Instrument Air Failure Scenario

[michael99]

Hi
I am looking at an oil and gas platform. I have worked out the fail scenarios if the main instrument air system is cut. The case i am looking at is if the air system is cut what is the maximum load on the flare header "blowdown". Alas alot of my valves on the platform and blowdown valves are air operated.

What i am considering is i have blowdown valves on top of my separators i also have PVs. These PVS open when the vessel reaches high set point for pressure. Most of these valves fail close but some fail in position as they have accumulators. When looking at the air scenario for blowdown do i have to consider the separator is at PSHH and the blowdown load as being the normal production flaring case for the PV plus the blowdown. Helpfull advice appreciated
michael

 

[uu78hswang]

Dear
I am not sure that your case is applicable to my suggestion.

The cases below may be applicable to the determination of relief loads caused by instrument air failure:

If:1.Instrument air is provided by a single compressor
or 2.No emergency supply is provided

Complete instrument air failure shall be considered

Hope this can help.

 

[JLSeagull]

I worked with an automated blowdown valve actuator design for offshore applications that was different than normal shutdown valves. Some projects use different failure signals for the electronic signal than the air supply. The example that I have done energizes the solenoid valve to open the blowdown valve. However the blowdown valve spring opens the valve upon loss of the air supply. In other words the electronic and pneumatic failures were opposite. Check the codes and standards to see if this concept may apply.