Effects of weld strength mismatch on J and CTOD estimation procedure for SE(B) specimens

This work examines the effect of weld strength mismatch on fracture toughness measurements defined by J and CTOD fracture parameters using single edge notch bend (SE(B)) specimens. A central objective of the present study is to enlarge on previous developments of J and CTOD estimation procedures for welded bend specimens based upon plastic eta factors (eta) and plastic rotational factors (r (p) ). Very detailed non-linear finite element analyses for plane-strain models of standard SE(B) fracture specimens with a notch located at the center of square groove welds and in the heat affected zone provide the evolution of load with increased crack mouth opening displacement required for the estimation procedure. One key result emerging from the analyses is that levels of weld strength mismatch within the range +/- 20% mismatch do not affect significantly J and CTOD estimation expressions applicable to homogeneous materials, particularly for deeply cracked fracture specimens with relatively large weld grooves. The present study provides additional understanding on the effect of weld strength mismatch on J and CTOD toughness measurements while, at the same time, adding a fairly extensive body of results to determine parameters J and CTOD for different materials using bend specimens with varying geometries and mismatch levels.

Further results in J and CTOD estimation procedures for SE(T) fracture specimens - Part I: Homogeneous materials

This study provides further developments of the evaluation procedure for J and CTOD in SE(T) fracture specimens based on plastic eta-factors and load separation analysis. Non-linear finite element analyses for plane-strain and 3-D models provide the relationship between plastic work and crack driving forces which define the eta-values. Further analyses based on the load separation method define alternative eta-values for the analyzed specimen configurations. Overall, the present results provide improved estimation equations for J and CTOD as a function of loading condition (pin load vs. clamp ends), crack geometry and strain hardening properties. (C) 2011 Elsevier Ltd. All rights reserved.

The crack tip strain field of AISI 4340 - Part II - Experimental measurements

Crack tip strain maps have been measured for AISI 4340 high strength steel. No significant creep was observed. The measured values of CTOD were greater than expected from the HRR model. Crack tip branching was observed in every experiment. The direction of crack branching was in the same direction as a major ridge'' of epsilon(yy) strain, which in turn was in the same direction as predicted by the HRR model. Furthermore, the measured magnitudes of the epsilon(y)y strain in this same direction were in general greater than the values predicted by the HRR model. This indicates more plasticity in the crack tip region than expected from the HRR model. This greater plasticity could be related to the larger than expected CTOD values. The following discrepancies between the measured strain fields for AISI 4340 and the HRR predictions are noteworthy: (1) The crack branching. (2) Values of CTOD significantly higher than predicted by HRR. (3) The major ridge'' of epsilon(yy) strain an angle of about 60 degrees with the direction of overall propagation of the fatigue precrack, in which the measured magnitudes of the epsilon(yy) strain were greater than the values predicted by the HRR model. (4) Asymmetric shape of the plastic zone as measured by the epsilon(yy) strain. (5) Values of shear strain gamma(xy) significantly higher than predicted by the HRR model. (C) 1999 Kluwer Academic Publishers.

Suurlujuusterästen hitsausliitoksen HAZ -vyöhykkeen murtumissitkeys

Suurlujuusterästen käyttö erityisesti auto-, kuljetusväline- ja nostovälineteollisuudessa on lisääntynyt jo pidemmän aikaa. Teräsvalmistajat kehittävätkin jatkuvasti lujempia ja paremmin hitsattavia teräslaatuja markkinoille. Lujempia teräksiä käyttämällä on mahdollista saavuttaa materiaali- ja painosäästöä, jolla on suora vaikutus hyötykuorman lisääntymiseen, polttoainetalouteen, suoritusarvoihin ja jopa valmistuskustannuksiin. Tässä diplomityössä tutkittiin kahdeksan eri suurlujuusteräksen ja kolmen kulutusteräksen HAZ-alueen murtumissitkeyttä kolmella eri lämmöntuonnilla tehdyllä hitsauksella. Suurlu-juusterästen myötölujuustaso vaihteli 650 MPa:n ja 700 MPa:n välillä, ja kulutusteräksillä vastaavasti 800 MPa:n ja 1000 MPa:n välillä. Murtumissitkeyskokeet tehtiin standardoidun CTOD-testausmenetelmän mukaisesti -40 °C lämpötilassa. Kokeissa käytettiin 10 mm x 5 mm SE(B)-kolmipistetaivutussauvoja. Koetuloksia voidaan käyttää apuna arvioitaessa eri teräslaatujen hitsauksellista sopivuutta erityisesti väsyttävän kuormituksen alaiseen rakenteeseen. Kokeiden tuloksena saatiin jokaiselle materiaalille neljä CTOD-arvoa. Kolmella eri lämmöntuonnilla tehtyjen koesauvojen lisäksi mitattiin ilman hitsausta olevista koesauvoista perusaineen murtumissitkeys. Yhteensä CTOD-koe tehtiin 44 koesauvalle ja lisäksi muutamalle harjoitussauvalle. Testattavien kappaleiden suuren määrän takia kokeet voitiin tehdä jokaiselle materiaali- lämmöntuonti- yhdistelmälle ainoastaan yhteen kertaan.

MRT letter: Extended depth from focus reconstruction method for stretch zone measurement in 15-5PH steel

The stretch zone width (SZW) data for 15-5PH steel CTOD specimens fractured at -150 degrees C to + 23 degrees C temperature were measured based on focused images and 3D maps obtained by extended depth-of-field reconstruction from light microscopy (LM) image stacks. This LM-based method, with a larger lateral resolution, seems to be as effective for quantitative analysis of SZW as scanning electron microscopy (SEM) or confocal scanning laser microscopy (CSLM), permitting to clearly identify stretch zone boundaries. Despite the worst sharpness of focused images, a robust linear correlation was established to fracture toughness (KC) and SZW data for the 15-5PH steel tested specimens, measured at their center region. The method is an alternative to evaluate the boundaries of stretched zones, at a lower cost of implementation and training, since topographic data from elevation maps can be associated with reconstructed image, which summarizes the original contrast and brightness information. Finally, the extended depth-of-field method is presented here as a valuable tool for failure analysis, as a cheaper alternative to investigate rough surfaces or fracture, compared to scanning electron or confocal light microscopes. Microsc. Res. Tech. 75:11551158, 2012. (C) 2012 Wiley Periodicals, Inc.

Estudo das propriedades mecânicas de aços microligados produzidos por laminação controlada seguida de resfriamento acelerado para tubos API/DNV usado no projeto pré-sal

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influência do tratamento térmico de alívio de tensões assoaciado à elevada energia de soldagem na tenacidade da zona termicamente afetada de um aço TMCP microligado aplicado em estruturas off-shore

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Determinação experimental da tenacidade à fratura em baixas temperaturas de tubos de aço API 5L X70

Because of the great metallurgical advances, the welded tubes by HF / ERW (High Frequency / Electrical Resistance Welding) have played a more active role in the oil and gas, gradually replacing tubes produced by other processes (UOE, SAW, and others) to deep water applications, in high and extremely low temperatures, highpressure conditions and in highly corrosive environments. However, studies have revealed that defects in the welded joints are in one of main causes of failures in pipelines. Associated with damage external and the stringent requirements of this sector, the welded joints become particularly critical for his toughness and the determination of this particular property is fundamental. This study aims to evaluate the toughness of the HF / ERW pipes in HSLA steel API X70 class, used in pipelines transport systems of gas and oil from data obtained with CTOD tests (Crack Tip Opening Displacement). The main objectives of this project are: mechanical and microstructural characterization of steels API X70 manufactured in Brazil; and evaluation of the toughness of weld process by HF / ERW steel API X70 national. After having the tests done, mechanical, chemical and metallurgical, we have the conclusion that those pipe are in agreement to API 5L 42ª edition for X70MO and the toughness behaves like the expected

Investigação experimental da tenacidade em tubos de aço API 5L X70 soldados pelo processo HF/ERW

Studies about structural integrity are very important when it desires to prevent disasters associated with flaws inherent in materials used in structural components. The welded joints in steel pipes used to conduction and distribution of oil and gas correspond to the regions most susceptible to flaw. Aiming to contribute to this research line, the present study was designed to assess experimentally the structural integrity of welded joints in steel pipes API 5L X70 used in pipeline systems. This assessment is given from tests of CTOD, whose aim is simulate in laboratory the real behaviour of crack from of his propagation on the welded joint obtained by high frequency electric resistance welding. In this case, the analyses are performed from specimens SE(B) obtained directly of steel pipe API 5L X70. The proposed methodology involves tests of CTOD at lower temperature, in order to assess the toughness of material in critical operation conditions. From performance of CTOD tests, was possible assess the toughness of welded joints in terms of quantity through CTOD parameter and in terms of quality from behaviour of curve load versus CMOD. In this study, also, sought to compare CTOD’s results obtained through rules ASTM E1820 (2008) and BS 7448 (1991). Although the two standards cited previously have adopted different parameters to calculated the value of CTOD, concluded that the values of CTOD tend to converge for a common value

Análise microestrutural de tubos API P110, para prospecção de petróleo e gás, soldados pelo processo HF/ERW

On the grounds of the great advances achieved over recent years, the process HF/ERW (High-Frequency/Electric Resistance Welding)welded pipe have played an active role in the oil and gas industry for deep water applications, at high and extremely low temperatures, under high pressure and in highly corrosive environments, gradually replacing manufactured pipes by other processes. However, studies have shown that defects in the welded joints are a the leading causes of pipelines failures, which has required the determination of toughness values in this region, in compliance with the strict recommendations of the codes and standards with manufacturers and construction companies, on the oil and gas sector. As part of the validation process required toughness values, this research project focuses on a microstructural analysis in HF / ERW tubes microalloyed, steel grade API 5CT P110, designed to explore oil and gas in deep waters, the subject of strategic relevance to the country because of the recent discoveries in the Santos mega fields: Tupi and Libra (pre-salt). In this scientific work will be presented and discussed the results of mechanical tensile and Charpy, a few CTOD tests curves (showing the trend of toughness values to be obtained), and the microstructures of the base material obtained by optical microscopy, with special emphasis on the formation of nonmetallic inclusions in the welded joint

Avaliação da tenacidade à fratura em juntas soldadas circunferenciais de tubulações de processo

This work aims to analyze the toughness of a welded joint in the presence of a crack through the analysis of maximum tension the material can withstand the presence of this type of defect, since a discontinuity is likely to occur in this type of joint and its detection and its design is simple, using non-destructive testing techniques. The study will be conducted through the CTOD test - Crack-Tip Opening Displacement, with type specimens SE (B) - Single Edge Bend taken from a weld in the L-C position in relation to the length (longitudinal axis) of a test tube. The main idea is to simulate the welding conditions for the manufacture of industrial pipes, made in boiler shops (pipe-shop) within petrochemical plants. These pipes are often subject to operation with flammable and toxic subjected to high pressures and temperatures, where one can break the line can cause irreparable damage to the plant, the environment and the health of surrounding communities. With this study we evaluate whether the weld metal has the same properties as fracture toughness of the base material. This study shows the importance of using a qualified welding procedure for performing quality welds while maintaining the properties of the fracture toughness of the base metal. It was found from the results of tests using a welding procedure described for carrying out welding ensures mechanical properties very close to the base metal, which in terms of design is great, since one can ensure that the weld will the same characteristics of the base metal specified for the assembly of the pipe

Análise microestrutural de tubos API N80 soldados pelo processo HF/ERW para prospecção de petróleo e gás

On the grounds of the great advances achieved over recent years, the process HF/ERW (High-Frequency/Electric Resistance Welding)welded pipe have played an active role in the oil and gas industry for deep water applications, at high and extremely low temperatures, under high pressure and in highly corrosive environments, gradually replacing manufactured pipes by other processes. However, studies have shown that defects in the welded joints are a the leading causes of pipelines failures, which has required the determination of toughness values in this region, in compliance with the strict recommendations of the codes and standards with manufacturers and construction companies, on the oil and gas sector. As part of the validation process required toughness values, this research project focuses on a microstructural analysis in HF / ERW tubes microalloyed, steel grade API 5CT N80, designed to explore oil and gas in deep waters, the subject of strategic relevance to the country because of the recent discoveries in the Santos mega fields: Tupi and Libra (pre-salt). In this scientific work will be presented and discussed the results of mechanical tensile and Charpy, a few CTOD tests curves (showing the trend of toughness values to be obtained), and the microstructures of the base material obtained by optical microscopy, with special emphasis on the formation of non-metallic inclusions in the welded joint

A study of acoustic emission technique for concrete damage detection

The Acoustic emission (AE) technique, as one of non-intrusive and nondestructive evaluation techniques, acquires and analyzes the signals emitting from deformation or fracture of materials/structures under service loading. The AE technique has been successfully applied in damage detection in various materials such as metal, alloy, concrete, polymers and other composite materials. In this study, the AE technique was used for detecting crack behavior within concrete specimens under mechanical and environmental frost loadings. The instrumentations of the AE system used in this study include a low-frequency AE sensor, a computer-based data acquisition device and a preamplifier linking the AE sensor and the data acquisition device. The AE system purchased from Mistras Group was used in this study. The AE technique was applied to detect damage with the following laboratory tests: the pencil lead test, the mechanical three-point single-edge notched beam bending (SEB) test, and the freeze-thaw damage test. Firstly, the pencil lead test was conducted to verify the attenuation phenomenon of AE signals through concrete materials. The value of attenuation was also quantified. Also, the obtained signals indicated that this AE system was properly setup to detect damage in concrete. Secondly, the SEB test with lab-prepared concrete beam was conducted by employing Mechanical Testing System (MTS) and AE system. The cumulative AE events and the measured loading curves, which both used the crack-tip open displacement (CTOD) as the horizontal coordinate, were plotted. It was found that the detected AE events were qualitatively correlated with the global force-displacement behavior of the specimen. The Weibull distribution was vii proposed to quantitatively describe the rupture probability density function. The linear regression analysis was conducted to calibrate the Weibull distribution parameters with detected AE signals and to predict the rupture probability as a function of CTOD for the specimen. Finally, the controlled concrete freeze-thaw cyclic tests were designed and the AE technique was planned to investigate the internal frost damage process of concrete specimens.

Fracture propagation and stress corrosion in the case of dissimilar laser hybrid welded joints

The paper addresses the fracture propagation and stress corrosion behaviour of laser hybrid welds achieved between low carbon steel and stainless steel thin sheets. The crack propagation within these overmatched in strength welds was investigated by crack tip opening displacement (CTOD) on CT specimens notched transverse to the weld. A Digital Image Correlation System was used to qualify and estimate the initial crack length obtained by fatigue. The results are associated with the fractographic examinations of various regions of laser hybrid joints. Stress corrosion behaviour of the joint is also discussed.

Cleavage initiation in the intercritically reheated coarse-grained heat affected zone:Part II. Failure criteria and statistical effects

In part 1 of this article, cleavage initiation in the intercritically reheated coarse-grained heat affected zone (IC CG HAZ) of high-strength low-alloy (HSLA) steels was determined to occur between two closely spaced blocky MA particles. Blunt notch, crack tip opening displacement (CTOD), and precracked Charpy testing were used in this investigation to determine the failure criteria required for cleavage initiation to occur by this mechanism in the IC CG HAZ. It was found that the attainment of a critical level of strain was required in addition to a critical level of stress. This does not occur in the case of high strain rate testing, for example, during precracked Charpy testing. A different cleavage initiation mechanism is then found to operate. The precise fracture criteria and microstructural requirements (described in part I of this article) result in competition between potential cleavage initiation mechanisms in the IC CG HAZ.