Development of Offshore X65/70 Steels for Deep Water Application

2012 ◽  
Author(s):  
Yun-Jo Ro ◽  
Seung-Hwan Chon ◽  
Jang-Yong Yoo ◽  
Ki-Bong Kang
Keyword(s):  
Low Temperature ◽  
Deep Water ◽  
Processing Parameters ◽  
Alloying Elements ◽  
Accelerated Cooling ◽  
Dual Phase ◽  
Effective Grain Size ◽  
Low Temperature Toughness ◽  
Shear Area ◽  
Linepipe Steels

Heavy gauge X65/70 steels have been developed for deep-water offshore application. As the thickness of linepipe steels is increased, Mo, Ni, V alloying elements are generally employed to improve the low temperature toughness and strength balance. However, the price of such alloying element has been rapidly increased. Hence, in the present work, a lean composition is designed to achieve thick X65/70 grade steels with better strength and toughness balance. To prevent the degradation of toughness or strength due to a lean alloying composition, the authors optimize processing parameters, such as a rolling stop temperature or accelerated cooling patterns. By in large, two strategies have been applied to develop linepipe steels; i) cooling starts in γ + α region, and iii) rolling stops in γ + α region. These strategies promote ferrite+bainite dual phase microstructures exhibiting a good low temperature toughness and strength balance. Such dual phase microstructures are characterized by using EBSD (electron back scattered diffraction) technique. The result shows a percentage of DWTT shear area is strongly correlated with effective grain size (misorientation ≥ 15°). As a result, the present work demonstrates that heavy gauge API steels grade X65/70 can be achieved with Mo+V free or small addition of Mo alloying elements.

The Effect of Hot Strip Mill Processing Parameters and Alloy Addition on Low Temperature Toughness of API-X70 Steel

2010 ◽  
Author(s):  
Kwang Seop Ro ◽  
Saad Al-Shammary ◽  
Adel A. Al-Butairi ◽  
Khaled F. Al-Hajeri
Keyword(s):  
Low Temperature ◽  
High Strength ◽  
Processing Parameters ◽  
Prediction Equation ◽  
Hot Strip Mill ◽  
Hot Strip ◽  
Statistical Equation ◽  
Alloy Addition ◽  
Low Temperature Toughness ◽  
Shear Area

Correlation of rolling conditions, microstructure, and low-temperature toughness of X70 pipeline steels was investigated in this study through statistical analysis. High strength API X70 steel grade with excellent DWTT toughness can be designed by the developed statistical equation. The predicted equation is as follows; ‘Pct Shear area of DWTT (−10°C) = 954 − 0.3*SRT + 0.5*TBT − 0.4*FRT + 0.04*CT − 306*C −60*(Mn+Ni+Cu) + 38*(Mo+Cr) − 791*(Ti+Nb+V) − 4*MA’ and the predicted equation showed very good relationship. M/A constituent showed high relationship with DWTT toughness. By inserting this effect into the equation, the reliability of the equation has been improved. By using the prediction equation, new chemical composition and relevant processing variables could be optimized and newly designed steel shows proper tensile properties with the excellent DWTT toughness at −10°C.

Fracture and Crack Propagation Behavior of 560 MPa Microalloyed Pipeline Steel under Different Cooling Schedules

2017 ◽  
Vol 898 ◽  
pp. 1094-1102 ◽  
Author(s):  
Jin Hua Zhao ◽  
Dong Fang Li ◽  
Guo Yuan ◽  
Xue Qiang Wang ◽  
Rui Hao Li ◽  
...  
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Crack Propagation ◽  
Pipeline Steel ◽  
Crack Arrest ◽  
Dominant Factor ◽  
Cooling Schedules ◽  
Effective Grain Size ◽  
Mixed Microstructure ◽  
Low Temperature Toughness

Three kinds of pipeline steel with different microstructures were fabricated by varying cooling schedules during thermo-mechanical controlled processing (TMCP). Charpy impact property of the pipeline steels were obtained, and the fracture and crack-arrest mechanisms were further studied. The results indicated that the steels were classified into two kinds according to their microstructures, the mixture of acicular ferrite (AF), quasi-polygonal ferrite (QF), granular bainite (GB) and small fraction of degenerate pearlite (DP), and the mixed microstructure of AF and GB, respectively. The processed steel with microstructure of AF and GB exhibited more excellent low-temperature toughness and crack-arrest properties with upper shelf energy of ~281 J and energy transition temperature of ~-76°C. The mixed microstructure (AF + GB) possessing smaller effective grain size hindered the propagating of crack and consumed large amount of energy during fracture. The effective grain size of microstructure was the dominant factor controlling low-temperature toughness and crack-arrest properties of pipeline steel, which increased the high-angle boundary length per unit area and further increased the crack propagation energy during fracture.

Effect of Rolling Parameters on the Low-Temperature Toughness and Microstructure of High-Strength Linepipe Steel

2016 ◽  
Author(s):  
C. Stallybrass ◽  
A. Völling ◽  
H. Meuser ◽  
F. Grimpe
Keyword(s):  
Electron Microscopy ◽  
Low Temperature ◽  
Electron Backscatter Diffraction ◽  
High Strength ◽  
Processing Parameters ◽  
Small Scale ◽  
Electron Backscatter ◽  
Low Temperature Toughness ◽  
Backscatter Diffraction ◽  
Scanning Electron

In recent years, large-diameter pipe producers around the world have witnessed a growing interest to develop gas fields in arctic environments in order to fulfill the energy demand. High-strength linepipe grades are attractive for economic reasons, because they offer the benefit of a reduced wall thickness at a given operating pressure. Excellent low-temperature toughness of the material is essential under these conditions. Modern high-strength heavy plates used in the production of UOE pipes are produced by thermomechanical rolling followed by accelerated cooling (TMCP). The combination of high strength and high toughness of these steels is a result of the bainitic microstructure and is strongly influenced by the processing parameters. For this reason, the relationship between rolling and cooling parameters of heavy plate production, the low-temperature toughness and the microstructure is at the center of attention of the development efforts at Salzgitter Mannesmann Forschung (SZMF) in collaboration Salzgitter Mannesmann Grobblech (SMGB). It has been shown previously that a variation of the processing parameters has a direct influence on the microstructure and correlates with mechanical properties that are accessible via small-scale tests. Modern characterization methods such as scanning electron microscopy in combination with electron backscatter diffraction have broadened our understanding of the underlying mechanisms and have helped to define processing conditions for the production of heavy plates with optimized low-temperature toughness in small scale tests. Within the present paper, the results of a recent laboratory investigation of the effect of a systematic variation of rolling parameters on the microstructure and low-temperature toughness of as-rolled and pre-strained Charpy specimens are discussed. In these trials, final rolling temperatures above the onset of the ferrite-austenite transformation and cooling stop temperatures above the martensite start temperature were selected. The microstructure of the plates was investigated by scanning electron microscopy and electron backscatter diffraction. In a series of Charpy tests in a specific temperature range, it was found that plate material in the as-rolled condition is not strongly sensitive to variations of the selected processing parameters, whereas pre-straining the Charpy specimens made it possible to assess the potential of individual processing concepts particularly with regard to low-temperature toughness. In addition to Charpy testing, the toughness was also quantified via instrumented drop-weight tear (DWT) testing. By comparing total energy values from regular pressed-notch DWT-test specimens to J-integral values determined in drop-weight testing of pre-fatigued DWT-test specimens, the impact of variations of specimen type on material tearing resistance is shown.

X100 Linepipe With Excellent HAZ Toughness and Deformability

2003 ◽  
Author(s):  
Yoshio Terada ◽  
Hiroshi Tamehiro ◽  
Hiroshi Morimoto ◽  
Takuya Hara ◽  
Eiji Tsuru ◽  
...  
Keyword(s):  
Low Temperature ◽  
Carbon Content ◽  
Heat Affected Zone ◽  
Uniform Elongation ◽  
Base Material ◽  
Controlled Rolling ◽  
Accelerated Cooling ◽  
Low Temperature Toughness ◽  
Sufficient Strength ◽  
Haz Toughness

Good low-temperature toughness of the base material (BM) and weld heat-affected zone (HAZ), and good deformability of the pipe body together with good field weldability are required for X100 linepipe to ensure the safety of pipelines and to facilitate field welding. It is, however, very difficult to attain these properties simultaneously because of the large addition of alloys. The technology of improving HAZ toughness by reducing carbon content through the reduction of M-A constituents harmful to low-temperature toughness was developed, and accelerated cooling after controlled rolling was applied to attain good low-temperature toughness of BM and high uniform elongation together with sufficient strength corresponding to X100. Two newly developed types of X100 linepipe, a “high HAZ toughness type” and a “high uniform elongation type”, exhibited excellent low-temperature toughness of the HAZ and high uniform elongation together with sufficient strength, respectively.

High Strength Heavy Plate Optimised for Application in Remote Areas and Low-Temperature Service

2010 ◽  
Author(s):  
Charles Stallybrass ◽  
Joachim Konrad ◽  
Heike Meuser ◽  
Fabian Grimpe
Keyword(s):  
Mechanical Properties ◽  
Low Temperature ◽  
High Strength ◽  
Alternative Methods ◽  
Accelerated Cooling ◽  
Processing Conditions ◽  
Remote Areas ◽  
Heavy Plate ◽  
Low Temperature Toughness ◽  
Ebsd Method

The last decades have seen a steady increase in the demand for high-strength linepipe steels. These offer the most economical option to transport large gas volumes at high pressures from remote areas to the market. Since the beginning of the 1980’s, high strength heavy plates, pipes and pipe bends were developed and produced at Salzgitter Mannesmann Grobblech GmbH and EUROPIPE. Since these days, these products were steadily improved for example in terms of toughness and weldability. As gas resources in increasingly hostile environments are developed, the requirements with regard to deformability and low-temperature toughness have gained growing significance. This is a strong focus of materials development around the world. Modern high-strength heavy plates used in the production of UOE pipes are generally produced by thermomechanical rolling followed by accelerated cooling (TMCP). If accelerated cooling starts above the ferrite-austenite transformation temperature, this processing route results in a microstructure that consists predominantly of bainite. The combination of high strength and high toughness of these steels are a result of the microstructure realised by TMCP and are strongly influenced by the rolling and cooling conditions. Classical light-optical characterisation of the microstructure of these steels is at its limits because the size of the observed features is too small to allow reliable quantitative results. Therefore alternative methods have to be used to obtain a better understanding of the influence of processing conditions on the microstructure. The mechanical properties of high strength plates produced at Salzgitter Mannesmann Grobblech (MGB) and of material rolled using a laboratory rolling mill at the Salzgitter Mannesmann Forschung (SZMF) was characterised with special emphasis on low-temperature toughness. The microstructure was investigated using the electron backscatter diffraction (EBSD) method. With this method, it is possible to gain quantitative information related to features of the microstructure and relate these to the mechanical properties of the plate material. It was found that a variation of the processing conditions has a direct influence on parameters that are accessible through the EBSD method and correlates with mechanical properties. These results can be used as valuable input for the definition of the processing window for heavy plate production depending on the required plate properties.

Effects of Processing Parameters on Microstructure Development in X70 Pipeline Steel

2010 ◽  
Vol 654-656 ◽  
pp. 298-301 ◽  
Author(s):  
A. Al Shahrani ◽  
Thomas Schambron ◽  
Ali Dehghan-Manshadi ◽  
James G. Williams ◽  
Elena V. Pereloma
Keyword(s):  
Low Temperature ◽  
Prior Austenite ◽  
Thermomechanical Processing ◽  
Pipeline Steel ◽  
Processing Parameters ◽  
Grain Structure ◽  
Microstructure Development ◽  
Austenite Grain ◽  
Low Temperature Toughness ◽  
Prior Austenite Grain

Achieving fine and uniform grains is the most effective way to enhance strength and toughness, which are required properties for pipeline steels. Steels microalloyed with Nb can exhibit a mixed grain structure, which can deteriorate low temperature toughness. In this work the effects of the thermomechanical processing parameters on the prior austenite grain structure before ferrite transformation have been investigated.

scholarly journals Effect of Bainitic Microstructure on Low-Temperature Toughness of High-Strength API Pipeline Steels

2020 ◽  
Vol 58 (5) ◽  
pp. 293-303
Author(s):  
Seung-Wan Lee ◽  
Sang-In Lee ◽  
Byoungchul Hwang
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Crack Initiation ◽  
High Strength ◽  
Processing Conditions ◽  
Absorbed Energy ◽  
Pipeline Steels ◽  
Bainitic Microstructure ◽  
Effective Grain Size ◽  
Low Temperature Toughness

In this study the correlation between bainitic microstructure and the low-temperature toughness of high-strength API pipeline steels was discussed in terms of crack initiation and propagation in the microstructure. Three types of API pipeline steels with different bainitic microstructures were fabricated using varying alloying elements and thermo-mechanical processing conditions, and then their microstructure was characterized by optical and scanning electron microscopy, and electron backscatter diffraction (EBSD). In particular, the effective grain size and microstructure fraction of the steels were quantitatively measured by EBSD analysis. Although all the steels were composed of polygonal ferrite (PF), and complex bainitic microstructures such as acicular ferrite (AF), granular bainite (GB), and bainitic ferrite (BF), they had different effective grain sizes and microstructure fraction, depending on the alloying elements and thermomechanical processing conditions. Charpy impact test results showed that when the martensite-austenite constituent fraction was lowest, it resulted in higher upper-shelf energy, and absorbed energy at room temperature due to the decrease in crack initiation. In contrast, excellent low-temperature toughness, such as lower ductile-brittle transition temperature and higher absorbed energy at low temperatures, could be achieved with a bainitic microstructure with fine effective grain size and high fraction of high-angle grain boundaries, which act as obstacles to prevent cleavage crack propagation.

Experimental Study on High Performance Welding Materials for Pipeline Steels

2004 ◽  
Author(s):  
Zhijun Huang ◽  
Kai Miao ◽  
Xiudi Cao ◽  
Yutao Wang
Keyword(s):  
Low Temperature ◽  
Charpy Impact ◽  
High Strength ◽  
Alloying Elements ◽  
Charpy Impact Energy ◽  
High Quality ◽  
High Toughness ◽  
Weld Metals ◽  
Low Temperature Toughness ◽  
Welding Materials

West-to-East Natural Gas Transmission Project is in great need of high quality steels of API grade X70 and suitable high quality welding materials. The weld of pipe should have high strength, high toughness and low sulphur and arsenic contents (less than or equal to 0.005 wt % respectively). The work performed in WISCO concerning welding wires of SAW, GMAW and SMAW and weldability of pipe steel is reported in this article. Steel grade X70 is a TMCP high strength and high toughness steel with low carbon equivalent. It has good weldability and is less susceptible to cold cracking in the heat-affected zone. Generally in order for weld to gain the same strength as the base metal, more alloying elements should be added into the weld. Therefore, it is likely that the weld is expected to be more susceptible to cold cracking. The mechanism of strengthening and toughening of the weld should be carefully investigated. WISCO has made great progress in both property improvement and manufacturing of welding materials. Through the addition of alloying elements, the influences of some alloying elements on the strength and toughness of welds, especially on the low temperature toughness were carried out. The results show that the upper shelves of the Charpy V transition curves for the weld metals remain high despite the different alloying elements. However, the influence of alloying degree on the low-temperature toughness is significant. The weld metals micro-alloyed with Ti,B and Ni, etc. have high acicular ferrite volume fractions in the metallographs, thereby possessing high strengths and high toughness. For SAW weld, the strength is more than 590MPa, the Charpy impact energy at −40°C above 180J; for the weld of gas metal arc welding, the Charpy impact energy at −30°C reaches 190J which are far better than some current specifications. If the welding is performed with caution, no cracks were found. HIC and SSCC test for corrosion resistance of the welds were also performed and the results fully met the requirements concerned. With respect to strength and toughness, chemistry and metallography, the HIC performance of welds was analysed.

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