PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.Since the relation between L and H is known for a given project, it is possible to calculate a "sinkingcurve" for p i as a function of L. This curve is essential during installation.∆h will appear as an under-pressure in the pipe and must be controlled against risk of buckling, (ref.A.3-16).To make the regulation of the sinking speed easier in the initial phase of the submerging procedure,it is an advantage to have a high value for the singular loss coefficient, k s . This can be done byusing a reduced inlet diameter (T-pipe) compared to the main pipe. A suitable diameter can be inthe range 1 / 3 D to 1 / 20 D (under-pressure must be checked).We recommend to keep this opening constant during sinking.There is a maximum sinking speed at which the sinking PE-pipe has a risk to oscillate.This speed can be estimated roughly from the formula :212k ⋅ π ⋅ D Ev = ⋅ ( )A.5-14)22 ⋅ S ⋅ H ⋅ n 2 ⋅ SDR ⋅ ρk = support factor (k = 1.0 for freely supported, k = 2.25 for a fixed situation)S = Strouhals number (≈ 0.2)D = external diameter (m)H = maximum installation depth (m)n = safety factor (assume n = 2.0)E = modulus of elasticity (short time) (kN/m 2 )ρ =mass of pipe, content (water) and oscillating water pr. unit of pipe volume(ρ ≈ 3.0 t/m 3 /m)If we assume E = 8⋅10 5 kN/m 2 , k = 2.0, and maximum depth = 50 m, formula A.5-10) can betransformed to :2−12v = 1.2 ⋅ D ⋅ (SDR)A.5-15)Formula A.5-15) gives an indication about the maximum sinking speed, but the buckling risk mustalso be considered. For small diameters, the formula is a bit conservative compared to experiences.Oscillations during sinking will normally not harm the pipe.Example 3Calculate the maximum sinking speed for a PE-pipeline as a function of diameter SDR classes26 and 33. Assume maximum depth to be 50 m and D ≥ 600 mm.Solution :We use formula A.5-15) and plotthe result graphicallyas shown in fig. A.5.3.V(m/s 0,90,80,70,60,5SDR = 26SDR = 330,4Fig. A.5.3 Maximum sinkingspeed to avoidoscillations0,30,20,1600 800 1000 1200 1400 1600 D(mm)Side 72 av 84