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.

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.

Mechanical and Metallurgical Aspects of the Resistance to Ductile Fracture Propagation in the New Generation of Gas Pipelines

2014 ◽  
Author(s):  
Igor Pyshmintsev ◽  
Alexey Gervasyev ◽  
Victor Carretero Olalla ◽  
Roumen Petrov ◽  
Andrey Arabey
Keyword(s):  
Ductile Fracture ◽  
Mechanical Test ◽  
Fracture Propagation ◽  
Rolling Plane ◽  
Full Scale ◽  
Charpy Test ◽  
Line Pipe ◽  
Surface Separation ◽  
Fracture Arrest ◽  
New Generation

The microstructure and fracture behavior of the base metal of different X80 steel line pipe lots from several pipeline projects were analyzed. The resistance of the pipes to ductile fracture propagation was determined by the full-scale burst tests. The high intensity of fracture surface separation (secondary brittle cracks parallel to the rolling plane of the plate) appeared to be the main factor reducing the specific fracture energy of ductile crack propagation. A method for quantitative analysis of microstructure allowing estimation of the steel’s tendency to form separations is proposed. The procedure is based on the EBSD data processing and results in Cleavage Morphology Clustering (CMC) parameter evaluation which correlates with full-scale and laboratory mechanical test results. Two special laboratory mechanical test types utilizing SENT and Charpy test concepts for prediction of ductile fracture arrest/propagation in a pipe were developed and included into Gazprom specifications.

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.

scholarly journals On Longitudinal Propagation of a Ductile Fracture in a Buried Gas Pipeline: Numerical and Experimental Analysis

2000 ◽  
Author(s):  
G. Berardo ◽  
P. Salvini ◽  
G. Mannucci ◽  
G. Demofonti
Keyword(s):  
Finite Element ◽  
Ductile Fracture ◽  
Driving Force ◽  
Fracture Propagation ◽  
Full Scale ◽  
Finite Element Code ◽  
Line Pipe ◽  
Real Phenomenon ◽  
Buried Gas Pipeline ◽  
Soil Pipe

The work deals with the development of a finite element code, named PICPRO (PIpe Crack PROpagation), for the analysis of ductile fracture propagation in buried gas pipelines. Driving force estimate is given in terms of CTOA and computed during simulations; its value is then compared with the material parameter CTOAc, inferred by small specimen tests, to evaluate the toughness of a given line pipe. Some relevant aspects are considered in the modelling with the aim to simulate the real phenomenon, namely ductile fracture mechanism, gas decompression behaviour and soil backfill constraint. The gas decompression law is calculated outside the finite element code by means of experimental data from full-scale burst tests coupled with classical shock tube solution. The validation is performed on the basis of full-scale propagation experiments, carried out on typical pipeline layouts, and includes verification of global plastic displacements and strains, CTOA values and soil-pipe interaction pressures.

Evolution of Line-Pipe Steel and Its Implications for Transmission Pipeline Design

2002 ◽  
Author(s):  
B. N. Leis
Keyword(s):  
Factor Of Safety ◽  
Pipe Steel ◽  
Full Scale ◽  
Line Pipe ◽  
Alternative Design ◽  
Reference Stress ◽  
Transmission Pipeline ◽  
Underlying Causes ◽  
Line Pipe Steel ◽  
Pipeline Design

This paper discusses the evolution of line-pipe steel against the background of the failure incidence and the design basis for transmission pipelines, with a focus on those transporting natural gas. Working-stress design (WSD) is introduced as background for analysis of incident experience. It is shown that failure incidence does not correlate with the WSD factor of safety on pressure-induced stress, leading to the underlying causes of failure and discussion of alternative design philosophies, and consideration of safety factors other than those based on stress, or the effect of pressure. Full-scale test data are discussed to rationalize why failure frequency does not correlate with factor of safety. These results point to a very large factor of safety on pressure, with failure pressure found much in excess of the specified minimum yield stress (SMYS), the reference stress for WSD-based pipeline design. Full-scale failure at pressures much in excess of that for in-service incidents motivates discussion of causes of such failures and brings into question the utility of alternative design philosophies. The role of toughness is introduced as key to the success of WSD and alternative design philosophies. The historical evolution of both strength and toughness is then introduced along with apparent differences in toughness depending on how it is characterized. Historical trends are contrasted to those for modern steels, with diametrically opposing trends evident. The implications for design are discussed with reference to fracture control plans and methods to characterize required arrest toughness.

Fracture Propagation in Underwater Gas Pipelines

1986 ◽  
Vol 108 (1) ◽  
pp. 29-34 ◽  
Author(s):  
W. A. Maxey
Keyword(s):  
Ductile Fracture ◽  
Pipe Wall ◽  
Fracture Propagation ◽  
Full Scale ◽  
Gas Pipelines ◽  
Buried Pipelines ◽  
Nitrogen Gas ◽  
Line Pipe ◽  
Fracture Velocity

Two full-scale ductile fracture propagation experiments on segments of line pipe pressurized with nitrogen gas have been conducted underwater at a depth of 40 ft (12 m) to evaluate the ductile fracture phenomenon in underwater pipelines. The pipes were 22-in. (559-mm) diameter and 42-in. (1067-mm) diameter. Fracture velocities were measured and arrest conditions were observed. The overpressure in the water surrounding the pipe resulting from the release of the compressed nitrogen gas contained in the pipe was measured in both experiments. The overpressure in the water reduces the stress in the pipe wall and thus slows down the fracture. In addition, the water surrounding the pipe appears to be more effective than soil backfill in producing a slower fracture velocity. Both of these effects suggest a greater tendency toward arrest for a pipeline underwater than would be the case for the same pipeline buried in soil onshore. Further verification of this effect is planned and a modified version of the existing model for predicting ductile fracture in buried pipelines will be developed for underwater pipelines.

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