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.

Microstructure Engineering of Thicker Gage Niobium Microalloyed Line Pipe Steel With Enhanced Toughness by High Temperature Processing Using TiN-NbC Composite Precipitate

2016 ◽  
Author(s):  
S. V. Subramanian ◽  
Xiaoping Ma ◽  
Chengliang Miao ◽  
Xiaobing Zhang ◽  
Laurie Collins
Keyword(s):  
Brittle Fracture ◽  
Ductile Fracture ◽  
Pipe Steel ◽  
Fracture Propagation ◽  
Full Scale ◽  
Laboratory Simulation ◽  
Austenite Grain Size ◽  
Line Pipe ◽  
Nano Scale ◽  
Line Pipe Steel

Prediction of crack arrestability of higher grade line pipe steel microalloyed with niobium in full scale burst tests based on laboratory simulation tests including Charpy impact, DWTT and CTOD is rendered difficult, as the full scale burst test is found to be far more sensitive to microstructure variables than current laboratory tests. This paper deals with nano-scale TiN-NbC composite precipitate engineering as an alternative approach to strain-induced precipitation of NbC to produce thicker gage plate or coil with enhanced toughness and resistance to ductile fracture propagation of line pipe steel. Microstructure engineering is based on identification of key microstructural parameters to which target properties can be related, and engineer the target microstructure through design of base chemistry and optimization of processing schedules. Nano-scale precipitate engineering based on control of spacing and size of TiN-NbC composite precipitate offers a new approach to achieve excellent strength and toughness (300J at −60C) of line pipe steels through control of target microstructure consisting of: (i) refinement of austenite grain size (under 30 microns) of transfer bar before pancaking, (ii) high volume fraction of acicular ferrite with adequate plasticity to increase resistance to ductile fracture propagation, (iii) high density and uniform dispersion of high angle grain boundaries that arrest micro-cracks to suppress brittle fracture initiation, (iv) less intensity of unfavorable {100}<011> texture component that facilitate the propagation of brittle fracture, (v) suppression of ultra-fine precipitates in the matrix, thereby enlarging plastic zone ahead of the crack tip to blunt the tip of the crack, and (vi) suppression of coarse brittle constituents (carbides or MA products) that initiate brittle fracture. Experimental results are presented on thermo-mechanically rolled X-90 and K-60 that validate the concept of microstructure engineering using TiN-NbC composite precipitate engineering to enhance strength and fracture toughness.

Fracture Behavior in West Jefferson Test Under Low-Temperature Condition for X65 Steel Pipe With High Charpy Energy: Current Activities in HLP Committee, Japan, Report 1

2016 ◽  
Author(s):  
Toshihiko Amano ◽  
Satoshi Igi ◽  
Takahiro Sakimoto ◽  
Takehiro Inoue ◽  
Shuji Aihara
Keyword(s):  
Transition Temperature ◽  
Low Temperature ◽  
Brittle Fracture ◽  
Pressure Vessel ◽  
Fracture Behavior ◽  
Line Pipe ◽  
Burst Test ◽  
Pipe Burst ◽  
Test Vessel ◽  
Fracture Appearance

This paper describes the results of pressure vessel fracture test which called West Jefferson and/or partial gas burst testing using Grade API X65 linepipe steel with high Charpy energy that exhibits inverse facture in the Drop Weight Tear Test (DWTT). A series of pressure vessel fracture tests which is as part of an ongoing effort by the High-strength Line Pipe committee (HLP) of the Iron and Steel Institute of Japan (ISIJ) was carried out at low temperature in order to investigate brittle-to-ductile transition behavior and to compare to DWTT fracture behavior. Two different materials on Fracture Appearance Transition Temperature (FATT) property were used in these tests. One is −60 degree C and the other is −25 to −30 degree C which is defined as 85 % shear area fraction (SA) in the standard pressed notch DWTT (PN-DWTT). The dimensions of the test pipes were 24inches (609.6 mm) in outside diameter (OD), 19.1 mm in wall thickness (WT). In each test, the test pipe is cooled by using liquid nitrogen in the cooling baths. Two cooling baths are set up separately on the two sides of the test vessel, making it possible to obtain fracture behaviors under two different test temperatures in one burst test. The test vessel was also instrumented with pressure transducers, thermocouples and timing wires to obtain the pressure at the fracture onset, temperature and crack propagation velocity, respectively. Some informative observations to discuss appropriate evaluation method for material resistance to brittle facture propagation for high toughness linepipe materials are obtained in the test. When the pipe burst test temperatures are higher than the PN-DWTT transition temperature, ductile cracks were initiated from the initial notch and propagated with short distance in ductile manner. When the pipe burst test temperatures were lower than the PN-DWTT transition temperature, brittle cracks were initiated from the initial notch and propagated through cooling bath. However, the initiated ductile crack at lower than the transition temperature was not changed to brittle manner. This means inverse facture occurred in the PN-DWTT is a particular problem caused by the API DWTT testing method. Furthermore, results for the pipes tested indicated that inverse facture occurred in PN-DWTT at the temperature above the 85 % FATT may not affect the arrestability against the brittle fracture propagation and it is closely related with the location of brittle fracture initiation origin in the fracture appearance of PN-DWTT.

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.

Development of Heavy Gauge X70 Helical Line Pipe

2018 ◽  
Author(s):  
L. E. Collins ◽  
K. Dunnett ◽  
T. Hylton ◽  
A. Ray
Keyword(s):  
Low Temperature ◽  
Large Diameter ◽  
High Strength ◽  
Helical Line ◽  
Slab Thickness ◽  
Long Distance ◽  
Austenite Grain Size ◽  
Line Pipe ◽  
Nitrogen Levels ◽  
Low Temperature Toughness

A decade ago, the pipeline industry was actively exploring the use of high strength steels (X80 and greater) for long distance, large diameter pipelines operating at high pressures. However in recent years the industry has adopted a more conservative approach preferring to utilize well established X70 grade pipe in heavier wall thicknesses to accommodate the demand for increased operating pressures. In order to meet this demand, EVRAZ has undertaken a substantial upgrade of both its steelmaking and helical pipemaking facilities. The EVRAZ process is relatively unique employing electric arc furnace (EAF) steelmaking to melt scrap, coupled with Steckel mill rolling for the production of coil which is fed into helical DSAW pipe mills for the production of large diameter line pipe in lengths up to 80 feet. Prior to the upgrade production had been limited to a maximum finished wall thickness of ∼17 mm. The upgrades have included installation of vacuum de-gassing to reduce hydrogen and nitrogen levels, upgrading the caster to improve cast steel quality and allow production of thicker (250 mm) slabs, upgrades to the power trains on the mill stands to achieve greater rolling reductions, replacement of the laminar flow cooling system after rolling and installation of a downcoiler capable of coiling 25.4 mm X70 material. As well a new helical DSAW mill has been installed which is capable of producing large diameter pipe in thicknesses up to 25.4 mm. The installation of the equipment has provided both opportunities and challenges. Specific initiatives have sought to produce X70 line pipe in thicknesses up to 25.4 mm, improve low temperature toughness and expand the range of sour service grades available. This paper will focus on alloy design and rolling strategies to achieve high strength coupled with low temperature toughness. The role of improved centerline segregation control will be examined. The use of scrap as a feedstock to the EAF process results in relatively high nitrogen contents compared to blast furnace (BOF) operations. While nitrogen can be reduced to some extent by vacuum de-gassing, rolling practices must be designed to accommodate nitrogen levels of 60 ppm. Greater slab thickness allows greater total reduction, but heat removal considerations must be addressed in optimization of rolling schedules to achieve suitable microstructures to achieve both strength and toughness. This optimization requires definition of the reductions to be accomplished during roughing (recrystallization rolling to achieve a fine uniform austenite grain size) and finishing (pancaking to produce heavily deformed austenite) and specification of cooling rates and coiling temperatures subsequent to rolling to obtain suitable transformation microstructures. The successful process development will be discussed.

Modified West Jefferson Burst Test for Assessment of Brittle Fracture Arrest in Thick-Wall TMCP Line-Pipe Steel With High Charpy Energy

2016 ◽  
Author(s):  
S. Igi ◽  
T. Sakimoto ◽  
J. Kondo ◽  
Y. Hioe ◽  
G. Wilkowski
Keyword(s):  
Transition Temperature ◽  
Brittle Fracture ◽  
Ductile Fracture ◽  
Base Metal ◽  
The Other ◽  
Line Pipe ◽  
Burst Test ◽  
Seam Weld ◽  
Shear Area ◽  
Fracture Arrest

Three partial gas pipe burst tests were conducted to assess the brittle-to-ductile transition temperature and brittle fracture arrestability of a heavy-walled TMCP line-pipe steel. This steel had a very high Charpy energy (400 J) which is typical of many modern line-pipe steels. In standard pressed-notch DWTT specimen tests this material 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 gives an invalid test by API RP 5L3, which makes the transition temperature difficult to determine. The first burst test was conducted in a manner that is typical of a traditional West Jefferson (partial gas vessel) burst tests. The crack was initiated in the center of the cooled vessel (with a partial air gap), but an unusual result occurred. In this test a ductile fracture just barely started from each crack tip, but one of the endcaps blew off. The pipe rocketed into the wall of a containment building. The opposite endcap impacted the wall of the building and brittle fractures started there with one coming back to the center of the vessel. The implication from this test was that perhaps initiation of the brittle fracture in the base metal gives different results than if the initial crack came from a brittle location. The second burst test used a modified West-Jefferson Burst Test procedure. The modification involved cutting a short length of pipe at the center of the vessel and rotating the seam weld to the line of crack propagation. The HAZ of the axial seam weld had a higher dynamic transition temperature. The initiation flaw was across one of the center girth welds so that one side of the initial through-wall crack had the crack tip in the base metal while the other side initiated in the seam weld HAZ. On the base metal side, the crack had about 220 mm of crack growth before reaching steady-state shear area, i.e., the shear area gradually decreased as the fracture speed was increasing. On the other side, a brittle fracture was started in the HAZ as expected, and once it crossed the other central girth weld into the base metal, the fracture immediately transformed to a lower shear area percent. These results along with those from the first burst test suggest that the DWTT specimen should have a brittle weld metal in the starter notch region to ensure the arrestability of the material. The final burst test was at a warmer temperature. There was a short length of crack propagation with higher shear area percent, which quickly turned to ductile fracture and arrested. In addition various modified DWTTs were conducted and results were analyzed using an alternative brittle fracture arrest criterion to predict pipe brittle fracture arrestability.

Effect of Ausageing on the Precipitation Behavior of MX Carbonitride in Modified 9Cr-1Mo Steel

2007 ◽  
Vol 539-543 ◽  
pp. 2976-2981
Author(s):  
Masataka Yoshino ◽  
Yoshinao Mishima ◽  
Yoshiaki Toda ◽  
Hideaki Kushima ◽  
Kota Sawada ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Single Phase ◽  
Equilibrium Phase ◽  
The Other ◽  
Austenite Matrix ◽  
Precipitation Behavior ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
The Matrix ◽  
Equilibrium Mole Fraction

The precipitation behavior of MX carbonitride during a normalizing heat treatment with and without ausageing was investigated in a modified 9Cr-1Mo steel. The normalizing heat treatment was performed at 1150 oC for 1800 s. Ausageing was conducted at 765 and 500 oC for 1800 to 86400 s during the cooling from the heat treatment. The matrix of the steel was austenite single phase during normalizing and ausageing, except for that ausaged at 765 oC for 86400 s. The initial austenite grain size and hardness were not influenced by ausageing, except for the sample ausaged at 765 oC for 86400 s. Although Nb-rich MX (NbX) and cementite were observed, V-rich MX (VX) was not observed under any of the conditions investigated. The amount of NbX in the steel ausaged at 500 oC was at least twice as large as that under the other conditions, and the amount in the steel ausaged at 760 oC was slightly larger than that in the steel that did not undergo ausageing. The precipitation of NbX took place during ausageing in the austenite matrix. On the other hand, it is well known that VX precipitates during tempering. An equilibrium mole fraction of VX in the austenite matrix calculated by Thermo-Calc. was larger than that of NbX at the ausageing temperatures. It is proposed that VX is an equilibrium phase at the ausageing temperature; however, VX nucleation takes much longer in the austenite matrix. It is postulated that the precipitation of VX is more strongly influenced by the interfacial energy rather than supersaturation. It is concluded that the precipitation of MX carbonitride, especially NbX, can be controlled by ausageing during cooling after a normalizing heat treatment.

scholarly journals Austenite Grain Growth Kinetics in API X65 and X70 Line-Pipe Steels during Isothermal Heating

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Asiful Hossain Seikh ◽  
Mahmoud S. Soliman ◽  
Abdulhakim AlMajid ◽  
Khaled Alhajeri ◽  
Waleed Alshalfan
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Heating Temperature ◽  
Heating Time ◽  
Austenite Grain Size ◽  
Line Pipe ◽  
Austenite Grain ◽  
Steel Grades ◽  
Grain Growth Kinetics ◽  
Reheating Process

The aim of the present work is to investigate the microstructural behavior of austenite grain size (AGS) during the reheating process of two different API steel grades (X65 and X70). The steel samples were austenitized at 1150°C, 1200°C, and 1250°C for various holding times from 10 to 60 minutes and quenched in ice water. The samples were then annealed at 500°C for 24 hours to reveal the prior AGS using optical microscopy. It was noticed that the AGS in X65 grade is coarser than that of X70 grade. Additionally, the grain size increases with increasing the reheating temperature and time for both steels. The kinetics of grain growth was studied using the equationdn-d0n=Atexp-Q/RT, wheredis the measured grain size,dois the initial grain size,nis the grain size exponent,tis the heating time,Tis the heating temperature,Qis the activation energy,Ris the gas constant, andAis a constant. To characterize the grain growth process the values ofn,Q, andAwere determined. Good agreement is obtained between the prediction of the model and the experimental grain size values.

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