsh medium environments, and existing material systems will be unable to support the needs of higher temperatures.For example, the maximum operating temperature of 2.25Cr1Mo0.25V steel for the outlet pipeline of a hydrogenation reactor is 482℃, which cannot meet the requirements of high-temperature hydrogen environments above 500℃.Moreover, when the temperature stays above 500 ℃ for a long time, the austenitic stainless steel welded joint will be in the sensitization temperature range, which will inevitably exacerbate the risk of intergranular corrosion.The research and development of new materials for chemical pipelines and the application of new scenarios require a large amount of testing data as support, so its development cannot be separated from the advancement of advanced testing technology and instruments.Although the damage of pipes in high-temperature and high-pressure hydrogen environments has been widely concerned, the difficulty of conducting in-situ tests in high-temperature hydrogen environments, especially under various coupled environments such as H₂-H₂S and multi axis complex stresses, has hindered further understanding of hydrogen damage mechanisms and the development of new materials.The Nelson curve based on foreign industrial data is an empirical curve and cannot be fully applicable to various hydrogenation units in China.The existing hydrogen damage testing methods mainly use high-temperature hydrogen charging and electrochemical hydrogen charging methods to simulate, but whether these methods can represent the damage failure modes and mechanisms in actual service environments remains to be discussed.In recent years, scholars at home and abroad have also developed high-pressure hydrogen environment testing instruments and technologies, but they are mainly applied in room temperature environments. Therefore, the development of high-temperature and high-pressure in-situ hydrogen environment testing technology and instruments is a key technical issue that needs to be addressed in the development of hydrogen pipelines.

2.2 Incomplete Pipeline Design Methods in Complex and Harsh Environments

Accurately predicting the failure of pipelines in different media is a prerequisite for pipeline design, and an accurate physical model is the key to solving this problem.A relatively systematic design method has been established for high-temperature environments, but considering the coupling effect between environmental factors and mechanical damage, the design method for harsh environments is not yet perfect.Taking coal chemical industry as an example, the research and prediction models for the coupling mechanism of solid multiphase flow erosion (abrasion) corrosion and erosion cavitation in high-temperature and high-pressure pipe valve systems are not mature, and cannot meet the engineering needs of coal chemical equipment design, operation, and risk prevention and control.Firstly, the presence of solid particles significantly affects the flash evaporation phase transition and cavitation erosion process, but the key forces, spatial distribution, deposition characteristics, and impact rebound relationship of solid particles in gas-liquid fluids under flash evaporation and cavitation conditions are not yet clear.The mechanism of the influence of particle presence on gas-liquid flash evaporation and cavitation phase change gas-liquid solid multiphase flow is unclear, which hinders the construction of multi field coupling models and prediction methods containing phase change temperature field, velocity field, and concentration field.Secondly, the coupling mechanism of solid multiphase flow erosion corrosion and erosion cavitation is complex.On the one hand, the protective film of corrosion products is repeatedly damaged and generated under the synergistic effect of solid particle erosion and corrosion, which exacerbates the local damage rate and failure risk; On the other hand, cavitation causes local loss of protection on the strengthened surface of the equipment, exacerbating local erosion and wear of the substrate material. Moreover, erosion corrosion or erosion cavitation is affected by multiple factors such as flow, mechanical, chemical, etc., which increase the risk of wall thinning, perforation, and rapid valve failure caused by uneven mass loss of the equipment material.The unclear coupling mechanism of solid multiphase flow erosion corrosion and erosion cavitation corrosion, as well as the lack of damage rate models, constrain the accurate quantitative prediction of erosion corrosion and erosion cavitation in pipe valve systems.

2.3 Difficulty in Regulating Pipeline Manufacturing and Processing Technology

The quality of welded joints is crucial for stress corrosion cracking and intergranular cracking in hydrogen and corrosive environments.During the welding process, defects such as slag inclusion, porosity, and lack of fusion are inevitably formed, which are weak areas in the welding structure.Moreover, the random distribution of internal welding defects makes the residual stress distribution more complex, and there is currently a lack of residual stress control methods for defect orientation control.Therefore, welding pipes with large diameters and thick walls to ensure the quality of welding joints is a technical challenge that needs to be solved for the long-term operation of chemical pipelines.Generally speaking, surface strengthening technology, corrosion protection technology, and material enhancement methods can improve the wear resistance, corrosion resistance, and gas corrosion resistance of materials facing a single damage mechanism, and to some extent, extend the service life of pipelines, valves, and fittings.However, traditional surface coating or surface hardening, ceramic lining corrosion protection, and single technology methods such as Cr, Ti wear-resistant alloys or corrosion-resistant alloy material upgrading are difficult to meet the service requirements in the coupled environment of erosion corrosion and erosion cavitation.Increasing material hardness can improve wear resistance, but it will result in more severe cavitation. The wear resistance and corrosion resistance of materials also have this inverted relationship.The material preparation and equipment protection technology based on the coupling mechanism of wear resistance, corrosion, erosion, and cavitation has not yet been formed. The surface strengthening technology of materials itself needs further improvement, and the parameter influence relationship of strengthening performance is not clear. The combined effect of multiple manufacturing and processing methods and the quantitative control technology of parameters need to be explored.

2.4 Pipeline Monitoring and Inspection Technology is difficult to Adapt to Extreme Service Environments

Early detection and prevention of risks is a prerequisite for pipeline risk prevention and control, and an important way to achieve the transition from post failure alarm to pre failure warning.The existing monitoring and inspection technology can effectively reflect the condition of pipelines by measuring strain, temperature, wall thickness, and defect information.However, these technologies cannot detect early damage and evaluate the degree of mechanical performance degradation of pipelines in a timely manner.Although methods such as nonlinear ultrasound, electromagnetic multiparameters, and micro indentation can characterize micro defects and measure some mechanical parameters, there is still a considerable gap in accurately characterizing the early damage state of pipelines online.On the one hand, the inherent physical correlation between the measured mechanical parameters and the non-destructive testing characteristic parameters has not been fully established; On the other hand, these techniques can only measure a few mechanical parameters, and the damage state of pipelines often cannot be accurately described solely based on a few parameters.Meanwhile, although these measurement characterization techniques have high measurement accuracy, they are easily affected by environmental factors such as high temperature and noise, which can affect their sensitivity.In addition, the detection of pipeline micro leaks is crucial for timely risk detection, and numerous technologies based on acoustic methods have been developed.However, the existing detection accuracy is not high enough, and the attenuation and distortion of small leakage signals after complex path propagation are very serious, which is difficult to meet the requirements of chemical toxic, flammable, and explosive media characteristics for micro leakage detection.For example, octafluoroisobutylene in the fluorine chemical production process is a highly toxic substance, and extremely low doses can lead to poisoning and death in humans. Therefore, how to break through the limits of existing micro leak detection technology and develop high-sensitivity micro leak detection technology is a huge challenge for chemical pipeline monitoring and inspection.

3.Development Suggestions

1) Developing pipeline design theory in harsh and complex environments to improve design quality

The diversity of medium characteristics and process parameters in chemical pipelines leads to complex damage mechanisms, and the lack of accurate prediction models has become a key constraint on the development of pipeline design theory in harsh and complex environments.It is necessary to study the multi damage coupling mechanisms such as creep fatigue corrosion under high temperature and corrosive media, and creep fatigue in hydrogen environments, explore the damage evolution law under the coupling of thermal, mechanical, and chemical fields, and establish a design method and theory based on multi damage mechanism coupling life prediction.Conduct in-depth research on the coupling mechanism of gas-liquid phase change gas liquid solid multi field with flash evaporation or cavitation, as well as the erosion corrosion and erosion cavitation coupling of multiphase flow with solid content. Explore quantitative prediction models for pipeline, valve, and pipe fittings damage, and form a design method for chemical pipeline valve systems, equipment, and components based on failure mechanisms.

2)Strengthen the research and development of materials and monitoring technologies to support the long-term safe operation of pipelines

In response to the requirements of high temperature, corrosion, and hydrogen environments for material wear resistance, corrosion resistance, hydrogen embrittlement resistance, and fatigue resistance, we break the inverted relationship between wear resistance and corrosion resistance requirements, explore wear-resistant corrosion cavitation, wear-resistant corrosion composite materials and alloy materials, develop new coatings and performance strengthening treatment processes, develop accurate and efficient welding residual stress control technology in the welding process, improve the comprehensive performance of materials and their connecting parts, and meet the needs of long-term continuous operation in harsh environments.At the same time, in order to support the research and development of new materials and processes, it is necessary to develop a large-span parameter adjustable gas-liquid-solid multiphase flow erosion corrosion/erosion cavitation experimental testing platform, develop in-situ testing technology for high-temperature and high-pressure hydrogen environments, and develop in-situ measurement instruments for multi axis complex stress in high-temperature hydrogen environments (up to 600°C).In addition, research and development of high-precision, anti-interference material performance real-time, in-situ, non-destructive characterization technology equipment, to achieve early diagnosis and quantitative evaluation of pipeline damage status; Develop high-sensitivity micro leak detection technology for chemical pipelines based on new structures, to promptly detect leaks of highly toxic chemicals.

3)Combining new generation artificial intelligence technology to achieve intelligent operation and maintenance of chemical pipelines

The multi damage coupling mechanism caused by complex and harsh environments is complex, and the contribution of each damage in different scenarios is difficult to reasonably evaluate.It is necessary to combine the new generation of artificial intelligence technology to carry out attribution analysis of pipeline performance degradation under multi damage coupling conditions. By combining online monitoring data such as pipeline wall thickness, temperature, strain, and real-time process data such as pressure and medium flow rate, a multi-dimensional fusion evaluation technology for pipeline service status driven by damage mechanism and monitoring data fusion should be studied.Based on multiple monitoring features and safety parameters, a data mining technology based on multimodal heterogeneous features is developed to form an intelligent assessment system for comprehensive damage of chemical pipelines in high-temperature and harsh scenarios. This system can timely determine the status of pipeline damage and develop operation and maintenance mitigation strategies to effectively control risks.In addition, it is necessary to develop intelligent monitoring, perception, and process parameter regulation technologies for pipeline intelligent operation and maintenance. By determining the location and severity of damage, automatic adjustment of process parameters and mitigation strategies can be achieved to control and prevent risks such as corrosion and wear.

4)Strengthen the construction of standards and regulations, promote the standardized development of chemical pipeline transportation

Exploring multidimensional optional parameter space characterization methods and critical characteristic determination methods for specific chemical process parameter conditions, researching spatiotemporal trend prediction methods for the coupling effects of abrasion, corrosion, and cavitation based on the characteristics of specific pipelines, valves, and pipe fittings and the working environment, local damage characteristics, and quantitative parameter influence relationships on design life, forming accurate and convenient industry standard specifications for determining equipment material selection and structure, size, flow rate (shear stress), valve opening, pH value, corrosion coefficient (K_p), Cl^‒ concentration and other parameter control ranges, as well as pipeline fixed-point thickness measurement, valve monitoring and detection, and safety evaluation and risk assessment methods.

4. Conclusion

With the development trend of large-scale chemical process equipment, harsh service environments, and long-term continuous operation, higher temperature and pressure, stricter media, and longer operating cycles have put forward higher requirements for chemical pipeline transportation.The hydrogen, high solid, high chlorine, high sulfur, and high acid characteristics of chemical pipelines, valves, and fittings transport media, as well as the high temperature, high pressure (difference), and high flow rate operating conditions, lead to various damages such as multiphase flow abrasion, corrosion, cavitation, creep, hydrogen damage, and their coupling effects. The relevant mechanisms are unclear, the rules are unclear, the prediction models are inaccurate, the preparation methods of specialized materials are missing, the performance enhancement process needs to be improved, the industry standards and specifications are not sound, and the online monitoring and early warning and intelligent control technology platform is lacking, making it difficult to form strong theoretical and technical support for China's chemical pipeline transportation.Therefore, it is necessary to strengthen the top-level design of pipeline design theory, material and monitoring technology research and development, intelligent pipeline operation and maintenance, and standard specification construction in harsh and complex environments based on the analysis of damage failure mechanisms and quantitative prediction models of chemical pipeline valve systems. New artificial intelligence research paradigms should be introduced to compensate for the difficulties in achieving damage in complex experiments and engineering, so as to adapt to the transportation needs of chemical pipelines with complex media in new scenarios and situations.