[Mark Pearson]

Hi all,

Am I losing my mind with this one ?……I’m used to having the extra allowance shown alongside the design dimension, i.e. if the design dimension is 575 with a FFW, then I expect to see the actual dimension on the isometric as 575+150 or 575 (+150)…..however, it would appear the way I’m used to having it, is not how it’s done in North America…..

…..instead it’s simply 575 with a cumbersome note added to the notes part….seems long winded to me, especially when the 575+150 can be automatically generated by isogen

Discussion

[James Pennock]

Another way of doing this is to include instructions for the added length in the Shop Fabrication Purchase Order in the form of a Specification or Mandatory Technical Notes.

[Mark Layport]

The basic concept here is that the “correct” dimension is not exactly known, so an additional length is added to the overall length of the pipe and the welders in the field will make the final determination during fit up. It is best to keep this effort as simple as possible (your drawing will pass thru a lot of hands before it gets to the field, and a lot of those people are not high on the pay scale … 😉 )!
What we normally do in my part of the world is just give the one dimension (in the scenario indicated here it would be 725) and then add the documentation “FFW” underneath that dimension, so two things will happen, when the spool is shop fabricated it will automatically be made to the 725 dimension (welders in the shop are only interested in a length they have to make …not why), and once it’s in the field the welders will see the FFW notation and know that that spool will be too long and they’ll have to measure and cut the excess off that leg of the spool for finally fit up. You could put a note on the Iso-drawing indicating that “an additional 150 is added to spool lengths for “field fit up” (FFW)”. However most experienced welders will know what’s going on once they see the FFW notation … they don’t really care how much extra has been added, and they’ll do what they have too to make the connection …simple as that.

[Alan Smith]

The point is that your model is built to the correct dimensions and the additional 150mm is required because of the uncertainty that a particular connecting component will not be where the model shows it.
The designer will place an FFW at this point
Isogen will therefore generate the dimension without the additional 150 and indicate FFW.
In my world I do not allow ANY manipulation of an Iso.dwg after it is generated.
FFW will be defined as “150mm longer than the dimension shown” in the fabrication spec.

[James Pennock]

Good comment Garzabla1 B)

[Mark Layport]

Garzabla1

…Isogen will therefore generate the dimension without the additional 150 and indicate FFW.
In my world I do not allow ANY manipulation of an Iso.dwg after it is generated.

…So you pass the confusion & difficulty on down the line to the “lower bidding fab shop”, where the real brainy people work, because the wages are lower, to fabricate your spool pieces, and hope they read and intrepid your notes correctly, to calculate the “correct dimension” for fabrication!??
So what is the present day definition of a good piping designer? One that generates and document piping systems in a “monkey see, monkey do environment” only according to the limitations of his 3D piping program? …OR designers that can see beyond the fancy 3D program down to the construction people and try to make piping drawings that are really easy to read and understand to help eliminate possible confusion and construction errors? Draw your own conclusions! 😉

(10+1 …10+1) @ JOP – Tsk –Tsk! … :huh:

[Alan Smith]

There are many requirements in a fabrication spec. It is the responsibility of the fabricator to interpret all of the clients requirements on their spool sheets. The welder uses cut sheets, NOT the Iso. The conclusion I draw is that your low opinion of the intelligence of fab shops and your lack of knowledge and obvious disdain for 3D CAD systems hardly justifies your status as a Platinum Member. It’s quality of posts not quantity

[Mark Layport]

Garzabla1

…The conclusion I draw is that your low opinion of the intelligence of fab shops and your lack of knowledge and obvious disdain for 3D CAD systems hardly justifies your status as a Platinum Member. It’s quality of posts not quantity

My my, did I ruffle someone’s feathers or what!?? You know I like your arrogance! I really mean that, a good piper has to have a fair amount to be really good at this profession. However you need to guard that it doesn’t close your eyes to other possibilities! …I’m here (as many are) to share my experience and to learn what others think about this great profession. I offered my “opinion” on a subject that is an issue (good or bad) with most of this industry today. You can learn from it or shut your eyes and continue blindly down the path.
You did peg me correctly as having “disdain” for 3D CAD systems, where it promotes a short cut on how to view a project, so engineers now no longer have to know how to read a technical drawing! Worse yet where it flattens that design into the “normal” 2D representation and generate drawings for construction that are so poor they don’t meet any drafting convention of the last 50 years! And lastly it gives the designer/draftsman the excuse that they can’t properly document drawings because the 3D program doesn’t have that capability! …Or the designer the knowledge to know how!
Do you really think all fab shops generate shop dwg.s for each spool? When Iso-gen lists all the cut lengths of each spool leg? I’ve seen shops fab from Iso’s …all part of that low bidding shop subject we touched on earlier. As far as my “Platinum Member” status you are correct, it is a rating of post quality, because I’m here and I contribute …where have you been!??
I offer one last “opinion” …If you’re willing to listen to people that disagree with your ideas; you have a chance of be coming very intelligent. If you only want to talk with people that agree with you, you will learn NOTHING.

[Mark Pearson]

Hey folks,

Thanks for the interesting comments, some of which turned into a bit of a heated, close to the knuckle debate.

My own preference on this, would be to show the dimension as 575(+150) or 575+150, this clearly defines on the iso what is required of the fabricator, regardless of what supplementary notes are/are not included, also regardless of the type of role the design company has be it EPC/EPCM, also regardless of any company fabrication spec or client fabrication spec or even fabricators own fabrication spec….in some cases you may require more than +150, so clearly defining this on the iso, surely is the simplest method and clarifies any possible confusion, also correct me if I’m wrong, but if it’s stated on the iso, then that should take governance…..

Cheers

[colow]

Hi everyone, my 2-bobs worth.

I totally agree with mtvalla. As both a fabricator and drafter the only thing the fabricator is interested in is a clearly defined Isometric.
By the time the fab shop receives the AFC drawing all things should be sorted.
The dimension plus allowance as described above is good as it cannot be interpreted as anything else.
Isometric drawings need to be as clear as possible with a minimum of unnecessary information as possible.
Too many times now we see drawings which are very difficult to read due to either unnecessary info or too much squashed onto one page.
There is no need to have the dimensions of standard fittings on the iso which seems to be very common now. Its only a matter of configuring the iso generation software to the desired output.

Cheers

[Author]

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