Plant North vs. True North

Not my field but:

True north is magnetic north corrected for variation, deviation, and local mechanical errors. So True is actually the line to the North pole.

That only leaves Plant north to be magnetic based, yet depending on your standard that could include or exclude magnetic variation, declination, local sensing error, and a host of other creeping errors.

The easiest way to determine is ask what that standard means within (presumably) your organization or the organization that did the drawing. Or you can take True, look up magnetic declination for your area and add or subtract as appropriate to see if you end up close to your Plant north. If not then there is more at work here.

GA

To the point!

LL

Magnetic North is not typically True North. Far as I remember, Polaris, the North Star is closer to true North. It has been awhile since I was flying around. Depending where you are, Magnetic North can be as much as 15 degrees off in North America, from True North, from what I remember. Hence we navigate by GPS, Loran, & VOR, these days for exactitude. As an experiment I suggest you compare a GPS location to a compass location.

P.S. I enjoy the question for it reminds me that I've forgotten some things, and need to brush up. Typically though, a compass is good enough.

Hi,

Thanks . R U Civil Engineer

I think your answer is better than mine.

I would add that "true" north implies an astronomical meridian not magnetic north. True north can be arrived at with stellar or solar observations. Magnetic observations may also be converted to true north though not without the likelihood of significant error.

generally speaking (I have been at this career for 33 years) there are various versions of this used for convenience. true north and magnetic north are pretty simple to say the direction to the north pole and the north magnetic pole.

However, these axis rarely fall neatly in line with the perpendicular axis of your project. Plant (or site, or project ....) north is as described by a previous respondent. a convenient application of the term 'north' to a primary axis of one of the major elements of your project.

Consider it the same as a Temporary Bench Mark on a construction site with an ASSUMED elevation. It is local and ONLY applies to your specific drawings and is for convenience of those working on this project.

In areas where development is pretty much non-existent (remote northern locations), why would the facility or plant north not match true north? thx

Because the local terrain is not convenient for NSEW orientation of a building.

Yes it may be matched there.

Is it not "Plan" North, not "Plant" North?

Only to people that care about these things.

Here is my answer to the same question from 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 a 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." Piping Isometrics must have a North Arrow on them but it is the Plant North, not a different north.

I hope this helps.

PennPiper

Thanks for explaining so easy.