Characterization of carburization of HP steels by non destructive magnetic testing

Silva, I.C. da; Silva, R.S. da; Rebello, J. M. A.; Bruno, A. C.; Silveira, Tito Fernando da

doi:10.1016/j.ndteint.2006.03.004

Cited by 24 publications

(9 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3c). At the same time, the Cr content is above 15% in the center zone of Cr35Ni45Nb alloy tube and the state is still paramagnetic (Takahashi et al, 2004; da Silva et al, 2006) (Fig. 8b).…”

Section: Discussionmentioning

confidence: 91%

“…This carbide precipitation brings about a decrease in the Cr concentration in the matrix. So with the increase of carburization, they gradually become ferromagnetic (Stevens et al, 2003; da Silva et al, 2006; Silva et al, 2007; Silva et al, 2008). In order to investigate the magnetism of the furnace tube after a long-term service, the magnetic hysteresis loop of the furnace tube was tested across the thickness at room temperature.…”

Section: Resultsmentioning

confidence: 99%

“…Silva (Silva et al, 2007; Silva et al, 2008) has studied the carburization of ethylene pyrolysis tubes by magnetic measurements. da Silva et al (2006) could successfully characterize the carburization of HP steels by nondestructive magnetic testing. Moreover, Kasai et al (2010) have employed a C core probe and a magnetizer for analyzing such magnetic carburized layers.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The Relationship Between Magnetism and Microstructure of Ethylene Pyrolysis Furnace Tubes after a Long-term Service

et al. 2018

View full text Add to dashboard Cite

The magnetism and microstructure of Cr25Ni35Nb and Cr35Ni45Nb alloy tubes after 5 years of service were investigated in this paper. The saturation magnetization of the Cr25Ni35Nb alloy tube in the thickness direction is more than 20 emu/g, and the tube becomes ferromagnetic. The inner and outer walls of Cr35Ni45Nb alloy tubes also become ferromagnetic. But the saturation magnetization of the Cr35Ni45Nb alloy tubes approaches to zero in the center zone. The primary carbides M7C3 and NbC are changed into M23C6 and G phase at the outer region of the furnace tube. However, the M23C6-type carbides were replaced by carbon-rich carbides M7C3 at the carburization zone. Cr-depleted zones are formed at the inner and outer walls of the furnace tubes owing to oxidation. Carburization and oxidation reduce the Cr content of the matrix. Accordingly, the saturation magnetization is very high at the carburization zone and Cr-depleted zone. The magnetism of Cr25Ni35Nb and Cr35Ni45Nb alloy tubes has a high correlation with the Cr content of the matrix. Carburization and oxidation are the main reasons that make the paramagnetic ethylene pyrolysis furnace tube change to ferromagnetic.

show abstract

“…3c). At the same time, the Cr content is above 15% in the center zone of Cr35Ni45Nb alloy tube and the state is still paramagnetic (Takahashi et al, 2004; da Silva et al, 2006) (Fig. 8b).…”

Section: Discussionmentioning

confidence: 91%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Relationship Between Magnetism and Microstructure of Ethylene Pyrolysis Furnace Tubes after a Long-term Service

et al. 2018

View full text Add to dashboard Cite

show abstract

“…The precipitation and growth of chromium carbides causes chromium depletion in the austenitic matrix. With increasing carburization, the matrix composition tends toward the binary Fe-Ni composition, and the matrix becomes progressively more ferromagnetic [2,5,7,[30][31][32]. The change in matrix chromium content, measured at a distance of 10 lm from the primary chromium carbide network, is shown in Fig.…”

Section: Chromium Depletion In the Matrix And The Paramagnetic To Fermentioning

confidence: 99%

Microstructure and Carburization Detection in HP Alloy Pyrolysis Tubes

McLeod

Bishop

Stevens

et al. 2015

Metallogr. Microstruct. Anal.

View full text Add to dashboard Cite

A highly carburized HP40-Mod alloy ethylene pyrolysis tube was characterized by means of scanning electron microscopy with backscatter electron imaging, electron back-scattered diffraction, energy dispersive spectroscopy, and etching using the NACE International Standard Test Method for evaluation of carburization of ethylene pyrolysis tubes. The response of the tube to eddy current non-destructive testing was measured using the carburization crawler under development at Quest Integrity NZL Ltd. The matrix was significantly depleted of chromium, as low as 4 wt% Cr at the inner wall. M 23 C 6 carbides transformed to M 7 C 3 at the inner wall region and NbC carbides partially transformed to the chromium-rich g-carbide at the outer wall region, both of which likely contributed to the chromium depletion of the matrix. The present results indicate that the NACE etchant attacks the austenitic matrix where chromium content is below approximately 12wt%. A comparison to other ex-service tubes indicates that matrix chromium content and the location of the M 23 C 6 /M 7 C 3 transformation front are useful microstructural characteristics for interpreting eddy current NDT response.

show abstract

“…The growth of chromium carbides and other chromium-rich phases due to carbon ingress results in a depletion of chromium in the matrix. In the as-cast condition the matrix is paramagnetic, but as carburization progresses it tends towards the binary Fe-Ni system and becomes progressively more ferromagnetic [3,4,[6][7][8]. The change in bulk permeability of the tube is measured by the eddy current system.…”

mentioning

confidence: 99%

Microstructural Characterization and Image Analysis in Ex-Service Ethylene Pyrolysis Tubes

et al. 2015

View full text Add to dashboard Cite

Ethylene is used extensively in the production of plastics, cabling, and automotive products. It is typically produced by the thermal cracking (pyrolysis) of more complex hydrocarbons, such as naphtha or ethane, at 950 to 1100°C inside HP alloy tubes (25%Cr-35%Ni) within an ethylene pyrolysis furnace. The main contributor to the failure of ethylene pyrolysis tubes is carburization of the tubes, which causes an increase in internal volume, a loss in weldability and a reduced ability to withstand thermal cycles [1][2][3][4]. Knowing the level of carburization of a tube in-situ can assist in remaining life estimates based on Finite Element Modeling, thermography, and fracture mechanics. Due to the changes in the microstructure and magnetic properties of the tubes over their service life, the level of carburization can be detected non-destructively using eddy current probes [3] and a tube crawler system [5]. However, the eddy current system requires calibration on ex-service tubes that have had their microstructure, mechanical properties and magnetic response characterized.The growth of chromium carbides and other chromium-rich phases due to carbon ingress results in a depletion of chromium in the matrix. In the as-cast condition the matrix is paramagnetic, but as carburization progresses it tends towards the binary Fe-Ni system and becomes progressively more ferromagnetic [3,4,[6][7][8]. The change in bulk permeability of the tube is measured by the eddy current system. As such, the volume fractions of the phases that contribute to the matrix chromium depletion and the distribution of these phases across the tube wall are of interest. The volume fractions and distributions are being characterized by way of imaging the tube microstructure along radial wall profiles, and using a combination of two programs, ilastik and FIJI, for the segmentation and processing of the images. ilastik is a free software package that enables automated classification and segmentation of batches of images [9].Initially, BSE (backscatter electron) images were proposed for image analysis, due to their high resolution, wide range of grayscale values for differentiating phases, and relatively short collection time. However, one major feature of BSE images of ex-service tubes proved to be detrimental to the success of automated segmentation using ilastik. A "watermark" effect is often visible in the austenitic matrix of highly carburized tubes when imaging in BSE mode, causing significant gradients in grayscale. Another phase often present in the microstructure of ex-service tubes, the η -carbide, also exhibits gradients in grayscale across the phase regions. As a result, automated segmentation of the BSE images of highly carburized tubes in ilastik proved to be impossible, as ilastik is unable to distinguish the η-carbide from regions of the matrix that exhibit this "watermark" effect. Despite testing numerous variations in the mechanical polishing parameters, the "watermark" effect was unable to be minimized. It is possible that it is a feat...

show abstract

Characterization of carburization of HP steels by non destructive magnetic testing

Cited by 24 publications

References 8 publications

The Relationship Between Magnetism and Microstructure of Ethylene Pyrolysis Furnace Tubes after a Long-term Service

The Relationship Between Magnetism and Microstructure of Ethylene Pyrolysis Furnace Tubes after a Long-term Service

Microstructure and Carburization Detection in HP Alloy Pyrolysis Tubes

Microstructural Characterization and Image Analysis in Ex-Service Ethylene Pyrolysis Tubes

Contact Info

Product

Resources

About