Submerged Density/Density of Composite Pipes
Submerged Density/Density of Composite Pipes
(OP)
Dear all
From a survey report of a subsea pipeline, i am managed to read off the weight of the pipe in per metre run (say X). This weight has taken account of the various components of the composite pipes (i.e. concrete, steel and anti corrosion coating etc) and the buoyancy.
However, i need the submerged density in kg/m^3 for input into a FE anaysis. How do i go about it. Using X and divide it by either the the steel area (main strucutral component) or the gross area of the composite section seems to yield relatively low density. Is this the right way to do it?
(Submerged weight is approximately 176 kg/m and the steel pipe is 665mm and 26mm thick, with a 50 mm concrete coating.)
thanks
sgdon
From a survey report of a subsea pipeline, i am managed to read off the weight of the pipe in per metre run (say X). This weight has taken account of the various components of the composite pipes (i.e. concrete, steel and anti corrosion coating etc) and the buoyancy.
However, i need the submerged density in kg/m^3 for input into a FE anaysis. How do i go about it. Using X and divide it by either the the steel area (main strucutral component) or the gross area of the composite section seems to yield relatively low density. Is this the right way to do it?
(Submerged weight is approximately 176 kg/m and the steel pipe is 665mm and 26mm thick, with a 50 mm concrete coating.)
thanks
sgdon





RE: Submerged Density/Density of Composite Pipes
Density = mass/ volume
Submerged Density = submerged mass/ volume
where the submerged mass is the mass in air multiplied by the seawater bouyancy factor (0.868 according to my Baker Tech Facts book). As a check, make sure it's greater than the density of seawater!
RE: Submerged Density/Density of Composite Pipes
I am a bit puzzled regarding the low weight you achieve with the input parameters. From what you provide, and ignoring any contents and coating, I get 208 kg/m not 176 kg/m.
You need to be careful with FE, because some packages then use the diameter for bending stress determination. They calculate this using the extreme fibre distance of the steel from the neutral axis.
So, I would then take the submerged weight and assume that it is contained within an equivalent pipe equal to the outside diameter of steel. You need to take account of the reduced volume of seawater to provide bouyancy.
So, the answer is a fudge depending on how the FE package is going to use it.
RE: Submerged Density/Density of Composite Pipes
The problem is partly solved currently as far as implicit fe code is used. Same problem will surface again if an explicit code is used since then sqrt(K/M) will come into picture.