Hi All,

We have Existing Carbon Steel Flare Header of DN 1000 size with thickness of 10mm ( C.A 1mm), Design/Operating temp. 120/45 degC

Client is looking forward to make a hot tap of DN400 size on this existing DN1000 flare header which is resting directly on steel without a shoe/cradle.

The concern is during Hot tap procedure , As an applied load is increased due to installation of DN400 pipe, the load might ultimately become large enough to cause the pipe to become unstable, ovalise and buckle.

As we know, the buckling capacity of thin walled pipe is dependent on "O.D to thickness" ratio. Normally when D/t ratio does not exceed 80, then steel pipe will not buckle and no reinforcement rings are required as pipe is thick enough to carry high loads.

Client cannot shutdown the flare line & wants to avoid these stiffner rings . Avoiding welding of stiffener rings on the running flare line is understandable, but these are required as per secondary checks we made for two adjacent supports near tie-in point due to high vertical loads.

Can anyone suggest an alternate way to solve this issue?

Sam,

You need to read CONCAWE Report 85/52 Acoustic Fatigue In Pipes which gives some recommendation for the flare lines. One of the recommendations is that the stiffening of nozzles has to be full circumferential against the acoustic fatigue, it is not for nozzle reinforcement only. Additionally it recommends the nozzle entrance to the main with a proper slope to reduce the flow restrictions. I guess the recommendations are 4 items, the wall thickness of the flare main has a minimum of 13 mm (I cannot remember this exactly). I cannot remember the fourth recommendation at the moment.

I hope you/your company are aware of this Concawe recommendations. Unfortunately I do not have it and do not know if there is an updated version of it either.

I was able to find this for acoustic fatigue by Google search:

http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&ved=0CDMQFjAD&url=http%3A%2F%2Ffiles.engineering.com%2Fdownload.aspx%3Ffolder%3D3065fc0d-bfe6-40dd-9238-e48de5595e14%26file%3D7-fatigue.pdf&ei=rHkQU4efFdHPkAXLuoCICA&usg=AFQjCNH6uftdezoziFIyivrrYIZ8o6YiCg&bvm=bv.61965928,d.dGI

Here is another one:

"MECHANICAL INTEGRITY DESIGN FOR FLARE SYSTEM
ON FLOW INDUCED VIBRATION"

http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&cad=rja&ved=0CCcQFjABOAo&url=http%3A%2F%2Fwww.gastechnology.org%2FTraining%2FDocuments%2FLNG17-proceedings%2FMaterials-5-Hisao_Izuchi.pdf&ei=dYYQU6a8HYGDlAWziYGICw&usg=AFQjCNHb-VOP2zJinjv0gy4AxgNPuo0QPw&bvm=bv.61965928,d.dGI

Thanks to Google, you can find a lot of information if you seek.

I have not seen this before.

"Solving Acoustic-Induced Vibration
Problems in the Design Stage"

www.sandv.com/downloads/1308bruc.pdf‎

Dear Ibrahim,

Thanks for your reply

Really appreciate your support