Pipe Bowing in a fired heater 2

[Zeyad Zahran]

Hello everyone,

I am investigating a problem of the bowing of the lower tubes of a VDU fired heater, what are the best approaches to prevent or mitigate this phenomenon.

 

[goutam_freelance]

Are there baffle supports? How the thermal expansion is taken care of?

A section drawing with thermal data will help understanding.

 

[LittleInch]

Not having cold liquid / hot vapour mix or vice versa.

Not much to go on here....

 

[TGS4]

Before you mitigate it, you need to figure out what's causing the bowing in the first place.

What possible causes have you investigated?

 

[btrueblood]

What does your professor say?

 

[Zeyad Zahran]

Hello everybody,

Sorry for late reply, I thought I will be notified when replied on my post.
Initially, it was assumed that the bowing was caused by temperature differences. However, I don’t believe this is the case, as the bowing occurs in the lower tubes, which are more resistant to flexion, and not in the upper tubes, which have a smaller diameter. This seems counterintuitive, especially since the middle tubes, which receive more heat flux, do not show the same behavior.

The second explanation, which I personally support, is the phenomenon of hogging. This occurs due to the lack of symmetry in the coil design, where the lower areas are restricted in their ability to expand. This restriction creates the bowing effect observed in the lower tubes.

I attach the design of the coil, front view and side view , the steam injection point in marked in red, which is the starting point of the radiant.



Thanks to everyone for their input, and Happy New Year!

 

[Zeyad Zahran]

Not having cold liquid / hot vapour mix or vice versa.

Not much to go on here....

Sorry for the late reply, i posted i comment in the end.
happy new year.

 

[NovaStark]

During transient scenarios is it possible that there is steam condensate collecting in the lower tubes such that they have a level of liquid in them? If they do, then the thermal bow may occur as LI was alluding to. Or alternatively, is the pressure drop along the coil causing condensation ?

 

[Zeyad Zahran]

During transient scenarios is it possible that there is steam condensate collecting in the lower tubes such that they have a level of liquid in them? If they do, then the thermal bow may occur as LI was alluding to. Or alternatively, is the pressure drop along the coil causing condensation ?

The pressure drop is around 4 bars and the pressure in the outlet negative, about -0.8 bars , also need to mention that in non operating conditions, the bowing disappears.

 

[georgeverghese]

Burner Flame envelope may be too close to the lower section of the radiant bank, causing higher metal wall temp than expected ? Take a look at the existing burner flame map at max firing rate and see if a different type of burner with narrower flame envelope will resolve this problem.

 

[dvd]

Without a good understanding about the materials, geometry, constraints, operating parameters, function, etc. of this piece of equipment, it is just a game of twenty questions. How about marking up where/how the tubes are supported on your image, and provide as much information as you can?