Good day

I have just started to design flare header .can some one can guide me in the detail stepwise procedure of doing this including everything.

CHEMEER,

Designing flare system is NOT easy stuff. Certain years of experiences and exposures is required... Moreover this is SAFETY related issue. I think you need a competence and experience people to guide you personally and look through in details on your design to avoid any mistake.

As a start, you may begin to read the "Pressure-relieving and depressuring systems" API STD 521 Fifth edition, JAN 2007. There are plenty of information there.

Whatever Joe told is correct. But I would like to describe steps in brief.

Steps for finding 'max' relief load for a specific process plant.
(1) Prepare flare relief load summary including all PSV with all of their relief cases.
(2) Find out maximum possible relief load for each of the cases.
e.g. For cooling water failure, all PSVs having this case will discharge simultaneously. So add up them.
(3) The biggest task is to find largest relief which can occur during "fire case". You need to analyze "fire envelops" as described in API. Take help of your seniors.
(4) Once you found max case among all the scenario, consider it as the 'governing' case for sizing your flare header.
(5) You need to find what is superimposed back pressure at plant battery limit. You need to calculate total back pressure based on superimposed back pressure and built up back pressure. All these calculations need thorough understanding of hydraulics and API guidelines.
(6) Once you perform above, you will have size of flare header !!!!

I hope it helps you to know 'little bit' of the 'big' task.