Line monitoring & SIL 3 applications??

[sameenkhan]

Hi Guys,

Is line monitoring mandatory requirement for SIL 3 Applications?


Regards,

Sameen

[ibrahim]

I think, you get confused with LOPA and SIL. Line (piping network or pipeline) monitoring is a function of LOPA (Layer Of Protection Analysis) and as far my knowledge it has no relation with Safety Integrity Level(s). SIL is a function of Electronic control and protection systems, where as inspection plans for pipelines, PSVs and other mechanical protections are governed by LOPA.

[sameenkhan]

Hi Ibrahim,

I am referring to E/EE/PE Systems... line monitoring is technique used within E/EE/PE systems to detect open circuit, short circuit fault and ground fault...

Now once again, Is line monitoring mandatory requirement for the SIL 3 applications???

Regards,
Sameen

[ibrahim]

yeap, I got it now. Sameen as far I know line monitoring technique is a sort of preventive maintenance. Either you have configured some logic in PLC to diagnose open or short circuiting to let operator know thru an alarm, or you do it thru a maintenance plan manually. Maintenance of associated SIS, for proper functioning is a mandate for that specific SIL. For example if a SIF loop failed to execute on demand due to lack of maintenance, safety integrity level decreased due to associated SIF failure.
So yes, line monitoring is mandatory requirement for all SILs. Mostly independent on-skid type PLCs force shutdown the system in case of open/short circuits. (I have experienced such configuration in SOLAR gas-turbine driven compressors).

[sameenkhan]

Hi Ibrahim,

I don't agree on account that line monitoring is used for maintenance.. it is one of fault detection technique same as Functionality checking, Consistency checking, Signal comparison, Checking pairs, Loopback testing, Watchdog timers, Bus monitoring, Power supply monitoring.. and safety PLC performs diagnose the system again and again to detect fault which can make system to fail in danger mode. Main objective of such huge number of diagnostic & fault techniques are to detect hidden (Latent) faults.. Thus, line monitoring in actual improves PFD of the system.. thus it is mandatory for SIL 3 application...
For a Fault Tolerant System three things are important, fault detection, fault Isolation & fault identification... mostly a simplex safety system is designed to fail safe on single fault detection but in redundant safety system architectures fault isolation & fault identification can really improve PFD figures of a safety system..

Major requirements for SIL 3 Loop is redundancy and line monitoring of IOs..

Line monitoring is mandatory requirement, but question arises that will it make the loop to fail in safe manner... the answer is NO (it is only fault detection technique),therefore, for SIL 3 loop, redundancy is must requirement, in case if there is STUCK ON or OFF the loop will be voted and fault will be detected and fault will be isolated for maintenance...

There were days when relay based systems were used to for ESD, BMS applications.. I don't think they were using any line monitoring.. , that is why they used to have many spurious trips and a lot of safety incidents...

Regards,
Sameen

[ibrahim]

Excellent knowledge sharing, I must say. So we concluded that line monitoring is a must but where redundancy is available, its better to alarm operator about faults in line, rather than just tripping the machine upon loose connection.

[ali.abbas]

Guys,

Thats a pretty good discussion here. Sameen, it seems quite convincing from your account that line monitoring is an important element as far as SIL implementation is concerned.

The next direct question that I wanna draw here is, how is line monitoring technique generally employed. Ive come across accounts where the use of an End-of-Line Module or Resistance s is discussed, but it still quite vague to me as to how is the technique generally useful. Can one of you guys throw some light on this please? Id even love if anyone of you can share some literature or link regarding the same.

Thanks!!