Nozzle orientation drawings - how to specify angles
Nozzle orientation drawings - how to specify angles
(OP)
This may be an odd one and I'm not sure if this the right forum but anyway...
I had a discussion with my colleagues about which way is the correct to specify angles when you specify nozzle orientations on vessel heads:
1. Should 0 degrees start at the X-axis or the Y-axis?
2. Should the angular dimension be specified clockwise or anticlockwise?
When vessels are specified, normally a datasheet is prepared with a nozzle orientation sketch. Later this will be transferred to an fabrication drawing.
Very often these are dimensioned clockwise starting at the Y-axis (12 o´clock)
At the same time all the CAD programs always use anti clockwise, starting from X axis. This is also the correct way according to any math book I have seen.
If one could agree to always use the "CAD" way, things might be less confusing, however I'm sure many think it should be the other way around.
Are there any good (historical/regional etc.) reasons why one should not use the CAD way? (I know the manway might end up at 270 degrees)
regards
Mogens
I had a discussion with my colleagues about which way is the correct to specify angles when you specify nozzle orientations on vessel heads:
1. Should 0 degrees start at the X-axis or the Y-axis?
2. Should the angular dimension be specified clockwise or anticlockwise?
When vessels are specified, normally a datasheet is prepared with a nozzle orientation sketch. Later this will be transferred to an fabrication drawing.
Very often these are dimensioned clockwise starting at the Y-axis (12 o´clock)
At the same time all the CAD programs always use anti clockwise, starting from X axis. This is also the correct way according to any math book I have seen.
If one could agree to always use the "CAD" way, things might be less confusing, however I'm sure many think it should be the other way around.
Are there any good (historical/regional etc.) reasons why one should not use the CAD way? (I know the manway might end up at 270 degrees)
regards
Mogens





RE: Nozzle orientation drawings - how to specify angles
However it is a matter of preference: the best is to follow the way shop people are accustomed to, as they might get confused.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Nozzle orientation drawings - how to specify angles
My experience is different from prex's. Most drawings I've drawn and seen start the orientation at the Y axis and go clockwise. Don't think of this as math. If you look at this from a construction - and more to the point, a surveying perspective, it might make more sense. North is up, 90° is East, 180° is South, and 270° is West. Most of the time these coordinates are adjusted to a "plant north" since most plants are not perfectly aligned on a north-south axis.
jt
RE: Nozzle orientation drawings - how to specify angles
Field erection crews seem to like this better, in our experience.
RE: Nozzle orientation drawings - how to specify angles
From memory also in the good old days of the drawing board piping design draughting departments used the same method.
It is only since the introduction of the CAD programs where this has been changed.
RE: Nozzle orientation drawings - how to specify angles
Based on what you said, to simplify matters I would use the North line as my reference and clockwise as the positive direction for angles to be consistent w/ your practices.
Dont forget most autocad designers are not engineers, they are drafters and they will practice those methods that they learned during their ACAD education.
RE: Nozzle orientation drawings - how to specify angles
prex
http://www.xcalcs.com
Online tools for structural design
RE: Nozzle orientation drawings - how to specify angles
This is not just preference issue. If the degrees go counterclockwise, shop people could interprete it as a view from the "other" end. The nozzle orientation would be messed up.
RE: Nozzle orientation drawings - how to specify angles
My reply should have said I agree with jte and dig1
North is 0 degrees and east 90 degrees
Every vessel drawing orientation I have seen or produced myself has been done in this way.