Submerged Pipeline weight

[maloneb]

Hey guys,

I'm trying to find the submerged weight of a pipeline and need to include the internal coating, the anti corrosion coating, the insulation and concrete coating.

Does anyone have an equation for this please?

Cheers

 

[BigInch]

You have to calculate the cross-sectional area of each material, knowing the thickness of each one. That would be area of a circle minus the area of the circle making up the other side of the material's thickness. Multiply by the density of each material and add them all up. That's the weight of the pipe and coatings and insulation per unit length. Now subtract the weight of a volume of water equal to the volume enclosed by the outermost circle, presumedly the insulation.

Are you sure you should be doing this problem?

Hopefully your answer will be greater than zero or the pipe will float.

We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky

 

[blacksmith37]

And it will depend a lot on what is in the pipe and into what it is submerged.
Footnote : In some situations of oil/gas in water, it is worth getting thicker pipe to reduce bouyancy.

 

[cvg]

for design purposes I would always assume the case where the pipe is full of air.

 

[chicopee]

The submerged weight will be the weight of the pipeline minus the weight of water that the pipeline displaces. The weight of the water is equal to its density times the volume of the pipeline. You should be able to figure the weight of the pipeline (including the concrete coating, insulation and paint) and the volume of the coated pipline.
My question is why would the submerged weight be important to you since there are a more important factors to figure out such as tension and bending stress when laying or raising the pipeline from a barge or to determine the anchoring details size when the pipeline becomes buoyant or displaced by currents.

 

[zdas04]

cvg,
I expand that to be "air at atmospheric pressure". I also add a big safety factor (i.e., if my pipe full of unpressurized air is less than 4 times the weight of the displaced water I add weights to the pipe). I had one float and don't really want to repeat that experience.

David

 

[maloneb]

Thanks guys. As always, very helpful.

The pipeline would initially contain water for the hydrotest of the pipe and eventually gontain oil or gas.

The submergred weight is needed for a design tool that calculates the wall thickness required. During the analysis of the desired WT, the submerged weight is found to go on to provide information needed to find the Bending Moment for operation/hydrotest.

 

[racookpe1978]

I think you missed the point of the many years of "real" experience just provided you.

Didn't you see the hazards of "underestimating" the buoyancy of a submerged pipe the previous engineers just wrote for you? Then you come back commenting about a theoretical case of a computer-designing the pipe wall thickness based a theorectical bending stress based on (??) criteria for water-filled pipe undergoing a hydro test?

The earlier comments showed that submerged pipes may require extra-thick walls just to provide enough weight to prevent bouyancy problems for an air-filled pipe being laid through the liquid/river water/mud/muck. Given that, why would you assume that the water-filled hydrostatic condition was a limiting stress case for pipe wall design?

 

[ilzafcukena]

you need to consider the Specific Gravity of the pipeline on the seabed during installation,hydrotest and during operation.

Make sure that the Specific Gravity is equal or higher than 1.1 based on DNV-OS-F101, Oct 2010. This is because the specific gravity is depends on the submerged weight of the pipeline for each case.

Thanks.