ISA Loop Tagging vs Equipment Tagging


Thread Starter

Bronson, Robert

I am interested in feedback on using Equipment tagging instead of ISA loop number tagging. (My experience is the Hydrocarbon Process Industry -
perhaps other industries have already solved this issue.)

ISA S5.1 - Instrument Symbols and Identification does a fairly good job of providing a method of naming instrument tags that are part of a process
loop. When ISA S5.1 is used to identify "tags" associated with process equipment/valves there are many who feel it comes up short. The
proliferation of HS's, XY's and ZSs do not provide clarity.

One important reason for this short fall is the fact that tags associated with equipment do not fit ISA's process loop numbering model. In the loop numbering model the object is the loop, i.e., F01. The attributes of the tag are instruments, i.e, FE-01, FT-01, FIC-01, FV-01.

With equipment tags, I feel the object should be the equipment, i.e., a pump P101. This fits with the digital compound points that are available in most DCSs. Some attributes of the pump that need to be identified would be the control command, P101-C, the run status, P101-S. The "hand switch" in the DCS would be the object itself, P101. The name of the object is assigned by the process engineer and shown on the P&ID.

An important advantage with this method is that the wire labels become self documenting. No more XY-435 for the P101 control command and HS-757 for the associated hand switch. (I am sure there are many who have spent hours trying to get the loop numbers to line up somehow.) If I'm looking at wires that are labelled MOV-101-OP and MOV-101-CL trouble shooting is much improved.

In the same way limit switches and open/close commands can be considered attributes of the valve object. FV01-OPND, FV-CLSD, FV01-OP and FV01-CL. There is no need for a separate ZSC-325A/B or XYs. In fact the notion of a Z325 being a process loop is false - except maybe for a positioner. The position of the valve is an attribute - it is not an equipment object or
process loop object.

I am hopeful that the above changes will move intrument tagging closer to a object.parameter naming without throwing away years of good instrument tag numbering. If you have standards that I could use for equipment object parameter naming I would be most interested.
Instrument loop tagging:
This problem has been a nightmare, not by itself but resulting from the different disciplines involved in a project; everybody wants to recognize his baby by the hairs.
I found ISA so retarded that in fact for most clients we had to customise some of the letters and for the loop number we usually mixed process systems and then our own loop.
I have never seen a process system well designed that would need more than (1)00 loop identifications.

Therefore, in 12 digits one may define first the plant area, then the type of loop number including the process system and then the true loop number.
As you know, an Instrument Man remembers easily numbers that are really meaningfull.
That way of doing, clients were delighted and the designers too !!!
I'm sorry for ISA, but don't hide the truth.
Occasionally, we had old plants that we could not work at all. At least for rationally minded person.

To be more explicit, a process system is for instance that heat exchanger. Including pump. reservoir... is the process area. Those become plant area with probably other ones.
I remember one huge plant, there were in the million drawings hanging, that means sizable number of PID drawings.
In the last one I was invloved there was about 300 PID drawings, some quite full. No problems.
Good luck.