A few years back I worked as a project engineer for a company that designed, fabricated, and assembled compressor packages in Calgary, Alberta. We did this for domestic and even sometimes international customers.
The job included designing and fabrication of pressure vessels, pressure piping, structural skids and rotational equipment mounting. We assembled these components and shipped them to customers.
The design work was communicated by issuing drawings for the vessels, piping and skids and also included process and instrumentation diagrams, and what we called service flow diagrams as well. Occasionally we were asked to stamp or authenticate the design and we always argued which diagrams we should be stamping.
Most of the professionals in the office were very reluctant to stamp diagrams. There was a thought that we were under significant risk if there was any sort of mistakes. Therefore there was a strong argument to simply stamp the P&ID diagram only. A confirming argument would be made along the lines of the P&ID being the only thing that is technically "designed".
However, we know from our Associations that any sort of drawing that is issued for construction needs to be authenticated. Thus the question becomes what if that drawing is not for the customer and is simply internal.
DO I STAMP INTERNAL AND EXTERNAL DIAGRAMS
To clear things up the Act that APEGA upholds does not distinguish between drawings used internally or externally. Therefore and simply stated, all final documents - not only drawings - that are issued and prepared by a professional, must be stamped by the engineer. Final refers to a professional document issued to another on which that person is permitted to rely on that design. Therefore the design documents that we issued to the shop all required a stamp regardless.
Although this is the Act and it is clearly stated, very few professionals follow this law.
UPDATE - I just found out that APEGA requires all final documents to be stamped. However, some Associations only require external documents. Stay tuned and I will do a bit more searching to update this document.
TO STAMP OR NOT TO STAMP
Its important to note that the stamp is not a warranty or a guarantee of accuracy. The stamp simply communicates that a licensed professional has accepted responsibility for the document. You are not expected to be perfect and mistake free. However, you are expected to utilize sound, professional judgement, in an area that you have expertise.
If you do not adhere to the professional standards that your Association requires, you will be punishable regardless of whether you stamped a document or not.
I hope that clears things up regarding the stamp as I know a lot of confusion exists in industry.