Mimentzos,
I hope this helps.

Definition: A piping "Isometric" is a three dimensional representation of a pipe line or part of a pipe line complete with all information necessary to purchase (the material), fabricate, install and test the line or part of the line.

In order to accomplish this there must be certain specific information included in or on the isometric drawing.  The "isometric drawing" form is divided into sections for the required information.  
These sections are:
1.    Identification (Title Block) Section
2.    Technical Data Section
3.    Graphic Section
4.    Bill of Material Section

The identification or title block section is further broken down to include:
•    The Line Number – The Line Number becomes the drawing number for the isometric.  The line number comes from the P&ID and the Line List.  Only part of the line number is included as the "Drawing Number" for the isometric.  The part that is used for drawing identification is only the numeric sequence number and the Line Class specification.  
•    Sheet Number – When a pipe line takes more than one sheet then there needs to be a way to identify each sheet in the Isometric log.
•    Project Number
•    The name of the person creating the line/isometric
•    Date the drawing was created
•    Date the Isometric is issued
•    The Revision Number
•    The record of Revisions

The Technical Data section Block section is further broken down to include:
•    The Piping Code applicable to the line – from the line class specification
•    The Insulation Type – from the line list
•    A designation of Shop or Field fabrication – Design instructions
•    Hydro-Test Pressure – from the Line List
•    Post Weld Heat Treat (PWHT) requirements – from the line list
•    Heat tracing criteria – Type, Temperature, etc.

The Graphic Section should include the following when applicable:
•    A North Arrow – indicating the direction of Plant North (for projects on land) or Platform North (for projects that are Offshore Platforms).  As much as possible all Isometrics should be drawn (Plotted) with the North Arrow in the same direction.  The recommended North direction is up and to the right.  Second is up and to the left.  
•    The configuration – Presented in a clear and simple manner that the shop and field can understand.  This should be one line or part of one line.  The key here is clear communication from the office to the shop and the field.  It is better to use two or more sheets for a line than to try to "Save paper and crowd so much on one sheet and end up with errors in fabrication.
•    Symbology – the symbols used on each isometric should be industry standard clear, concise and consistent no matter how many different people draw them or what CADD system is used.  Piping is a language and the office is "talking" to the shop and the field.  The communications should not be damaged by free-lance individuals who want to do-it their own way.
•    Dimensions – what is needed here is all the dimensions necessary to fabricate the spools shown on the isometric.  Do not include dimensions that are not necessary.  Dimensions should be given for over-all lengths, for the location of branches, changes in direction and in-line objects such as valves.
•    Spool Mark Numbers – These are the identification numbers that should be painted on the spool piece that helps the Field reassemble the "Puzzle" of pieces.
•    Notes & Callouts – Sometimes objects are required for the line (isometric) that a simple symbol is not enough.  Notes or callouts are used to define what the object is and the size of the object.  This information comes from the design instructions.
•    Reference Location Point – Every isometric need's to have a reference location point to aid the field in location where the line is in the big picture.  If the line shown on the isometric originates (or terminates) at a piece of equipment then the equipment number should be indicated along with the specific nozzle designation.  This is normally sufficient for location.  For isometrics that do not originate (or terminate) at a piece of equipment then one nearby pipe support column should be indicated with its number and coordinates.  
•    Elevation – at least one elevation should be given on the isometric.

The Bill-of-Material Section should include the following when applicable:  It should be noted that there are two methods for doing the "BOM" for an isometric.  These are attached (same sheet) and separate (two sheets of paper) isometric and BOM.  
If the BOM is on the same paler as the isometric then include:
•    The count of the material object (pipe. fittings, flanges, etc)
•    The primary size (and secondary size when applicable) of the object
•    The Item Code Number of the object – This is found in the Piping Material Line Class Specifications.
•    The Description of the object
•    Comments Box

If the BOM is a separate piece of paper from the isometric then the following must also be included:
•    The Line Number ( Isometric Number)
•    The Sheet Number
•    The Project Number
•    The Revision Number
•    Date of Issue

Piping Isometrics (also called Isos) are made three ways:
 - Manually - This is an isometric of a line drawn by hand.  This can be done in the office or in the field. It is the best and cheapest way to create piping isometrics for very small revamp jobs and/or for Tie-In Isometrics.
 
 - 2D Cad Iso program - This is somewhat like the hand drawn iso but done with the aid of a data base oriented 2D CAD program which will also produce the BOM (Bill-of-Material). This is good for small to medium sized projects where the engineering & design company does not have 3D capability.

 - Isogen - This is the tool for producing piping isometrics as an extraction from a fully developed 3D Design Model program. This requires a fully developed data base of material and matching graphics.  This is considered the best for medium to very large projects and an engineering & design company who has the 3D (PDS, PDMS, etc) capabilities.
 

Thank-you, sir...

Dik

Pennpiper first I want to thank you for your reply.
Secondly I want to ask you if all this procedure included officialy in any Standard code like ASME, ISO etc.

Thanks in advance

Mimentzos,
There are ASME Standards that tell you how to make pipe, fittings, flanges and valves.  There are Codes that tell you the minimum requirements for building pipelines and different types of process plants. But, there is no "Code" (to my knowledge) that addresses the subject of how to create isometrics even to the limited degree that I did above.  Sorry!

There are some text books that would help you but I do not think you are looking to go back to school.
Example:
Piping Drafting and Design
        (Using manual, AutoCAD and Pro-Pipe Applications)
    Roy A. Parisher and Robert A. Rhea
    Gulf Publishing Company
    ISBN 0-88415-657-5
        Also available by the same author
    Piping Drafting and Design "Workbook"
        And
    Piping Drafting and Design "Instructors Guide"

Process Piping Drafting (this book is out of print but you may be able to find someone who has a copy)
    Rip Weaver
    Gulf Publishing Company
    ISBN 0-87201-761-3
        Also available by the same author
    Process Piping Drafting "Workbook"

I also suggest you visit www.pipingdesigners.com  Look at the "Training", "Tips", "Tools" and "Forum" links, you will find a lot of information about piping design.