Magnetic force microscopy of a carburized ethylene pyrolysis tube

Stevens, Kenneth N.; Parbhu, A; Soltis, Jared; Stewart, David B.

doi:10.1088/0022-3727/36/2/315

Cited by 21 publications

(16 citation statements)

References 10 publications

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“…The element segregation through the HPM tube wall has been quantified using energy dispersive X-ray analysis (EDAX) linescans on a SEM [2]. The measured compositions were compared to Curie temperature data for iron, nickel and chromium alloys.…”

Section: Resultsmentioning

confidence: 99%

“…1 is one of a larger set that shows a transition from paramagnetic (light grey) to ferromagnetic (dark) material [2]. Ferromagnetic material first forms in the chromium depleted volume around the paramagnetic carbides embedded in an otherwise paramagnetic matrix.…”

Section: Resultsmentioning

confidence: 99%

“…This enables planned replacement of tubes before failure occurs in service. The magnetic force microscopy (MFM) images are compared to conventional atomic force microscope (AFM) micrographs [2].…”

Section: Introductionmentioning

confidence: 99%

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Magnetic force microscopy and cross-sectional transmission electron microscopy of carburised surfaces

Stevens¹,

Parbhu

Soltis

2004

Current Applied Physics

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Magnetic force microscopy and cross-sectional transmission electron microscopy of carburised surfaces

Stevens¹,

Parbhu

Soltis

2004

Current Applied Physics

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“…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.

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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.

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“…Since there are more chromium carbides formed at the carburization zone, so the chromium of matrix decreases and the field structure is rich in Ni or Fe–Ni. When the Cr content of the matrix in Fe–Ni–Cr alloys decreases to 15%, it is on the boundary between ferromagnetic and paramagnetic; when the Cr content reaches to 11%, the matrix should be ferromagnetic at room temperature; while, with the Cr content above 18%, it would be paramagnetic (Majumbar, 1984; Stevens et al, 2003). The magnetism of the furnace tubes is related to the depth of carburization zone.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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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.

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Magnetic force microscopy of a carburized ethylene pyrolysis tube

Cited by 21 publications

References 10 publications

Magnetic force microscopy and cross-sectional transmission electron microscopy of carburised surfaces

Magnetic force microscopy and cross-sectional transmission electron microscopy of carburised surfaces

Microstructure and Carburization Detection in HP Alloy Pyrolysis Tubes

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

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