Whats the difference between Plant North with that of earth north..............?

The following is my answer to the same type of question on another forum.

North, Geographic, Plant, etc.
The question:
What is the difference between geographic north, plant north and isometric north? What are the criteria to apply to these directions during plot plan development and piping study?

My answer:
You have asked a very good question. There are a number of “North’s” and every designer, engineer, project manager and client needs to know and understand what these are and what they means to the project.
So let’s look at the list of common North’s that are found on process plant projects along with a description of what it is and why it is used.
• True North: Every place on earth has a True North and it is pretty much the same no manner where you are. It is located at 90 degrees north of the equator, it is the North Pole. It does not move.
• Geographic North: Same as True North. The term True North is normally the preferred terminology for this.
• Magnetic North: Magnetic North is not normally used on the average process plant project. The magnetic North Pole is always moving. In 2005 the earth’s Magnetic North was located at 82.7 degrees North Latitude and 114.4 degrees West Longitude. This places it far off the north coast of Canada. Because it is always moving it is not reliable as t fixed reference point.
• Plant North: For a project on dry land this is the most important North Arrow used in the process plant engineering, design and construction business. It is rare to find a piece of property that has the major axis of the property aligned with True North. Because of the way all of our ancestors settled the countries and lands of the world then built roads everything is out of alignment with the North Pole. When a project is first started, the property (of some shape) is displayed on a property map that will normally include a North Arrow showing True North. The property may be at any angle (angle of declination) off True North. It is very difficult to do any kind of design if everything is at an odd angle. To simplify the design process a new North is created for the project and this is called the Plant North. It is normal to include the Plant North and the True North on the project Plot Plan along with the angle of declination. Other documents such as structural foundations and piping plans only need the Plant North. as a reference point.
• Platform North: For an offshore drilling platform or processing facility platform this is the most important North Arrow. The Platform North will be assigned for each specific platform and may or may not relate to actual north.
• Isometric North: There is not (or should not be) anything called an “Isometric North.” Isometrics must have a North Arrow on them but it is the Plant North, not a different north.

Dear Mr JOP,

You gave an appreciable comprehensive answer .
What we see on compass is true North or magnetic North ? If one of it is marked by a hand held compass how the other one is measured and marked in field ? Does the Magnetic North have any relevance in plant engineering

Beast regards

Venugopal

well......well...well..

what i understand from the discussion is that plant North is always different than True North(Earth North) ...... Plant North is nothing to do with True north ..........

All Process Plants have their own North , East , West , South ......................Is it..........?

Plant North can be in any direction. It is just a common reference as Jop says.

Years ago two small gas platforms installed in the southern north sea. They were joined by a bridge which actually lay around east / west to the compass. Imagine the surprise when it was found that north arrows at either end of the bridge pointed at eachother. Pity the guys doing stress iso's for bridge piping.

AVenugopal

A Compass works because of the magnetic Flux between the earths poles. What you see on a Compass then is Magnetic North not True North.

You must get a copy of the chart (see your local Library) that locates the current position of the Magnetic North Pole (Current because it moves) and the relative angle of deflection of the True North from your actual plant location to determine the relationship between True North, Magnetic North and Plant North.