Dear all,
I agree that Isometrics are to be dimensioned. This would also be the
basis for developing shop drawings.
I have seen while working with with one of the Petrochemical plants, where
consultants have provided them Node numbers and Node-to-Node distance as a
table on Isometrics with no information on supports. Working with such
Isometrics is definitely painful.
Showing locations/type of supports on Isometric is a good idea, but I have
seen difference of practice by different consultants.
In addition to the information as indicated by Mr Adolphus, the FIELD WELD
locations are also shown by some of the consultants in Engineering phase
which are usually verified (changed if required) by the field peronnel.
There are cases where Isometrics are developed for lines < 1-1/2", if they
are critical process lines. For other small lines (<1-1/2"), usually
utilities, a "Guidance" isometric is prepared for the pupose of arriving
at required Material Take-off.
With best regards,
D.K.M.Rao.
adolphus.o.omodu@exxonmobil.com
04/13/2005 08:34 AM
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PipingDesign@yahoogroups.com
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Subject
Re: [PipingDesign] Dimensioned Isometrics
Gents,
I decided to respond to this mail as it interestingly coincided with a
discussion we had some 4 days ago in my department.
My experience over the years is that piping isos are normally dimensioned although they are not usually drawn to scale. This is why somebody could describe them as rough guides "normally given to pipe fitters". It is also partly because of this "not usually drawn to scale" issue that Piping General Arrangement drawings are very important alongside the Piping Isos.
The benefits that accrue when isos are dimensioned cannot be
overemphasized. Someone has already spoken about Piping stress analysis
which are often carried out b/w nodes (with defined length/diameter
dimensions) created out of isometric drawings. There are several other
design issues like Settle-Out pressures in piping downstream of
compressors
- where you require pipe lengths and vessel volumes to estimate pressures,
instrument tie-in points/locations along plant piping as these often
require specified minimum lengths from other fittings for good operation,
piping supports locations where you must necessarily indicate distances
b/w
adjacent supports for flexibility anlaysis etc.
Just to make the point clearer may i just quote verbatim a piping/layout
specification that was required from bidding contractors on a major EPC
job
(>$ US 500M) that has been successfully completed in Nigeria by one of the
Oil producing majors (Not MPN).
"Produce a complete set of piping isometrics for all piping other than
such
small diameter minor services (generally 11/2" and below). Isometric Sheet
should include a full material take - off (MTO) for each drawing c/w
piping spools and fitting dimensions. Isometrics shall include hydrostatic
test requiremenst, stress relief limits, field welds and insulation
thickness, All welded attachment pipe supports shall be shown"
For me, i'll go for dimensioned isometrics anyday.
Hope i have not taken much of your time.
Adolphus Omodu
"Steve McKenzie"
<Mechproj@xtra.co.nz> To:
PipingDesign@yahoogroups.com
cc:
Subject:
[PipingDesign] Dimensioned Isometrics
04/07/05 01:32 PM
Please respond to
PipingDesign
Gents+2
I have just had a friendly discussion with a South African colleague
who maintains isos are normally dimensioned and are used as part or the
formulation of the Schedule of Quantities; BOM; whatever.
My experience with isos is that they are comics that we give to the
pipefitters as a rough guide. Occasionally I have used dimensioned isos
to display fixed and toleranced dimensions around critical plant for
shop spooled piping, but in general I just use them as a sort of road
map. We are not talking 3D CAD here.
My question is do you guys normally put dimensions on Isos, and if you
do what sort of plant do you normally work with?
Cheers
Steve
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[Non-text portions of this message have been removed] Received on Wed Apr 13 04:22:00 2005
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