PLEM PLET protection against trawling 1

[heyjaehey]

Hi I need to come up with a general senerios of protecting subsea structures against trawling. I found DnV F111 which talks about protecting against pipeline but can't find any for structures. Could you guys give me some starting point?

Thanks!

 

[GregLamberson]

heyjaehey

In addition to trawling damage, you may also want to consider protection against dropped objects from vessels.

I believe API RP 14C gives some guidance on safety systesm, including trawling damage. Also, try API 1111. Depending on your location, you can check 30 CFR 250, 49 CFR 192, and 49 CFR 195.


Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[GregLamberson]

heyjaehey

Had to run earlier, but wantesd to throw in a few other thoughts. There are basically two means of protecting subsea systems, be it pipelines/flowlines or equipment. These are, 1) reduce the marine activities in the area, or 2) engineer out or mitigate the risk by design.

Ideally, if you can eliminate the problem (vessels in the area), that is ideal. As far as the 2nd item, there are an 7umber of ways to approach – one is the use of passive protective structures that at least mitigate accidental snagging or dropping loads on to whatever it is that needs protectiong. This protection can be provided by the template base structure, tree guide frame, or some other independent protective structure. Another option is to design the facility to withstand the expected loads.

You can also install a "fence" either among or around the equipment. In this case, a horizontal structural member held by columns to a height just above the level of the equipment on the structure provides damage protection primarily from dragged objects. A fence tends to keep the dragged line, chain or cable from snagging or falling among the equipment and provides a snag point such that the pull will be taken by the fence instead of the equipment.

Another option is to install "covers" made of steel, concrete, fiberglass or soem other suitable material. These covers are primarily for the purpose of deflecting a dragged object or protecting from a dropped object. Protective covers can be provided (at least in theory), to protect against any dropped object. However, the cost goes up big time as the weight and velocity of the dropped object increases. In essence, larger, heavier covers themselves become a dropped object hazard.

I have not anyone try to provide damage protection for dropped objects more than the equivalent of a +/- 200 lb steel ball, or against dragged objects causing more than 100t lateral load. I would think, if you can meet those rule of thumb protections, then it should be sufficient to protect from frequently dropped small objects, and from fishing boats or service boat anchor lines.



Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[BigInch]

While what Greg says is true for pipeline tie-ins and other miscellaneous pipeline appurtences protruding above the mudline which are likely to be located almost anywhere in open seas, a PLEM will always be located close to a buoy or other structure within a restricted marine terminal loading/offloading area. These areas must be strictly and totally closed to all operations, further enforced by coast guard or terminal patrol boats when necessary. All ops not specifically related to the marine terminal's activities must be prohibited in these areas... especially trawling.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/