I would say that the thermal gradients are important in the stress profile of the tube and could easily lead to failure in combination with the pressure. The alumina has some mechanical properties, including fracture toughness, since it is not an jnfinitely ducctile material. Small defects in the alumina will accumulate hydrogen because of its mobility at temperature and form small gas bubbles at the defects. This is a common issue with hydrogen embrittlement of weld metal and base metal that creates high internal gas pressures at the discontinuities and can lead to gross failure of the base metal in combination with other stresses. Fracture mechanics design calculation applicable to the alumina would allow designing the tube to avoid failure, if failure of the tube is not wanted.
The analyses of determination of embrittlement is an easy problem with the right software and knowledge of defects in the alumina and its hydrogen permeability with temperature. Acoustic emission sensors could be attached to the alumina to monitor the micro cracking to determine the location of defects and high stress regions. Such would be a desirable pre -test evaluation to understand the condition of the alumina reactor tube, hydrogen permeability with temperature and the effects of thermal stresses and temperature gradients. Bob Sent from Windows Mail From: Mark Jurich Sent: Sunday, February 8, 2015 2:56 AM To: [email protected] I believe there maybe an error in this pressure estimate and that the calculated pressure will be exactly half of 19,861 psi (i.e., 9,930.5 psi). Although 0.0141 moles of Hydrogen are released, 0.00706 moles of Hydrogen Gas (H2) are released. I don't believe that free H atoms/ions contribute to the gas pressure in the free volume of the cell, and that the actual gas there is H2 Gas. Please see the following post for the details: https://www.mail-archive.com/[email protected]/msg101557.html Mark Jurich -----Original Message----- From: Craig Haynie Sent: Sunday, February 08, 2015 1:44 AM To: [email protected] Subject: Re: [Vo]:Re: Dog Bone Project Pressure inside the dog bone is calculated to have been near 19,861 psi at the time of failure. https://docs.google.com/document/d/1BWYbi6tBHcjZ4PyQ0BaWn-G1NkdQdkirb-_Qx2HypKs/edit Craig
