Steel cleanness requirements for X65 to X80 electric resistance welded linepipe steels

Abstract

In Australia, a large proportion of the gas pipelines traverse rural areas of low population density with considerable distances between population centres. As these pipelines transport non-sour gas, there have been considerable economic advantages to be gained from the use of thin walled, small diameter, high strength linepipe grades. The successful development of these X65 to X80 grades has required a balance to be constantly maintained between process parameters, alloy design constraints and quality control measures. This paper considers this mixture of metallurgical and processing challenges in the context of steel cleanness. The steelmaking and casting processes are required to not only produce a low volume fraction of suitably morphology modified inclusions, but also to ensure their dispersion in cast and hot rolled structures. Critical in the achievement of these aims was found to be the order in which calcium treatment and vacuum processing of the liquid steel are carried out. As these steels are complex microalloyed grades, the clean steel concept was extended to include the composition and precipitation of the carbide and nitride species. This broad approach to steel cleanness was achieved while also maintaining a narrow range of casting temperature and chemical composition.     

高级别X80/X100管线钢的包辛格效应

利用单轴压缩-拉伸试验研究了炉卷轧机生产X80/X100管线钢不同变形情况下的包辛格效应.结果表明:随着预压缩变形量的增大,包辛格效应绝对值增大,X100管线钢的包辛格效应在1.5%的预压缩变形量下达到饱和;包辛格效应绝对值随着板卷强度的提高而上升;在试验范围内,X80、X100管线钢分别表现出了瞬时软化和永久软化.分析X80/X100管线钢的化学成分与显微组织特点,认为管线钢组织中的软、硬相(如M/A岛)的强度差、硬相的体积分数以及初始组织中的位错密度是不同包辛格现象的关键因素.     

Structure and properties of weld joints in X80, X90, and K70 pipe steel

The phase transformations of austenite in the thermal-influence zone of pipe steel (strength classes X80, X90, and K70) are studied by plotting thermokinematic diagrams that simulate the thermal cycle of welding. The influence of the maximum temperature and cooling rate on the structure and properties of sections in the thermal-influence zone is established. The risk of cold crack formation and softening in the steel is assessed by means of the dependence of the hardness on the cooling rate. The results are confirmed by the correlation of the hardness and the type of structural components in laboratory and industrial samples.     

Investigation of separation phenomenon in high-toughness X70 thick-walled linepipe steel

Separation is a commonly observed phenomenon during drop weight tear testing in high-toughness linepipe steels. Severe separation is harmful because it may cause fracturing or bursting of pipes. In this study,a quantitative measurement of separation was proposed,and using this new method,a relationship between the separation and microstructure was determined and discussed. The microstructures observed using optical and scanning electron microscopy revealed that the separation was related to the mixed ferritic and bainitic microstructures,or rather,it was related to the carbon enrichment in bainite.     

Correlation of microstructure and fracture properties of API X70 pipeline steels

Effects of microstructure on fracture toughness and transition temperature of high-toughness X70 pipeline steels were investigated in this study. Three types of steels were fabricated by varying alloying elements such as C, Cu, and Mo, and their microstructures were varied by rolling conditions such as finish rolling temperature and finish cooling temperature. Charpy V-notch (CVN) impact tests and pressed notch drop-weight tear tests (DWTT) were conducted on the rolled steel specimens. The charpy impact test results indicated that the specimens rolled in the single-phase region of the steel containing a reduced amount of C and Mo had the highest upper shelf energy (USE) and the lowest energy transition temperature (ETT) because of the appropriate formation of acicular, quasipolygonal, or polygonal ferrite and the decreased fraction of martensite-austenite constituents. Most of the specimens rolled in the single-phase region also showed excellent DWTT properties as the percent shear area (pct SA) well exceeded 85 pct, irrespective of finish cooling temperatures, while their USE was higher than that of the specimens rolled in the two-phase region. Thus, overall fracture properties of the specimens rolled in the single-phase region were better than those of the specimens rolled in the two-phase region, considering both USE and pct SA. are jointly appointed with the Materials Science and Engineering Department, Pohang University of Science and Technology.     

Correlation of microstructure and fracture properties of API X70 pipeline steels

Effects of microstructure on fracture toughness and transition temperature of high-toughness X70 pipeline steels were investigated in this study. Three types of steels were fabricated by varying alloying elements such as C, Cu, and Mo, and their microstructures were varied by rolling conditions such as finish rolling temperature and finish cooling temperature. Charpy V-notch (CVN) impact tests and pressed notch drop-weight tear tests (DWTT) were conducted on the rolled steel specimens. The Charpy impact test results indicated that the specimens rolled in the single-phase region of the steel containing a reduced amount of C and Mo had the highest upper shelf energy (USE) and the lowest energy transition temperature (ETT) because of the appropriate formation of acicular, quasipolygonal, or polygonal ferrite and the decreased fraction of martensite-austenite constituents. Most of the specimens rolled in the single-phase region also showed excellent DWTT properties as the percent shear area (pct SA) well exceeded 85 pct, irrespective of finish cooling temperatures, while their USE was higher than that of the specimens rolled in the two-phase region. Thus, overall fracture properties of the specimens rolled in the single-phase region were better than those of the specimens rolled in the two-phase region, considering both USE and pct SA.     

输油气管线钢X52的开发

为了满足管线钢的市场需求,韶钢在研制X52管线钢板的过程中,采用低碳 Nb、V、Ti微合金化的成分设计和采用合理的控轧控冷工艺进行试制.试制结果表明,韶钢生产的X52管线钢板性能达到了标准和用户的要求.     

Effective grain size and charpy impact properties of high-toughness X70 pipeline steels

The correlation of microstructure and Charpy V-notch (CVN) impact properties of a high-toughness API X70 pipeline steel was investigated in this study. Six kinds of steel were fabricated by varying the hot-rolling conditions, and their microstructures, effective grain sizes, and CVN impact properties were analyzed. The CVN impact test results indicated that the steels rolled in the single-phase region had higher upper-shelf energies (USEs) and lower energy-transition temperatures (ETTs) than the steels rolled in the two-phase region because their microstructures were composed of acicular ferrite (AF) and fine polygonal ferrite (PF). The decreased ETT in the steels rolled in the single-phase region could be explained by the decrease in the overall effective grain size due to the presence of AF having a smaller effective grain size. On the other hand, the absorbed energy of the steels rolled in the two-phase region was considerably lower because a large amount of dislocations were generated inside PFs during rolling. It was further decreased when coarse martensite or cementite was formed during the cooling process.     

微观组织对X70管线钢浆料磨损特性的影响

利用湿砂橡胶轮磨损试验机对同成分不同组织的三种管线钢进行了浆料磨损实验,随后对磨损后的试样表面进行扫描电镜观察和三维白光干涉分析,研究组织类型影响耐磨性的原因及磨损的微观机理.结果表明:当磨损机理以微观犁沟和微观疲劳为主时,复相组织中共存的两相硬度差别越大,磨痕的微观变形越不易协调,磨损质量损失越明显;当整体力学性能接近时,粒状贝氏体+针状铁素体的复相组织最为耐磨,粒状贝氏体+多边形铁素体复相组织次之,板条贝氏体+多边形铁素体复相组织耐磨性最差.      

Correlation of rolling condition,microstructure, and low-temperature toughness of X70 pipeline steels

Correlation of rolling conditions, microstructure, and low-temperature toughness of high-toughness X70 pipeline steels was investigated in this study. Twelve kinds of steel specimens were fabricated by vacuum-induction melting and hot rolling, and their microstructures were varied by rolling conditions. Charpy V-notch (CVN) impact test and drop-weight tear test (DWTT) were conducted on the rolled steel specimens in order to analyze low-temperature fracture properties. Charpy impact test results indicated that the energy transition temperature (ETT) was below −100 °C when the finish cooling temperature range was 350 °C to 500 °C, showing excellent low-temperature toughness. The ETT increased because of the formation of bainitic ferrite and martensite at low finish cooling temperatures and because of the increase in effective grain size due to the formation of coarse ferrites at high finish cooling temperatures. Most of the specimens also showed excellent DWTT properties as the percent shear area well exceeded 85 pct, irrespective of finish rolling temperatures or finish cooling temperatures, although a large amount of inverse fracture occurred at some finish cooling temperatures.     

X70管线钢中析出相的分析

介绍了X70管线钢经过不同的控轧控冷工艺制度后,MC、M(C,N)相的粒度大小分布,以及对M(C,N)、Fe3N、AlN、MS等相的测定结果.试验结果表明,在适当范围内,增大轧制变形量和冷却速度有利于增大M(C,N)相粒子的析出量,且有利于M(C,N)相析出粒子的细化.     

Research and development of deepwater offshore linepipe of Baosteel UOE SAWL X70 of heavy wall thickness and large diameter

Baoshan Iron & Steel Co.,Ltd.,(referred to as Baosteel) in China first succeeded in developing the U-ing-O-ing -Expanding(UOE) longitudinal submerged arc welded pipes(SAWLs) offshore linepipe of a maximum thickness/ outside diameter(T/D) 0.042 in 2011.Described in this paper is the research and development of the X70 UOE SAWL pipes by the company.The result shows that the said X70 linepipe has been in compliance with relevant requirements as specified in Specifications DNV-OS-F101,and has been successfully used in the South China Sea deepwater gas pipeline project.     

A comparison of hydrogen permeation and the resulting corrosion enhancement of X65 and X80 pipeline steels

In this work, corrosion and electrochemical hydrogen permeation behaviour of two grades of pipeline steel, X65 and X80 steels, were investigated by hydrogen-charging, electrochemical impedance spectroscopy measurements and metallographic observation. It was found that the corrosion and hydrogen permeation behaviour of steels is affected by their metallurgical features. Upon hydrogen-charging, both high grade of X80 pipeline steel and low grade of X65 steel show enhanced corrosion activity. The electrochemical hydrogen permeation current measurements and calculations show that the X80 steel contains a higher density of hydrogen traps than X65 steel, which may potentially result in the increased susceptibility of X80 steel to hydrogen-induced cracking (HIC).

Dans ce travail, la corrosion électrochimique de l’hydrogène et un comportement de perméation de deux qualités d’acier de pipeline, X65 et X80 aciers, ont été étudiés par l'hydrogène charge, électrochimiquemesures de spectroscopie d’impédance et l’observation métallographique. On a constaté que lela corrosion et de l’hydrogène comportement de perméation des aciers est affectée par leurs caractéristiques métallurgiques.Sur hydrogène charge, à la fois de haute qualité en acier de pipeline X80 et X65 de bas grade de spectacle en acierune activité améliorée à la corrosion. L'hydrogène perméation électrochimique des mesures de courantet les calculs montrent que l’acier X80 contient une plus grande densité de pièges à hydrogène de X65acier, ce qui peut potentiellement entraîner l’augmentation de la sensibilité de l’acier X80 pour induite par l’hydrogène; Fissuration (HIC).     

PSL2X65深海卷管的研制

卷管式铺管法要求管线管具有优良的力学性能、焊接性和耐腐蚀性能,特别是抗疲劳断裂性能.天津钢管集团股份有限公司生产了1批PSL2 X65管线管,按照深海卷管的要求对其进行相关评价试验.结果表明:其拉伸、冲击、硬度和抗腐蚀能力符合PSL2 X65深海卷管规范要求;韧脆转变温度在-80℃以下,低温性能优良;5%应变后的应变时...     

X80级高强低合金管线钢组织与冲击韧性

 为了研究准多边形铁素体/板条贝氏体/粒状贝氏体显微组织的高强低合金X80管线钢的低温韧性与冲击裂纹扩展特点,用OM、SEM、EBSD和TEM等多尺度手段进行了表征。结果表明,与针状铁素体/粒状贝氏体相比,在－60 ℃以上时,准多边形铁素体/板条贝氏体/粒状贝氏体表现出更好的阻止裂纹扩展的能力,准多边形铁素体可以分割显微组织并细化有效晶粒尺寸,增加大角度晶界比例,协调约束冲击裂纹扩展,进而提高韧性;当温度在－60 ℃以下时,这种准多边形铁素体/板条贝氏体/粒状贝氏体对裂纹扩展的协调约束作用减弱,成为显微组织的“软区”,使得材料韧性下降。     

Influence of vanadium and nitrogen on the structure formation and properties of K60 (X70) rolled steel coils

The production of microalloyed steel coils (thickness 8 mm) of strength category K60 (X70) with requirements on the low-temperature strength is studied in industrial trials. Microalloying of the steel with 0.10% V and 0.020% N and controlled rolling in the casting and rolling system, with a final deformation temperature of 800°C, results in the production of metal with high strength (σ_B ≥ 600 N/mm², σ_y ≥ 520 N/mm²) and plasticity (δ₅ = 28%) with satisfactory strength at –40°C according to impact-flexure and drop tests.     

Magnetic properties of maraging steels in relation to nickel concentration

Magnetic properties of maraging steels have been investigated as a function of nickel concentration. The alloys nickel content varied from 12 to 24 wt pct, while other alloying constituents were kept at a level maintained in the 18Ni-2400 MPA-grade maraging steel. The magnetic properties were determined following aging for 1 hour in the temperature range of 450 °C to 750 °C. In every alloy investigated, the coercive field increased with aging temper-ature, reaching a maximum around 670 °C ± 30 °C. The saturation magnetization values were lowest around temperatures where maximum coercive field was observed. The coercive field increased from ∼55 to ∼ 175 Oe (∼4380 to ∼ 13,900 amp/meter) and the corresponding sat-uration magnetization decreased from ∼18,500 to ∼ 4000 G (∼1.85 to ∼0.4 T) in the alloys containing 12 and 24 wt pct Ni, respectively. The reverted austenite increased from 25 vol pct at 12 wt pct Ni to 100 vol pct at 24 wt pct Ni. The hardness and Charpy impact strength of the alloys have also been determined. An attempt has been made to correlate magnetic properties with different phase transformations occurring in maraging steels.