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These items or systems are, for the major portion of their life, waiting to work, but not actually working. Thus a Relief Valve normally remains closed, and should only open on the odd occasion when the operating pressure exceeds the set pressure. If the Relief Valve is unable to lift in this condition, we will not know until after the event, by which time it may be too late - we may have a burst vessel in a our facility! So it is important that we have protective equipment that we can rely on. In many cases, protective equipment cause the Plant, system or protected equipment to shut down, when they operate. So the key question is this - how do we know that protective equipment will fulfill their function on demand?

As protective equipment do not operate during normal operations, we have to wait until they come out for overhaul and resetting or recalibration. At this time we can find out if they would have worked if there was a need for them to do so i.e. if there had been a demand. We do pre-overhaul inspections to find out whether they would have worked had they been required to do so in service.

Each of these protective systems or equipment has to meet certain performance standards. For example:

Relief Valves must lift between 90% and 110% of their set pressure and must remain open until the pressure falls below a pre-set value (blow down pressure). They must not lift before the 90% value is reached.
ESD (Emergency Shutdown) valves must open on demand within a given time period (e.g. Oil & Gas ESD valves must open fully in 60 seconds). They must not operate without an initiating signal.
Heat, Fire and Gas detectors must sense the presence of heat, fire or gas of a stated intensity. They must not operate without an initiating signal showing the stated level of heat, fire or gas respectively.
Fire Pumps and Fire Deluge systems must provide the volumes stated within the stated time. They must not operate without an initiating signal from the heat/fire/gas detection system.
Blow down valves must open when an initiating signal, based on system pressure or the fire detection system or some other trigger that the designer has built in. They must not operate without an initiating signal.

What data should we collect?

These performance standards indicate what the data required; it is important to record the first test result, before adjustment, cleaning or servicing. Sometimes, in anticipation of an 'official' test, an unofficial pre-test may be done. This is not a good idea, but it is not uncommon. In such a case, the pre-test result should be recorded e.g. what happened on the first test start of the fire pump?

For protective equipment, we need at the minimum, the following data:

Date installed, date of test, result of test with respect to performance standard; both whether it worked to specification when it should and whether it worked when it should not work.
For single items such as pumps, relief valves or ESD valves, tag number, and if they can be installed in two or more locations, unique numbers.
For groups of items such as gas detectors, the number installed, number tested, and how many passed. Of those that failed, how many failed to detect the threshold level of gas and how many detected gas when it was below threshold level.

As discussed in last month's Performance TiP , the above is enough to compute basic reliability parameters. However, additional data collected can be used for more detailed analysis where the performance standards are more stringent. Further, this will demonstrate to the Regulator that you are professional and prudent. Record for example:

As found condition (e.g. fouling or broken) in long text.
The failure mode (what is damaged) that caused the item to fail the test.
The environment in which it works, if relevant.
Any other pertinent information.

How do we process this data?

If you'd like more information on how this subject please e-mail data_process@snoino.com.

What benefits can we get from this data?

Reduced facility, system or equipment downtime, thus improving Integrity and Production Availability. Often the correct level of testing (as demonstrated to the Industry Regulator) can mean a reduction in test frequency with resulting savings. We can make minor improvements to the environment where the equipment is situated to make significant equipment performance improvements. Chronic problems in items that cause high levels of production loss or impair integrity, can be designed out.

If you'd like more information on how this works in practice please e-mail info@snoino.com.

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Thanks to V. Narayan for his contribution to this month's Performance TiP.