Influence of yield-to-tensile strength ratio(Y/T) on failure assessment of defect-free and corroded X70 steel pipeline

The effect of yield-to-tensile strength ratio(Y/T) on failure pressure of X70 pipeline without and with corrosion defects was investigated.The stress-strain response of materials was characterized by a power-law hardening curve.Two formulas to estimate the strain hardening exponent n for a special Y/T were obtained by least squared regression method and the influence of Y/T on n was analyzed.As an application of n-Y/T expression,the analytical solutions of burst pressure for X70 pipeline without and with corrosion defects were also obtained.The results indicate that the burst pressure of defect-free X70 pipe without corrosion defects is a function of the Y/T,pipe geometry t0/D0 and engineering tensile strength,and increases as Y/T or t0/D0 increases; whilst the burst pressure of corroded X70 pipe decreases with the increase of defect depths,d/t.Comparisons indicate that the present analytical solutions closely match available experimental and numerical data.

Latest Development and Application of High Strength and Heavy Gauge Pipeline Steel in China

Over the past twenty years, significant advances have been made in the field of microalloying and associated applications, among which one of the most successful application cases is HTP practice for heavy gauge, high strength pipeline steels. Combined the strengthening effects of TMCP and retardation effects of austenite recrystallization with increasing Nb in austenite region, HTP conception with low carbon and high niobium alloy design has been successfully applied to develop X80 coil with a thickness of 18.4 mm used for China＇s Second West-East pipeline. During this process, big efforts were made to further develop and enrich the application of microalloying technology, and at the same time the strengthening effects of Nb have been completely unfolded and fully utilized with improved metallurgical quality and quantitative analysis of microstructure. In this paper, the existing status and strengthening effect of Nb during reheating, rolling and cooling have been analyzed and characterized based on mass production samples and laboratory analysis. As confirmed, grain refinement remains the most basic strengthening measure to reduce the microstructure gradient along the thickness, which in turn enlarges the processing window to improve upon low temperature toughness, and finally make it possible to develop heavy gauge, high strength pipeline steels with more challenging fracture toughness requirements. As stated by a good saying that practice makes perfect. Based on application practice and theoretical analysis, HTP has been extended to develop heavy gauge and high strength pipeline steels with increasing requirements, including X80 SSAW pipe with a thickness of 22.0 mm and above, X80 LSAW pipe combining heavy gauge and large diameter, heavy gauge X80 LSAW pipe with low temperature requirements, as well as X90 steels. In this paper, alloy design, production processing, as well as mechanical properties and microstructure used for these products would be illustrated.

The relationship between microstructure and stress-strain behavior in tension in high strength pipeline steel

In this paper the relationship between microstructure and stress-strain behavior in tensile test of high strength pipeline steel was investigated.The steel with polygonal ferrite-bainite(PF + B) microstructure has a "round-house" type tensile stress-strain curve with low Y/T ratio,highly uniform elongation and high n-value,which means PF + B microstructure has the best deformability(i.e.Ideal stress-strain behavior) among the four microstructures.The steel with acicular ferrite-martensite&austenite(AF + MA) microstructure has a "continuous-yielding" type tensile stress-strain curve,whose deformability is worse than that of PF + B microstructure.Both the steels of polygonal ferrite-acicular ferrite(PF + AF) and polygonal ferrite-pearlite (PF+P) microstructure have "luders elongation" type tensile stress-strain curve with high Y/T ratio,low uniform elongation and low n-value,which means PF + AF and PF + P microstructures have the worst deformability among the four microstructures.

Experimental study on 830 MPa grade pipeline steel containing chromium

The diversity of microstructure and properties of 830 MPa grade pipeline steel containing chromium was investigated by optical microscope and transmission electron microscopy. The main microstructures were multiple configurations, containing lath bainite and granule bainitc. Mechanical properties test results showed that the yield strength and tensile strength improved with increasing chromium content. The toughness and elongation decreased at the same time, so temper process was introduced. Appling proper temper parameters, the values of toughness and elongation were improved dramatically, and the strength decreased slightly.

Microstructure and Mechanical Properties of X80 HTP Pipeline Steel Produced by Steckel Mill

The demand for energy becomes a bottleneck in development of China. Economically delivering natural gas and oil through pipeline is an urgent problem to be solved. In the present work, X80 pipeline steel with high toughness and thickness 21.0 mm was produced through HTP （ High Temperature Processing） by Steckel mill rolling. And the microstructure and mechanical properties of the X80 pipeline steel, which produced by different processing parameters such as reheating temperature of slabs, resume temperature, finishing temperature, accelerated cooling exit temperature and cooling rate, were analyzed. The results show that finishing temperature of 800 - 820℃ and cooling rate above 20℃/s are necessary to obtain fine and uniform acicular ferrite with high solute niobium in XS0 pipeline steel.

油气田钢质管道内检测结果评价方法及分析

介绍一种依据ASME B31G和DNV RP-F101管道腐蚀缺陷标准的油气田钢质管道内检测结果评价方法,并以某均匀腐蚀管线钢管为例,运用该方法对其内检测结果进行评价。该方法可逻辑判断缺陷类型及量化方法,计算管道失效压力及腐蚀速率预测。该方法具有计算结果准确、易操作、应用前景广等优点。

稀土元素Ce对X80管线钢DWTT性能影响研究

文章以X80管线钢为研究对象,在实验室开展稀土元素Ce对管线钢DWTT性能影响研究。研究结果表明,稀土元素Ce的添加有利于提高试验钢的低温韧性,-40℃时添加稀土元素Ce后的试样冲击功达到210 J,与未添加稀土的试样相比增幅达到19.3%。添加稀土元素Ce有利于降低管线钢的韧脆转变温度。不添加稀土元素的试样焊后热影响区的冲击功为189 J,添加稀土元素Ce后的试样热影响区冲击功达到216 J,增幅为14.3%。

含双腐蚀缺陷高钢级油气管道剩余强度研究

为了加强含双腐蚀缺陷高钢级管道的安全评价,基于塑性失效准则,利用Workbench有限元分析软件对缺陷处的等效应力和剩余强度进行了模拟,考察了缺陷长度、缺陷深度和缺陷间距等参数对剩余强度的影响,利用99%相互作用准则确定极限作用距离,形成双腐蚀缺陷剩余强度评价方法,并进行数据验证。结果表明,随着内压的增加,管道先后经历弹性阶段、屈服阶段和强化阶段;在缺陷深度较深时,轴向间距对缺陷轴向分布时的最大等效应力影响较大,不同环向间距下的最大等效应力几乎不发生变化。当相邻腐蚀轴向间距系数n小于2.5、相邻腐蚀环向间距系数c小于1.26时,需考虑缺陷间的相互作用和影响;修正后公式可用于计算含双点腐蚀缺陷的高等级钢剩余强度,结果较DNV-RP-F101规范更接近有限元分析结果,最大相对误差不超过1.74%。研究结果可为提高管道完整性管理水平提供理论依据和实际参考。

不同强度匹配对X80管线钢环焊缝抗氢致裂纹性能的影响研究

环焊缝的强度匹配形式和耐腐蚀性对管道可靠运行至关重要。文中分别采用低强匹配、等强匹配和高强匹配三种匹配形式对D1219×18.4 mm X80螺旋焊管进行焊条电弧焊,对焊接接头进行抗氢致开裂(HIC)试验,并综合包括化学成分、微观组织、接头强度和韧性等各种因素分析,研究不同强度匹配形式对X80管线钢环焊缝抗氢致裂纹性能的影响。结果表明,三种匹配方式下的X80管线钢焊接接头的抗HIC性能均能满足相关要求,且采用三种强度匹配焊条焊接接头的裂纹长度敏感率(CLR)、裂纹厚度敏感率(CTR)以及裂纹敏感率(CSR)随着匹配强度的升高而升高;焊缝金属的C、P、S含量对HIC敏感性有显著影响,降低这些元素的含量有助于提高焊缝的抗HIC性能;微观组织观察表明,焊缝金属的组织类型和形态对HIC敏感性也有重要影响,热力学平衡且稳定的细小组织是抗HIC的理想组织。

Strength, strain capacity and toughness of five dual-phase pipeline steels

The effect of microstructures on strength,strain capacity and low temperature toughness of a micro-alloyed pipeline steel was elucidated.Five various dual-phase microstructures,namely,acicular ferrite and a small amount of(around 2 vol.%)polygonal ferrite(AF+PF),polygonal ferrite and bainite(PF+B),polygonal ferrite and martensite/austenite islands(PF+M/A),polygonal ferrite and martensite(PF+M)and elongated polygonal ferrite and martensite(ePF+M),have been studied.Experimental results show that AF+PF microstructure has high yield strength and excellent low temperature toughness,whereas its yield ratio is the highest.Polygonal ferrite-based dual-phase steels,PF+B,PF+M/A and PF+M microstructures show better strain capacity and low temperature toughness.The strain capacity and low temperature toughness of ePF+M microstructure are the worst due to its high strength.The relationship between microstructure,strength,strain capacity and toughness has been established.Based on the results,the optimum microstructure for a better combination of strength,strain capacity and toughness is suggested to be the one having appropriate polygonal ferrite as second phase in an acicular ferrite matrix.

HIC and SSC Behavior of High-Strength Pipeline Steels

In this study,hydrogen-induced cracking（HIC） and sulfide stress corrosion cracking（SSC） behaviors of highstrength pipeline steels in four different strength grades（X70,X80,X90 and X100） with the microstructure of acicular ferrite were estimated.The results showed that both of X70 and X80 steels exhibited better HIC resistance,and their susceptibility to HIC increased with the strength grade.HIC parameters,including cracking length ratio,cracking thickness ratio（CTR） and cracking sensitivity ratio,were all increased,and among these,the CTR increased most,with the increase in the strength grade.HIC was found to initiate and grow along the hard boundaries such as large size martensite/austenite（M/A） islands and bainitic ferrite.In addition,the density of hydrogen-induced blister on the steel surface was increased with the decrease in p H value for the same-grade pipeline steels.SSC susceptibilities of X80,X90 and X90-C were revealed to subsequently decrease,which was related to the large size M/A islands.

Effect of Crystallographic Texture on Anisotropy of Yield Strength in X100 Pipeline Steel

The anisotropy of microstructures and mechanical properties in commercial American Petroleum Institute （API） X100 pipeline steel was systematically investigated by experimental measurements. The experimental results show that anisotropy of yield strength could be observed considerably, which should be attributed to the crystallographic rex tures due to deformation and transformation of texture components. This is because the effect of the inhomogeneity of microstructure in different directions on the mechanical properties could be reasonably neglected based on the ex perimental investigation of grain size distribution. The effect of crystallographic texture on the anisotropy of yield strength was interpreted theoretically based on the relationship between yield strength and average orientation factor.

Effects of Rolling Processes on Bainite and Mechanical Properties of Ultra-High Strength Pipeline Steel

Ultra-high strength pipeline steels were rolled by thermal mechanical controlling process (TMCP),and effects of the volume fraction,the size and microstructure morphologies of three different bainite (AF,GB and LB) on mechanical properties were investigated by optical microscope.The results showed that,X120 ultra-high strength pipeline steel was rolled through the reasonable thermal mechanical controlling process (TMCP),and the yield strength and the low temperature charpy impact energy (-30℃) were higher than 840MPa and above 230J,respectively,meanwhile,the ratios of tensile strength to yield strength were lower below 0.82.As for X100 pipeline,of which the mechanical property were higher than that by X100 pipeline steel of ISO standard,yield strength of the steel was 715 MPa,ultimate tensile strength 963 MPa,impact energy 282J,and yield ratio 0.74.

高钢级管线环焊缝强度匹配的仪器化压痕法测试研究

为获得在役管线环焊缝强度及与母材的强度匹配情况,选用仪器化压痕法对高钢级管线环焊缝的强度及匹配情况进行检测。为验证仪器化压痕法检测结果的准确性,对经过压痕检测的环焊缝取常规拉伸试样进行检测并对比结果。两种强度测试方法的结果对比表明,压痕测试的屈服强度比拉伸测试结果高约6%、抗拉强度比拉伸测试高约16%。利用阵列硬度对焊缝及母材的硬度分布进行表征,发现焊缝内硬度分层分布、近外壁区域硬度较高,母材硬度相对均匀。仪器化压痕测试的材料为近外壁的高硬度区,拉伸测试的材料为管道壁厚的平均结果,材料性能的沿厚度方向的分布特征是压痕法测得结果偏高的原因之一。

天然气掺氢输送环境下的腐蚀与氢脆研究进展

氢能作为清洁、高效、零碳的能源载体,被视为最具发展潜力的清洁能源之一。利用现有的天然气管线进行掺氢输送被视为实现氢气长距离、大规模、高效、经济输送的有效方式。然而,长输天然气掺氢输送环境为CH4、高压H2、少量H2S和CO_(2)等杂质及游离水共存,不可避免的会导致金属材料的腐蚀与氢脆。为此,系统综述了国内外现有的长输天然气掺氢输送环境下腐蚀与氢脆的研究进展,并对天然气掺氢输送技术中腐蚀与氢脆进行了展望。研究结果表明:①气相充氢的实验研究方法更贴合天然气掺氢输送环境,但气相充氢技术未建立统一标准,而液相充氢法已经趋于成熟,但仍与工程实际偏差较大;②长输天然气掺氢输送环境下腐蚀与氢脆存在协同和竞争关系,但具体的失效机制和变化规律仍不明晰,还需进一步开展实验研究,明确腐蚀与氢脆共存时的失效机理;③长输天然气掺氢输送环境下腐蚀氢脆的失效机制受H2S和CO_(2)分压比、掺氢比、材料强度等关键性因素影响,3种关键性因素的提高,均会使得管线材料腐蚀更严重、氢脆敏感性更高。结论认为,该研究成果可以为长输天然气掺氢输送关键技术的研究和项目发展提供有效参考,将有助于推动天然气掺氢行业的高质量发展。

考虑应力三轴度影响的X80管线钢延性断裂研究

为了得到X80管线钢在不同应力三轴度下的延性断裂特征,通过标准拉伸试件的准静态拉伸试验标定了X80管线钢的Johnson-Cook本构模型参数。通过不同应力三轴度下的准静态试验和有限元分析得到了各试件的平均应力三轴度和断裂应变,并得到了应力三轴度对断裂应变、抗拉强度和延性的影响规律。结果表明,建立的X80管线钢本构模型与失效模型能够较好地表征X80管线钢在不同应力三轴度下的力学行为与断裂特征。在不同的应力三轴度区间内,X80管线钢的断裂应变与平均应力三轴度的关系满足不同的函数类型,当应力三轴度为0.80~1.56时为递减的Johnson-Cook失效模型函数,当应力三轴度为0~0.80时为递增的线性函数,当应力三轴度为-1/3~0时为递减的幂函数。X80管线钢的抗拉强度与应力三轴度的函数关系满足二次函数的分布形式并单调递增,而延性随着应力三轴度的增加而降低。

氢环境对高钢级管线钢力学性能影响规律研究

在“双碳”目标背景下,天然气管道掺氢将成为未来大规模、长距离输送氢气的主要方式。但氢气的掺入将会对现有天然气管道运行、安全维护等方面带来新的挑战。针对纯氢环境下高钢级管道力学性能劣化规律不明确的问题,通过总结并对比现有试验过程中纯氢环境模拟方法,优选出高压动态气相充氢作为试验的纯氢环境模拟方法,并在不同纯氢环境、1.01×10^(-4)和1.01×10^(-5)mm/s这2种位移速率下,针对X80管线钢开展了多组高压慢应变速率拉伸试验,获得试验数据及试样断口形貌,分析氢对管线钢力学性能的影响。分析结果认为:在纯氢环境中X80管线钢的屈服强度、极限抗拉强度相对于空气环境中略微增加,增加程度均小于8%;在1.01×10^(-4)和1.01×10^(-5)mm/s这2种位移速率的氢环境下,X80管线钢的断后伸长率分别减小了6.04%和14.88%,表明随着位移速率的减小,管线钢氢损伤程度增大;气相缓蚀剂和环己胺对X80管线钢氢损伤均有抑制作用。研究结果对高压天然气管道掺氢或纯氢管道的设计与评价具有一定的参考价值。

基于小厚度小冲杆试验的管道钢力学性能表征

为解决常规力学性能测试手段无法对高钢级管道局部区域材料的力学性能进行精细表征的问题,对小厚度试样小冲杆试验表征管道钢材料力学性能的经验关联方法进行了研究。对不同钢级管道钢材料分别开展了单轴拉伸试验与标准厚度试样小冲杆试验,通过两者数据关联得到了标准厚度试样小冲杆试验确定高钢级管材屈服强度及抗拉强度的经验公式。在此基础上,以X80钢为例开展了系列非标小厚度试样小冲杆试验,对经验公式进行了厚度效应修正,最终形成了基于小厚度试样小冲杆试验的高钢级管材力学性能表征方法,并进行了适用性验证。研究结果表明:考虑厚度效应的力学性能经验关联公式对于不同批次的X80钢非标小厚度试样小冲杆试验结果适用性良好;关联所得屈服强度及抗拉强度与单轴拉伸试验结果相比最大误差分别为9.87%和5.61%,均满足工程需求。研究结果可为不同高钢级管材力学性能研究提供理论基础与技术支撑。

西四线18.4 mm厚X80M管线钢的生产开发

针对西四线X80钢级螺旋埋弧焊管对热轧板卷提出的技术要求,介绍京唐公司18.4 mm X80M热轧钢卷的成分工艺设计,以及批量生产钢的力学性能、低温韧性。结果表明,京唐公司为西四线开发生产的18.4 mm厚热轧钢卷性能稳定,具有良好的低温韧性和低屈强比,各项理化性能全部满足管道工程技术标准要求。

Microstructure and Mechanical Properties of Nb-Microalloyed X100 High Deformability Pipeline Steel

A low carbon Nb-microalloyed high deformability pipeline steel with X100 grade has been processed by TMCP and followed two-stage cooling process.The microstructure is characterized by ferrite/bainite multiphase.The effective grain size is 1.85μm in average.The volume of ferrite is about 10-15% and the grains sizes are mostly less than 5μm.The bainite consists of granular-bainite and lath-bainite,with M/A islands finely dispersed.The longitudinal tensile yield strength,uniform elongation,yield ratio are 647MPa,7.6% and 0.78,respectively.Ferrite/bainite multiphase have large strain hardenability that resulting high strength and high deformability combination.Precipitation of Nb also improves the strength and uniform deformability by precipitation strengthening and grain refinement.