Material for Fire Tube
Material for Fire Tube
(OP)
Hi,
I'm designing a gas heater in which a salt bath is heated by 2, 650mm OD fire tubes. These fire tubes are conected to a burner at one end, which delivers a 2.5m long flame with 750mm in diam, 1.6E6 Kcal/h and which has 2000°C at its hotest point (inside feather). For protecting the fire tubes from the flame there is another inside tube (length= 3m) made of Incoloy or Inconel. I'm wondering why do they use this material??
The flame has 2.5% of O2 (excess air) and it's expected to have 1300°C in contact with the sorrounding tube (not = to the inner wall temp).
Why can't I use a low carbon steel for this??
PS: Design pressure= atmospheric.
Thanks,
Diego.
I'm designing a gas heater in which a salt bath is heated by 2, 650mm OD fire tubes. These fire tubes are conected to a burner at one end, which delivers a 2.5m long flame with 750mm in diam, 1.6E6 Kcal/h and which has 2000°C at its hotest point (inside feather). For protecting the fire tubes from the flame there is another inside tube (length= 3m) made of Incoloy or Inconel. I'm wondering why do they use this material??
The flame has 2.5% of O2 (excess air) and it's expected to have 1300°C in contact with the sorrounding tube (not = to the inner wall temp).
Why can't I use a low carbon steel for this??
PS: Design pressure= atmospheric.
Thanks,
Diego.





RE: Material for Fire Tube
RE: Material for Fire Tube
The question is how can I estimate the service life of a low carbon steel tube exposed to those 1300 degC flames with 2.5% excess O2??
RE: Material for Fire Tube
incoloy will easily takes 2000F or more
genb
RE: Material for Fire Tube
I know Inconel is the best material for this application; but the question is: if I'd used CS, how long will it last? For this application a life expectancy of only 1 year would be fine. Besides, there are a lot of direct fire vessels made of CS and the last many years, take a cooking pan for example...
Diego.
RE: Material for Fire Tube
Creep strength should be considered for carbon steel at temperature 1300 C.
Frankly speaking, I do not have experience to design fire tube of gas heater with 1 year design life.
RE: Material for Fire Tube
You are incorrect,..... ASME VIII does NOT permit nor encourage use of carbon steel in continuous duty over 800F. I do not understand how you came to this conclusion.....
It has long been known that carbon steel will degrade via a mechanism known as "graphitization" above 800F.
See: http:
-MJC
RE: Material for Fire Tube
See ASME Sec II Part D, Table 1A. Now, if you say this is not applicable, tell me where in the ASME can I find what you say is the limit.
Apart from this, I know for a fact that fire tubes are made of plain CS (SA 106 GrB) and they work at above 500°C (932°F). They last many years and limiting factor is the salt corrosion (about 0.1mm per year).
Diego.
RE: Material for Fire Tube
1. Do they have enough strength at the use temp?
2. What will the external corrosion rate be in the hotter sections?
3. What will the internal corrosion (oxidation) rate be in the hotter sections.
Usually the answers to all of these are bad news. These thin liners result in huge gains of durability.
I have seen direct flame-exposed test stands fail in weeks, where the Ni alloy version ran for many years.
Now if you only need a year could you use 430 stainless? It might be worth a look. The next step might be 310, and after that 800. There are options other than 600.
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Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Material for Fire Tube
In this case the CS will have practically no stress since it's only a liner that separates the fire tube (SA 106 Gr.B) from the flame. The fluid outside this liner is still combustion gas and on the inside there is a flame.
The flame may be touching the liner's inside wall; but based on calculations we don't expect a temp higher than 1000°C (1832°F). What I don't know is what will the corrosion rate be, so my worry is whether this liner will last a week or 1 year (accepted design life).
May be I should insist on Inconel and forget about it...
thanks,
Diego.
RE: Material for Fire Tube
Some of the in between alloys might though....
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm