PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.A.3 Static designIn this chapter we will present formulas to decide the wall thickness of the pipe taking into accountinternal and external forces acting on the pipeline.The internal diameter of the pipe is decided by the formulas in chapter A.2.We will underline that quite a few of these calculations are necessary to carry out in a realproject. It is important to sort out the significant factors with respect to the pipe’s service life.A.3.1Internal pressureThe internal pressure will create stress in the pipe wall both in the hoop direction and the longitudinaldirection. The stress in the longitudinal direction is dependent on the way the pipeline is able tomove (fixed or free movement).A.3.1.1 Hoop directionFig. A.3.1.1.1 indicate the static system.Fig. A.3.1.1.1 Static system forinternal pressure, cut pipe.Nσ rp PD mNσ rSNo shear stress will occur due to the internal pressure. There will only be a tensile force (N) inthe ring direction.If we integrate the pressure components we find the following result based on equilibrium offorces :2 ⋅ N = p ⋅ D m A.3-1)N = tensile force (N)p = pressure (N/m 2 = Pa)D m = mean diameter (m)Introducing the ring stress (σ r ) and the wall thickness (s), we can develop the following formulas :N=σ r ⋅SA.3-2)p ⋅ D mσ r =A.3-3)2 ⋅ Sp ⋅ DmS = A.3-4)2 ⋅ σrSince D m = D – s s = p ⋅ D(2 ⋅ σ r + p)A.3-5)σ r = design stress (see table A.1.2)D = external diameterSide 28 av 84