3 replies to this topic

[Jags]

Good Day,

I have attached some pictures of a failed thermowell on one of our Ammonia Plants. From your knowledge on thermowells, are you able to suggest what may cause it to fail like this?

Material of thermowell – Kanthal
Operating Temperature – 1850F
Mass Flow Rate – 600-650 klbs/hr
Velocity – 100 ft/s
Density – 0.3659 lb/ft^3
Pressure – 550 psig

[Whit123]

Good Day,

I have attached some pictures of a failed thermowell on one of our Ammonia Plants. From your knowledge on thermowells, are you able to suggest what may cause it to fail like this?

Material of thermowell – Kanthal
Operating Temperature – 1850F
Mass Flow Rate – 600-650 klbs/hr
Velocity – 100 ft/s
Density – 0.3659 lb/ft^3
Pressure – 550 psig

Apparently from the pictures it appears that under the process conditions, the material of the thermowell has become soft and malleable (perhaps even melted). What is the MOC of the process vessel/pipe in which this is used? Can the same MOC be an option? Have you tried Ceramic material thermowells?
If Kanthal is not supposed to behave like this under the process conditions that you have specified then it may be either that
1) The MOC is NOT Kanthal, perhaps you should get it tested from a lab?
2) The Process conditions have deviated substantially due to a process upset?

[riven]

Can you give an indication of how much of the thermowell was inside the process stream?

For example if nearly all of the thermowell was inside the stream there is no reason why the deformation would not be seen along the entire length.

To me the damage initially looks like a deformation caused by mechnacial stress of some sort i.e. incorrect removal of the thermowell.

[davebartran]

piece of cake, but there are several factors involved:

[1.] pressure collapse of the protection tube
[2.] materials of construction (Kanthal good for furnce environment but not your service)
[3.] a secondary isssue is that at 100 ft/s you are going to see the well just fold over

there are engineered solutions

Dave


Material of thermowell – Kanthal
Operating Temperature – 1850F
Mass Flow Rate – 600-650 klbs/hr
Velocity – 100 ft/s
Density – 0.3659 lb/ft^3
Pressure – 550 psig
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