Jinheng Luo

Underground gas storage (UGS) is critical to national reserves and seasonal peak-shaving, and its safe operation is integral to energy security. In UGS surface process pipelines, heterogeneous bimetal composite pipes—carbon-steel substrates lined with stainless steel—are widely used but susceptible under coupled thermal–pressure–flow loading to geometry-induced instabilities (local buckling, adhesion, and collapse), which can restrict flow, concentrate stress, and precipitate rupture and unplanned shutdowns. Conventional ultrasonic testing and magnetic flux leakage have limited sensitivity to such instabilities, while standard eddy-current testing is impeded by the ferromagnetic substrate’s high permeability and electromagnetic shielding. This study introduces magnetically saturated pulsed eddy-current testing (MS-PECT). A quasi-static bias field drives the substrate toward magnetic saturation, reducing differential permeability and increasing effective penetration; combined with pulsed excitation and differential reception, the approach improves defect responsiveness and the signal-to-noise ratio. A prototype was developed and evaluated through mechanistic modeling, numerical simulation, laboratory pipe trials, and in-service demonstrations. Field deployment on composite pipelines at the Hutubi UGS (Xinjiang, China) enabled rapid identification and spatial localization of liner collapse under non-shutdown or minimally invasive conditions. MS-PECT provides a practical tool for composite-pipeline integrity management, reducing the risk of unplanned outages, enhancing peak-shaving reliability, and supporting resilient UGS operations.

The response surface methodology (RSM) is utilized to construct a corrosion prediction model for steel pipelines for underground gas storage (UGS). Four key corrosion-influencing factors—the CO₂ partial pressure, Cl⁻ concentration, temperature, and flow rate—are identified by investigating the operating parameters of 14 UGS extracted pipelines (Nos. S1–S14) in China. Based on the operating parameters, 29 sets of high-temperature and high-pressure autoclave corrosion tests are designed and carried out. A quadratic regression equation model for corrosion rate prediction is fitted using the data from the corrosion test results. The p-values of the model’s four influencing factors are p-value is 2 of the model is 0.9753, which is close to 1. Therefore, the observed value and the response value of the model are obviously correlated: i.e., the model has a high degree of truth. The model is used to predict the corrosion rate of 14 UGS pipelines: S3 and S14 are severely corroded, while the others are moderately corroded.

With the continuous development of oil and gas fields, the demand for corrosion-resistant tubing is increasing, which is important for the safe exploitation of oil and gas energy. Due to its excellent CO₂ corrosion resistance, 13Cr-110 martensitic stainless steel is widely used in sour gas-containing oil fields in western China. This paper describes a case of stress corrosion cracking (SCC) in a 13Cr-110 serviced in an ultra-deep gas well. The failure mode of the tubing is brittle along the lattice fracture, and the cracks are generated because of nitrogen gas-lift production-enhancement activities during the service of the tubing, leading to corrosion damage zones and cracks in the 13Cr-110 material under the synergistic effect of oxygen and chloric acid-containing environments. During subsequent production, the tubing is subjected to tensile stresses and cracks expanded at the 13Cr-110 lattice boundaries due to reduced structural strength in the corrosion region. To address the corrosion sensitivity of 13Cr-110 in an oxygen environment, it is recommended that the oxygen content in the wellbore be strictly controlled and that antioxidant corrosion inhibitors be added.

Gas reservoir-type underground gas storage (UGS) plays a critical role in China’s natural gas reserves and peak shaving, serving as an essential component of the energy security system. Its unique cyclic injection and production operations not only stabilize the natural gas supply but also impose stringent requirements on the safety and integrity of geological structures, wellbores, and surface facilities. Weaknesses in current practices can cause accidents, directly threatening energy security. Therefore, continuously improving integrity management is the key to mitigating energy risks. Currently, the integrity management of gas storage faces challenges such as an abundance of standards and the complexity of management elements, which affect both operational safety and management efficiency. To address these issues, this study systematically analyzes domestic and international standards related to gas storage and establishes a technical system based on “three-in-one” integrity management (geological structure, wellbore, and surface facilities). Key elements of integrity management are identified and optimized, and recommended execution standards for critical factors are proposed to provide a theoretical basis and decision-making support for the safe operation of gas storage. This study not only offers a reference for optimizing and implementing integrity management standards but also has significant practical implications for enhancing energy security and reducing energy risks, ensuring the smooth execution of China’s natural gas reserve and peak shaving initiatives.

Protective coatings are typically applied to enhance their resistance to corrosion. There is considerable research on the corrosion resistance of coated casings. However, few research studies have focused on the erosion resistance on coated casings. In this work, the erosion resistance of resin- and metallic-coated casings in liquid–solid two-phase fluids were investigated using a self-made erosion facility. The results show that the resin coating tends to peel off the material base in the form of brittle spalling or coating bulge in the high-speed sand-carrying liquid. Both resin and metallic coatings were broken through within 20 min in a liquid–solid two-phase flow environment. Compared to resin coatings, metallic coatings exhibit weaker erosion resistance in similar liquid–solid flow. Through the analysis of experimental results and fitted curves, empirical constants for materials and sand content influencing factors were determined using non-dimensional processing. The erosion prediction model of metallic coatings and resin coatings was established based on the ECRC/Zhang model with the change in flow rate, angle, and sand content. This research contributes to a better understanding of the erosion resistance performance of casings used in oil and gas fields, thereby contributing to potential improvements in their production.

With green and low-carbon developments in oil fields, an increasing amount of repaired oil tubing is being used as oil and gas transmission pipelines in China. However, due to differences in manufacturing standards between oil tubing and transmission pipelines, there are inevitably some issues during their use. This paper investigates a case of cracking failure in repaired oil tubing used as a gathering and transportation pipeline. The failure occurred after eight months of operation and was characterized by a circumferential crack at the male thread end of the tubing joint. To determine the root cause of the failure, a series of experiments were conducted on the oil tubing. The experiments included visual inspection, chemical composition analysis, mechanical properties testing, hardness testing, metallographic examination, and microstructure analysis. The results revealed that the thread of the cracked tubing was not tightened to the specified position; the connection between the tubing and the coupling was welded in a circumferential direction; and cracks occurred in the heat-affected zone of the weld. Chemical composition, tensile performance, and the Charpy impact of the tubing meet the requirements of API 5CT for P110 material, and no abnormalities were found in the metallographic structure. The microstructure at the weld toe of the fracture is martensite, and the hardness is 476 HV10. Based on the thermal simulation verification test, when the material of the tubing cools from 1200 °C, which is located in the coarse HAZ temperature zone, the base metal transforms into martensite with a little granular bainite, exhibiting its highest hardness value at 371 HV10, which is higher than the allowable hardness for carbon steel and indicates the material has poor weldability. The reasons for the cracking and failure of the tubing are that the P110 repaired tubing has a high carbon equivalent and poor weldability. During the welding process, martensitic structure was formed at the weld toe, and cold cracks appeared in the heat-affected zone, resulting in failure. To avoid the reoccurrence of such failure, recommendations are proposed.

Underground hydrogen storage represents an innovative approach to energy storage. To ensure the secure operation of subterranean hydrogen storage strings, a computational fluid dynamics (CFD) methodology was employed to devise an erosion assessment model tailored for high-velocity conditions. The research delved into the erosion and abrasion dynamics of these storage strings when subjected to high-speed gas flows. This study further examined the impacts of gas velocity, particle size, pipe material, and pipe wall corrosion imperfections on flow patterns and erosion wear rates across the column. The outcomes revealed several noteworthy trends. As fluid velocity increased, the flow field’s maximum pressure augmented, while it decreased alongside enlarging pipe diameter and particle size. P110 pipe material exhibited higher maximum pressure in comparison to N80. The effect of centrifugal force induced pressure to surge from the inner to the outer portion of the column. In the curved pipe section’s outer wall, the frequent occurrence of high-angle collisions engendered elevated rates of erosion wear over time. Particularly noteworthy was the observation of the highest erosion rate in curved pipes showcasing three corrosion defects, attributed to the backflow effects of erosion pits.

The use of duplex stainless steel (DSS) in various fields is promising due to its excellent anti-corrosion properties, but traditional welding can lead to the formation of unfavorable phases that deteriorate its quality. This study aimed to use the rotary friction weld (RFW) technique to prevent the formation of harmful phases in the welding of an S32205 alloy pipe. The welding parameters used included a rotating speed of 20 m/s, a friction pressure of 10 MPa, a friction time of 30 s, and a forging pressure of 30 MPa. The microstructure and mechanical properties of the resulting RFWed joint were investigated. The results revealed that the weld zone exhibited a microstructure consisting of ferrite and austenite phases, with no deleterious phase detected. The ferrite content was measured to be 53.3%, 54.5%, and 68.7% in the base metal, thermomechanical affected zone (TMAZ), and weld, respectively, owing to the rapid cooling rate in the RFW process, which prevented any harmful phase formation in the weld zone. Furthermore, the RFW process successfully produced an ultrafine grain with a ferrite/austenite grain size of 0.40 μm and 0.41 μm, respectively. The weld zone and TMAZ contained more low-angle grain boundaries (LAGBs) compared to the base metal, which was attributed to the dynamic recovery (DRV) within a grain. The high heating and cooling rates and short welding time of the RFW process did not allow sufficient time for the dynamic recrystallization of the microstructure in the weld zone. However, a slight increase in the ferrite content in the weld zone resulted in grain refinement and an increase in the dislocation density, resulting in a slight increase in the 358 HV0.2 hardness and 823 MPa tensile strength of the weld zone. This study offers a novel approach for obtaining ultrafine grain duplex stainless steel pipes with exceptional mechanical properties through the application of RFW.

An unstable assembly gap is detrimental to the formation and performance of the pipeline butt girth weld joint. Therefore, a numerical model of an 18.4 mm-thick X80 pipeline girth weld by a homogeneous body heat source was established to investigate the effect of the butt gap on the joint temperature and stress field, and carrying capacity. The accuracy of the simulation results was verified by measuring the welding thermal cycle with a thermocouple. The investigation results showed that the weld pool, heat-affected zone (HAZ) width, and maximum circumferential stress of the joint rose with the increase in the butt gap. The tensile stress unfavorable to the joint quality was mainly distributed in the weld metal and partial HAZ, and the distribution areas gradually expanded as the gap increased. The Von Mises stress peak value of the joint appeared in the order of 3 mm > 2 mm > 1 mm > 0 mm gap, reaching the maximum of 467.3 MPa (3 mm gap). This variation trend is directly related to the improvement in welding heat input with increasing butt gaps. The maximum Von Mises stress of the joint was positively correlated with the carrying capacity of the pipeline, which diminished as the butt gap enlarged. The pipeline carrying capacity reached 17.8 MPa for the joint with no butt gap, and dropped to 13.1 MPa for the joint with a 3 mm gap. The relationship between the carrying capacity (P) and butt gap (C) was described by P = −0.125C² − 1.135C + 17.715, through which the pipeline carrying capacity with other butt gaps can be predicted.

T-joint welding is a key manufacturing process of large storage tanks. However, complex residual stresses are generated and have a great effect on the structural integrity of storage tanks. The high residual stress caused by welding and the discontinuous structure may result in tank cracking and failure. In this work, the residual stress distributions on the inner surface, outer surface, and thickness direction of the T-joint were investigated by using the finite element method and indentation test method. The effect of local PWHT with different heating temperatures, heating rates, and heating widths on the residual stress distribution was also discussed. Results show that the residual stress of the T-shaped joint is high due to the serious structure discontinuity, multi-layer welding, and high strength. Among all the stresses, the circumferential residual stress is the highest and most concentrated in the outer weld connected with the annular plate. The residual stress gradually decreases with the increase in the heat treatment temperature. When the heating rate is less than 106 °C/h, the residual stress gradually decreases with the decrease in the heating rate. The large thermal deformation caused by heat treatment can be simultaneously avoided by heating the inside and outside of the T-joint. The residual stress decreases with the decrease in the width of the heating zone. The residual stress can be regulated by using a smaller width in the heating zone. An optimized heat treatment scheme with a heating temperature of 700 °C, heating rate of 56 °C/h, and heating width of 200 mm was proposed, which has a good ability to control residual stresses and improve the quality of the T-joint. It also has a good application in engineering.