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installation phases of underwater HDPE intake lines - request for technical support

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Luigi Esposito
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I'm trying to build up costs for the installation of 4 x DIA 900mm HDPE pipelines, PN6.4, SDR26, PE100 from the shore into the sea for 1100m in dregded trenches. Installation shall include all material to bury and anchor on shore and to screens underwater the pipes. I'm wondering if someone can support me with an estimate of time and costs (equivalent standard manhours direct and indirect shall be sufficient) for the installation works and if it is possible a description of activity execution plan with equipment and organisation needed. We are in shallow water with pipe installation at 2.5m from 0 to -10m. Those are the only info I have and I can supply. Thanks for your support.

 

Luigi
 

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Luigi Esposito
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Yes for that I put a little contingency in the estimation but the tender is quite clear that those are recoverable costs. There is anyway the main area of risk that we do not have full control at the moment of the entire marine process. Mainly we are going to consider a dedicated suprintendent for this area during the engineering phase up to completion. What is the grey area? Permissions, Marine Authorities, Environmental study.

Luigi

Rafael Davila
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I also found Mike post very enlightening.

Just to make sure Murphy is not around check on the soil conditions under the seabed What if you got rock?

Luigi Esposito
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Rafael really getting a lot of info from that link. Good source of hints. Actually I made a sort of reverse costing from some similar quotations we received and our previous build experience. I set up a review meeting tomorrow with engineers to go thru and check if we missed any area. Both Mike and your contributions helped a lot in stepping forward.

Regrads

Luigi

Rafael Davila
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Actually I am not involved in marine construction, we do civil and building works and when as part of the job there is marine work such as in boat terminals we subcontract the marine part. Two months ago we quoted a ferry boat terminal, one of two similar quotes on this year but we were not the lowest bidder.

Last time I was directly involved on the estimate for a marine work, the company won and build the job. It was for the construction of an oil terminal for docking of ships to unload petroleum. The interesting part was on the construction of some dolphins. We rented the barge locally and the pile driving equipment from a Texas contractor.

I recall the mechanical engineering department of this company to use Gulf Books as reference mostly for piping works on pharmaceutical process piping.

At times we still use some reference books for our estimates when recorded production is not available, we use RS Means and adjust crew costs and crew production to our experience. In your case I believe Gulf Publishing books shall be a better reference.

For general knowledge the following might be of interest.

http://www.4shared.com/file/yzAFEGoh/Construction_of_Marine_and_Off.html

Luigi Esposito
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Posts: 9

Thanks Rafael for the references. Are you actually using one of those? Can you suggest one for our technical library in particular (cost estimation dept.)?

 

Luigi

Luigi Esposito
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Mike 100% clear. Appreciated very much. If any further question, I'll bother you again.

 

Thanks again Luigi

 

Luigi

Mike Testro
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Hi Luigi

There are two methods for this sort of shallow water pipeline over relatively short distances.

1.  Push out from an onshore anchor point using pipe jacks.

2.  Float out using bouyancy tanks.

If using the push out method you will need to dredge the channel and then install temporary guide piles along the line.

If floating out you will have to drag the bouyant pipes along the dredged line before sinking into the trench.

Dredging can be done from a 360 backacter on a shallow barge - piling can be done from a similar rig.

In any case the pipes will have an ante floatation concrete casing.

Production is governed by the welding and this is determined by whether you are using automatic or semi automatic methods.

With such a relatively small pipe 500m a day is acheivable using automatic welding and 200m a day for semi.

Hand welding would achieve less than 100m.

So the entire 1100m pipe can be laid in 3-4 days.

In either process you can only work during daylight so a 24 hr rolling shift would not be possible.

The process is continuous in the following sequence.

String pipes to the welding position from the stockpile using cranes and rollers.

The pipe is moved - either pushed or pulled through the welding stages

The welded areas are tested and then jointed.

A FOC cable is usually strapped to the pipe

If pushed the pipe is guided along the trench underwater.

If pulled the entire length is positioned over the trench and then sunk.

The trench is then backfilled (after removal of any guide piles) - depending on the tidal conditions the trench can be expected to silt up in anything up to 21 days.

I hope that helps,

Best regards

Mike Testro

Rafael Davila
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