Carbide composition and stress measurement in ethylene pyrolysis tubes
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Date
2010-02-05
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Publisher
Australian Institute of Physics
Abstract
Ethylene is important in the production of polyethylene, used in thin film packaging, piping and cable sheathing. It is produced by steam cracking of naptha, LPG or ethane at temperatures around 950°C at high flow velocities. Carburisation of ethylene pyrolysis tubes (typically of nominal composition 31%Fe, 37%Ni and 25%Cr) causes a loss in weldability, corrosion resistance and ductility, and provides a source of micro-cracking. Plant operators prefer to replace tubes at planned outages and are interested in remaining life assessments
assisted by description and modelling of the progress of carburisation. The powder diffraction beamline at the Australian Synchrotron has been used to radially scan mounted and polished tube sections prepared from ex-service carburised tubes. Radial dependence of carbide phases in the tubes is being quantified using Bruker TOPAS software for whole pattern line fitting. Composition analysis and microscopy is being used to create a representative microstructure in Abaqus Finite Element Analysis (FEA) models and to interpret non-destructive eddy current measurements [1] of carburisation. The austenite diffracting planes give a peak shift response to stress that is anisotropic and is being interpreted with FEA based crystal plasticity models. Neutron diffraction at the Kowari beamline at OPAL (Open Pool Australian Lightwater reactor) was used to measure strain in unsectioned tubes at room temperature. This was compared to FEA models of the strain created by differential thermal expansion between carbide phases and austenite, assuming creep relaxation at normal tube operating
temperature.
Description
Keywords
Carbides, Ethylene, Tubes, Polyethylenes, Cables, Ethane, Temperature range 0400-1000 K, Weldability, Corrosion, Cracking, Finite element method
Citation
Stevens, K. J., Ingham, B., Ryan, M., Luzin, V., & Cheong, K. (2010). Carbide composition and stress measurement in ethylene pyrolysis tubes. Poster presented to the 34th Annual Condensed Matter and Materials Meeting 2010, Waiheke Island Resort, Waiheke, Auckland, New Zealand 2 - 5 February 2010. Retrieved from: https://physics.org.au/wp-content/uploads/cmm/2010/