The devil is in the details. IMHO, the primary cause of the failure was not pressure related. When the video of the event is viewed at 1/4 speed, at 2.29 a white spot caused by high heat buildup first appears in the field of scarlet near the point of failure. This bit of evidence shows that the power produced at 2.29 is greatly increasing. This overheat reaction is not caused by a short circuit in the heater element because the power is steady at that time. As 2:29 progresses the white spot grows in size.
The area of white expands throughout the 2.30 timeframe and at the end of that time period, the power to the heater surges as the heater begins to short out. The exploding sound occurs at the end of 2:30. The area of white is at its maximum at the end of 2.30 and begins to return to scarlet stating at 2:31 as hydrogen is venting from the tube. The power going through the heater is at its maximum at 2:32 until 2.34. The power is minimized at 2:35. The heater is completely shorted at 2:55 with 0 current flow. There is a fration of a second starting at 2:29 before the tube fractured as marked by the sound of explosion near the end of 2:30 when high heat is building up at the point of failure. The hydrogen detection instrument sounds produced by venting hydrogen does not begin until 2.30 after the sound of the explosion. This failure was caused by explosive overheating. On Sun, Feb 8, 2015 at 4:12 PM, a.ashfield <[email protected]> wrote: > Jones Beene wrote: > > "If the failure was only pressure-related, it would happen near the middle of > the cavity, which is the region of least structural strength against internal > pressure - but since the failure (apparently) happened at almost exactly the > place where the temperature gradient would be maximized – that explanation > seems to fit the circumstances." > > I find it far more likely to be determined by a defect in the Al2O3 tube. The > ceramic is very brittle. > I have had those thermocouple tubes break for no apparent reason when > inserting them in a furnace. > They also require handling with reasonable care. > >
