PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

More documents

Recommendations

Info

Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.The buckling pressure p bucl can be written :pbucl2.2 ⋅ s ⋅ E k= ⋅ p buc ⋅A.3-18)lFl = length between the supports (centre distance – width of support)p buc = buckling pressure for unsupported pipe (ref. formula A.3.16), k=1.0)s = wall thicknessk = reduction factor due to ovaling, ref. fig. A.3.2.1.1F = safety factor (2.0)Example 8The pipe described in example 7 is equipped with concrete weights with a centre distance of 3 m.The width of the blocks is 0.4 m and the diameter of the pipe is Ø 600 mm.Calculate the safety factor against buckling.Solution :The wall thickness is :Distance between the supports :600s = mm = 18,2 mm33l = (3-0.4) m = 2.6 mBuckling pressure for unsupported pipe, assumed k= 1.0 in formula A.3-16) :pbuc2 ⋅ 200=21 − 0.41⋅(33 −1)3MPa = 0.0145 MPa≈1.5 mwcWe apply formula A.3-18) with F = 1.0 :p bucl2.2 ⋅18.2⋅=2600200⋅0.0145⋅ 0.65 MPa= 0.017 MPa≈1.7 mwc1.7The safety factor against buckling is : F = = 0. 852.0As we see the safety factor has increased from 0.5 to 0.85, but the pipe will still buckle.Buckling will happen when the creep modulus. E, is approximately 275 Mpa. This happens afterabout 10 years of operation (ref. fig. A.1.1).To reach a safety factor of 2.0 in this specific case, the following solutions can be considered :−−−−−Shorter distance between the concrete weightsSupport of steel ringsInstallation of the pipe in a trenchIncrease of pipe diameter to reduce the under-pressure caused by frictionIncrease the wall thickness to improve the capacity against bucklingThe choice of solution must be based on a technical/economical assessment. For more advancedcalculations see [12].In next chapter we will consider buckling of a pipe installed in a trench.Side 34 av 84
Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.A.3.2.2 Buckling of pipe in trench / soil pressureA pipe installed in a trench has a significant better capacity against buckling than an unsupportedpipe. The most important factors are :−−Ring stiffness of the pipeModulus of elasticity for the soil (tangential modulus)The buckling pressure (q) can be estimated by formula A.3.19) [8]:q = 5.63⋅ 1R ⋅ t ⋅ αFA.3-19)α = δ1 − 3 ⋅DA.3-20)S R = termring stiffness, shortS R = E312 ⋅ (SDR −1)A.3-21)1E t = 2 E 1 s = tangential modulus for the soil1E s = secant modulus for the soil (ref. fig. A.3.2.2.1)δD = ovaling ( ≈ 0.05)F = safety factor (should never be less than 2.0)Secant ModulusE`s MN/m 2Filling heightH mFig. A.3.2.2.1 Secant modulus for granular soil versus filling heightin submarine trenches.For a pipe installed in a trench we have to add the pressure caused by soil cover to the underpressurecaused by hydraulic flow.The soil pressure (q s ) around a PE-pipe is considered to be uniformly distributed alongthe perimeter.q s = (γ-γ w )⋅h A.3-22)γ = specific gravity of soilγ w = specific gravity of waterh = height of soil coverSide 35 av 84
Page 1 and 2: Pipelife Norge ASTechnical Catalogu
Page 3 and 4: Pipelife Norge ASPE CATALOGUE-SUBMA
Page 33: Pipelife Norge ASPE CATALOGUE-SUBMA

PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

Create successful ePaper yourself

Delete template?

Save as template?