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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The maximum tensile force (Z) is exhibited at the bursting head (1), but without a bending moment. With the weld factor αw, the net cross section AQ,n (after deduction of the screw holes) and Ez≥ Edis the tensile stress calculated: Equation 5: (Formula: Ermittlung der maximalen Zugspannung σZ) (→ Table: Equation variables) of mathematical variables (Image: Inside view of the pulling head with bolt connections) (Image: Pulling head with bolt connections … |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) At the old pipe (2), the determination of the σZ is based on the tensile force (Z), the new pipe cross-section area, the bending moments and the moment of resistance of the cross-section: Equation 6: (Formula: Ermittlung der maximalen Zugspannung σZ Am Altrohr) with (Formula: Wq) With full wall systems (Formula: Wq bei vollwandsystemen)(Table: Equation variables) |
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May 12, 2020 AE-08 Replacement: Pulling-In the Pipe String during the Pipe Bursting Process NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The tensile force Z [kN] produces a tensile stress σZ in the pipe, which must be less than the allowable tensile stress. (Formula: Rohr Zugspannung σZ) The allowable stress is dependent on
Only winches capable of measuring and recording the pulling force should be used. |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The compressive stress in the old pipe (2) is calculated as follows: Equation 7: (Formula: Die Druckspannung am Altrohr) (Table: Equation variables) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The tensile stress from equation 5 and equation 6 is used to calculate the expansion, and the compressive stress from equation 7 is used for the compression. Equation 8: (Formula: Berechnung der Stauchung εz) Equation 9: (Formula: Berechnung der Stauchung εd) (Table: Equation variables) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) (Image: Tabellenicon) Taking into account any later occurring axial expansion due to internal pressure in non-pressure pipes or bending strains in curved pipes, the expansion εzshould not exceed of 2.0 % during the pulling in. If an expansion of 2 % is allowed during the pulling in, the expansion in the bends is also to be a further 1 to 2 %. |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The new pipe is fed through a support bracket, located at the top edge of the insertion pit, into the old host pipe with sufficient clearance (due to the expansion). In general, it is recommended to shorten the insertion pit by using additional roller supports, at a distance I3 from the edge of the trench, to increase the clearance Δh3 [mm] above ground level. Equation 10: (Formula: minlG) For PE pipes (SDR 33, 26, 21 and 17) without additional support (… |
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May 12, 2020 AE-08 Replacement: Pulling-In the Pipe String during the Pipe Bursting Process NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The minimum insertion pit dimensions are determined using the following parameters [DWA-A 143-2]:
(Image: Pipeline and insertion pit parameters (sufficient overcut … |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) Basis for the calculation model The required insertion pit length lG is determined for an unrestrained pipe, i.e., freely stored at the top edge of the pit, insertion with clearance between expansion and the new pipe (i.e. Ᾱ1 = 0). lGresults from the following conditions:
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) Interpolation between the curves is allowed. Input values: (Formula: minlG) (→ Table: Equation variables) of mathematical variables (Image: Diagram for the required pit length lG for PE pipes SDR 21 (SN 8) during the insertion into the old pipeline (clearance Δh / dL,a)) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) Below are the diagrams for determining the pit length for PE pipes (SDR 33, 26, 21 and 17). (Image: Required insertion pit length lG for PE pipes SDR 33 (SN 2) pulled into a host pipe (clearance Δh / dL,a) [DWA-M 143-2 draft]) (Image: Required insertion pit length lG for PE pipes SDR 26 (SN 4) pulled into a host pipe (clearance Δh / dL,a) [DWA-M 143-2 draft]) (Image: Required insertion pit length lG for PE pipes SDR 21 (SN 8) pulled into a host pipe (… |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) If the insertion pit is excavated along its entire length, pipes can be pulled in two directions. (Image: Insertion pit for the pulling in of two pipelines) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The maximum strain of σ = 21 N/mm2 (Short Term) applies to PE pipes before buckling damage occurs, which is limited to (γ = 1.4) max σ ≅ 15 N/mm2 during installation. This strain includes the short-term modulus Eσ=15 = 500 N/mm2 and the elongation max ε = 3 % (DVS 2205-1 guideline). In order to prevent pipe buckling during the pulling in procedure, the radius of curvature is to be determined as per equation 11: Equation 11: (Formula: Krümmungsradius … |
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May 12, 2020 AE-08 Replacement: Pulling-In the Pipe String during the Pipe Bursting Process NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) To the max. RKbelongs the maximum allowable strain εK, with: Equation 12: (Formula: die maximal zulässige Dehnung εK) Due to the buckling danger, the strain max σKmust be reduced accordingly (see table on the next page). The associated modulus of elasticity can be approximated by interpolation: Equation 13: (Formula: E-Modul) (Table: Equation variables) |
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May 12, 2020 AE-08 Replacement: Pulling-In the Pipe String during the Pipe Bursting Process NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) In addition, the variability of stresses and thus the effective modulus of elasticity Em [N/mm2] of the pipe over the pit length lG , and the pipe diameter are taken into account as follows: Equation 14: (Formula: E Modul Em N mm2) (Formula: a von EModul Em Gleichung) If the pulling in of the pipeline takes place in temperatures other than 70 °F (20 ° C), the pit length can be corrected as follows: Equation 15: (Formula: Ermittlung des maximalen … |
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May 12, 2020 AE-08 Replacement: Pulling-In the Pipe String during the Pipe Bursting Process NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) With a longer interruption of the insertion process, the pipe in the insertion pit must be secured so that the maximum allowable bending radii (radii of curvature) are not exceeded. |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) Congratulations! You have successfully finished this module. Next you will have the opportunity to review the newly acquired knowledge with an interactive questionnaire. You can still navigate back to any point in the lessons if you wish to review a specific point or subject. Stay curious! |
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May 12, 2020 This module focuses on the parameters that must be considered when pulling in the pipe string for gas, water and wastewater pipelines. In addition to a basic description of the replacement procedure, the importance of tensile forces, bending radii, and the dimensioning of the excavation pit is therefore the focus of attention. After completing this module, you will have a sound knowledge of:
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