Taking the 23Cr2Ni4MoV steel forging as the research object，long‑term hydrogen charging tests were conducted at room temperature under different hydrogen pressures.The hydrogen concentration in the test steel was measured using the thermal desorption method，its hydrogen trap types and binding energies were analyzed，and its resistance to hydrogen‑induced cracking was evaluated using modified wedge open loading（WOL） specimens.The results show that under a room temperature，35 MPa hydrogen environment，hydrogen penetration into the 23Cr2Ni4MoV steel forging is difficult；when the pressure is increased to 70 MPa，the hydrogen permeation amount is approximately 3.41×10^-6；further increasing to 110 MPa，the hydrogen permeation amount increases to 4.45×10^-6.Thermal desorption analysis reveals that three types of hydrogen traps exist in the test steel，with binding energies of 10.24，19.93，59.88 kJ/mol in ascending order.The hydrogen that penetrates under the room‑temperature high‑pressure hydrogen environment is mainly captured by the shallow traps with a binding energy of 10.24 kJ/mol.Under a room temperature，110 MPa hydrogen environment，the hydrogen‑induced cracking stress intensity factor threshold value of the material is relatively low；when the applied stress intensity factor exceeds 58 MPa·m^1/2，the WOL specimens all exhibit significant cracking.Based on a comprehensive assessment，the 23Cr2Ni4MoV steel forging is not suitable for use as a forging for ultra‑high‑pressure hydrogen storage vessels.

To address the short‑term overtemperature issues during service of ultra‑high‑pressure polyethylene tubular reactors，optical microscopy （OM），scanning electron microscopy （SEM），energy‑dispersive X‑ray spectroscopy （EDS），Vickers hardness testing，and nanoindentation were employed to systematically investigate the effects of overtemperature temperature，duration，and overtemperature cycles on the microstructure and mechanical properties of key material 30CrNiMo8 steel.Results show that during overtemperature for approximately 30 s，the primary effect on 30CrNiMo8 steel shifts from phase transformation to changes in grain size and morphology，manifested as enhanced brittleness and reduced hardness.When overtemperature exceeds the complete austenitization temperature A_{c_{\mathrm{3}}} to 860 ℃，material hardness first sharply increases then decreases due to massive martensite precipitation，carbide formation，and segregation of C，Cr，and Mo elements at grain boundaries.After 6 overtemperature cycles，martensite laths significantly widen with altered bundle orientations，causing grain structure coarsening and mechanical property degradation.This study provides data support and design references for safe operation of ultra‑high‑pressure polyethylene tubular reactors.

To address the issues that existing pipeline gouge failure assessment methods neglect the changes in surface material properties and have insufficient understanding of the cracking risk caused by gouges in high‑strength steel pipes，a gouge simulation and characterization method based on a biaxial loading platform is proposed.A dedicated gouge processing platform was designed and built to prepare gouge specimens under different process parameters（tool shape，vertical pressure，scratching speed），and their cross‑sectional microstructure and mechanical properties were systematically analyzed.The results show that gouges induce significant plastic deformation in the near‑surface layer，forming a distinctly layered metamorphic layer；the grains in the region near the root are severely deformed，resulting in a denser microstructure.Vickers hardness tests reveal that the hardness at the root reaches up to 388HV，nearly twice that of the base material（200HV），and it increases with higher vertical pressure and scratching speed.Based on the hardness distribution，the thickness of the metamorphic layer was determined to exceed 2 mm.Additionally，residual compressive stress exists at the gouge root，with the longitudinal residual stress increasing with depth，while the transverse residual stress decreases with depth.This study provides direct evidence distinguishing gouges from ordinary metal loss defects and offers an important basis for crack initiation analysis and safety assessment of gouges in high‑strength pipeline steel.

Creep is a major damage mechanism for high‑temperature components in nuclear power plants，and the temperature‑ and time‑dependent stress intensity limit S_t is an important material parameter for creep assessment.In the ASME Code，safety factors are directly applied to the three criteria for determining the stress intensity limit S_t，but the implied failure probability and conservatism of this method have rarely been reported.To quantify the failure probability of S_t，functional expressions for the failure probability corresponding to each criterion were derived in this study based on creep data of Alloy 617，combined with the relationship between each S_tcriterion and the average creep rupture life equation.The failure probabilities of the three criteria for S_t of Alloy 617 were calculated，and the effects of safety factors（1.0，1.25，1.5） on the failure probabilities were discussed.The results show that the stress intensity limit S_t of Alloy 617 exhibits a relatively low failure probability（at 750 ℃，10⁻⁹~10⁻⁵；at 850 ℃，10^-8~10^-5；at 950 ℃，10^-8~10^-4），indicating a high level of conservatism.The minimum stress for the onset of tertiary creep criterion and the minimum creep rupture stress criterion play a controlling role in S_t，depending on the stress level.The findings can provide a theoretical basis for the probabilistic evaluation of material parameters related to high‑temperature strength assessment.

Aiming at the local stress concentration problem at the large‑section rectangular inlet of the double‑inlet decoking drums with a diameter of 3 400 mm used in a 1.2 million tons per year ethylene cracking unit，the finite element calculation model of the decoking tank cylinder and the large‑sized double tangential inlet nozzle was established by using the Ansys software.The stress distribution of the large‑size tangential rectangular inlet pipe was obtained under various scenarios of rib thickness and spacing.The analysis primarily investigates the effect of rib thickness and spacing on the stress at the connection between the decoking drums and the tangential inlet pipe.The results indicate that the optimized rib thickness is 32 mm，with a spacing of 280 mm.Upon applying the actual combined loads encountered in engineering applications to the dual tangential inlet drum and assessing its strength according to pressure vessel design standards under both design and operational conditions，it is confirmed that the strength of the optimized drum meets the required standards.The research results provide a reliable basis for the engineering application of dual tangential inlet coke cleaning tanks.

Addressing the critical issue that defects such as pits and cracks significantly reduce the load‑bearing capacity of pressure vessels and lead to safety accidents under harsh operating conditions involving high temperature，high pressure，and corrosive media，this study employs the linear matching method（LMM） to systematically analyze the influence mechanism of geometric characteristics of pitting defects on the fatigue behavior of high‑temperature pressure‑bearing structures.The results indicate that local thinned pits significantly reduce the reverse plastic limit，with the axial local thinned pit having the most significant impact，while the limit load of elliptical pits is largely unaffected by pit size.Under high‑temperature environments，the axial local thinned pit increases the total strain range by 53.8%，whereas the circumferential local thinned pit increases it by only 18.1%.The total strain range of elliptical pits is significantly influenced by pit size，increasing with the short axis（axial dimension） and decreasing with the long axis（circumferential dimension）.This study provides a theoretical reference for extending equipment service life and improving production efficiency.

For the mechanical analysis of the D‑shaped flanged convex head structure，three analytical methods are adopted in this paper：GB 150/ASME Ⅷ-1（Method 1），the method from ASME Ⅷ-2 based on the improved approximate solution theory for spherical shells approximated as cylindrical shells（Method 2），and the proposed method based on the approximate solution theory for spherical shells approximated as shallow shells（Method 3）.A comparative study is carried out among the three analytical solutions and the finite element analysis（FEA） results.The results show that for flange stress，the errors between Method 1 and FEA range from 82.32% to 130.73%，those between Method 2 and FEA range from 3.99% to 5.19%，and those between Method 3 and FEA range from 7.09% to 9.21%.For the edge stress of the spherical head（not calculated by Method 1），the errors relative to FEA range from 3.16% to 7.73% for Method 2 and from 0.4% to 6.24% for Method 3.

To address the problem of premature aging failure of some domestic P91 pipes in process industry due to excessive aging rates under high‑temperature and high‑pressure environments，a scheme is proposed to identify abnormal aging rates based on the distribution state of grain boundary misorientation angles from electron backscatter diffraction（EBSD） testing.The results indicate that high‑mobility high‑angle grain boundaries generated when the high‑temperature tempering temperature exceeds the actual heating phase equilibrium temperature Ac_{\mathrm{1}} are one of the causes of abnormal aging rates in P91.When such abnormal aging rates occur，abnormal “spikes” appear near 30° and 45° on the EBSD grain boundary misorientation angle distribution map.Based on the above characteristics，the problem of abnormal aging rates in P91 caused by excessively high high‑temperature tempering temperatures can be identified.This study provides a reference for improving the manufacturing quality inspection of P91 pipes and avoiding premature aging failure.

To address the issues of insufficient generalization ability and low leakage detection accuracy of models under small sample conditions for oil and gas pipelines，a retrospective prototype network（VRPN） based on learnable variational mode decomposition was proposed and applied to the leakage detection of oil and gas pipelines.The end‑to‑end optimization of mode decomposition and dynamic weight allocation were achieved by using learnable convolution kernels and adaptive parameters.Introducing a double‑layer Inception multi‑scale convolutional branch to capture multi‑dimensional signals and extract more precise feature information.Introducing retrospective prototype classification into the historical prototype buffer，the integration of current and historical prototype network to suppress vibration，improve the identification accuracy.A joint optimization objective function of cross‑entropy loss and prototype separation loss was designed to enhance training stability and efficiency.Experiments show that the proposed VRPN network framework performs excellently under limited sample and cross condition scenarios，achieving an average accuracy of 98.50%，which is 0.67% higher than that of ProtoNet.The research can provide a new effective solution for oil and gas pipeline leakage detection.