Safety Integrity Level for Check Valves??? 2

[gustorf]

Dear All,
A customer is asking for a compliance certificate in accordance with IEC 61508 regarding the safety integrity level (SIL) of check valves.
As far as I know, this only applies to actuated safety valves.
Does anyone know if this applies to check valves also?

 

[stanier]

A check valve should not be regarded as a safety device.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[gerhardl]

Interesting!

Brought me to look up the definition.

http://en.wikipedia.org/wiki/IEC_61508

'IEC 61508 is an international standard of rules applied in industry. It is titled Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems (E/E/PE, or E/E/PES)' (Underlining by me).

The below is my personal opinion.

It seems that Wikipedia (if reliable!?) has a thorough and relatively simple overview in this case, which, as I thought, excludes your checkvalve, as it is a single mechanical component.

If your single valve includes other components, as for instance electronic limit switches (also including the electrical signal system), or is a part of a larger system,( including electrical operational signal components ), the system as such (including your valve) could fall under a category where SIL certification of the whole integrated system might be done (but not of separate, purely mechanical components alone).

In my opinion SIL is (among other things?) intends to ensure and lengthen a 'non failure operation time' of a 'system'.

This is different from including 'safety devices' alone. 'Safety component's for a system will include all components to ensure a safe and controlled operation, within the limits given by the process, eg. all controlling and regulating devices.

For instance could a solenoid valve (mechanical device operated by an electrical actuated coil and magnetic core) have a SIL certificate, and as such be defined as a system. The certified solenoid alone, however, says nothing of the SIL level of the system it is integrated and used in. The total system, with all components, must be analyzed.

I must confess I have a very limited experience with SIL, but SIL evaluations includes dependability statistics and failure probability. If your (mechanical) checkvalve has operational records (number of operations without failure), failure statistics or good expected lifelength figures or statistics, this will probably be a positive contribution in a discussion.

Good luck!

 

[gustorf]

Thanks stanier and gerhardl.

The story behind it is:

A big German compressor manufacturer (SieXXXX) is evaluating the designs and layouts of their compressor units including surrounding components like check valves, isolating valves and syfety valves, etc.
Based on sub-suppliers indications of SIL levels, they are re-designing (either with less or more safety components) their complete systems.

The problem for us is to determine the SIL level as there are many unclear defined figures (Failure, safe failure, unsafe failure, etc. etc. etc.) Even our customer and their specialists can't tell us exactly what this is and how to count and calculate.

In today's world, where lawyers rule instead of engineers I am very reluctant to give written statements which can come back to me and kick me in the....

So for now we decided to state N/A for check valves, we will see if they accept that.

 

[gerhardl]

This is a typical commercial/technical situation, where culture collisons could occure. In my experience German engineers are 'straightforward' with very solid technical background. It might however be that competitors of yours do not have your ethical view and 'produce' certificates, where certificates might be relevant or not.

(Have happened to me, but not for SIL)

One way to strengthen your position is to invite and prepare for technical dialogue. You could for instance present or mention what type of available references and statistics you have, and ask if this is relevant. At the same time you could ask for their demands for your specific product, as their specifications arises discussions on exact requirements.

You could also (as I am sure you often do) offer your assistance at their factory, or invite to your factory to
check/see testing and quality control procedures.

Good luck!

 

[hydtools]

Interesting opinion position from CRP:

http://www.crp.co.uk/technical.aspx?page=271

Ted

 

[gerhardl]

Thanks hydtools, enlightening!

 

[stanier]

Last time I looked a check valve was neither an "electronic" or "instrument" item. How could it even be relevant to a SIL level?

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[gustorf]

Thanks, hydtools, very useful.

gerhardl, we have done all what you have recommended.
Your statement about competitors is too true, unfortunately. It happens all the time to us.

We have a very long great business relationship with the customer, they know our products since decades, but...

The guy in charge is a very young, energetic, but less experienced "expert" who is good at being demanding, but doesn't fully understand his own requirements.

I will leave it with the N/A statement for the moment.