PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.R 1 = bending radius in water filled section (m)R 2 = bending radius in air filled section (m)EJ = pipe stiffnessFollowing mathematical relations can be developed :PR 1 min =R 2 min =w 1Pw 2A.5-4)A.5-5)T = P + w 1 ⋅ hA.5-6)Pcosα =P + A.5-7)w h1 ⋅As mentioned earlier w 2 > w 1 if the design air filling rate is less than 50 %. The radius R 2at surface will be critical in this case, ref. A.5-4) and A.5-5).The relationship between w 1 and w 2 can approximately be written :w1 − a= A.5-8)a2 ⋅ w1a aa a = air filling rate (a > 20%)From formula A.5-4) and A.5-5) we can find the necessary pulling force using the critical radius,R min , from table A.3.5.1.1.P 1 = w 1 ⋅ R minP 2 = w 2 ⋅ R minA.5-9)A.5-10)The greatest force of P 1 and P 2 will be the pulling force to be applied in the project.Example 2A Ø 500 mm PE80 SDR26 pipe is to be installed to 50 m water depth.The pipeline has a loading degree corresponding to 25% air filling. The sinking shall be carried outusing a safety factor 2.0 against buckling. Density of seawater can be set to 1025 kg/m 3Decide the following factors :a) Minimum bending radiusb) Necessary pulling force in the end of the pipec) Maximum tension stress in pipe walld) The angle, α, at the return point in the S-curveSolution :a) Minimum bending ratio is taken from table A.3.5.1.1 :SDR = 26 ⇒R = 34DRmin = 35 ⋅ 0.5 m = 17 mSide 69 av 84