Collapse Pressure of Subsea Pipelines

[maloneb]

Hey guys,

I don't know if this is posted in the correct section or not, I'm new to the site.

I'm currently working on a design tool to calculate the nominal wall thickness of a subsea pipe for variable inputs. In order to find the wall thickness for collapse, Equation G.1 from from PD8010 is manipulated to find the value of Pc. The equations is given below.

((P/Pe)-1)*(((Pc/Py)^2)-1)=(Pc/Py)*((Fo*Do)/tnom)

Where P is external pressure, Pe is critical pressure for an elastic circular tube, Py is the yield pressure, Pc is the characteristic external pressure (collapse), Fo is the initial ovalisation of the pipe cross section, Do is the outer diameter and tnom is the nominal thickness of the wall. This equation is rearranged to a value of Pc through use of the quadratic equation.

The program has been written so that for a given value of P, tnom is increased until the Value of Pc is greater than the value of P.This gives a nominal value of the minimum wall thickness needed to resist collapse of the pipe. This section of the program works fine, giving the same wall thickness required as in a previous version of the tool using a different method.

The problem arises when a value of Pc is needed further into the tool. The value of Pc is about 5 MPa greater than in the previous version. I believe there is a fault with how I have rearranged the equation.

So my question is, how would you rearrange the above equation to give a value of Pc, and what would the reformulation be?

Thanks

Ben

 

[BigInch]

Assuming this is a pipeline you should post in the pipeline fluid forum, as I know you already have. Please refrain from making more than one post in the future. Most of us cruise related forums anyway and we usually see both posts, then we don't know which one to answer.

We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer