API 14C Combustible Gas Detection

[142846]

hello every body.
page 22 api 14c 8th edition 2017 for primary protection for LEAKAGE says:
"Primary protection from small gas leaks that occur in an inadequately ventilated area and cannot be detected by component sensing devices should be provided by a COMBUSTIBLE GAS DETECTION system."
In the following for secondary protection system api 14c says:
"Secondary protection from all detectable leaks and small gas leaks in an inadequately ventilated area shall be provided by the ESSs." and we know COMBUSTIBLE GAS DETECTION is subsystem of ESS.
I confused why api 14c firstly says COMBUSTIBLE GAS DETECTION is primary and Immediately says COMBUSTIBLE GAS DETECTION is secondary protection.Thank you for any responding.

 

[1503-44]

Combustible gas detection is not a primary or secondary anything. Combustible gas detection can be (may be, or is) a strategy that can be employed in either, or both, a primary, or a secondary protection level strategy.

Example

Primary. Combustible Gas Detection shuts down compressor unit.
Secondary: Continued gas detection shuts down all non-essential electrical systems and sounds evacuation alarm.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[142846]

ax1e thanks a lot.
let me ask my question in another form.
what is two level protection for LOW leakage of gas from a separator? we know that because of low leakage PSL has not any credit for this scenario. Please note that we are talking about two level protection based on API 14C approach, not another standard or specification.Because each standard has own definition.

 

[1503-44]

I think you are looking for two levels of protection for a gas leak. Here are three possiblities.
1. PSL activates if leak is sufficiently large to lower the pressure enough to trip your PSL.
2. If the leak is small so that the PSL does not trip, then your Gas Detector trips at 25% of lower explosive limit.
3. Odorizer. Someone notices gas oder and trips the manual ESD.

Two levels of protection for a very low level leak that does not trip a PSL might be,
1. Gas detector trips at 25% of LEL.
2. Oderizer. Someone notices gas oder and trips the manual ESD.

If those do not work for you, you probably do not have a condition to be concerned about. There is probbly no need to do anything.

Yes, it could be a good idea for you to ask these kinds of questions in an instrumentation Engineering forum, as these are not directly related to "Petroleum Production Engineering". However keep in mind that DOUBLE POSTING typically only creates confusion for everybody and should always be avoided.






“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[142846]

ax1e
Thanks about your good technical comments and also thanks about your hint in last para.

 

[142846]

ax1e,
Would you please help me about the below question?

Two levels of protection for a very HIGH level leak might be,
1. Gas detector trips at 25% of LEL.
2. Oderizer. Someone notices gas oder and trips the manual ESD.

QUESTION:Why the above should be mistake because of completion of two level protection for very high leakage scenario?
If it is right, it might be omitted PSL for high leakages and decrease instrument system?

 

[1503-44]

I would say,
High leakage rate would be expected to reduce pipe pressures rather quickly and with a PSL trip you could take command of that situation almost immediately.
I would prefer to have a second leak indication level based on flow rate, as an increasing flow rate after a low pressure trip is a very reliable indicator of a large leak. Otherwise, a further decreasing pressure, or low differential pressures might be helpful.
Whereas,
Gas detection is less reliable, because it happens mostly in a confined space, not subject to wind direction and velocity. In exterior environments, you might pick up by detection, you might not. Light gases go up, some gasses sink down. Not reliable as it depends on sensor location in relation to the leak.
Oderizer and manual ESD activation depend on personnel presense. Perhaps already a dangerous situation in progress.



“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"