PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.b) To decide the puling force we have to know w 1 and w 2 .We apply formula A.4-2) to estimate w 1 (w 1 = w cw + w pipw w )w12d0.4618= a a ⋅ π ⋅ ⋅ γ w w1 = 0.25 ⋅ π ⋅ ⋅1025⋅ 9.81 N/m = 420 N442w 2 can be estimated from A.5-8) :The maximum pulling forceis given by formula A.5-10) :1 − 0.25w 2 = 420 ⋅ N = 1260 N0.25P = 1260 ⋅ 17 N = 21.4 kNc) Maximum tension force in the pipeline will appear in the return point.Formula A.5-6) gives :T = P + w 1 (1-a a ) ⋅ HT = (21400 + 420 (1-0.25) ⋅ 50 ) N = 37.2 kNThe corresponding stress in the pipe wall can be decided to :σ =π⋅ (D4T 2237200=N/m2 π 22− d ) ⋅ (0.5 − 0.4618 )4= 1.3 MPaIn addition there will be a stress in longitudinal direction due to internal pressure andPoisson’s number, ref. A.3.1.2. Formula A.3-13) gives :0.5 ⋅ 0.125σ l max = ⋅ (26 −1)MPa =20.78MPaMaximum tension stress is the sum of σ and σ max :σ max= (1.3+0.78) Mpa = 2.08 MpaFrom table A.1.2 we see that short time burst stress is 8 ⋅ 1.6 Mpa = 12.8 Mpafor PE80.12.8Safety factor regarding tension stress becomes: C = = 6. 152.08This result underlines that buckling is the most critical damage that can occur duringsinking (C = 2.0)d) The angle, α, at the return point is given by formula A.5-7) :21400cos α = = 0.58 = 5421400 + 420⋅(1− 0.25) ⋅50α ºAs shown in example 2, we can calculate the pulling force, P, to secure a safe installation combinedwith internal pressure.Experiences indicate that the pulling force calculated by the formulas in this chapter, givehigher values than more advanced methods.Side 70 av 84