dimension on piping ISO drawing

[davidysong]

Do we have to ensure the dimensions on ISO drawing is even? for example, from equipment nozzle to elbow should be 2300mm instead of 2297mm; control valve station from one elbow to another elbow should be 4200mm instead of 4186mm? etc...

thank you!

 

[MikeHalloran]

Did you mean drawings per ISO standards, or isometric drawings?
No matter.

That may be a local requirement, i.e. specific to your company, or even specific to certain kinds of documents or a specific department.

I have seen dimensions like that on documents supplied to external customers of companies that have a Technical Marketing Department or something similar. The operating assumption seems to be that people who buy their products are too stupid to do math very well.

From an engineering perspective, it's a litle silly, and the external customers sometimes find that the rounding to decimeters happens entirely within the Marketing Department, and is not representative of the product actually delivered. Where the interfaces are inflexible or crowded, this can lead to misunderstandings, waste, and hard feelings.



Mike Halloran
Pembroke Pines, FL, USA

 

[davidysong]

thanks Mikehalloran.

I know round dimension looks nicer, my question "do we have to?"

in fab and construction, people prefer round number on iso overall dimension or single component (fitting dimension is fixed, only non-fitting dimension is variablle)?

 

[McDermott1711]

What about the tolerances? I think that's almost always missed in computer generated isometric drawings.

 

[posture]

My company uses cadworxs for pipe models and generating isometrics. One of the guys spends lots of time hunting back through the model because when he tots up the dimensions on the iso, they don't match the overall dimension. Generally they are out by about 1mm because of the way Cadworx tends to round the dimension up/down.

My view is that 1mm is going to be irrelevent by the time the fabricatior has tacked up and welded the pipe. The fabrication tolerence is a couple of mm per meter. I see his point that you want the drawings to be 100% right but the time involved is not worth it.

Regarding the original point, we talked about this recently at work. We design skids so we get a fixed space and we have got make everything fit. Inlet here, outlet there, fit everything else in between as best you can. If the dim turns out as an odd number then we just get on with it because we haven't go the space to round them all up. We do it where we can.

 

[XL83NL]

Shouldn't the question be 'how can we assure our spools fit to the equipment, so we can have a safe operation'?
In that case, would it matter if a spool is 2314 mm in length, or 2250 mm, or even 2200 mm? What matters is you fitter/welder makes the tolerance, and you have a system in place to catch any misfit. Not saying all should fit 100%, that's impossible for this money.
Making a spool of exactly 2250 mm is just as difficult as one which should be 2314 mm.

Would you buy a car that didnt look all that fancy, but runs properply, or would you buy that Porsche for a price that's telling you somethings's off the hook?