My name is Ger and I’m undertaking the Validation level 7 and would be happy to help out with the reading of P&ID’s. They don’t follow the grid referencing you mention as the P&IDs are process flow diagrams that show the piping and process flow details, but are not drawn to scale. To help read the layouts the pipework typically have line numbers which provide a reference to the size, ID number, type of utility and type of insulation and this line number is key to the traceability of the pipework and the materials of construction used.
Components in the field have a unique tag ID (etched metal tags) which are traceable to the P&ID and the design documents again providing traceability to identify the materials of construction. ASME BPE are a set of design and reference standards that are widely used in the industry for pipework, components. The key message is the P&ID is a map of the process that shows the pipework and components, with some key process requirements it shows the line number and Tag ID’s so that each part is traceable to ensure its fit for its intend purpose.
P&IDs are a big topic, so I’m happy to share my experience, so drop in and out of the forum if you have questions.
Regards and happy Friday
Hope this helps