High Temperature Excursion on a Reactor Tube
High Temperature Excursion on a Reactor Tube
(OP)
I have a reactor tube that (during an excursion) saw pressures of about 43.5ksi (300MPa) and reached 2372F (1300C) for approximately 45 seconds (very worst case scenario). The reactor tube is AISI4340 material and approximately 2" thick (2" ID). Reaction was instantly killed after that excursion and temperature and pressure came down to ambient and zero, respectively, in a question of minutes.
I have two questions:
- How deep/ thick into the wall of the tube could have gotten above 727C during that period? (there must be an equation for this?) Assume the reactor tube outside surface is chilled with water at 20C and there is no fouling on the inside of the tube.
- Could the internal pressure on the pipe have any effect on the melting point of the steel?
Thanks!
I have two questions:
- How deep/ thick into the wall of the tube could have gotten above 727C during that period? (there must be an equation for this?) Assume the reactor tube outside surface is chilled with water at 20C and there is no fouling on the inside of the tube.
- Could the internal pressure on the pipe have any effect on the melting point of the steel?
Thanks!





RE: High Temperature Excursion on a Reactor Tube
You can approximate a mean wall temperature profile IF what you describe is correct in that the OD surface of the reactor tube was exposed to cooling water, and the ID surface reached 2372 deg F. Do you monitor the coolinbg water temperature?
No.
After everyting settles down, I would perform the following inspections;
1. Measure the wall thickness and OD of the reactor tube to determine if the the high temperature exposure resulted in creep deformation.
2. Perform a visual inspection of the tube ID surface to check for fissures running along the length of the reactor tube.
RE: High Temperature Excursion on a Reactor Tube
Just for curosity what are the design conditions for the reactor?
Where were the safety devices?
RE: High Temperature Excursion on a Reactor Tube
Design pressure for the reactor is 45ksi, all relief devices are set to this, and the reactor never got above that pressure. I was just concerned about the temperature effects. I am very limited regarding inspection and NDE options: no internal access (even for remote camera) and the tubes are permanently jacketed (no external inspection like UT in lieu of internal).
Cooling water temperature floats with ambient temperature (cooling tower), but thermocouples are on the inside of the tube (no local cooling water thermocouples on the reactor). I'd say that the water temp probably didn't change much.
RE: High Temperature Excursion on a Reactor Tube
I am going to ask this question because I find it odd that no internal inspection can be performed. This is obviously a pressure vessel, and it probably is insured, and it probably is regulated. How in the heck do you get around not being able to inspect this vessel and still operate it with no internal inspection capability?
RE: High Temperature Excursion on a Reactor Tube
I would assume that a significant amount of the material has been heated well above acceptable temperatures. Problems may include cracking or tearing, excessive grain growth, possible corrosion attack.
Or if no one can possibly get killed or hurt when it fails go ahead and run it. Your gamble.
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Plymouth Tube
RE: High Temperature Excursion on a Reactor Tube
My hunch is the steel is not significanly damaged (this hunch is worth what you paid for it).
RE: High Temperature Excursion on a Reactor Tube
I don't know if the Fourier modulus is in the proper range for this application, but if not then there are other solution approximations available to handle estimation of short term non-steady state heat transfer.
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Plymouth Tube
RE: High Temperature Excursion on a Reactor Tube
Just to add. Yes, this is registered equipment, but it's a tubular reactor, so it's actually considered a really long segment of pipe (not a vessel). Inspection requirements are a little different for pipe versus vessel around here. I can get away with X-ray, etc. I can actually disassemble sections of tubing to look inside with a camera (but this is not exactly your average flange + gasket).
I've dug up some old FEA modeling work for this system that shows that it would take few minutes for the material to get that hot (tube acts like a big heat sink) and my process data says it was actually less than 10 seconds (as opposed to 45sec. as I originally posted) at the high temperature range.
Again, thanks for the help.
RE: High Temperature Excursion on a Reactor Tube
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Plymouth Tube
RE: High Temperature Excursion on a Reactor Tube