Piping models vs. Isometric drawings

[zdas04]

[Rant]
I've always found isometric stick drawings (Iso) of piping fabrications to be confusing and difficult to work with. From the results I've gotten from people who say they like them, I'd say that I'm not the only one who finds them misleading. Especially when piping comes together at odd angles (few people can actually pick a 45[°] elbow out of an Iso).

Consequently, since I got AutoCAD 9 and CadWorxx I've been generating actual piping models to scale. The drawings are beautiful and have all the detail of a photograph of something that hasn't been built yet. Welders build what I've designed instead of what is in their heads. Pipe Fitters put it together right. It is so much more effective that I can't believe it.

Well, I guess I shouldn't believe it since I just got a call from one of my clients who required that I generate Iso's for a project that I gave him models on--he said that his field guys can't work from models and need the presentation they're used to. I asked him if he had actually shown the models to the field guys and he said "I don't have to, I know what they require". Meaning "I don't want to give them a better presentation than I've always given them because then they'll expect it all the time".

Like a good little whore, I generated Iso's for him. It is easy in CadWorxx to generate an Iso from a model, but the result is an Iso with material bullets so close together that I don't know how you tell anything from it.

I suppose the next call will require a blueprint.

[end rant]

David

 

[TGS4]

David, perhaps for uninitiated, a comparable piping isometric would be useful for comparison.

The biggest issue between isometrics and models are that the model maintains a scale, whereas the piping isometric, while maintaining directionality, does not have any requirement for scale; the scale is arrived at from the dimensions. For example, a 20' long pipe could be represented by a line the same length as a 2' long pipe, and the reader would have to interpret the dimensions to know that. Conversely, the model would show them in relative scale to each other.

It is possible to follow an isometric to understand what's going on, but you will need to do some "interpretation" when you stand before a fabricated pipe and check it against an isometric. Whereas, from 6 feet away, you could easily see whether or not what was built matches the model drawing.

Probably the best analogue that I have for this situation is comparing a photograph, which maintains scale and perspective, to a textual description of the photograph, with some representative, but not to scale, sketches.

 

[zdas04]

Kenat,
If you look at a top view (or bottom, or side) of every Iso I ever saw and you get a line. Look at a different view of a 3D model and you see another view of the model. So if the standard Iso view hides something, then it is forever hidden. I've attached a drawing for the install of a device I've applied for a pattent on. There are a lot of odd angles and complex relationships. The model shows them pretty well. The Iso doesn't.

TSG4,
The model retains the scale (and relative sizes), it also is viewable from multiple angles and allows someone to SEE what goes behind what and what direction they go (Iso's don't always show that even though they should, people start applying the P&ID rules to Iso's). Take a look at the attached.

David

 

[patprimmer]

Back in the dark ages when I learned to draw and the only devices where pen and pencil and paper and a few instruments, we showed sectional views to display hidden detail.

It did get complicated and took time though.

Regards
Pat
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[ewh]

How many of today's "drafters" know and can use descriptive geometry?

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[MikeHalloran]

Back when I was in college I spent two summers doing piping isometrics.
Got pretty good at it. ... or at least pretty fast.


Then I got assigned to do details and assembly of some minor mechanical thing.
So I did an isometric assembly drawing; quicker for me than three views, and clearer, too.
The Boss had a fit "because the customer wouldn't want to pay for such a fancy drawing".
So I erased it, and drew three orthogonal and confusing views.
Expensive, indeed; I was making almost twice minimum wage.


When the pipes get close together and splay out in several directions, like in a pig launcher, isometric single-line drawings get confusing real fast. In this day and age, it makes sense to use the tools we have available, and produce a nice 'piping model' drawing.


Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

OK, got it.

So in the piping world when you say 'isometric' you're talking a non orthographic schematic more or less.

Closest I get to that is the odd simple wiring or pneumatic diagram.

Posting guidelines faq731-376

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[MikeHalloran]

Yeah, sort of like a P&ID wrapped onto orthogonal planes then presented as a 2D isometric drawing, with pipes represented as lines, components greatly simplified, not necessarily drawn to scale, but including dimensions, e.g. from elbow to elbow and from elbows to static features like building walls or corners or floors, etc.



Mike Halloran
Pembroke Pines, FL, USA

 

[stanier]

zdas04,

I looked at your model picture. Yes it maybe helpful to get a general idea but has no dimensions.

With your experience you know that an isometric contains not only the dimensions but support details, materials list, test pressure operating temperature and pressure, sign off for designer, checker, stress engineer etc etc.

Modern packages do generate isometrics and include all the embedded attributes from the model.

I do not support the use of such documents as they are dumbing down the industry. It is retrograde to use a simple sketch and let the piping be field run. Disasters such as Flixborough occurred because of slackness in design and documentation. A reactor was bypassed without design of the interconnecting piping and the bellows squirmed.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

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[BJC]

The Object is communication.
The better you communicate the better the project goes.
It's see the Forest, See the Trees, See the beetles on the bark.
Models are great for seeing the forest.
Isos, spool drawings, hanger details and weld details help you nail the beetles.
The cost of drawings and a model is nothing compaired to the cost of a bunch of confused pipefitters.