Hi all:

Working thru a High pressure flare line (36" SS line, 7.92 mm THK, 6.42 Kg/m^3 gas density) connecting KO drum to flare (around 250 m apart)with huge flow (650 kg/s) resulting in 160 m/s velocity. Line operates between +100 Deg C and -92 Deg C condition with a section of it operating at 400 Deg C due to radiation effect.

This line raise to 80 m to connect to the flare tip which is sitting on the pipe. This raiser pipe is anchored at bottom of the stack and well guided up thru.

I am following Energy Institute guidelines to check Flow Induced Turbulence (FIT)which based on quantitative basis calculate the LOF (Likelihood of failure) based on various parameters.

Question #1 : Determining Support Arrangement type based on Energy Institute 2nd Edition guidelines which indicates span length criteria and also Typical Fundamental Natural Frequency

Now lets say for a this piping system dead weight span meet the criteria for "Medium Stiff" supporting arrangement but fundamental natural frequency can be very low (Even less than 1Hz as piping is kept flexible to absorbe expansion), in this case what should be Support Arrangement (Medium Stiff or Flexible). I am bit confused by the mention of fundamental natural frequency in the table.

Question #2 : Is this necessary to calculate the reaction forces due to mass flow out of flare tip causing reaction downwards affecting the anchor loads

Question#3 : Do I need to consider the forces in the piping system
due to Change of momentum (gas having density of 6.42 Kg/m^3)


Thanks in advance for all suggestions

Any suggestion...?????

FIV (flow induced vibration) usually occurs on SB lines. You need to check your flare against AIV (Acoustic induced vibration). There are many guide lines to do this.
You need to get the process department involve asap. In fact, all the input should come from them. They should tell you if you really have a problem.
The basic rule of thumb is to use a thicker header in your case 15.875 mm for 200 diameters downstream the noise source +full wrap in Tee connections. . See guide lines
Look up for the Carruci and Mulle (C&M)r dat +MTD Publication 99/100.

Also do searches on this forum, you will find useful info. Do not rush and go ahead and propose a thicker header. Tell the process department to perform and AIV study for you based on (C&M) and if the noise level for a 36 in line is above 160 Db aprox. You have a problem.

On the unlikely event, according to my expertise, to have a FIV on this type of line .Yes you need to check the forces and the LOF. Restraint the line on change of direction (Stops) and use hold downs where applicable.


Hope this helps