PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS
PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS
PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS
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<strong>Pipe</strong>life <strong>Norge</strong> <strong>AS</strong><strong>PE</strong> CATALOGUE-SUBMARINE APPLICATIONS, PI<strong>PE</strong>LIFE NORGE <strong>AS</strong>, December 2002.DFormula A.3-15) can be transformed by introducing the SDR ratio ( SDR = ) :s2 ⋅ E kp buc = ⋅A.3-16)231 − ν (SDR −1)From fig. A.3.2.1.1 we realize that the ovaling of the installed pipe is of significant importanceregarding the capacity against buckling. For a standard pipe an ovaling corresponding1-1,5% is acceptable. This gives a reduction factor k = 0.65.Example 6Calculate the buckling pressure capacity p buc for an unsupported pipe Ø 900 mm <strong>PE</strong>100, SDR26exposed to pressure surge. Short time E modulus is 1050 Mpa. Assume ovaling 1% and ν = 0.4.Solution :By use of formula A.3-16) and fig. A.3.2.1.1 we get :2 ⋅10500,65p buc = ⋅ MPa = 0,099 MPa 10 mwc231 − 0,4 (26 −1)=In practice this means that the pipe for a short period of time can withstand full vacuum.It is, however, usual to introduce a safety factor, F=2.0, for such calculations.We will not recommend to expose the actual pipe for an under-pressure greater thanp buc 10= mwc = 5 mwcF 2Example 7Calculate the safety factor against buckling for an unsupported <strong>PE</strong>100 pipe, SDR33 used as anintake pipeline. The pipeline is exposed to a constant under-pressure 2 mwc in the most criticalpoint. Long term E-modulus can be set to 200 Mpa. Ovaling is 1% and ν= 0.4.Solution :Using formula A.3-16) and. fig. A.3.2.1.1 we obtain :2 ⋅ 200 0,65p buc = ⋅ MPa = 0,0094 MPa 1mwc231 − 0,4 (33 −1)=p buc 1Factor of safety : F = = = 0, 5p 2appearThe pipe will buckle due to under-pressure before it reaches a lifetime of 50 years.Theoretically the pipe will buckle when the E modulus equals 400 Mpa. This will happen alreadyafter 1-2 years of operating (ref. fig. A.1.1).Underwater pipelines exposed to under-pressure can be supported by concrete weights if thedistance between the weights is small enough. Hence the capacity against buckling will increase.If the distance (l) between the supports (weights or rings) is in the range :s ⋅ D m 1.56 ⋅ s4 ⋅ < l ≤A.3-17)20.5(s/D )mSide 33 av 84
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