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.

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.

Investigation of X80 Line Pipe Steel Fracture during Tensile Testing Using Acoustic Emission Monitoring

2019 ◽  
Vol 794 ◽  
pp. 21-27 ◽  
Author(s):  
Turbadrakh Chuluunbat ◽  
Andrii G. Kostryzhev ◽  
Olexandra Marenych
Keyword(s):  
Acoustic Emission ◽  
Tensile Testing ◽  
High Speed ◽  
Fracture Behavior ◽  
Oil And Gas ◽  
Pipe Steel ◽  
Small Scale ◽  
Wave Form ◽  
Line Pipe ◽  
Line Pipe Steel

The acoustic emission (AE) monitoring technique is widely used in mechanical and materials research for detection of plastic deformation, fracture initiation and crack growth. However, the quantitative dependences of the AE signal parameters on material fracture parametersare not completely understood. This paper presents recent research results on AE monitoring of the fracture behavior of X80 line pipe steel, a critically important material for the oil and gas transportation industry.Fracture of this steel was studied using tensile testing of small scale specimens coupled with AE monitoring and high speed video camera. The dependence of fracture behavior and AE parameters on loading conditions (strain rate and presence or absence of a notch) was investigated. The AE parameters were analyzed using the “Average Hit” features and “Wave Form and Power Spectrum” methodologies. The fracture surface was characterized using scanning electron microscopy and a dependence of the AE parameters on the average void size has been obtained.

The EPRG Recommendations for Crack Arrest Toughness for Line Pipe Steel (Third Edition)

2018 ◽  
Author(s):  
Andrew Cosham ◽  
Robert Andrews ◽  
Tanja Schmidt
Keyword(s):  
Pipe Steel ◽  
Crack Arrest ◽  
Pipe Steels ◽  
Line Pipe ◽  
The Third ◽  
Line Pipe Steel ◽  
Definition Of ◽  
Quantitative Definition ◽  
Design Factors ◽  
Arrest Toughness

The third edition of the EPRG recommendations for crack arrest toughness for line pipe steels is presented. The third edition extends the applicability of the recommendations to pipelines transporting lean natural gas at pressures up to 100 barg (1450 psig), in diameters up to 1422.4 mm (56 inch), in grades up to Grade L555 (API 5L X80), and design factors up to 0.8. A quantitative definition of a lean gas is included in the third edition. The recommendations are intended to be applied to new pipelines. The recommendations are not intended to be applied retrospectively to existing pipelines.

Exploiting a Simple Spectrophotometric Method for the Determination of Manganese in High Strength Line Pipe Steels

2011 ◽  
Vol 284-286 ◽  
pp. 1158-1164
Author(s):  
Xiaodong Shao
Keyword(s):  
Spectrophotometric Method ◽  
Pipe Steel ◽  
High Strength ◽  
Ammonium Persulfate ◽  
Pipe Steels ◽  
Line Pipe ◽  
Relative Standard ◽  
Characteristic Wavelength ◽  
Line Pipe Steel

The use of high strength line pipe steels is beneficial for the reduction the cost of gas transmission pipelines by enabling high pressure transmission of large volumes of gas. The high strength line pipe steels will become the preferred materials for modern natural gas transmission pipeline. It was well known that manganese was an important element in the high strength line pipe steels. In this paper, a simple spectrophotometric method was described for determination of manganese in high strength line pipe steels. The method was based on the oxidation-reduction reaction between ammonium persulfate and manganese(II) producing manganese(VII) in the presence of silver nitrate as a catalyst. The characteristic wavelength of maximum absorption of manganese(VII) was obtained locating at 530 nm. Under the optimum reaction conditions the absorption value was proportional to the concentration of manganese in the range of 0.18%~2.0% (R2 = 0.9997), and the relative standard deviation was less than 3.0% (n=5). The proposed method was applied successfully to determine manganese in API grade X80 line pipe steel and API grade X70 line pipe steel samples.

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.

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.

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