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TOPIC: Dimensioning Piping Layout Drawings

7 years 5 months ago #8185

  • Anton
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The subject of dimensioning practices on Piping Layout Drawings has come up on the forum as part of another question.

There is so much in this subject, that you could write a book .... or at least make a topic for the training section!

So, lets talk dimensioning .... what are the "Do's" and "Don'ts" from your perspective?

What are the best / worst practices you have seen?


Discuss.
- If you're the smartest person in the room ... you're in the wrong room.

Re: Dimensioning Piping Layout Drawings 7 years 5 months ago #6454

  • Jop
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I will start the discussion:

A) Maximize the use of Coordinates and minimize the use of dimensions.

B) Major items shall be located by Coordinates based on North/South/East/West and starting from the Clients base survey monument and coordinate grid. Major items are defined as: Column Center Lines (buildings, Pipe Racks, etc.), Equipment Center Line with one Key Nozzle Center Line, Center Lines of Roads.

C) Minor items should be located from the nearest Major Item locating Center Line. Minor items include pipe runs, Valve manifolds, etc.
Do it once and Do it Right

Re: Dimensioning Piping Layout Drawings 7 years 5 months ago #6455

  • 11echo
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This is a subject near and dear to me, and one that goes far beyond just documenting data on a drawing. Like the path to becoming a piping designer in today's world, a shorten version of becoming a draftsmen exist too! One of the easiest ways to determine a drafter’s experience/skill level is to look on how they dimension drawings! Two major issues normally pop out, first there is a drafting standard convention on how dimensions are done, this is taught in the first year of drafting and the lesson there is suppose to be learnt & carried throughout a draftsman/designers career. Secondly, the other issue is dimension standards relating to discipline, dimensions are presented a certain way, dictated by decades of practice and convention in a particular discipline.
Unfortunately these has been usurped by two major events …and they both were generated by the adoption of the computer! AutoCAD was/is basically based on a default format of the architectural discipline! So unless you know exactly what you’re technical discipline dimensioning particularities are and how to “turn-on” those switch in AutoCAD, it defaults to the architectural format. This is normally highlighted by the use of “broken line dimensions and double dimensioning”. A broken line dimension is where the dimension line is broken in the middle and the dimension text placed in this location. Only two disciplines use this style they are architectural & machine drawings! Only two disciplines routinely use double dimensioning …again architectural & structural. All other disciplines deem this use as “bad practice” and avoid it. …SO if you work in a discipline, other then the ones stated, what do you first think when someone working in your discipline uses that dimension style? …First thing I think is the draftsman/designer is not that experienced or they just don’t know, and then I start to question the quality of the design! This is complicated even farther when first year drafting mistakes in dimensioning convention are also present on the drawing! This is a “red flag” for a couple of reasons …the draftsmen/designer is not that competent! Secondly, it may put into question that the capabilities of any engineering company that passes this “effort” down to the client as an acceptable drawing! I don’t believe any engineering firm cares to have the quality of their work put in a bad light because of incompetents by its junior members (however the ability to “know good works” is sadly missing in a lot of engineering firms)! …And the issue can down cascade down from there.

Re: Dimensioning Piping Layout Drawings 7 years 5 months ago #6338

  • Anton
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What about dimensioning an item on plan AND section ....... a big no-no in my book - you're doubling the chances of a mistake, especially when things change, as they inevitably do!

This is a point that relates to 2D drafting, when you draw a plan and cut a section.

3D modelling might make this a moot point, but the reasoning behind it is still valid, and can be applied to many situations.
- If you're the smartest person in the room ... you're in the wrong room.

Re: Dimensioning Piping Layout Drawings 7 years 5 months ago #6337

  • shrivallabha
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Some part of this discussion is of relevance to this thread:
viewtopic.php?f=1&t=2529

From above posts by Anton, Jop & 11echo following two points seem to hold the key:
1. What items to dimension?
2. How to dimension these items?
And nowadays one or the other software would be used so probably the third would be:
3. How to customize the software to better manage the two points stated?

From what I have seen, some departments that use Autodesk ACAD for 2D work use multiple "ViewPorts" for sectioning and I am told it is very effective technique to avoid duplicity as the model remains constant. However, my knowledge of ACAD is pretty limited. So others who are proficient in this might be able to add from this perspective.

Re: Dimensioning Piping Layout Drawings 7 years 5 months ago #6543

  • 11echo
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shrivallabha ...3. How to customize the software to better manage the two points stated?
NOW this is the issue! Everyone "thinks" a computer ...or computer program can fix the issue! WELL I'm here to tell you it can't! The computer IS the problem!!! ...OR at minimum, caused the problem. AND THAT IS ...putting "un-trained" people into positions they are not qualified for. PEOPLE need to be FULLY trained on HOW, WHERE, & WHAT to do, and to start remembering that a computer is nothing more then a fancy pencil and/or eraser! Until that happens these issues will continue on, and probably grow worse ...IMHO

shrivallabha ...Nothing personal, unfortunately you have inadvertently put your message on a "red flag" and waved it in front of an old "bull headed designer"!
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