Crack Formation in Charpy Tests of the Heat-Affected Zone of Large-Diameter Linepipe Material

2018 ◽  
Author(s):  
Lars Schemmann ◽  
Charles Stallybrass ◽  
Jens Schröder ◽  
Andreas Liessem ◽  
Stefan Zaefferer
Keyword(s):  
Base Metal ◽  
Heat Affected Zone ◽  
Volume Fraction ◽  
Large Diameter ◽  
Base Material ◽  
Fusion Line ◽  
3D Analysis ◽  
Pipe Material ◽  
Austenite Grain Size ◽  
Secondary Cracks

Double submerged arc welding is an efficient process used during the production of longitudinally-welded large-diameter pipes. It is well known that the associated high heat input has a negative influence on the toughness of the heat-affected zone (HAZ). The toughness drop is related to changes in the HAZ microstructure compared to the base metal. The austenite grain size increases significantly and larger carbon-rich martensite/austenite particles (M/A-particles) are formed within a coarse bainitic matrix during the phase transformation compared to the as-rolled base material. The exact relationship between the microstructure, the processing conditions, base metal composition and the weld metal are at the focus of attention of materials development efforts at EUROPIPE and Salzgitter Mannesmann Forschung GmbH (SZMF). In the present study, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to investigate the HAZ of X70 large-diameter pipe material as well as tested Charpy specimens from the same material. Secondary cracks in the direct vicinity of the primary fracture surface of tested Charpy specimens from the HAZ were analyzed by EBSD and SEM to investigate the damage mechanism in detail. It was found that these cracks originate at M/A-particles and that the dominant crack path depends on the crystallographic orientation of the surrounding matrix. The analysis of several EBSD measurements and a 3D-analysis of the propagation direction of the crack showed that secondary cracks frequently propagate parallel to {100} and rarely along {110}-planes. It is known from literature that these are preferred cleavage planes in ferritic steels. The SEM analysis performed in the HAZ of the investigated steel showed that the volume fraction of elongated M/A-particles is elevated close to the fusion line and decreases within the first few hundred micrometers distance from the fusion line. The EBSD measurements illustrate that the geometrically necessary dislocation density is significantly increased in the neighborhood of M/A-particles. This indicates that the bainitic matrix is work-hardened around the M/A-particles during testing and is therefore more prone to the formation of microcracks than other surrounding regions.

Application of FIB/SEM/EBSD for Evaluation of Residual Strains and Their Relationship to Weld Metal Hydrogen Assisted Cold Cracking

2012 ◽  
Author(s):  
W. L. Costin ◽  
I. H. Brown ◽  
L. Green ◽  
R. Ghomashchi
Keyword(s):  
Residual Stresses ◽  
Weld Metal ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Ion Beam ◽  
Base Material ◽  
Welding Process ◽  
Cold Cracking ◽  
Predictive Methods ◽  
Residual Strains

Hydrogen assisted cold cracking (HACC) is a welding defect which may occur in the heat affected zone (HAZ) of the base metal or in the weld metal (WM). Initially the appearance of HACC was associated more closely with the HAZ of the base metal. However, recent developments in advanced steel processing have considerably improved the base material quality, thereby causing a shift of HACC to the WM itself. This represents a very serious problem for industry, because most of the predictive methods are intended for prevention of HACC in the HAZ of the base metal, not in the weld metal [1]. HACC in welded components is affected by three main interrelated factors, i.e. a microstructure, hydrogen concentration and stress level [2–4]. In general, residual stresses resulting from the welding process are unavoidable and their presence significantly influences the susceptibility of weld microstructures to cracking, particularly if hydrogen is introduced during welding [5]. Therefore various weldability tests have been developed over the years which are specifically designed to promote HACC by generating critical stress levels in the weld metal region due to special restraint conditions [4, 6–8]. These tests were used to develop predictive methods based on empirical criteria in order to estimate the cracking susceptibility of both the heat-affected zone and weld metal [4]. However, although the relationship between residual stress, hydrogen and HACC has received considerable attention, the interaction of residual stresses and microstructure in particular at microscopic scales is still not well understood [5, 9–21]. Therefore the current paper focuses on the development and assessment of techniques using Focused Ion Beam (FIB), Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction for the determination of local residual strains at (sub) micron scales in E8010 weld metal, used for the root pass of X70 pipeline girth welds, and their relationship to the WM microstructure. The measurement of these strains could be used to evaluate the pre-existing stress magnitudes at certain microstructural features [22].

Structure Analyses of Experimental Welds Designed for Repair Welding of VVER 1000 Presssure Vessel

2015 ◽  
Vol 647 ◽  
pp. 131-140 ◽  
Author(s):  
Miroslava Matějová ◽  
Dagmar Jandová ◽  
Josef Kasl
Keyword(s):  
Heat Affected Zone ◽  
Microstructural Analysis ◽  
Base Material ◽  
Fusion Line ◽  
Structure Transformation ◽  
Repair Welding ◽  
Weld Joints ◽  
The Third ◽  
Energy Inputs ◽  
Welding Metal

Microstructural analysis and microhardness measurement of experimental repair weld joints were carried out in heat affected zone (HAZ) of the base material (BM) – steel 15Ch2NMFA after weld deposition of several layers by welding metal of Inconel FM 52. A temper bead welding (TBW) technique was used. Required microhardness up to 350 HV0.1 in heat affected zone of base material in distance 0.5 mm from fusion line was exceeded in all three experimental blocks with various welding energy inputs during deposition of three or five weld layers. Metallography showed reaustenitization and structure transformation in HAZ after the deposit of first layer in all three blocks. After deposit of the last layer the structure of HAZ in two blocks was tempered only and one variant of them have been recommended for futher technological tests. Structure of HAZ of the third block was not full tempered even after the last layer deposit.

scholarly journals MODELING THE WORK OF THE HEAD OF A HYDROMECHANICAL EXPANDER FOR WELDED PIPES OF A LARGE DIAMETER

2020 ◽  
pp. 35-42
Author(s):  
L. M. Gurevich ◽  
V. F. Danenko ◽  
A. A. Istrati ◽  
V. A. Sonnova
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Internal Pressure ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Welded Joint ◽  
Large Diameter ◽  
Design Parameters ◽  
Maximum Stresses ◽  
Distribution Of Stresses

Finite element simulates of changing stresses and strains under loading by gradually increasing internal pressure of cylindrical welded vessels was carried out. The vessels had an annular mechanically inhomogeneous welded joint with different mechanical properties of the joint, heat-affected zone, and base metal. Maximum stresses developed in the caps of the vessels, and the annular joint are lightly loaded. The distribution of stresses and strains in joint at various design parameters of the vessels is investigated.

CTOD Fracture Toughness Assessment Under Different Notch Type (Fatigue Pre-Cracking and EDM)

2019 ◽  
Author(s):  
Israel Marines-Garcia ◽  
Aaron Aguilar ◽  
Kristian Carreon ◽  
Philippe Darcis
Keyword(s):  
Fracture Toughness ◽  
Crack Length ◽  
Heat Affected Zone ◽  
Crack Tip ◽  
Fusion Line ◽  
Testing Time ◽  
Pipe Material ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Electro Discharge Machining

Abstract The standardization of any mechanical material characterization is aiming to get homogenization on the testing physical execution by independent laboratories and to drive for accurate material evaluation between different entities. However, from time to time, standard tests may be reconsidered in order to improve their efficacy, execution time and incorporate new testing techniques or technologies without compromising the testing results and consistency. In the present work, fracture toughness crack tip opening displacement (CTOD) testing is addressed and particularly the need to perform fatigue pre-cracking prior monotonic testing. Without the fatigue pre-cracking, CTOD testing time can be significantly reduced during the preparation of specimens, meaning that specimens can be tested as soon as they are machined. Wire electro-discharge machining (EDM) technique allows generating sharp tip notches, and presents a good alternative to the standards specified fatigue pre-cracking [1–2]. In addition, this machining technology reduces the risk of rejecting the specimen testing, particularly when targeting weld heat affected zone/fusion line (HAZ/FL) microstructure on specimens with surface notch DNV-ST-F101 Figure B-9 [3], where it is specified that the crack tip shall be within a narrow distance (0.5 mm) from the fusion line (FL) or assess grain coarsened heat affected zone (GCHAZ) microstructure as indicated in DNV-ST-F101 section B.2.8.7 [3]. Herein, it is presented an assessment carried out in order to identify the notch type effect over the fracture toughness (CTOD) considering notches conditions as standard fatigue pre-crack and wire electro-discharge machining (EDM). Fifteen (15) CTOD specimens were manufactured from plain pipe material (same pipe), 251.3 mm OD × 20.9 mm WT, SMLS 450PD and tested according to ISO 12135 recommendations [1], they were distributed as follow; five (5) specimens according to standard recommendations with fatigue pre-cracking length ≥ 1.3 mm or 2.5%W (whichever is bigger), five (5) specimens with a fatigue pre-cracking length < 1.3 mm (between 0.5 mm to 1 mm), and five (5) specimens without fatigue pre-cracking (EDM notch), additionally, results from five (5) specimens previously tested in a round robin (RR) testing performed internally by Tenaris using the same LP material and standard fatigue pre-crack length. The crack length target (a/W) was kept 0.5 for all cases. Even if the sampling population is relatively small considering the three notch conditions, it seems that EDM might be an alternative to the standard specified fatigue pre-cracking. Thus, this experimental assessment aims to open the discussion on the use of EDM notch as alternative.

scholarly journals STRENGTH AND FRACTURE TOUGHNESS OF THE WELDED JOINTS MADE OF HIGH-STRENGTH FERRITIC STEEL

2013 ◽  
Vol 7 (4) ◽  
pp. 226-229 ◽  
Author(s):  
Ihor Dzioba ◽  
Tadeusz Pała ◽  
Ilkka Valkonen
Keyword(s):  
Fracture Toughness ◽  
Heat Affected Zone ◽  
Welded Joints ◽  
Ferritic Steel ◽  
Base Material ◽  
High Strength ◽  
Experimental Results ◽  
Strength Characteristics ◽  
Fusion Line ◽  
Weld Material

Abstract The paper presents experimental results of the characteristics of strength and fracture toughness of the material from the different zones of welded joints made of different participation of the linear welding energy. Strength characteristics and fracture toughness were determined in the weld material, in the area of fusion line, in the material of the heat affected zone and in the base material

scholarly journals Microstructure Evolution and Distribution of Mechanical Properties in Shielded Metal Arc Welded Dissimilar DSS 2205 and HY80 Joints

2019 ◽  
Vol 269 ◽  
pp. 06004
Author(s):  
Sunoto Mudiantoro ◽  
Winarto Winarto ◽  
Herry Oktadinata
Keyword(s):  
Weld Metal ◽  
Base Metal ◽  
Microstructure Evolution ◽  
Heat Affected Zone ◽  
Steel Plate ◽  
Fusion Line ◽  
Dissimilar Welding ◽  
Hardness Distribution ◽  
Butt Weld ◽  
Coarse Grains

Dissimilar welding is a unique and complex process because in each zone in the different welding area have unique structures and characteristics. The modified structure may have a significant effect on weld metal properties. In this research, the primary objective is to investigate the microstructure evolution and hardness distribution mode of a different joint HY80 steel plate and Duplex type 2205 welded by using thick weld or shielded metal arc weld (SMAW). The microstructure of weld metal zones was observed. The test plates were welded in both butt joint and fillet joint by using E309L filler metal. It was found that the 309L electrode provides the equilibrium between austenite and ferrite phase in the different weld metal zones of DSS 2205 and HY80 steel joint. The results show that hardness distribution of different joint of both butt weld and fillet weld presents sinusoidal trend, where hardness in HAZ is highest. The peak value of hardness appeared in HY 80 base metal near the fusion line. The microstructure of base metal DSS 2205 shows fine grains of ferrite and austenite grains with dark and light shades respectively. The microstructure of weld metal shows coarse grains of austenite along with some slag inclusions as dark spots. The Heat Affected Zone of HY80 steel plate shows coarse grains of austenite and ferrite, while the heat affected zone of DSS 2205 shows thin fusion line with coarse grains of ferrite as dark zones and coarse grains of austenite as light zones. There is, a degree of variation in weld metal ferrite content was observed. Keywords: Duplex Stainless Steel, HY80, SMAW, Dissimilar Joint, Hardness, and Impact Toughness.

CTOA Measurements of Welds in X100 Pipeline Steel

2008 ◽  
Author(s):  
Elizabeth Drexler ◽  
Philippe Darcis ◽  
Christopher McCowan ◽  
J. Matthew Treinen ◽  
Avigdor Shtechman ◽  
...  
Keyword(s):  
Stress Field ◽  
Base Metal ◽  
Pipeline Steel ◽  
Base Material ◽  
Fusion Line ◽  
Opening Angle ◽  
Seam Weld ◽  
Weld Material ◽  
X100 Pipeline Steel ◽  
Girth Welds

A suite of tests characterizing X100 pipeline steels was initiated at the National Institute of Standards and Technology (NIST) in Boulder. Part of the test matrix included testing the toughness of the base metal, welds, and heat-affected zones (HAZ) by use of modified double cantilever beam specimens for crack tip opening angle (CTOA) testing. The thickness of the test section was either 3 mm or 8 mm. Girth welds perpendicular to the growing crack, and seam welds and their HAZ parallel with the crack, were tested with a crosshead displacement rate of 0.02 mm/s (with the exception of one girth weld specimen for each thickness, which were tested at 0.002 mm/s). Analysis of the data revealed some general differences among the weld specimens. The tests where the crack ran perpendicular to the girth weld demonstrated changes in CTOA and crack growth rate as the crack moved through the base metal, HAZ, and weld material. We observed the values for CTOA increasing and the crack propagation slowing as the crack moved through the weld and approached the fusion line. The stress field appeared to be strongly influenced by the thin HAZ, the fusion line, and the tougher base material. Consequently, the CTOA of the HAZ associated with the girth weld was larger than that of the seam-weld HAZ. It was not possible to obtain CTOA data for the seam weld, with the crack parallel within the weld, because the crack immediately diverted out of the stronger weld material into the weaker HAZ. CTOA values from both girth welds and seam-weld HAZ were smaller than those of the base material. The 8 mm thick specimens consistently produced larger CTOA values than their 3 mm counterparts, introducing the possibility that there may be limitations to CTOA as a material property. Further tests are needed to determine whether a threshold thickness exists below which the constraints and stress field are sufficiently changed to affect the CTOA value.

Effects of Loading Mode on Brittle Fracture of X70 Pipe Girth Welds

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel
Keyword(s):  
Brittle Fracture ◽  
Weld Metal ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Large Diameter ◽  
Outer Diameter ◽  
Ductile Crack ◽  
Single Edge ◽  
Brittle Crack ◽  
Girth Welds

A series of single-edge notched tension (SENT or SE(T)) and single-edge notched bend (SENB or SE(B)) testing was carried out at −15 °C using B × B specimens machined from two API X70 large diameter pipeline girth welds. An initial notch was placed either on the heat-affected zone (HAZ) or the weld metal center from the outer diameter side of pipe to simulate a circumferential surface flaw. SE(T) and SE(B) tests were performed according to the CANMET procedure and ASTM E1820, respectively. For all HAZ SE(B) specimens machined from one pipe, ductile cracks initially propagated away from the fusion line and toward the base metal side due to asymmetric deformation, and then pop-in (i.e., the initiation and arrest of a brittle crack) occurred after ductile crack growth of approximately 1 mm, where the crack reached around the intercritical heat-affected zone. HAZ SE(T) specimens also showed that the ductile crack propagation deviated toward the base metal side, but an unstable brittle crack extension was not observed from any SE(T) specimens as opposed to SE(B) specimens. None of the weld metal SE(T) and SE(B) specimens showed pop-in or brittle fracture at −15 °C or room temperature. The difference in test results, for the same material, is associated with the different constraint levels in the two loading modes, taking into account that pop-ins were triggered in high-constraint SE(B) tests, while it was not the case for low-constraint SE(T) tests.

Effects of Loading Mode on Brittle Fracture of X70 Pipe Girth Welds

2016 ◽  
Author(s):  
Dong-Yeob Park ◽  
Jean-Philippe Gravel
Keyword(s):  
Brittle Fracture ◽  
Weld Metal ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Large Diameter ◽  
Outer Diameter ◽  
Ductile Crack ◽  
Single Edge ◽  
Brittle Crack ◽  
Girth Welds

A series of single-edge notched tension (SENT or SE(T)) and single-edge notched bend (SENB or SE(B)) testing was carried out at −15°C using BxB specimens machined from two API X70 large diameter pipeline girth welds. An initial notch was placed either on the heat-affected zone (HAZ) or the weld metal center from the outer diameter side of pipe to simulate a circumferential surface flaw. SE(T) and SE(B) tests were performed according to the CANMET procedure and ASTM E1820, respectively. For all HAZ SE(B) specimens machined from one pipe, ductile cracks initially propagated away from the fusion line and toward the base metal side due to asymmetric deformation, and then pop-in (i.e., the initiation and arrest of a brittle crack) occurred after ductile crack growth of approximately 1 mm where the crack reached around the inter-critical heat-affected zone. HAZ SE(T) specimens also showed that the ductile crack propagation deviated toward the base metal side, but an unstable brittle crack extension was not observed from any SE(T) specimens as opposed to SE(B) specimens. None of the weld metal SE(T) and SE(B) specimens showed pop-in or brittle fracture at −15°C or room temperature. The difference in test results, for the same material, is likely due to the different constraint levels in the two loading modes. While pop-ins were triggered in high-constraint SE(B) tests, it was not the case for the low-constraint SE(T) tests. This paper presents these observations and discussion.

Influence of Alloying Elements on the Toughness in the HAZ of DSAW-Welded Large-Diameter Linepipes

2012 ◽  
Author(s):  
Charles Stallybrass ◽  
Olga Dmitrieva ◽  
Andreas Liessem ◽  
Jens Schröder
Keyword(s):  
Arc Welding ◽  
Large Diameter ◽  
Base Material ◽  
Processing Parameters ◽  
Submerged Arc Welding ◽  
Alloying Elements ◽  
Fusion Line ◽  
Steel Composition ◽  
Submerged Arc ◽  
Haz Toughness

There is a strong interest worldwide to transport large gas volumes from remote areas and hostile environments to the market. Pipe producers are therefore faced with increasingly demanding requirements both with regard to the toughness of the base material and the heat-affected zone. The toughness of the base material depends primarily on the steel composition and the TM processing conditions. Impressive levels of toughness in the base material were achieved by extensive alloy and process development over the past decades. These were realised by balancing the steel composition and processing parameters to give an optimum microstructure with a low grain size and homogeneous distribution of phases. During double submerged arc welding (DSAW) in the production of large-diameter linepipes, the heat-affected zone (HAZ) undergoes severe changes in the microstructure that include grain coarsening by about one order of magnitude and phase transformation during cooling and intercritical reheating. These have a negative impact on the toughness close to the fusion line. The higher austenite grain size close to the fusion line leads to a coarser structure after the phase transformation with larger carbon-rich M/A-phase particles than are typically observed in the base material in the as-rolled condition. This causes a drop of the toughness close to the fusion line compared to the base material. Classically, the carbon equivalent is an empirical measure for the weldability of steels and is known to correlate with the maximum hardness. However, its purpose is not to reflect the effect of individual alloying elements on the HAZ-toughness. The present paper addresses the relationship between base material composition and the HAZ-toughness of linepipe steels. An experimental investigation was carried out at EUROPIPE GmbH in cooperation with Salzgitter Mannesmann Forschung GmbH in which the chemical composition of laboratory heats was varied systematically. These heats were thermomechanically rolled to a wall thickness of 30 mm and subsequently used for submerged arc welding trials. The processing parameters during rolling and welding were held constant in the trials in order to ensure that the effect of the alloying elements could be isolated. The fusion line toughness was tested at −30°C and the microstructure was investigated by high-resolution scanning electron microscopy. This was complemented by microstructure investigations in the HAZ of large-diameter pipe material between the X65 and X80 strength levels. It was found that the influence of alloying elements on the HAZ-toughness is only reflected to some degree by the commonly used carbon equivalents, especially at similar strength levels. The results of the investigation were used for optimisation of the HAZ-toughness in production.

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