Thanks Geoff...
We did propose to design our network at 1.0m/s, however as you note
energy is extremely cheap here in the Middle East. The additional
pump head means bigger motors and greater power consumption, as you
say life cycle costing plays a huge role. We are in the process of
having the network analysed to ascertain the effects of the higher
velocities with regards to surging and water hammer.
Have you witnessed a large reticulated system undergoing water
hammer, from your experiences as far as a rule of thumb goes what
scenarios must we avoid?
Do you have an affiliation with Tyco? They are selling ABS here,
however our ring mains are at between 1050mm and 1200mm. I have been
informed ABS is only supplied up to 800mm.
The concern we have with plastics such as HDPE or ABS is the
expansion, apologies- contraction, upon filling the network and
chilling it to 4 degrees. The contraction rates are significantly
greater and in our case we need to minimise the contraction as much
as humanly possible- pipes move then streets and infrastructure
move...We designed with steel and utilise thrust blocks, anchors and
expansion loops to reduce any effects on the site from contraction.
Steel obviosuly has the ability to sustain greater stresses than
plastics.
We designed with the structural reliability of steel, and trust me we
understand the problems associated with a break in the vapour seal
and the possibility of ground water ingress. We have very stringently
specified the jointing of the jacketing and will pay very very close
attention on site to installation procedures and the like.
Do you have any experiences with leak detection systems? I'm told
they don't work....
What are your experiences with contracting companies in the Middle
East? I'm told to be careful....
Thanks again for your time
Ken Eppleston
Middle East
- In PipingDesign@yahoogroups.com, Geoff Stone DD&D Australia
<blenrayaust@y...> wrote:
>
> Hi Ken,
>
> I am also involved in the design of reticulated chilled water
systems in the Middle East. I have undertaken the surge analysis and
the pipe stress analysis of the chiller and cooling tower rooms. In
addition was responsible for the design philosophy of the buried
pipelines.
>
> The velocities that you are designing for appear high but it
comes down to a life cycle cost analysis. It isnt a real problem if
energy costs are low as in the Middle East. Hogher initial velocities
do add to the likelihood of high surge pressures due to loss of
power. It is a question of change of momentum.
>
> As for the material of choice the pre insulated ABS has so many
benefits compared to steel. You raise the prospect of failure. With
insulated buried steel you have the long term risk of failure from
corrosion. This corrosion is both inside and outside of the pipe.
Maintaining the vapour barrier for buried steel is a nightmare.
>
> ABS is not the same grade that is used in the USA. It has been
manufactured in Australia, Malaysia, Indonesia, Switzerland and the
UK for over 30 years. The relavant standard is AS 3518. Design of the
bruried pipelines should be to AS 2566. It is the material of choice
for Sydney Water's sewerage treatment facilities. These are important
infrastructure assets that cant stand failures. The prime reason
being that to bypass the plant would cause an environmental and
health hazard. The plants never get turned off!
>
> In Europe 95% of pipelines for the water and wastewater are
plastic. It is as prevalent in the USA but they have established
ductile iron industries . Their raw material is scrap iron and
steel. Without this low cost feed stock the industry wouldnt compete.
>
> As for waterhammer this has to be taken seriously. ABS offers the
benefits of a low modulus compared to GRP, steel and ductile iron.
This translates into lower celerity and hence lower surge pressures.
>
> GRP has some real hooks in design if you consider the design
requirements of BS 7159 or ISO 14692. Other standards do not cut it
as far I am concerned.
>
> I will send you some technical papers on the comparative criteria
betweeen ABS and GRP.
>
> regards
>
> Geoffrey D Stone
>
> Ken Eppleston <keneppo@y...> wrote:
> Hi
>
> I am an Australian engineer working in the Middle East designing
some
> particularly large district cooling networks.
>
> My experiences have been somewhat restricted to smaller systems
> within Australia and I am looking to tap into the expertise of this
> forum to educate myself on the best design practices for large
> systems.
>
> One of the critical factors obviously in the pipework sizing is the
> tradeoff between pipe diameter, velocity and system head losses. We
> are looking at designing our network with a maximum pressure loss
of
> 100Pa/m and allowing the velocity to go as high as 2.5-3m/s on the
> main ring of the system.
>
> The branch take offs are being designed at a lower pressure drop
than
> the ring main to ensure we can get adequate flow into the branch
> lines.
>
> Anybody have any comments or suggestions regarding these design
> parameters?
>
> Further to this we have selected our piping material to be of steel
> only as we view any risks associated with a rupture as
catastrophic.
> We understanding that GRP has been used previously on this type of
> application but we are hesitant. Does anybody have an agreeing or
> disagreeing opinion to these comments or justifications for using
> GRP? I understand that the significant benefit is resistance to
> corrosion.
>
> These projects we have here in the Middle East are somewhat beyond
> the scope of your average building chilled water project, any that
I
> have experience with anyhow, and it is extremely important that I
> consider all phenomena which may occur.
>
> Are there any rules of thumb, or good design papers, or the like,
> which are applicable to thrust block, anchors or expansion loop
> design, and the best locations within a network to use these
> components, which may assist in our preliminary designs.
> At present we are very much relying on the stress analyst to
provide
> advice.
>
> Other problems such as water hammer I understand are also important
> considerations, cause if it is missed now it can be very
troublesome
> further down the road, as with any project.
>
> Does anybody have any suggestions regarding those considerations in
> the design of a large cooling water network which MUST be factored
in
> to the network design at an early stage to ensure at the end of the
> day the system runs efficiently and trouble free.
>
> To give you an understanding of our design, it involves approx 80km
> of network piping flow and return lines to a number of plants on
the
> site.
>
> Thank you in advance for all suggestions and I eagerly await some
> responses.
>
> Thanks and kind regards
>
> Ken Eppleston
> Mechanical Consulting Engineer
> Middle East & Australia
>
>
>
>
>
>
>
>
>
> =========================================
> PipingOffice - Excel Spreadsheets for Piping Calculations
> http://www.pipingoffice.us/
> =========================================
> Main site: http://www.pipingdesign.com
>
>
>
>
> ---------------------------------
> YAHOO! GROUPS LINKS
>
>
> Visit your group "PipingDesign" on the web.
>
> To unsubscribe from this group, send an email to:
> PipingDesign-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to the Yahoo! Terms of
Service.
>
>
> ---------------------------------
>
>
>
>
>
>
>
> Design Detail and Development (a division of Blenray Pty Ltd)
>
> Mail Address PO Box 1351 Castle Hill NSW 1765 Australia Tel Mob
0402 35 2313 Office 02 8850 2313 AH 02 8850 2324
> We specialise in pipe network and waterhammer analysis, pipe stress
analysis, the design of buried pipelines and thermoplastic pipe
systems.
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
Received on Sat Dec 17 00:32:00 2005