3 replies to this topic

[Andron]

Dear colleagues,

I am a salesman of a fabrication company. Company has lots of experience in fabrication of gas flares but the design capabilities leaves much to be desired.

The problem is. Wet natural gas in a pipeline from x-mas tree to an early gas facilities has a pressure of 120 bara. There will be emergency flares every 6-7 km. Time of pressure relief via burning gas from one section of a pipeline is about 15 minutes. Estimated tip diameter is 250 mm; stack height is 35 m. But engineers can not calculate wall thickness of a flare stack for such a valuable pressure because they even have no design model for that. Please support me with some information on this problem in order to estimate the thickness.

Thank you!

Edited by Andron, 07 June 2012 - 02:02 PM.

[qadi]

Dear gentleman

 

I think design flare thickness same as design pipeline at the mention pressure in addition to 20%  design pressure  above relieve mention pressure, and hydrotest pressure should be 1,5 time relieve pressure plus 5-10 % safety margin, and stack flare must be insulated by proper ceramic in the flare tip 

so use the weymouth equation (API 14E,5th edition) to calculate diameter

 

Q=1.11 X D^2.67 {( p1^2-P2^2)/L S.G.Z H)}^0.5

From NPS table you will find estimated wall thickness

 

Good luck

Qadi

[fallah]

 

Andron, on 07 Jun 2012 - 7:11 PM, said:

But engineers can not calculate wall thickness of a flare stack for such a valuable pressure because they even have no design model for that.

 
Andron,

Flare stacks aren't normally to be designed as pressure equipment because their operating pressures are near atmospheric...

The exceptions are the stacks included a KOD or a liquid seal at the base or the stacks in which the flare tips might create back pressure in stack risers. In such cases the stack bases should be considered as pressure vessels and to be designed accordingly...

As per API 537, design of the base sections of the stacks included a KOD or a liquid seal (as pressure vessels) shall include provision for internal pressure loads and simultaneous wind loads (based on 70% of the design wind velocity)...

[flarenuf]

Andron

 

As Fallah says Flare stacks are not pressure vessels and consequently their design is based on mechanical criterion as opposed to Process.

By this i mean considerations as to the type of support of the stack, environmental conditions ( wind , snow , Ice loadings ) , height and diameter of the stack etc.
 

The required wall thickness of a  250mm  35m high  stack is obvioulsy less than that of a 120m high 1000mm diam one even though they see similar internal pressures.
 

take a look at the

http://webwormcpt.bl...ination-of.html

 

and also the John Zinc Combustion Handbook for more details

 

Flarenuf