Papers by Keyword: Pipeline Steel

Abstract: With search for clean and sustainable energy sources European union is determined to fully substitute natural gas with hydrogen in 2050. With these requirements it is really important to study materials used in existing gas infrastructure and evaluate their resistance to hydrogen embrittlement, which is common phenomena in material degradation. In this article, a comparative study was conducted using slow strain rate testing (SSRT) in situ at 10 MPa hydrogen pressure and tensile testing in air on X-52, X-60, and X-70 pipeline steels commonly used in Czech gas infrastructure. The results revealed reduction in elongation and a significant reduction in contraction in SSRT samples exposed to hydrogen compared to those tested in air, while yield and tensile strengths remained nearly unchanged. Furthermore, fracture morphology transitioned from ductile dimple to cleavage/quasi-cleavage. These findings suggest that hydrogen primarily affects the plastic properties of the materials, leading to a shift towards a lower energy fracture mechanism.

Abstract: The fatigue endurance of API 5L X42 pipeline steel was assessed through axial fatigue tests amongst Longitudinal (L), Diagonal (D) and Circumferential (C) directions. The S-N fatigue life curves were linearized by the stress-life relationship provided in the ASTM E-739 Std., and fatigue strength exponent was calculated by the linear regression method. Results showed an anisotropic behavior of fatigue properties, which is mainly controlled by the pearlite banding degree (A_i) and the ferritic grain orientation parameter (Ω₁₂). The interactions of the fatigue crack tip with the microstructure during the crack propagation stage have a significant effect on fatigue endurance. The C direction with the lowest values of banding degree (A_i) and grain orientation parameter (Ω₁₂) showed the strongest fatigue endurance behavior. Furthermore, fatigue strength exponents exhibited significant directional dependence, representing a reduction of up to 20% in fatigue lifetime depending on the evaluated direction.

Abstract: The burst failure of a high frequency welded (HFW) pipe used for nature gas pipeline in an oilfield was analyzed systematically by macro analysis, physical and chemical property test, scanning electron microscope (SEM), etc., and the limit internal pressure of the pipeline under operation condition was predicted based on finite element method (FEM). The results showed that the chemical composition and mechanical properties of the pipe meet the requirements of relevant standards. The failure results showed that the dent damage of the straight pipe section was at 12 o'clock. In the service of the pipeline, the stress in the dent area exceeds the yield strength, which leads to the plastic deformation of the pipeline, resulting in necking and thinning, and the reduction of wall thickness further leads to the decrease of ultimate internal pressure, until the ultimate bearing capacity of the dent area is less than the internal pressure of pipeline operation, resulting in burst. It is suggested to strengthen the supervision of pipeline construction to avoid the pipeline dent damage. Meanwhile, the operation monitoring of the pipeline with dent damage should be strengthened, and timely repair or depressurization operation should be carried out if necessary.

Abstract: The pipeline steels which are used for transportation of natural gas and crude oil suffer from hydrogen damage at their internal as well as external surfaces. The internal surfaces of pipelines are generally affected due to hydrogen induced cracking and the external surfaces due to the soil environmental conditions which cause stress corrosion cracking. In the present investigation, the electrochemical corrosion behavior of X70 pipeline steel was studied in sour environment and near neutral soil environment. To assess the mechanism of hydrogen damage in steel, electrochemical hydrogen charging and permeation techniques were used to characterize the hydrogen distribution, trapping and its diffusion in X70 pipeline steel. It has been found that corrosion behavior of pipeline steel in the sour environment is higher than the near neutral soil solution. From the hydrogen permeation study it is established that the hydrogen permeation rate increases with the square root of the charging current density, and the increase of hydrogen flux is directly proportional to the subsurface hydrogen concentration.

Abstract: The influence weights of various sensitive factors, such as steel grade, applied potential, temperature and soil environment, on stress corrosion cracking behavior of high-grade pipeline steel were studied by means of orthogonal test at mixed level and slow strain rate test. The stress corrosion behavior of X80 pipeline steel in near neutral and high pH simulated soil solution under overprotection potential was observed by SEM. The results showed that the applied potential has the greatest weight on stress corrosion index of ISSRT, followed by temperature, steel grade and soil environment. X80 pipeline steel exhibits high stress corrosion sensitivity in near-neutral and high pH simulated soil solutions at applied potential of -1500mV, and its SCC mechanism is hydrogen embrittlement (HE). This study can provide guidance for practical engineering application of pipeline steel.

Abstract: Derrick and substructure is one of rig’s core equipment components, and it is also the most important weight component of rig. The working environment of derrick and substructure is very serious, whose material should has high strength, excellent plasticity, toughness and weldability property. In this paper, the chemical composition, micro-structure, tensile property, impact property, hardness and weldability of high strength pipeline steel with strength grades of X70 (485MPa)~ X100(690MPa) were systematically analyzed. The analysis and study of the service environment of rig derrick and substructure as well as the technical requirements of the material, showed that the performance of high strength pipeline steel was obviously better than that of the same grade high strength low alloy structural steel used in rig derrick and substructure at present, and it can fully meet the technical requirement of rig derrick and substructure. The application of high strength pipeline steel to rig derrick and substructure will improve the service property, optimize the design , and fully ensure the service safety of rig derrick and substructure.

Abstract: The fracture toughness of X80 pipeline steel, which has been widely used in China, plays a key role in pipeline safety insurance. In order to know the accurate fracture toughness of X80, the methods of acoustic emission and high K ratio have been carried out to judge the initiation of crack propagation and improve flatness of fatigue pre-crack front. By this method, fracture toughness of base metal, weld and heat affect zone of X80 pipeline steel have been tested, and failure assessment curves of X80 have been established and fitting equations has been provided. The results suggested that different failure assessment curves should be established according to different crack sizes and material parameters.

Abstract: Comprehensive analysis on the requirement and evaluation result of pipeline steel for sour service is carried out in this paper. So as to provide technical support for the development of the high toughness sour service pipeline steel with low manganese content.The evaluation results shows that the high toughness sour service pipeline steel with low manganese content has excellent comprehensive properties, and the excellent comprehensive mechanical properties and corrosion resistance properties of trial products are achieved through reasonable composition and micro-structure design. The HIC and SSC test result complies with pipeline steel requirement for sour service drafted by major international manufacturers. In order to guarantee the application prospect of the trial products, the weldability of the sour service pipeline steel is analyzed finally, and the test result shows that HAZ softening can be improved when the cooling rate was higher than 20 °C /s.

Abstract: DWTT (Drop weigh tear test) is an effective way to evaluate the fracture propagation for pipeline steel. The effects of slab reheating temperature, soaking time, single pass reduction ratio during recrystallization zone rolling and transfer bar ratio during non-recrystallization zone rolling on DWTT performance were studied for heavy gauge pipeline steel. And the grain refinement and toughening mechanism were discussed. It was found that the grain in the core of the plate can be refined by reducing the reheating temperature, increasing the single pass reduction ratio during recrystallization zone rolling and setting suitable transfer bar ratio during non-recrystallization zone rolling, which promote the DWTT property improvement for heavy gauge pipeline steel. The 30.9mm heavy gauge pipeline steel plate was industrial produced and the X70 UOE welded pipe with dimension in Φ1219×30.9mm was manufactured. The DWTT 85%FATT (fracture appearance transition temperature) of pipe body is as low as -20°C.

Abstract: Constant increase of energy consumption in modern industry requires construction of heavily loaded pipelines with high throughput capacity. Therefore, high-strength steels should be used for the cost reasons. Additionally, the pipelines are also often used in the areas with cold climate and high seismicity. Therefore, strength and plasticity reduction is unacceptable. Bainitic steels with retained austenite (RA) or martensite/austenite (M/A) constituents meet these requirements. The purpose of this investigation is to determine thermo-mechanical treatment parameters with further accelerated cooling and additional isothermal holding for M/A-phase and mechanical properties formation. Experimental modeling of the production process was carried out using Gleeble HDS-V40 thermo-mechanical simulator. All investigations were realized with two high-strength micro-alloyed steels with different molybdenum and carbon content. Results showed that decrease of temperature and duration of isothermal holding as well as addition of molybdenum promote bainitic microstructure nucleation and reduce grain size and M/A-constituents. All these factors lead to a slight improvement in mechanical properties.