System Codes / KKS

We have existing plants that i'm struggling to deal with in terms of organizing and unifying the codes used. Now i'm dealing with System Codes (e.g. FGA = Fuel Gas System, PMB = Corrosion Protection System..etc.) and with other vendor drawing scope and submittals were uses different system code as KKS...based from my research KKS is usually used in european and adopted by other companies here in the US...now i'm puzzled where this FGA etc.. came from...or any Standard Reference...I'm familiar with the fluid codes like FW = feed water; BW = Boiler Water...
Anybody familiar with this code and can share a copy of the original of this code...hopefully it was not a company std...
Or by chance aside from KKS is there other Identification system for Power Plant...this is related to system codes.
Thanks.

Thank you for your reply. I'm familiar with the fluid codes. However it confuses me with the system codes they used for establishing the plant. I'm looking for a numbering system for a new plants...It was used which they call as System Codes..(similar with KKS Numbering System)..I believe this is an EPC owned system...Is there anyone encountered working with new plants that uses System Codes?..My past experiences usually rely on KKS Numbering System which is very systematic and organized...Unlike this System Codes that i'm looking for a documentation that explains where those codes coming from...how they where derived...etc..