DESIGN OF MUDMAT TO CARRY A PLEM (PIPE LINE END MANIFOLD) 2

[g550]

Hi all, Trying to design a mudmat to carry a PLEM (pipe line end manifold) to be located 11m below water surface, soil bearing =15kN/m2, besides the centriod of PLEM wrt that of the mud mat, what other factors do i consider?

 

[ishvaaag]

This article gives interesting ideas about. It is mainly dealing with expansion in such way that horizontal forces be minimized and interference with other necessary equipment in the area.

http://asme-ipti.org/files/1953/

 

[g550]

Thank you so much ishvaaag i found this very helpful, i am still concern about the mudmat and PLEM moving after installation due to water currents, the mud mat is already existing as 7.2m X 4.8m perforated carbon steel plate platform with 10mm thick steel plates forming 600mm x 600mm x 600mm grillage under the carbon plate platform.

 

[Ussuri]

Are you checking the soils capacity or designing the structure of the mudmat itself?

Typical loads you should consider include:

On bottom weight of the structure
Expansion loads from pipeline
Hydrodynamic which would be a combination of wave, current, tidal etc.
Fishing loads, but in 11m of water I guess that is not a concern.
Could impact from a passing vessel be a concern?
Loading applied at the connection/tie in

The foundations then need to be checked for various combinations of the above as determined by the designer.

The loads are assessed to determine the sliding and overturning forces the structure will be subjected to

For the foundation typically you would need to check bearing resistance and sliding resistance and also the overall stability envelope. Its also worth doing an assessment of settlement to see if this has an effect on the pipeline.

Other considerations include:

Seabed topopgraphy, is it flat or will your mudmat end up sitting at an angle?
Restrictions of the lay vessel, can the mudmat be actually be laid? Is there space or do you need hinged mudmats. More of an issue for reel lay where you have more of a space restriction.
Other restrictions during installation?

There will be other considerations but these will be obvious to you as the designer.

As a reference for foundation design you could look at DNV Classification Note 30.4 Foundations as this is one method commonly used.

 

[g550]

Thank you so much for finding the time to respond ussuri, your information is very helpful, I am doing both and was wanting to ensure i have taken into account all relevant considerations.