To investigate the applicability of gas metal arc welding （GMAW） in high‑temperature molten salt storage tank engineering，two welding process tests，with and without pulse application，were conducted on 347H stainless steel.The microstructure of the welded joints was observed using optical microscopy and scanning electron microscopy，and their mechanical properties were evaluated.The results show that the welded joint without pulse application exhibited slag inclusion defects，while the welded joint with pulse application showed no slag inclusion，porosity，or other defects；the weld microstructure mainly consisted of columnar and dendritic austenite and precipitated phases.In contrast，the welded joint with pulse application exhibited high‑temperature tensile properties at 565 ℃ （R_m≥139 MPa，R_p0.2≥360 MPa） and low‑temperature impact properties at -196 ℃ （≥31 J） that met the requirements of GB/T 150—2024 and related manufacturing engineering technical specifications.This study provides theoretical and experimental support for the reliable application and quality assurance of GMAW welding technology in the manufacturing field of stainless steel pressure vessels.

In view of the tendency in the analysis and design of heat exchanger tube sheets to overemphasize technical means while neglecting engineering factors，this paper，based on previous research results combined with three failure cases and relevant engineering experience，identifies the issues worthy of attention in modeling，including non‑pressure‑bearing structural members and the distortion of actual operating conditions.In some cases，the absence of baffles，tie rods，spacer tubes and partition plates in the tube bundle model will lead to analysis results inconsistent with engineering practice.In the analysis and discussion of the cases，analytical models improved to varying degrees are proposed.The synergistic complementarity of finite element secondary analysis technology，conventional design technology and engineering auxiliary technology to the analysis and design technology is a better handling countermeasure.Through the discussion of 7 points of understanding across 3 topics—including the content and integrity of analysis and design，the concept and verification of the analytical model，and the objective resources and subjective awareness of analysis and design—the necessity of adopting the dual criteria of stress and displacement in the analysis and design of tube bundles is put forward.It is suggested that in analysis and design，the cultivation of engineering literacy and the conscious improvement of individual skills should be strengthened.

To address the difficulty in accurately monitoring and predicting the prestress loss of long‑distance prestressing strands in large‑scale structures due to duct friction，anchor deformation，and stress relaxation，a comprehensive prediction method integrating fiber optic sensing measurement data and machine learning is proposed，based on a liquefied natural gas storage tank project.This method uses fiber optic sensing technology to conduct long‑term monitoring of long‑distance prestressing strands in actual engineering，obtaining prestress loss data.Based on the measured data，a numerical simulation dataset of long‑term prestress loss is established.Multiple machine learning algorithms are used to construct prediction models，and the SHAP interpretability algorithm is further introduced to analyze the prediction basis and key influencing factors of the models.Experimental and simulation results show that the total losses of the circumferential and vertical prestressing strands of the storage tank are approximately 390 MPa and 320 MPa，respectively.The average percentage errors of the six established machine learning models in both the training set and the test set are below 3.5%，among which the XGBoost model has the smallest error，achieving 1.19% on the test set.Through SHAP analysis of multiple influencing factors，the length of the prestressing strand has the most significant effect on long‑term loss，followed by the elastic modulus of concrete，the elastic modulus of the prestressing strand，and the tensioning control stress.The research shows that machine learning models can accurately predict prestress loss and analyze the important factors causing prestress loss.This study is of great significance for the accurate evaluation of the service performance of prestressed structures.

Rectangular tangential nozzles are often used as special process interfaces in petrochemical equipment（such as multiphase flow cyclone separators），but their structural strength design has not been clearly specified in design codes such as GB/T 150.The finite element limit load analysis method was used to calculate the pressure‑bearing capacity of cylindrical shells with rectangular tangential nozzles，and the weakening effects of rectangular tangential nozzles with different dimensionless structural parameters（width‑to‑diameter ratio W/D_i，diameter‑to‑thickness ratio D_i/T，and thickness ratio t/T） on the strength of the cylindrical shell were investigated.It was found that the cylindrical shell with a square tangential nozzle having a side length ratio of 1 has the maximum pressure‑bearing capacity.Therefore，a limit load reduction factor reflecting the strength reduction of the cylindrical shell due to the provision of a square tangential nozzle was defined.The influences of the three dimensionless structural parameters W/D_i，D_i/T，and t/T were studied，and regression analysis was performed on the limit load reduction factor based on a large number of numerical calculations.This is helpful for the strength design or safety assessment of cylindrical shells with square tangential nozzles.It was also found that for the same opening area，the pressure‑bearing capacity of the cylindrical shell structure with a square tangential nozzle is significantly lower than that with a circular tangential nozzle.In other words，the strength weakening effect of a square tangential nozzle on the cylindrical shell is significantly greater than that of a circular tangential nozzle.Therefore，from a strength perspective，using a circular tangential nozzle is more reasonable than using a square tangential nozzle.

A 2507 duplex steel （S25073） U‑shaped tube reboiler in a chemical plant experienced a leakage during operation.After disassembly，it was discovered that the U‑shaped bend exhibited severe corrosion and perforation，resulting in the failure of the reboiler.To address the above issues，various methods such as macroscopic inspection，microscopic morphology analysis，chemical composition analysis，metallographic analysis，mechanical property analysis，residual stress analysis，and heat exchange vibration analysis were employed to investigate the causes of failure.The results show that inadequate circulation of the liquid phase material at the U‑shaped bend causes the corrosive medium to evaporate and concentrate，thereby increasing the risk of corrosion.Meanwhile，residual stress in the U‑shaped bend region reaches up to 231 MPa.Under the combined effect of these two factors，the heat exchange tube corrodes and failes at the U‑shaped bend.The straight pipe section do not experience significant corrosion because the concentration effect of the liquid phase material is not obvious and the residual stress is low，ensuring that the corrosion resistance still met the requirements.Based on the analysis of the failure causes，suggestions for improving the selection of the reboiler under this operating condition are proposed.After the actual operation under the working conditions，it has been verified that the reboiler with the improved selection performes well under the same conditions.This case shows that in the design of heat exchange with corrosion tendency，apart from the conventional calculation of heat transfer，vibration analysis and strength calculation，the corrosion problem caused by local concentration should be paid more attention.

To overcome the problems of strong magnetic force interference，low transduction efficiency，and poor detection performance existing in current electromagnetic acoustic surface wave transducers when detecting structural defects in ferromagnetic metals，a novel electromagnetic acoustic surface wave transducer based on a U‑type pulsed electromagnet with high conversion efficiency and strong adaptability，as well as a corresponding detection method，were designed and developed.Finite element numerical simulation was used to optimize the transducer configuration and verify the feasibility of the detection method.A pulsed electromagnet‑type electromagnetic acoustic testing system was established.The effects of pulse number，excitation voltage，and defect size on the transducer performance were analyzed，and the performance differences between this transducer and existing electromagnetic acoustic transducers were compared.The results show that the pulsed electromagnet‑type transducer has significantly better near‑surface defect detection capability in DH36 low‑alloy carbon steel compared to existing electromagnetic acoustic transducers.This study provides a new method for addressing near‑surface defects in ferromagnetic metals.

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.