Pre-Trench vs. Continuous Burying

The best method is the one you are most familiar and comfortable with. If you are not the contractor who will do the installation but the one who must choose between competing contractors then you must do a diligent evaluation. One method to do this is through a series of meetings, first you must assemble a group of concerned individuals to identify and weight a series of important criteria (cost, time for installation, environmental impact during construction and after installation, etc.) All of these concerns should permit some numerical grading and a weighting factor to show the importance of each concern. Now only once this decision matrix has been agreed upon should another group meeting be held to evaluate each approach. This will give you a reasonable method to evaluate these two complicated approaches.

Dear Avatar Indo

Most if not all of the remarks made by Refred are sound and should "light the way ".

There are few clarifications which are needed to complement the advices given to you. These are :

1.What is the material of the pipe , its : diameter, lenght ?

2.Is it for : water, oil or gas ?

3.What are the constraints of the environment as this may mean that one of the methods you ( or we ),may suggest will not apply or need to have curtains to mitigate the sediments whilst digging the trench.

4.If the pipe is for petroleum it is generally cleaned by way of a pneumatically propelled piston or "pig " with which it is : emptied and or cleaned. In such case the pipe becoming empty can : float to the surface. To counteract this the pipe is straddled with concrete anchors ( at regular intervals ) which are tightly fitted to the pipe and keep it to the bottom.

5.If the pipe is not for petroleum what surfacing protection does it have for a semi permanent protection for many years in salt water ? Will it have : gunited concrete? cathodic protection ? anodes ? These aspects must be dealth with a great deal of care .

In conclusion it is right that you ask for advices because these underwater project work and their execution need to be very carefully planned and performed before burying ( a mistake can be very costly for your Employer - and for your Future - ! )

Labor Omnia Vincit

And don't forget about the environmentally detrimental affects regarding your Contractor plowing through vital coral beds! Is there any way to route this pipeline of your's around the coral beds and avoid their destruction?

I'm assuming that your are not in the USA, so does the country in which this project is being construction have any environmental laws regarding disturbance of coral beds? If yes, do YOU and your superiors know what those laws entail and how they will affect your project?

Mitigation procedures regarding destruction of coral beds?

A more environmentally friendly way is to directional drill the pipe into place. this of course depends on distance and budget, but it is easy enough to do to get under the coral and give you the required depth of burial.

Kindly advise where this trenching is to be located.

I have contact with a small firm who has trenching machines of various sizes that can help you, either doing the job, or advising you.

The pipeline diameter is API 5L gr X52 with diameter 16". The fluid is LPG phase liquid.

1. If we use pre-trench method (in coral seabed), is there any posibility problem because of erupted trench?

2. How we know that the buried pipa is 2 meter below the seabed?

3. When, we do the hydrostatic test ? before or after burying pipeline?

4. For submarine pipeline near the beach, there are need any drain or venting line?

Thanks for your advice

Dear Avatar Indo,

Your first answer on the size of the pipe gives you an indication : API . Itself if you look up the webb site should give you the :testing procedures with which the Institure itself regulates the Petroleum Industry world wide.

2.The second about: eruption is doubtfull (unless there are seismic risks, this goes back to having the line weighed down if it is ever likely to be empty ( wherein it might float and put upward pressure on the corral-cover backfill). (see below :5)

3.Regarding the hydraulic testing it again depends on the lenght of the pipe. Is it likely to be flanged ? If it is in segment with flanges both ends then it is best to have the individual lenghts tested ashore as removing air bubles needs : competence and experience to be certain of the results.

4.You have not said whether the pipe ends are likely to have the ability to receive an internal pipe cleaning. If yes , then the pipe would have at both ends a box which could allow you to have the internal air operated piston ( known in industry as " pig") which would largely assist you with the questions you have in mind.

5.Never forget that empty pipe floats quite well and this is why I originally asked whether your underwater section would be externally : gunited (high velocity air entrained cement ) to coat the pipe for protection but , as well , for keeping it where it should be : in the trench,

I think that all contributors have a warning on most if not all issues you have raised :

"Get the best technical advices and do not fool around with innovations or know-alls "

Labor Omnia Vincit.

Dear milister

Belong to discussion with submarine installation vendor, pre-trench work will be perform only for 100-200m from near beach. It means that not all of pipeline segment will be pre trench. that method is true? there are any reference can be justify the method?

The method to laying pipeline is push-pulling. Where is the more efective methode, pulling from offshore or onshore?

Thanks

Belong to discussion with submarine installation vendor, pre-trench work will be perform only for 100-200m from near beach. It means that not all of pipeline segment will be pre trench. that method is true? there are any reference can be justify the method?

The method to laying pipeline is push-pulling. Where is the more efective methode, pulling from offshore or onshore?

As far i know, marine mastic in concrete line-pipe functionally is continues string. If i did not use the material, there is any problem? Can i perform pipe stringing without fill the gap between pipe concrete?

Thanks

You can post trench or pre trench - post trench is usually easier as it can be difficult to keep the trench open, and to lay the pipeline in a trench.

Push v pull / onshore v offshore, depends on access and equipment availability. if the pipe is being installed from a lay barge, then you would "pull the pipe off the barge " from an onshore winch. if you have prefabricated the pipe and are using a towed method, then either would work. Building the pipeline onshore requires a big staging area for fabrication, but offshore winches are easy to find for pulling the pipe out.

Yes you can perform stringing without filling the "field joint" gap as long as it will be buried, otherwise you are providing an opportunity for fishing nets, anchors to easily hold / pull up your pipeline. (Subject to client approval) There are many methods of filling in field joints