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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) Depending on its nominal size and material stiffness, the pipe is either rolled up completely on a coil reel or welded together on site using discrete long pipe sections. (Image: HDPE discrete long pipes DA 20 in (500 mm)) (Image: HDPE pipe on a coil reel) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The pipe front tip is equipped with a pulling head, which is attached to the pulling cable and winch. The tensile forces are transferred from the pulling head to the pipe through:
(Image: Conventional sliplining process with annular space - Design of pulling heads for pipes DN 6 in (140 mm) to 47 in (DN 1200 mm)) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) (Image: Temperatur) Monitoring temperature variations when working with plastic pipes, particularly on hot summer days, is essential to prevent substantial variations in the pipe length. To avoid this issue, it is recommended that the pipe insertion takes place in the early mornings, once the temperatures of the new pipes, the air, and the old pipes are almost the same. |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) (Image: Plus/Minus) Depending on the old sewer or pipe depth, the construction of relatively long insertion pits is necessary to avoid very small bending radii and prevent damage to the new pipe.
(Image: Static pipe bursting - Pulling-in of the new pipeline) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The pit length can be determined using the following formula [DWA-M 143-13]: (Formula: Die Baugrubeläange) lG : Length of the insertion pit in [m] hG : Depth of the pit (Pipe invert depth) [m] R : Minimum bending radius in m (manufacturer specified) (Image: Example design of an insertion pit for the insertion of plastic pipelines in a reference to [DWA-M143-13]) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The length of the insertion pit is determined by several factors, the most relevant being the minimum radius of curvature RK [m] of the new pipe. Plastic pipes are distorted during the bending process in such a way that the outside bend of the pipe (1) is elongated and the inside bend is compressed (2). Therefore, the pipe strain limits must be taken into account during the insertion process, and a distortion or stress analysis is to be completed.… |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The determination of the elongation strain is carried out by means of the maximum tensile stress σz. For this, the determination of the σz is necessary at both the bursting head (1) as well as at the old pipe (2). The larger value is used for the elongation strain determination. (Image: Static pipe bursting - Pulling-in of the new pipeline) |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The elongation limits for various plastic materials free from residual stress (isotropic material) are presented in the table below. The limits for safe installation conditions (short-term, γ = 1.4) are also given in the table. (Table: Elongation limits of various plastics [DVSM2205]) For PE pipes, the total outer bend elongation (from pulling and bending) may not exceed ε = 3 %. Due to the risk of buckling during compression, the max εK applies (see … |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The limiting values specified in the following table apply for HDPE pipes (materials free from residual stress - isotropic material). Other materials require further verification. (Table: Limiting values for PE-HD) 1. Diameter / wall thickness ratio (dL,a, dL,i [mm] Outside-/Inside diameter of the pipe / liner). 2. Allowable bending radius. 3. Allowable compression reduced by for 3 % for stability purposes. 4. Allowable longitudinal tension reduced by |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) (Table: Material properties of plastics (excerpt from DWA-A 143-2)) 1ASTM Legend: 2 ) Determined from liner deformation measurements. 3 ) Compressive stresses can be a decisive factor, particularly for thin walled liners. 4 ) Tested in accordance with DIN 54852 (4- point bending creep test), test procedure according to DIN 53457 , test specimen manufactured according to DIN 16776-2. 5 ) Higher values can be used in the calculation if they are approved … |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) (Image: Pipeline pulling force tension) (Image: Pipeline pulling force angle) The force required for the pulling in of the pipe is determined by:
(Image: Static pipe bursting pulling force) (→ Table: Equation … |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) Tensile forces from the friction between the new and the old pipe underground and above ground (coefficient μG) Equation 1: (Formula: Zugkraft aus Reibung des Rohrstranges im Altrohr Untergrund und auf dem Gelände)
Tensile force from the friction against the guide rollers (rolling friction, coefficient μR) Equation 2: (Formula: Zugkraft aus Reibung an Umlenkrollen (… |
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May 12, 2020 NA-08 - Replacement: Pulling-In the Pipe String during the Pipe Bursting Process (Demo) The table below provides the allowable tensile force for the pulling-in of HDPE and PE pipes. (Table: Maximum permissible tensile forces for pipes made of PE 80) |
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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) Interpolation between the curves is allowed. Pipeline weight: ḡL = AQ • YL [kN/m] A1 = (A1/ ḡL) • ḡL (→ Table: Equation variables) of mathematical variables (Image: Chart A1 / 6 bearing forces of PE pipes SDR 21 (SN 8) on the old pipe(A1) and the edge of the pit (A2)) |
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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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