中海油(天津)管道工程技术有限公司

As more submarine pipelines are put into service and operated for extended periods,the issue of corrosion in ag-ing submarine pipelines has become increasingly severe.However,maintenance costs for offshore oil and gas fields are typi-cally constrained,despite their high production pressures,leading to an urgent need for low-cost and highly efficient in-situ repair technologies for these pipelines.To address this need,this paper presents a systematic review of the characteristics and challenges associated with traditional repair technologies for submarine pipelines.It particularly focuses on the features and applications of three new in-situ repair technologies:lined composite hoses,the insertion of reinforced thermoplastic pipes(RTP),and in-situ internal coatings.Research results are summarized as follows:① The repair technology based on lined composite hoses can effectively prevent the progression of corrosion in repaired pipelines by isolating the conveying medium from the pipeline itself,thereby extending its service life.However,the construction process is challenging,and the technology is relatively complex.② The insertion of RTPs as a repair technology allows the RTPs to replace the submarine pipeline for medium transmission while maintaining resistance to corrosion from both the medium and seawater.Nonethe-less,the reduction in diameter of the RTPs complicates the insertion process and presents technological challenges.③ The repair technology utilizing in-situ internal coatings is suitable for pipelines with remaining wall thickness and strength that still meet design and operational requirements,regardless of their intended use,including the transportation of water,gas,and oil.The concluding section further discusses the application scenarios and future research directions for these three new in-situ repair technologies,providing valuable insights for their continued research and application.

The B10 copper-nickel alloy pipeline used for seawater transportation on a certain platform was found to have corrosion perforation at the weld joint between the elbow and the flange during a shutdown inspection.In this study， the failure mechanism of corrosion perforation was analyzed using macroscopic morphology observation，scanning electron microscopy (SEM)，energy-dispersive spectroscopy (EDS)，X-ray diffraction (XRD) and metallographic examination.Results showed that “sugar cube”-like intergranular corrosion morphologies were commonly observed at the bottom of corrosion pits on the flange， in erosion-wear areas， corrosion grooves， perforated regions and at the bottom of corrosion pits on the elbow.Locally， a “stepped” exfoliation morphology was observed， where grains were progressively stripped layer by layer.The preferentially corroded grain boundaries formed a circuit， and the surrounded grains were selectively denickelized and dissolved， resulting in grain spalling.The reduced hardness and coarse columnar grain structure of the flange further decreased the material’s corrosion resistance.The corrosion perforation of the copper-nickel alloy pipeline occurred in the erosion-sensitive zones and the weld heat-affected zones with the poorest corrosion resistance.This failure was the result of the synergistic effects of erosion wear， intergranular corrosion and selective dealloying.Enhanced corrosion monitoring is recommended for similar locations in service pipelines.

The origin of tribo-magnetization correlates to the plastic deformation of subsurface caused by interfacial tribological sliding,the plastic deformation of subsurface affects the friction coefficient and friction state,in turn.This allows to establish the relationship among the wear state of the interface,the plastic deformation of the subsurface layer and the magnetic field upon the sliding surface,which helps to develop a new detection and prediction technology of wear state so as to make up for the shortcomings of the existing technologies.According to the theory of ferromagnetism,the elastic-plastic deformation of ferromagnetic materials in the process of tension or compression can lead to the change of magnetic domain structure in varying degrees.Different from the simple tension or compression condition,the effect of plastic deformation caused by interfacial tribological sliding on the magnetic domain structure is more complex.So far,it is not very clear about the specific microstructure changes and corresponding domain structure changes of the subsurface region under the complex tribological sliding.In this paper,the plastic deformation underneath the sliding interface and the changes of magnetic domain structure caused by the interfacial tribological sliding were deeply studied to reveal the evolution of tribo-magnetization of ferromagnetic materials.The friction tests of nonmagnetic 316L stainless steel/commercial pure iron were carried out at room temperature under the geomagnetic field The number of reciprocating sliding of each specimen was set to 3 000 times.The magnetic field signal upon the surface of commercial pure iron was detected before and after friction.The friction during sliding was monitored in real time The results indicated that when the friction variance increased,the mean value of the magnetic field increment upon the sliding surface also increased,indicating that there was a certain relationship between the tribological behavior of the sliding interface and the tribo-magnetization.Here,scanning electron microscopy （SEM） and electron backscatter diffraction （EBSD） were used to obtain the microstructure of the subsurface region of commercial pure iron after sliding then calculated the GOS value of the grain.The results showed that the friction variance was 3.26×10 -5 ,1.64×10 -3 7.02×10 -3 and 7.23×10 -2 respectively,the corresponding GOS peaks were 5.76°,6.69°,8.60°and 5.89°,and the depth of deformation area were 2.33×10~2,2.65×10~2,2.80×10~2 and 3.24×10~2μm.The depth of deformation area was defined by the depth of GOS value from large fluctuation to relatively stable fluctuation.Concurrently,the magnetic domain structure of the subsurface region underneath the sliding interface was observed by using the Bitter method.The results showed that at the depth of 162.5μm underneath the sliding interface,the domain structures of the two grains present strip-shaped with different directions before sliding.After sliding,their width increased from 1.6μm to 3.7μm,their spacing increased from 3.1μm to 10.7μm,and some magnetic domains were in circular arc shape.Interestingly,the phenomenon that the magnetic domain crossed the grain boundary appeared,which can be speculated from the change in grain boundary misorientation under the tribological contact.Moreover,scanning electron microscopy （SEM） image and geometrically necessary dislocation （GND） density map showed that many sub-grains were formed,especially near the grain boundary.The geometric necessary dislocation density near the grain boundary increased obviously.The changes of magnetic domain structure were closely related to the changes of microstructures as mentioned above.The results mentioned above can provide the theoretical basis for using the effect of tribo-magnetization to detect and predict the friction and wear state.