Learning and applying IEC/ISO 81346 – Reference Designations

I mentioned some time ago that we had been required to incorporate the IEC/ISO 81346 standard into the asset registration process for functional (tag) numbers.
As this standard had not been applied previously, we had to determine rules for existing assets, it is not feasible to rename existing plant to fit the standard!
The standard needed to apply to new assets – and I was approached to help apply reference designations to a new design.


Through reading the standard, and following the techniques provided by Systems Engineering A/S, I learned that the concept behind the standard is not about just creating tag numbers – it’s about structuring the system while providing a standardised approach to naming objects.
The traditional approach is to name a component based on what it is, or what it’s for. For example – a company can tag all of their temperature control valves by the acronym TCV, and make it functionally unique by having a set of digits at the end (12345). This works up to a point, but can soon fall apart when: different components have the same acronym, run out of unique digits, move across from one company to another where valves follow a different logic etc.
IEC/ISO 81346 takes a hierarchical systems approach, basing the tagging of the object on an aspect. It does not apply the traditional logic, so for new users, it looks illogical in comparison. Through working through an example using a systems-based logic, rather than bottom-up component approach, the logic becomes clearer.

Object Aspects

We approached the problem from the functional aspect. We developed an example using an existing system in the Joint European Torus (JET); the Active Gas Handling System (AGHS) has a gas chromatography system. Within that system is an oil temperature control system, with a temperature control valve.

Asset Hierarchy of temperature control system in gas chromatography; focusing on the control valve
Simplified P&ID, the blue envelopes represent the control valve, averager, and associated instruments

In our example we focused on naming the gas chromatography system downwards, approaching the instrument and signalling components, specifically around the control valve and averager (blue boxes).

Application of IEC/ISO 81346 reference designations for the temperature control system in gas chromatography
  • The first level is the entry class, denoted by a single letter. I believe we chose U at the time as a placeholder for the gas chromatography system; but on reflection, it probably fits P as a “presenting object”.
  • The second level is the inherent function, denoted by two letters (sub-class). The oil temperature control system fits the definition of a thermal energy transfer object, so this was denoted by EG.
  • We kept to the sub-class methodology for the components, until we reached the final component in the hierarchy, denoting by 3 letters (sub-sub-class). The temperature control valve fits the definition of a “controlling object for varying the flow of fluids in sealed enclosures”, so is denoted with QN. The fluid that passes through the valve is oil, so the sub-sub class is QNA “sealed fluid varying object of a liquid flow”.

Note how the definitions do not specify the type of component; it focuses on what the object’s function is. Note how it is also not sub-typed by what it is trying to control (temperature, pressure, flow etc) – this is already denoted at the system level. To aid with understanding, we added the old logic at the end for the presentation – the standard also allows for descriptors to be added.


Through this example, we were able to show the design team how to apply the reference designation for the functional numbers on the P&ID. Unfortunately, we were not able to convince the design team to approach this from the systems level, at this time. I am hopeful from this example, we can convince future design to apply this at a conceptual stage, as they start identifying the systems, so that the systems-based application happens naturally.

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