Offshore Pipeline routing - straight section before bend 1

[robb4]

Which are the main parameter to decide the straight length of a pipeline at the starting point, before any bend? How to determine the minimum feasible length? As far as I know this length is connected to the friction of soil and should be at least one catenary length. Any help will be appreciated...

 

[BigInch]

Lateral friction of the straight length must be sufficient to provide the force necessary to initiate the bending action, otherwise the pipe will remain straight, or try to straighten out if you do manage to put an elastic bend in it. Pretend it is a cantilever beam of length x laying on the bottom. Length x = distance to the point where you will be beginning the bend. Apply a horizontal force at that point = the available friction and calculate the deflection and rotation at the beginning of the bend point due to that force. You must always be bending a little less than what that force will be able to bend the cantilever beam.

Independent events are seldomly independent.

 

[LittleInch]

From my limited knowledge, it is a mix of pipe tension, angle of pipe lay, water depth, soil friction, bend radius, pipe weight and strength and stiffness of your pipe. One catenery length sounds like a good start point to work from but might be a lot more. Unless you're working for an installation conractor, you probably should get buy in from an installation contractor that this bend can work. If you've got a piggy back be very careful as you will get added torsion and possible twisting, which for the main pipe that's probably Ok, for the piggy back....

Also don't forget that your installation vessel will need to perform a route arc on the surface wider than your final on bottom radius so you might run into what ever you're trying to avoid with your vessel or run out of water depth if you're not careful.....

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Also: There's usually a good reason why everyone does it that way