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Pipe Thruster:different applications for the installation of pipelines

Author: Dipl. Ing. Diana Pfeff, Herrenknecht AG, Germany

1. AbstractThe Herrenknecht Pipe Thruster series with thrust and pulling forces of 300, 500 and750 tonnes plays a powerful key role in the installation of pipelines worldwide,ranging from 8 to 60 diameter. Originally developed as a push/pul l unit to assist theHDD process, the multifunctional Pipe Thruster is now an established assistance toolin the trenchless pipeline laying industry.

As part of the system equipment for the Direct Pipe and Pipe Express method it isused to install the pipeline in one step directly into the ground. Furthermore, the PipeThruster increases the versatility of the HDD method towards even longer pipeline

crossings with larger diameters or under more difficult ground conditions by havingmore capacity & safety installed. On challenging HDD projects one or more PipeThruster(s) can be installed at the pipe side and support the HDD rig during pipelineinstallation with variably adjustable loads. Other applications include the recovery ofstuck or defective pipelines, the installation of pipelines into existing tunnels or HDDlandfall projects where the pipeline can be pushed from onshore to offshore in orderto save costly offshore equipment. More than 50 successful projects have proventhat the coatings made of PP, PE, GRP, FBE or of concrete are not damaged duringoperation.

This paper points out the different application fields of the Pipe Thruster and its

benefits proven in some selected case studies.

2. Pipe Thruster: Overview of application fieldsThe Pipe Thruster was originally designed as an auxiliary tool for the pipe pull-in withthe HDD method. After its presentation to the public in 2006 on the Hannover Fair thefirst project was realized in The Netherlands.

Figure 1: The Pipe Thruster HK500PT exhibited at the Hannover Fair in 2006 clamping a 48" steel pipe

http://www.herrenknecht.com/en/functions/glossary.html#Pipelinehttp://www.herrenknecht.com/en/functions/glossary.html#Seahttp://www.herrenknecht.com/en/functions/glossary.html#Seahttp://www.herrenknecht.com/en/functions/glossary.html#Pipeline

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The fields of application where the Pipe Thruster can be used are described below.1. Auxiliary tool for Horizontal Directional Drilling (HDD)2. Installation of pipelines into existing boreholes or tunnels3. Recovery of pipelines from the ground4. The Direct Pipe Method (DP)

5. The Pipe Express Method (PEX)

2.1. Auxiliary tool for HDD (Horizontal Directional Drilling)The Pipe Thruster is installed on the pipe-site and can be used during pipe pull-in tohelp to push the pipeline into the borehole (in case of too high pull forces). The PipeThruster provides additional installation forces, the applied push force is added to thepull force of the HDD-Rig. A HK500PT Pipe Thruster and a 400-ton HDD-Rig forexample can apply 900 tons of installation force. In most of the cases the PipeThruster is installed as a reserve, but not always needed.

Figure 2: Pipe Thruster as auxiliary tool for HDD on a project in Saudi Arabia

2.2. Installation of pipelines into tunnels or existing boreholes orPushing pipelines into excavated open bore holes (e.g. created by means of HDD) orinto existing tunnels (e.g. created by means of Microtunnelling) is another applicationfield of the Pipe Thruster which is becoming more an more common in the pipelineindustry. This method has already been implemented in several projects worldwide.The maximum length of a pipe pushed in like this is currently 14,270ft (4,350 m).

Pipeline pull-in in tunnels

Saipem Australia, the principal contractor on the large Santos GLNG GasTransmission Pipeline Project in Queensland, Australia has used a 750to. Pipe

Thruster to install the 4,35km long pipeline in a segmentally lined tunnel. TheNarrows crossing was necessary to link the mainland to the Santos GLNG LNGfacility on Curtis Island. After the tunnel works had been finished in early February2014, the pipeline pull-in was able to start. As the tunnel was completely flooded tohost the pipeline there were no installations in the tunnel necessary and the pipelinewas pushed in by the Pipe Thruster within 14 working days in early April 2014.

Rig-site with HDD-Rig Pipe-site with Pipe Thruster

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2.3. Recovery of pipelines from the groundOld pipelines which shall be removed from the grid can be pulled out with theHerrenknecht Pipe Thruster whereas directly a new pipeline can be pulled in, in thesame hole. Also in case of a coating damage after trenchless installation of apipeline, the pipe can be pulled out again and the coating can be reworked for using

the pipeline again.

Figure 6: The Pipe Thruster pulling out a pipeline of the ground in the USA

2.4. The Direct Pipe method (DP)The Direct Pipe method was developed for the trenchless installation of pipelinesunder obstacles (like rivers or streets). Thus far, worldwide 38 projects have been

successfully completed with a maximum drilling length of 4,590ft (1,400m).

Figure 7: The Pipe Thruster used to push the pipeline into the borehole created from the Direct Pipe machine

Comparable with the jacking frame used for standard pipe jacking (Microtunnelling)with short concrete pipes, the Pipe Thruster acts as the thrust unit in Direct Pipe. It

separation plant

Pipe Thruster

Direct Pipe machine

Control container

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hydraulically grips the pre-fabricated and outlaid pipeline and pushes it into theground in strokes of five meters. Coated product pipes (with a diameter rangebetween 28 and 60) can be pushed directly. The required bore hole is excavated bythe Direct Pipe machine (AVN slurry machine). The machine is deployed at the frontend of the pipeline and pushed into the ground together with the pipeline. The

excavated material removed by the slowly rotating cutterhead at the tunnel face ismixed inside the machine with the drilling fluid (bentonite suspension) and then fedthrough a discharge line through the entire pipeline to the separation plant on thesurface (through a separate discharge line). After treatment, the material is pumpedback into the circuit via a feed line. The drilling fluid thus not only discharges theexcavated material but also supports the tunnel face.

2.5. The Pipe Express method (PEX)In contrast to Direct Pipe the Pipe Express method was developed for the half-openinstallation of pipelines where larger diameter pipelines (36 - 60) with lengths of upto 6,500ft (2,000m) can be installed. During the installation process, the soil is

excavated by the Pipe Express machine and transported directly to the surface by achain trencher and conveyor belt. The tunnelling machine is accompanied on thesurface by a buggy and the operators control vehicle. The pipe thruster installed inthe launch pit pushes the machine and the pipeline through the ground. Thesimultaneous excavation of the soil and insertion of the product pipe creates anoptimum pipe bedding situation.

Figure 8: The Pipe Thruster used to push the pipeline into the borehole created from the Pipe Express machine

The PEX system is used on projects where the open-cut installation of pipelineswould cause high investment due to special requirements. The system has manyadvantages in unstable soil or where the open-cut installation of pipelines wouldrequire measures such as groundwater lowering.

Pipe Thruster

Chain trencher

Pipe Express machine

Operator control vehicle

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3. Characteristics of the different Pipe Thruster ModelsHerrenknecht provides 3 different Pipe Thruster Models for different requirements(e.g. desired maximum clamping diameter).

Figure 9: Components of the Pipe Thruster [here: in operation as push unit of Direct Pipe]

Table 1: Characteristics of the three different Pipe Thruster models

Pipe Thruster Models HK300PT HK500PT HK750PT

Max. push and pull force (kN / tons) 3,000 / 300 5,000 / 500 7,500 / 750

Max. clamping diameter (inches) 36 48 60

Attack angle () 0 to 15

Weight (tons) 40 53 78

Dimensions (m)Length / Width/ Height Length / Width/ Height Length / Width/ Height

7,90 / 3,80 / 3,30 8,90 / 4,10 / 3,56 10,3 / 4,98 / 4,05

3.1. Design of the clamping unitTo match the specific pipeline diameter the clamping unit of the Pipe Thruster ismainly adapted by changing the clamping inserts. The clamping unit was designed toavoid damaging the coating of product pipes, such as gas or oil pipelines. Thecontact surface between the pipe and the clamping inserts is covered with hot-

vulcanized rubber. The surface area of the clamping inserts is dimensioned tominimize the contact pressure (3.5 N/mm) and shear forces (1.2 N/mm) on thecoating. Table 2 shows typical values for factory-coated coatings in comparison tothe effects of the Pipe Thruster HK500PT (under full clamping and thrust force).

In order to assure the lowest possible degree of damaging contact of the clampingunit with the coating of the steel pipe and to compensate unevennesses of thecoating or the pipe, the clamping inserts are coated with hot vulcanized contactrubber. The rubber applied on the clamping plates comes with a shore hardness of65 +/- 5 Shore A. Rubber according to ISO 868-2003 (DIN 53505).

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Figure 10: Clamping unit of the Pipe Thruster with clamping inserts with vulcanized contact rubber

Table 2: Comparison of characteristics of different pipeline coatings with the impact of the Thruster

SPECIFIC VALUES OF FACTORY-COATED STEEL PIPELINES(STANDARD CHARACTERISTICS) IMPACT OF PIPETHRUSTER

Coating Material Polypropylen (PP) Polyethylene (PE) HK500PT / HK750PT

Shear Strength /Shear Force [N/mm]

10 > 10 < 1,21)

Compression Strength /Contact Pressure [N/mm]

17,5 - 20 > 10 < 3,52)

Figure 11 and 12 show exemplary the specific clamping plates for a 48-pipeline

(OD=1290 mm) for the pipe Thruster HK500PT and HK750PT. Also marked are theloads given onto the clamping plates (and therewith to the coating and/or pipeline)under full clamping pressure of the hydraulic system (in the clamping cylinderspressing the clamping plates onto the pipe).

Figure 11: Clamping plates of Pipe Thruster HK500PT for a 48-pipe (clamping area = 5.240.000 mm) and loadsof hydraulically driven clamping plates (4 x 4181 kN)

1) shear force with an advance force of 5000 kN (500 to) / 7.000 kN (700 to) from Pipe Thruster (steel pipe DN1200 = 48).

2)contact pressure on the coating caused by the clamp of the Pipe Thruster HK500PT / HK750PT (steel pipe DN1200 = 48).

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Figure 12: Clamping plates of Pipe Thruster HK750PT for a 48 -pipe (clamping area = 7.264.000 mm) and theloads of hydraulically driven clamping plates (4 x 6272 kN)

3.2. Tests with different coatings executed in the workshop of Herrenknecht AG

Since 2008 Herrenknecht AG demonstrated in cooperation with various gas suppliersand construction companies by means of several coating tests in their workshop inGermany that no damage is caused to the coating. Pipes with PE (Polyethylene), PP(Polypropylene), Glasfibre Reinforced Plastic (GRP on PE) and Fusion BondedEpoxy (FBE) coating were tested at full clamping force of the clamping unit and at fullthrust force of the two large hydraulic cylinders.

Together with the German Gas Supplier E.ON Ruhrgas (today called Open GridEurope) it was shown that under full impact of push force (500 to) neither the PE-coating nor the GRP-coating was damaged by the clamping unit. No compensation ofthe wall thickness or debonding was observed.

Figure 13: PE-coated 48-pipe (left picture) and GRP on PE-coated 48-pipe (right picture)

Within the framework of these tests, two field joint coating materials were tested. Atclamping a PE-shrink slieve as well as a wrapping tape and additional one-component GRP mat - in opposition to the factory-made coating - clear damages onthe field joint coating were generated. The resulting consequence is that the field joincoating must not be clamped with the Pipe Thruster. It is recommended that theoperator has to recess this area with an additional safety zone. The clamp can onlybe attached were no irregularity on the coating is recognized.

Together with the Dutch Gas supplier Nederlandse Gasunie PP-coating(Polypropylen) was tested.

Thrust direction

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Figure 14: Test with a PP-coated 48-pipe with a Pipe Thruster HK500PT

4. Advantages / Field of application of the Pipe Thruster

- Reserve force for the pipeline pull-in in difficult HDD projects (large diameter,long distance)

- Central component for the Direct Pipe and Pipe Express method- Installation of pipelines into existing tunnels / boreholes- Maximum push and pull force of up to 7.500 kN (750 tons)- Installation of 2 or 3 Pipe Thrusters behind each other possible (push or pull

forces are added- Clamping unit highly flexible in case of moving pipeline due to mounting of the

hydraulic thrust cylinders onto the cardan joint- Minimum 22 Pipe Thruster successfully operating in the market since 2006- More than 60 successful projects without any damages neither on the coating nor

the pipeline- Several coating tests executed with several pipeline coatings where is shown

that the coating is not damaged by the Pipe Thruster: Polyethylene (PE),Polypropylene (PP), Glasfibre Reinforced Plastic (GRP), Fusion Bonded Epoxy(FBE), Concrete Coating

- Maximum shear stress on the pipeline coating (between clamping unit andcoating)is 1,2 N/mm

- Maximum surface pressure on the pipeline coating (between clamping unit andcoating)is 3,5 N/mm

- Power transmission via two big hydraulic cylinders- Cardan joint as connection for the hydraulic cylinders to the steel base frame with

0-15 vertical deviation and minimum 1,5 deviation to each side in the horizontal- Ability to fully open the clamping unit to fit it over the pipeline and thus no need to

guide the clamping unit over the product pipe- Infinitely adjustable clamping pressure- Infinitely adjustable push-/pull force- Easy centralizing of the pipeline in the clamping unit by a top-carriage- Integrated and height adjustable pipe-support- Measuring of the twist of the pipeline, for safe handling of the pipe

Thrust direction