Design and Processing of Niobium Microalloyed Cost Effective Line Pipe Steel With Enhanced Strength and Fracture Toughness

2013 ◽  
Author(s):  
S. V. Subramanian ◽  
J. M. Gray
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Brittle Fracture ◽  
Heat Input ◽  
Large Strain ◽  
Cost Effective ◽  
Accelerated Cooling ◽  
Pipe Steels ◽  
High Angle ◽  
Line Pipe

The functional role of niobium in the original HTP X-80 design of high niobium (0.1wt%), low interstitial ( C 0.03 to 0.04, N<0.005wt%) cost-effective base chemistry is (i) to use Zener drag from strain induced precipitation of NbC during thermo-mechanical rolling and solute drag from solute niobium to retard static recrystallization, (ii) to impart adequate rolling reduction below temperature of no recrystallization to promote large strain accumulation in pancaked austenite, and (iii) to promote fine ferrite grain size by strain induced phase transformation under accelerated cooling conditions, thereby obtain high strength and fracture toughness at low temperature through grain size effect. Residual niobium in austenite is used to impart additional strength through transformation hardening, dislocation hardening from accelerated cooling and precipitation strengthening of ferrite through accelerated cooling and interrupted cooling at coiling temperature. Recent research has confirmed the importance of control of density and dispersion of crystallographic high angle boundaries which are superimposed on the morphological microstructure in order to prevent the initiation of brittle fracture. Extensive research has been carried out in HTP base chemistry to determine the processing options to control the density and dispersion of high angle boundaries to produce higher grade (>X-80) line pipe steels with enhanced fracture toughness. Whereas the resistance to ductile fracture is measured by Charpy toughness, the resistance to brittle fracture is inferred from ductile to brittle transition temperature and percentage shear in DWTT. The research has underscored the importance of austenite grain refinement in upstream processing of HTP before pancaking in finish rolling to control density and dispersion of high angle boundaries in order to prevent brittle fracture initiation. Experimental results are presented which demonstrate that HTP base chemistry is a cost effective design to produce higher grade line pipe steels, not only to achieve high resistance to ductile and brittle fracture in the base plate, but also in HAZ regions associated with relatively high heat input welding in weld fabrication of pipes from plates, and Girth field welding of pipes involving low heat input multi-pass welding.

Niobium Microalloyed Line Pipe Steels: Technological Overview

2013 ◽  
Author(s):  
J. M. Gray ◽  
S. V. Subramanian
Keyword(s):  
Process Integration ◽  
Target Strength ◽  
Accelerated Cooling ◽  
Pipe Steels ◽  
Line Pipe ◽  
Steel Technology ◽  
Quantitative Understanding ◽  
Line Pipe Steel ◽  
Low Levels ◽  
Evolution Of Microstructure

A quantitative understanding of hierarchical evolution of microstructure is essential in order to design the base chemistry and optimize rolling schedules to obtain the morphological microstructure coupled with high density and dispersion of crystallographic high angle boundaries to achieve the target strength and fracture properties in higher grade line pipe steels, microalloyed with niobium. Product-process integration has been the key concept underlying the development of niobium microalloyed line pipe steel technology over the years. The development of HTP technology based on 0.1 wt % Nb and low interstitial was predicated by advances in process metallurgy to control interstitial elements to low levels (C <0.03wt% and N< 0.003wt%), sulfur to ultra-low levels (S<20ppm), as well as in product metallurgy based on advances in basic science aspects of thermo-mechanical rolling and phase transformation of pancaked austenite under accelerated cooling conditions, and toughness properties of heat affected zones in welding of niobium microalloyed line pipes. A historical perspective/technological overview of evolution of HTP for line pipe applications is the focus of this paper in order to highlight the key metallurgical concepts underlying Nb microalloying technology which have paved the way for successful development of higher grade line pipe steels over the years.

Brittle Fracture Arrest in High Charpy Energy Steels: Comparisons With Some Existing Data

2014 ◽  
Author(s):  
G. Wilkowski ◽  
D-J. Shim ◽  
Y. Hioe ◽  
S. Kalyanam ◽  
M. Uddin
Keyword(s):  
Brittle Fracture ◽  
Pipe Steels ◽  
Shelf Energy ◽  
Line Pipe ◽  
Pipe Burst ◽  
Sensitivity Studies ◽  
Shear Area ◽  
Fracture Arrest ◽  
Pipeline Design ◽  
Very High

Current line-pipe steels have significantly higher Charpy upper-shelf energy than older steels. Many newer line-pipe steels have Charpy upper-shelf energy in the 300 to 500J range, while older line-pipe steels (pre-1970) had values between 30 and 60J. With this increased Charpy energy comes two different and important aspects of how to predict the brittle fracture arrestability for these new line-pipe steels. The first aspect of concern is that the very high Charpy energy in modern line-pipe steels frequently produces invalid results in the standard pressed-notch DWTT specimen. Various modified DWTT specimens have been used in an attempt to address the deficiencies seen in the PN-DWTT procedure. In examining fracture surfaces of various modified DWTT samples, it has been found that using the steady-state fracture regions with similitude to pipe burst test (regions with constant shear lips) rather than the entire API fracture area, results collapse to one shear area versus temperature curve for all the various DWTT specimens tested. Results for several different materials will be shown. The difficulty with this fracture surface evaluation is that frequently the standard pressed-notch DWTT only gives valid transitional fracture data up to about 20-percent shear area, and then suddenly goes to 100-percent shear area. The second aspect is that with the much higher Charpy energy, the pipe does not need as much shear area to arrest a brittle fracture. Some analyses of past pipe burst tests have been recently shown and some additional cases will be presented. This new brittle fracture arrest criterion means that one does not necessarily have to specify 85-percent shear area in the DWTT all the time, but the shear area needed for brittle fracture arrest depends on the pipeline design conditions (diameter, hoop stress) and the Charpy upper-shelf energy of the steel. Sensitivity studies and examples will be shown.

Determination of Brittle-to-Ductile Transition Temperatures of Large-Diameter TMCP Linepipe Steel With High Charpy Energy by Use of Modified West Jefferson Testing

2016 ◽  
Author(s):  
Y. Hioe ◽  
G. Wilkowski ◽  
M. Fishman ◽  
M. Myers
Keyword(s):  
Transition Temperature ◽  
Brittle Fracture ◽  
Large Diameter ◽  
Pipe Steels ◽  
Line Pipe ◽  
Brittle To Ductile Transition ◽  
Pipe Burst ◽  
Drop Weight Tear Test ◽  
Fracture Appearance ◽  
Shear Area

In this paper the results will be presented for burst tests from a Joint Industry Project (JIP) on “Validation of Drop Weight Tear Test (DWTT) Methods for Brittle Fracture Control in Modern Line-Pipe Steels by Burst Testing”. The JIP members for this project were: JFE Steel as founding member, ArcelorMittal, CNPC, Dillinger, NSSMC, POSCO, Tenaris, and Tokyo Gas. Two modified West Jefferson (partial gas) pipe burst tests were conducted to assess the brittle-to-ductile transition temperature and brittle fracture arrestability of two 48-inch diameter by 24.6-mm thick X65 TMCP line-pipe steels. These steels had very high Charpy energy (350J and 400J) which is typical of many modern line-pipe steels. In standard pressed-notch DWTT specimen tests, these materials exhibited abnormal fracture appearance (ductile fracture from the pressed notch prior to brittle fracture starting) that occurs with many high Charpy energy steels. Such behavior makes the transition temperature difficult to determine. The shear area values versus temperature results for these two burst tests compared to various modified DWTT specimens are shown. Different rating methodologies; DNV, API, and a Best-Estimate of steady-state fracture propagation appearance were evaluated.

Effect of Sour Acidizing Treatments on the Fatigue Crack Growth and Fracture Toughness Behavior of C-Mn Line Pipe Steels

2016 ◽  
Author(s):  
Weiwei Yu ◽  
Jonathan Bowman ◽  
Apurva Batra ◽  
Ramgopal Thodla ◽  
Colum Holtam ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Compact Tension ◽  
Pipe Steels ◽  
Production Environment ◽  
Line Pipe ◽  
Fatigue And Fracture ◽  
Girth Welds

Acidizing treatments are typically performed intermittently during the life of a well. However, more recently there has been a desire to perform an increased number of acidizing treatments in order to improve production. The acidizing treatments typically involve highly corrosive acids, such as hydrofluoric (HF), hydrochloric (HCl) and acetic acid, which are known to cause significant corrosion. In the presence of hydrogen sulfide (H2S), these acidizing treatments could cause environmentally assisted fatigue and fracture (i.e. increased fatigue crack growth rates and reduced fracture toughness). A test program is underway to evaluate and quantify the effect of sour acidizing treatments on the fatigue and fracture behavior of welded C-Mn line pipe steels. This paper describes the preliminary findings from fatigue crack growth rate (FCGR) and fracture toughness (FT) tests on as-welded (i.e. unstrained) pipe. All tests were conducted at room temperature (RT) using compact tension (CT) specimens notched in the parent pipe (PP). Frequency scan FCGR tests were performed in the following sour acid conditions: simulated production environment (PE), spent acid without inhibitor and spent acid with residual corrosion inhibitor. The PE consisted of a simulated brine with pH = 4.5 and partial pressure of H2S (pH2S) = 0.21psia. FCGRs in the sour PE were of the order of 20 times faster than in air. The pH2S was the same for the tests in spent acid environments, but the pH was lower (approximately 3.5). As would be expected, the FCGRs were much higher in the low pH environment. The highest FCGRs were observed in the inhibited sour spent acid environment and were up to 100 times faster than in air. Sour FT tests were also conducted in the PE and in spent acid with and without inhibitor. In all cases, the measured FT values were significantly lower than in air. The test in PE exhibited higher FT than in the sour acidizing environment. The lowest FT values were observed in spent acid with inhibitor. Future work will investigate the effect of reeling on the fatigue and FT performance of pipe girth welds in sour acidizing environments.

Control of %age Shear Area in DWTT at Low Temperature in Niobium Microalloyed Line Pipe Steel

2018 ◽  
Author(s):  
Sundaresa Subramanian ◽  
Xiaoping Ma ◽  
Xuelin Wang ◽  
Chengjia Shang ◽  
Xiaobing Zhang ◽  
...  
Keyword(s):  
Low Temperature ◽  
Brittle Fracture ◽  
Cube Texture ◽  
High Angle ◽  
Austenite Grain Size ◽  
Line Pipe ◽  
Nano Scale ◽  
Austenite Grain ◽  
The Matrix ◽  
Shear Area

Microstructural engineering to obtain 100% shear area in DWTT at low temperature requires target parameters to suppress brittle fracture. In-depth characterization of benchmarked steels has confirmed that %age shear area is decreased by high number density of ultra-fine precipitates (<10nm) that contribute to precipitation strengthening, high intensity of rotated cube texture and coarse brittle constituents like M/A or carbides. The control of these parameters by nano-scale precipitate engineering of TiN-NbC was covered in a previous presentation in IPC 2016 [1]. The present paper focuses on crystallographic variants selection that controls the density and dispersion of high angle boundaries, which arrest microcracks to suppress brittle fracture, thereby increasing %age shear area in DWTT at low temperature. Studies on crystallographic variants selection in single undeformed austenite grain have clarified crystallographic variants configuration which gives rise to high angle boundaries is influenced by hardenability parameters, i.e., alloying, cooling rate and austenite grain size. The profound effect of carbon and solute niobium on density and dispersion of high angle boundaries in CGHAZ is demonstrated by analyzing EBSD data to reconstruct the shear transformation of undeformed austenite using K-S relationship. Moreover, pancaking of austenite influences crystallographic variants through Sv factor and dislocation density. Experimental results on nano-scale TiN-NbC composite precipitate engineered steel confirm that adequate solute niobium (>0.03wt%) is retained in the matrix, which is aided by the suppression of delayed strain induced precipitation of ultra-fine precipitates of NbC. The hardenability from solute niobium is found to be adequate to give high density of high angle boundaries to give about 95% shear area in DWTT at −40°C in 32 mm gage K-60 plate and 100% shear area in 16.3 mm X-90 strip. Both steels were processed by nano-scale precipitate engineering of TiN-NbC composite to control size and uniformity of distribution of austenite grains before pancaking.

How New Vintage Line-Pipe Steel Fracture Properties Differ From Old Vintage Line-Pipe Steels

2012 ◽  
Author(s):  
G. Wilkowski ◽  
D.-J. Shim ◽  
Y. Hioe ◽  
S. Kalyanam ◽  
F. Brust
Keyword(s):  
Brittle Fracture ◽  
Fracture Behavior ◽  
Pipe Steel ◽  
Full Scale ◽  
Actual Behavior ◽  
Correction Factors ◽  
Pipe Steels ◽  
Line Pipe ◽  
Line Pipe Steel ◽  
Fracture Control

Newer vintage line-pipe steels, even for lower grades (i.e., X60 to X70) have much different fracture behavior than older line-pipe steels. These differences significantly affect the fracture control aspects for both brittle fracture and ductile fracture of new pipelines. Perhaps one of the most significant effects is with brittle fracture control for new line-pipe steels. From past work brittle fracture control was achieved through the specification of the drop-weight-tear test (DWTT) in API 5L3. With the very high Charpy energy materials that are being made today, brittle fracture will not easily initiate from the pressed notch of the standard DWTT specimen, whereas for older line-pipe steels that was the normal behavior. This behavior is now referred to as “Abnormal Fracture Appearance” (AFA). More recent work shows a more disturbing trend that one can get 100-percent shear area in the standard pressed-notch DWTT specimen, but the material is really susceptible to brittle fracture. This is a related phenomenon due to the high fracture initiation energy in the standard DWTT specimen that we call “Abnormal Fracture Behavior” (AFB). This paper discusses modified DWTT procedures and some full-scale results. The differences in the actual behavior versus the standard DWTT can be significant. Modifications to the API 5L3 test procedure are needed. The second aspect deals with empirical fracture control for unstable ductile fractures based on older line-pipe steel tests initially from tests 30-years ago. As higher-grade line-pipe steels have been developed, a few additional full-scale burst tests have shown that correction factors on the Charpy energy values are needed as the grade increases. Those correction factors from the newer burst tests were subsequently found to be related to relationship of the Charpy energy values to the DWTT energy values, where the DWTT has better similitude than the Charpy test for fracture behavior (other than the transition temperature issue noted above). Once on the upper-shelf, recent data suggest that what was once thought to be a grade correction factor may really be due to steel manufacturing process changes with time that affect even new low-grade steels. Correction factors comparable to that for X100 steels have been indicated to be needed for even X65 grade steels. Hence the past empirical equations in Codes and Standards like B31.8 will significantly under-predict the actual values needed for most new line-pipe steels.

Role of crystallographic texture, delamination and constraint on anisotropy in fracture toughness of API X70 line pipe steels

2017 ◽  
Vol 708 ◽  
pp. 254-266 ◽  
Author(s):  
Soumya Chatterjee ◽  
Soumyajit Koley ◽  
Subhankar Das Bakshi ◽  
Mahadev Shome
Keyword(s):  
Fracture Toughness ◽  
Crystallographic Texture ◽  
Pipe Steels ◽  
Line Pipe

Brittle Fracture Avoidance Technology in Large Structures with Thick Steel Plates

2021 ◽  
Vol 21 (9) ◽  
pp. 4926-4930
Author(s):  
Gyubaek An ◽  
Jeongung Park ◽  
Hongyeol Bae
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Brittle Fracture ◽  
Steel Plate ◽  
Control Process ◽  
Brittle Crack ◽  
Fine Grain ◽  
Nano Structures ◽  
Class Steel ◽  
Thick Steel

The 460-MPa-class steel was developed by thermomechanical control process for shipbuilding, and the maximum plate thickness was 100 mm, which has the fine grain size as 5–20 µm. The surfaces were studied in terms of micro and nano structures, surface roughness, and surface energy to evaluate the effect of fracture toughness in large steel structure. The thick steel plate has possibility to occur unstable fracture because the fracture toughness will be decrease with increase of thickness. The increase in the temperature in thermomechanical control process accelerated the surface energy and created both micro and nano structures on the surfaces more effectively. It was effective to avoid brittle fracture in the base metal when the brittle crack was deviated into base metal. The developed 460-MPa-class steel plate improves the brittle fracture safety despite being a thick steel plate through the fine grain size. They had to be designed in such a manner as to avoid crack initiation, especially in welded joints. In this study, brittle crack arrest designs were developed for large weld construction using arrest design concept and micro and nano structures in high strength steel plate.

Sign in / Sign up

Export Citation Format

Share Document