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ISSN 0340-3386 - K 1252 EISSN 0340-3386 - K 1252 E VULKAN VERLAVULKAN VERLAG

International

Journal fl for Pr Piping, E, Engineering, P, Practice

Special Edition 13/2002

Steel Pipelines

The Steel Pipe used for trenchless installation

Dr. rer. nat. Hans-Jürgen Kocks, Röhrenwerke Gbr. Fuchs GmbH, Siegen (G)Dipl.-Ing. Hauke Joens, Röhrenwerke Gbr. Fuchs GmbH, Siegen (G)

Frank Föckersperger, Georg Föckersperger GmbH, Aurachtal (G)Dipl.-Ing. Günther Walter, Universität der Bundeswehr, München (G)

erschienen in 3R international Special Edition 13/2002

Vulkan-Verlag GmbH, Essen

Ansprechpartner: Nico Hülsdau, Telefon 0201/82002-33, E-Mail: n.huelsdau@vulkan-verlag.de

3R international 41 (2002) Special Steel Pipel ines2

The Steel Pipe used for trenchless installation

Dr. rer. nat. Hans-Jürgen KocksRöhrenwerke Gbr. Fuchs GmbH, Siegen (G)Tel. +49(0)271/691-170E-Mail: hans-juergen.kocks@fuchsrohr.de

Dipl.-Ing. Hauke JoensRöhrenwerke Gbr. Fuchs GmbH, Siegen (G)Tel. +49(0)271/691-171E-Mail: hauke.joens@fuchsrohr.de

Frank FöckerspergerGeorg Föckersperger GmbH,Aurachtal (G)Tel. +49(0)9132/7844-0E-Mail: info@kabelpflug.de

Dipl.-Ing. Günther WalterUniversität der Bundeswehr, München (G)Tel. +49(0)89/6004-2698E-Mail: guenter.walther@unibw-muenchen.de

IntroductionTrenchless procedures for layingpipelines have gained acceptance in allareas of the supply and disposalindustry. The use of shield tunnelling,ram and thrust drilling processes forspecial construction measures such asunder-running of buildings, river coursesor traffic arteries, is state-of-the-art. Insuch cases the open installation iscompletely uneconomical. There are twodifferent directed drilling procedures:

� water-flush drilling and

� dry drilling [1].

With water-flush drilling procedures (asopposed to dry drilling), wider pipediameters as well as longer pipe sectionscan be used, since these "wet"procedures allow for a smoother towing-in of the pipes. To a great extent, theloosened ground material can be easilyremoved from the bore tunnel bypressing Bentonite in. The remainingmaterial is used to fill back the annulusspace between pipe and bore tunnelwall. As for the statics, the filling-back ofthe annulus space is a crucial advantageof trenchless laying, in that any damageof the rod surface caused by a followingsettlement can be avoided [2]. Thenecessary processing of the drillingsuspension is a disadvantage of thewater-flush procedures. In addition, thereis the danger of "out-blowing" due to thehigh medium pressure, which means, forexample, that Bentonite could escapefrom frost cracks in underbored roads.These disadvantages are irrelevant fordry-drilling procedures.

Economically, the conventional and thetrenchless procedures compete directly

for work within the cities, unlike specialconstruction works. Advantages oftrenchless procedures are:

� low damage of the road bed becauseof avoiding settlement

� bores are filled with a mixture ofloosened ground material andBentonite

� fast laying as no reinstatement of thesurface is necessary

� no impact on residents and traffic inthe construction area

� lack of highway obstruction becauseof the small excavation, and there isno construction noise because thereare no construction vehicles andconstruction activities as known withconventional laying.

The high density of pipes in the groundunder our cities is a main disadvantageof trenchless procedures, jeopardizingthe success of a drill. Geo-radar andgeo-electronic screenings are tried andtested for transport pipelines in the opencountry. However, regarding existingpipelines, the resolving of such proce-dures are a crucial factor if information inthe net maps of the inner cities is missing[3].

In the cities, some special renovationtechniques such as the Burstlining useexisting pipelines for orientation,therefore reducing jeopardizing otherconstructions in the ground. For largenumbers of residential connections, theeconomical benefits of trenchless new-laying and renovation procedures,gained through avoiding an expensivereinstatement of the surfaces, are soonexhausted.

Outside the cities, directional drillingprocedures are of only minor importancesave for the above-mentioned specialconstruction works, or for instance forsome conditions imposed on installationworks in nature reserves. The ploughingprocedure could gain acceptance forinstallation of transport pipelines wherethere are favourable ground conditions,and this would be for pipe dimensions ofcurrently up to DN 300. The maincompetition tool is the use of ditch millmachines as commonly used forconventional installation. There is anunavoidable increase in costs for thepipe material over pipe material costs forconventional laying, but there is asignificant decrease in laying costs.Consequently - as with the economicalcomparison of both procedures - thecosts for additional measures, (in orderto ensure a sufficient longitudinal lockingforce or the mechanical protection ofpipes for trenchless laying) are becomingmore and more crucial. From thisviewpoint, choosing the right design ofpipes for each type of laying is of vitalimportance. This article shows thedifferent steel pipe designs used fortrenchless installation procedures withinstallation examples, and the versatilityfor using this technique.

Steel pipe designs for trenchlessinstallation procedures For conventional as well as trenchlesslaying, choosing the most suitable pipedesign depends mainly on the layingprocedure and the local conditions foreach project. There are particular re-quirements for the installation whichhave to be met at the planning, layingand pipe towing-in stages, depending onthe pipe design.

Connecting techniques

A main advantage of steel pipes is theversatility of possible connecting tech-niques. State-of-the-art for trenchlessinstallation of gas, water and sewagepipelines use welded joints. For watersupply lines, longitudinal force lockingjoints are also used. Welded joints have

Over the last few years the trenchless pipe installation technique has become moreand more important for gas and water supply as well as for sewage disposal.Depending on the installation conditions, different processes have been developedwhich will perfectly meet specific requirements. Steel pipe is the most appropriatesolution for a trenchless line installation technique, due to its very high permissibletensile force, combined with the three-layer plastic coating as an optimum corrosionprotection, and the additional fibrous cement mortar coating for special mechanicalrequirements. This article deals with the use of steel pipes for trenchless installationand a variety of possible applications.

the advantage of longitudinal forcelocking combined with longitudinalconductivity. With welded joints, themechanical strength of steel canthoroughly influence the level of thepermissible tensile strength. Above all,the economical advantages of trenchlessinstallation can be shown by using themaximum towing-in lengths. Differingsteel qualities and their different materialstrengths combined with the optimumpipe wall thickness, offer a great varietyof economical product designs.

Two types of welding joints are used:

� butt-weld and

� socket weld (Figure 1).

The longitudinal conductivity of thesepipes, allow the use of cathodiccorrosion protection. For the installationwork it is not important whether thewhole pipeline or only the trenchlessinstalled section, is cathodically pro-tected by the means of local equipment.An element of uncertainty for trenchlessinstallations is the possible damage ofthe towed-in pipe section. However,unlike all other pipe materials, the weldedsteel pipelines combined with cathodiccorrosion protection, will preserve thefunction and service life of the towed-inpipeline even in the case of damage suchas scores in the coating.

For planning, not only tensile forces butalso the bending radius of steel pipeshave to be taken into account. Elasticbending radii are determined in DVGWworksheets according to each kind ofapplication. For water and sewagepipelines this is Rmin = 500 Diam. For gaspipelines the data in the DVGW worksheets G 462 and G 463 have to be takeninto account. For an overview of thesedata and calculation principles refer tothe DVGW work sheet GW 321.

Bending radii will influence the pipelineguiding and determine the size of thepilot bore for the towing-in process. Inthe case of welded pipelines, therequired space for assembling the usedpipe sections has to be considered. Forthat, the single pipe sections are usuallyput on rollers.

A lack of space for pipe sectionassembling, requires either costly singlepipe welding in the pilot bore, or usingaxially force-locking socket pipes ascommonly used for water supply sys-tems. Depending on the tensile forces ofsteel pipes within the dimension rangefrom DN 80 to DN 300, there are twodifferent designs of socket pipes: Tyton-Sit and DKM joints (Figure 2 and 3).

For an overview of the maximumpermissible tensile forces in accordancewith the socket design refer to Table 1.

Sockets, unlike welded joints, mayrequire a wider opening of the bore

tunnel as well as higher tensile forcesdue to the socket design. Incomingmaterial can block the sockets in thebore tunnel. Sockets, unlike weldingjoints, can suffer a failure of axially force-locking at excessive tensile forces.Usually, the first joint behind the tow-head collapses due to extremely tightsteel pipe tolerances, as this is where thefriction and weight forces, occurring onall single pipe lengths, are greatest.Therefore, especially for flush drillingprocedures, it is recommended to installa sealed unit behind the first socket joint,

particularly for drinking water pipelines.Thus, a pollution of the cement mortarlining by incoming drilling suspensioncan be avoided. In the case of failure, thealready installed pipe section canpossibly be uncovered and the resultingpit can be used as a new starting pointfor further installation.

Coatings

Standard coating for steel pipes is madeof a three-layer polyethylene systemaccording to DIN 30670. Alternatively, apolypropylene coating in compliancewith DIN 30678 can be used. Forparticularly demanding and difficultinstallations, an FCM coating accordingto DVWG worksheet GW 340 can beadditionally applied to the plastic coating(Figure 4).

The three-layer polyethylene coating acc.to DIN 30670 consists of an epoxy resinprimer, an adhesive and the plasticcoating made of polyethylene. Standardcoatings can be used for operatingtemperatures up to 50 °C, and a special'S' coating for temperatures up to 70 °C.The standard layer thickness (n) dependson the pipe size, and ranges from 1.8 mm

3R international 41 (2002) Special Steel Pipel ines 3

Fig. 1: Welding joints

Fig. 2: Tyton-Sit socket Fig. 3: DKM socket

Table 1: Permissible tensile forces (kN) andbending, dependent on socket design (pipelength 6 m)

Fig. 4: Layer structure of water (a) and gas (b) pipe

Cement-mortarSteel pipe

Epoxy resin primerAdhesion promoter

PolyethyleneFiber cement-mortar

Steel pipeEpoxy resin primer

Adhesion promoterPolyethylene

Fiber cement-mortar

a) b)

to 3.0 mm (Table 2). The enforced layerthickness (v) is about 0.7 mm, and ifrequired an increased layer thickness ispossible.

Polypropylene coating is produced acc.to DIN 30678 and is of a similar design tothe polyethylene coating, but offers ahigher mechanical resistance. Curentraw material will allow the use of thecoating for operating temperatures of upto 100 °C while the layer thicknessdepends, (like the polyethylene coating)on the pipe size (Table 2).

FCM coating according to DVGWworksheet GW 340 was originallydeveloped in order to dispense with thesand-cushioning usually used with con-ventional pipe installation in stony androcky ground. The compressive strengthand impact resistance especially, aremany times over the values for plasticcoatings. Special coating types weredeveloped later, allowing the use fortrenchless laying. Pipe towing can causehigh shear loads due to jacket friction,which have to be transmitted from thecoating to the pipe.

On-site treatment of joint areasAll pipe joints need corrosion protectionand, if required, a mechanical protectionin the joint areas before pipes are towedinto the ground. Generally, field coatingwith corrosion protection tapes orthermo-shrinking materials according toDIN 30672 can be used for all poly-

ethylene coatings. Alternatively or ratheradditionally, there are products such asCanusa TBK (Thrust Bore Kits) GRP orDuroplast filler, which are speciallydesigned for trenchless pipe laying withits higher mechanical stress during thepulling of the pipes.

Polypropylene requires GRP or fillerbecause of their higher adherence whichis better than that of common fieldcoating materials according to DIN30672. Completion of the pipe joint areais done by using the FCM coating alongwith the common corrosion protectionsystems according to DIN 30672. As thecast mortar coating (FCM) should have aminimum thickness of 7 mm, the differ-ence can be completed by an easy-to-use casting mortar (Figure 5). GRP orDuromer systems can also be used,these systems are much more expensiveand not so easy-to-use but reach theirfull hardness after much shorter curingtimes.

Trenchless installation of steel linepipes Starting with shrouder pipe thrusting asused for example for railroad-crossings,the controlled horizontal drilling proce-dures became more and more importantat the end of the 80s, especially forspecial construction projects such asriver-crossing. Development started withpipes of wide diameters and continuedwith smaller pipe sizes used for gas andwater supply. Scholz, at a seminar oncontrolled horizontal drilling atthe Institute for SewerageSystems at the Bochum RuhrUniversity on 24 September1996, reported on a rivercrossing implemented byusing controlled horizontaldrilling [4]. This overviewstarted with the river crossingof the Danube in 1990 over alength of 550 m and with apipe diameter DN 800.Further examples followed inthe period up to 1996 withdimensions of up to DN 1200and installation lengths of upto 1160 m (Table 3)

Development in the area of smaller pipesizes went much slower. The firstinstallation with a polyethylene coatedsteel line pipe with cement mortar coatwas documented at the NGW Rheinbergin 1990 (Figure 6).

It is a gas line DN 100, which was towedin under a parking lot and a Federal road,over a length of 130 m. This installationwas the state-of-the-art for this sizerange at that time. Referring to thisproject, Bayer reported in an articleabout the principles of the controlledhorizontal drilling procedures in the 3Rinternational 1991 on installationpossibilities for the utility service [5]: "Bymeans of the controlled horizontal drillingprocedure, the following products can beinstalled underground: ... thin-walledsteel line pipes up to a maximumdiameter of 150 mm, but the latter onesonly in case of especially soft ground andwith sufficient space for longer starting

3R international 41 (2002) Special Steel Pipel ines4

Fig. 5: Field coating of FZM coating withcasting mortar

Tab. 3: River crossing with Ruhrgas involved from 1990 to1996 [4]

Fig. 6: Rheinberg, DN 100 (1990)

Tab. 2: Standard layer thickness of polyethylene and polypropylene coating

pits. (Steel pipelines with a diameter ofup to DN 100 are much easier to install.)"

In 1996, on behalf of the Saarferngas, a368 m DN 200 high pressure gas pipleinewas drilled under the Moselle. Groundconditions were completely different tothe soft ground required only a few yearsago. Under the Moselle, 80 m of veryhard quartzit had to be drilled through [6].

In the same year, a 576 m DN 300polypropylene coated steel pipeline wasdrilled for the first time for VNG Leipzig inWesenberg (Figure 7).

Further stages of development were thefirst trenchless installation of socketpipes in Offenbach in 1997 using theTyton-Sit-connection and the pulling ofsocket pipes with DKM-connection withthe dimension DN 200 on behalf ofHamburg Waterworks in 2000.

Controlled horizontal drilling procedurecould gain acceptance in the field ofspecial construction projects such asriver-crossings, running under buildings,traffic routes and nature reserves, as wellas in local service areas. However,installing pipes in the open field iscurrently uneconomical. In such cases,the ploughing procedure has been

established according to ground con-ditions especially in the dimension rangeup to DN 300.

Using the rocket plough (developed andpatented by Föckersberger Company),the pipe is directly mounted onto theextending piece (rocket) and pulled in thecavity made by the rocket (Figure 8).

The extending piece is able to makecavities up to 500 mm diameter and topull in pipes up to DN 250 (even widerdiameters are possible, depending onthe ground and route conditions).

At the same time, an installing shaftmounted onto the rocket can be used toinstall additional protection pipes, cablesand tracing bands. Exactness of theposition can be adjusted and checked bymeans of a panoramic laser device.

With the rocket plough, the pre-extendedpipe string is arranged behind theentering shaft towed by the traction unit.In the case of uncertain groundconditions it might be sensible to use anadditional pipe with fibrous cementmortar coating (FCM). It is possible tocheck the arising tensile forces on thepipe string. Inserting a Bentonite-suspension can reduce friction forcesand consequently the required tractivepower. Within the framework of a pilotscheme, the maximum arising tractivepowers for pulling in a steel pipe weredetermined. It was a cement-mortarcoated design with the dimension DN200 which was pulled in withoutBentonite-suspension. The measuringand evaluating of the results was carriedout by the Institute for Water Nature atthe Army University Munich (Institut fürWasserwesen der Universität der Bun-deswehr München).

In Münchaurach there was mainly a silty,slightly-clay like soft sand, stiff in someplaces with a semi-solid consistency.Due to the semi firm sandstone, the soilcould be displaced only with medium to

large difficulties. In order to determinethe tensile force, the pre-assembled steelpipe string was mounted on atension/pressure cylinder. A transducertransformed the transferred hydraulicpressure in an electric signal which wasrecorded and saved by a data loggerwith a sampling interval of one second.Simultaneously with the tensile forcerecording, the distance was recorded bymeans of a contact, measuring at thefront wheel of the plough.

At the pulling of the pipe string a tensileforce of 80 kN was reached. Consideringthat for example with steel grade St 52.0,a permissible tensile force of approx. 570 kN is possible, it shows that it is notthe pipe length, but the towing capacityof the winch, which limits the possiblepipe length for the pulling-in installation.

Concluding remark Suitability of pipe systems mainlydepend on the mechanical load-carryingcapacity of the pipes and their coatingrespectively. Due to their suitability forwelding and their mechanical strength,steel pipes allow very high tensile forces.So they can be used for all types oftrenchless installation. In every individualcase, wall thickness and steel quality canbe adjusted to the relevant pipe load. Theprotection effect of the coating is asimportant as the mechanical strength ofthe pipe. After the pulling-in procedure,the corrosion protection coating has tobe in a proper condition without anydefects. This can only be guaranteed ifthe outer pipe protection is also adjustedto the existing ground conditions.Worksheet GW 321 "Controlled, hori-zontal drilling procedures for gas andwater pipelines" gives information aboutthe steel pipe designs, the permissibletensile forces and bending radii.

References[1] DVGW-information: Controlled, trenchless

pipe installation procedures, gas/waterinformation no 7, 11/94 publ. DVGW,Eschborn, Nov. 1994

[2] Kiesselbach, G.: Trenchless pipelineinstallation compared to conventionalinstallation under the geo-mechanical andpipe-technological aspect

[3] Busch, C; Kathage, A.F.: The technologyof georadar: state of development andusage, gwf gas - natural gas, 137 (1996)584-590

[4] Scholz, H: River-crossing, lecture on theseminar "horizontal flash drillingprocedure", Institute for sewer technologyat the Ruhr University Bochum

[5] Bayer, H.J.: The principle of controlled,horizontal flush drilling, 3R international,30 (1991) 511-517

[6] Kocks, H.J.; Joens, H.; Reekers, C.:Fibrous cement mortar coating - amechanical protection for plastic coatedsteel line pipes, bbr, 48 (1997) H. 8 S.32–38

3R international 41 (2002) Special Steel Pipel ines 5

Fig. 7: Wesenberg, DN 300 (1996)

Fig. 8: Münchaurach, DN 200 (2001)