DUCTILE IRON PIPESUBAQUEOUS CROSSINGS

®

Introduction

DUCTILE IRON pipe withboltless ball and socket jointsis an extremely versatile pro-duct for use in subaqueous

construction. Important in this contextare the flexibility and the restraintagainst joint separation provided by theball and socket. In addition, the provenstrength and durability of Ductile Ironpipe assure a trouble-free installation anda maintenance-free pipeline. The highpressure rating and large safety factorsused in the design of this pipe alsoprovide assurance against unforeseenpressure increases.

Although Ductile Iron pipe with balland socket joints is not inexpensivecompared with the various types of landpiping, its adaptability with respect torigorous construction techniques and itslong, dependable service life make it aprudent choice for subaqueous crossings.

The installation of underwater pipe-lines is a challenging undertaking, and inorder to achieve maximum economy, theconstructor must be free to choose thebest procedure for a particular job. Sincethe available construction methods aredemanding not only on the skill of thecontractor but also on the strength andversatility of the pipe material, thatmaterial most suitable to the widestrange of installation methods should bespecified. The characteristics of DuctileIron subaqueous pipe have for manyyears made it a favorite of utilities,engineers, and contractors.

This brochure will present generalmethods of construction that are used ininstalling Ductile Iron ball and socketpipe and the factors that must beconsidered in choosing the properprocedure for a specific project.The first section discusses the basiccharacteristics of the ball and socketjoint, followed by a discussion of thevarious underwater construction prac-tices and the several factors that must beconsidered to successfully install sub-aqueous pipelines.

DUCTILE IRON PIPESUBAQUEOUS CROSSINGS

Typical ball and socket rivercrossing joints.

Flex-Lok® (4” - 24”)

Flex-Lok® (30” - 54”)

Snap-LOK™ (6” - 24”)

Ball and Socket (6” - 36”)

USIFLEX® (4” - 36”)

USIFLEX® (42” - 48”)

1

The JointThe ball and socket joints available

for Ductile Iron pipe are boltless. Theyconsist of a precision-machined ballwhich fits into a machined socket, arubber gasket to provide a pressure-tightseal, and a retainer ring which provideslongitudinal restraint. The joint isdesigned so that the rubber gasket isproperly compressed and the joint isleak-free throughout the full range ofdeflection.

Maximum deflection is 15º per jointin sizes up to and including 24-inch pipe;in sizes 30-inch and larger, maximumdeflection varies from 121/2º to 15º. Atmaximum deflection, the joint remainspressure-tight and retains the full flowarea available in the undeflected joint.

Above: Workers use come-alongs while installing Ductile Iron pipe with boltless ball and socketjoints. These joints consist of a precision-machined ball that fits into a precision-machinedsocket, a rubber gasket that provides a pressure-tight seal, and a retainer ring that provideslongitudinal restraint. The joint is leak-free throughout the full range of deflection.

Below: In many subaqueous installations, the majority of the assembly can be done on dryland. Here, a crew lowers a piece of Ductile Iron pipe into place on top of a launchingramp from which cables will pull it across the water.

Good design practice dictates that nojoint be installed in a final position in afully deflected alignment. This allows forslightly more deflection, if needed,during subsequent settlement of the line.For design purposes, the deflectionshould be limited to 80 percent of themaximum recommended by the manu-facturer. Ductile Iron ball and socket pipeis normally furnished in 18- and 20-feetnominal laying lengths, depending on theparticular pipe being used. Wheregreater deflection of the line is requiredthan is available in one joint, pipe of shortlaying lengths can usually be furnished toprovide additional deflection.

The Ductile Iron ball and socketjoints are designed to provide endrestraint against joint separation not onlydue to internal pressure in service, butalso against the large longitudinal loadsthat may be encountered duringconstruction. Allowable safe end loadsfor each type of joint can be supplied bythe manufacturer. Assembly of the balland socket joints is relatively simple.

Each manufacturer provides detailedinstructions for the proper and mostefficient assembly of its particularjoint. Special lubricant which clingstenaciously to joining surfaces is recom-mended for underwater or extremelywet installation conditions (this includescases where water is flowing into and outof joints during installation). Such speciallubricant can be obtained from pipemanufacturers.

Construction MethodsDuctile Iron pipe with ball and socket

joints is adaptable to the full range ofsubaqueous construction methods;therefore, the constructor is free toselect the most economical procedure.The method used will necessarily beunique to the requirements and specifi-cations of each particular job.

There are three general categories ofconstruction techniques employed inlaying subaqueous pipelines: the pipe canbe assembled on one bank and pulled

Above: An installation crewmember is shown driving a steelwedge into a pipeline joint. Thewedge provides a lock thatprevents rotation of the lockinggland after assembly.

Next Page:For some pipe sizes,it is necessary to provideadditional buoyancy to float thepipe into position. Here, steeldrums are used for that purpose.

3

into place from the other bank; the pipecan be lowered from a barge; or thewater can be diverted and the pipe laid ina dry trench according to normal goodinstallation practice.

Bank installation. Except in small,shallow streams where the water caneasily be diverted, assembly of the pipeon a bank and pulling the line into placefrom the opposite bank is usually themost economical means of construction.Joints should be assembled in line withthe crossing and pulled as straight aspossible to avoid over-deflection of thejoints and excessive beam loads duringinstallation.

In this method, sections of pipeconsisting of one or more lengths areassembled on the bank. The assembledsection of the line is then pulled into the water and the process repeated untilthe installation is complete. The pullingforce is usually provided by a winchlocated on the opposite bank, attached to the leading end of the line by a steelcable.

In the vast majority of installations,the pipe is pulled along the bottomthrough a previously prepared trench. Itis recommended that the first length ofpipe be floated in order to prevent itsleading end from digging into the trenchbottom. While this method is preferable,the line may be floated into position andsubsequently lowered to the bottom ifdictated by rough bottom or othercircumstances. If the line is floated intoposition, it should be lowered to thebottom in a controlled manner to avoiddamage to the pipe. In such instances,particular care should be taken to avoidover-deflection of joints in the bankapproach locations. In such installations,it may also be necessary to consider theeffects of fluid drag on the pipeline due tocurrent, etc.

It is highly recommended to cap orplug the lead end of the first pipe toprevent water from entering, therebyproviding buoyancy and reducing the endpull required to move the pipe once it isin the water. Ductile Iron ball joint pipe in

smaller sizes, generally 4-inch through16-inch, is heavier than the water itdisplaces and will not float even when itcontains no water.

Additional buoyancy can be providedfor long pulls or for the flotation methodof installation by attaching steel drums orother flotation devices to the pipe as it isassembled.

Ductile Iron ball joint pipe, par-ticularly in the 18-inch and larger sizes,may be lighter than the water it displacesand therefore float when empty of water.Heavier classes of pipe may be availablefor installations where flotation is notdesired or weights may be attached tothe pipe to overcome buoyancy.

Buoyancy data for each type of ballpipe can be supplied by the manufacturer.

When employing the pulling method,a cable or harness is attached behind thefirst joint and the pulling cable is securedto the lead end to keep it up duringpulling. Special pulling flanges are alsoavailable from some manufacturers.Under certain conditions it may be

4

advisable to provide the lead end with asled to reduce resistance from the trenchbottom.

To determine whether the pullingmethod of construction is appropriate fora given job, several factors must beconsidered. First, there must be accessto the banks. On the assembly bank,there must be room to store thepipe, to accommodate the pipe-handlingequipment, and to effect the assembly.The condition of the bank is also critical.It must be sufficiently stable to supportthe pipe and the required equipment.The bank must be graded to provide anangle of entry for the pipe into the waterthat does not exceed the designdeflection. On the opposite bank, theremust be adequate access and space toaccommodate the pulling equipment.

The length of the crossing is anotherimportant factor. For extremely longcrossings, the pulling force required tomove the entire line may be excessive.Also, strong currents may precludefloating the pipeline into position orrequire special alignment control.

When the pulling method is employed,a ramp is often constructed extending intothe water from the assembly bank. Thecompleted ramp, which is often built ofpreviously used materials such as railsand cross-ties, structural members, andtimbers, provides certain advantagessuch as an assembly location off theground, facilitating clean joints duringassembly, and reduction in force requiredto pull the pipeline.

Next Page: Finishing assemblytouches are made to a Ductile Ironpipe joint. This particular pipeline iscradled in an inclined launching rampthat prevents the pipe from touchingthe ground. This facilitates clean jointsand will make it easier and faster topull the pipeline across the water.

Below: Portions of three parallelpipelines assembled on land are shownprior to their being pulled across thewater. Ductile Iron pipe’s durability anddeflection capabilities make it ideal forinstallations in this situation as wellas other rugged water crossings.

Left: Ductile Iron pipelines can beassembled on a barge and loweredby means of a chute extended tothe bottom of the waterway. Here,that procedure is used for a set ofparallel lines. Pipelines can also beassembled by lowering sectionsfrom the barge into the waterwhere assembly is performed byunderwater divers.

Next Page: In some situations,barge installations are a necessity.That includes situations in whichthe route of the line is not straight,where the banks are unsuitable or unavailable for assembly, whenthe bottom is unstable and atrench will not remain open longenough for a bank installation, orwhere the line being installed isextremely long.

Below:Several lengths of DuctileIron pipelines can be assembledabove the water and lowered on astrongback to underwater diverswho will connect the assembly tothe pipeline. Concrete collars havebeen attached to ensure that thepipe sinks properly into position.

7

Installation from a barge. Layingpipe from a barge can be accomplished byeither of two general methods. In thefirst method, the pipe is simply loweredfrom the barge and assembled under-water by a diver. Variations of thismethod involve assembling two or morejoints aboard the barge; then, usingslings or a strongback, the assembledsection is lowered to the diver forconnection to the line.

The second method of installationfrom a barge employs a launching chuteextending from the barge to the bottomof the waterway. The pipeline isassembled on the ramp and as theassembly progresses, the barge is movedforward, allowing the pipe to slide downthe chute into position on the bottom.The chute should be designed to supportthe pipe all the way to the bottom to

protect the joints from excessive beamloads during installation. The hanging ofseveral lengths of pipes in full deflectionwithout support can result in undesirablebending moments being exerted onjoints.

Although installing ball joint pipefrom a barge is generally less economicalthan from a bank, in many cases it is theonly suitable method. Such cases mayinclude installations where the route ofthe line is not straight, where the banksare unsuitable or unavailable for bankinstallation, where the bottom isunstable and a trench will not remainopen long enough for a bank installation,or where the line being installed isextremely long.

Dry installation. The third generaltype of subaqueous construction is “dry”installation. When crossing small or

shallow streams where there is room todivert the water from the constructionarea, normal dry land pipe layingpractices are used.

Designing andPlanning theSubaqueous Crossing

The most economical installation of asubaqueous pipeline crossing is theresult of careful design and planningprior to construction. Factors must beconsidered in the design and planningstages of the project to assure the mostefficient and successful completion.

Permits. When a pipeline is to beinstalled across a navigable waterway, apermit from the U.S. Army Corps ofEngineers is required. “Permits for Workin Navigable Waters,” a Corps of

8

Engineers publication, explains theprocedure for obtaining such a permit. Ingeneral, the designer should keep inmind that the Corps must approve anydesign and that emphasis will be placedon the effects of the project onnavigation, both during and afterconstruction.

A check should also be made withlocal and state governmental units;permits and approval from such agenciesare often required in addition to permitsfrom the Corps of Engineers.

Corrosion protection. The manyinstallations of Gray and Ductile Ironsubaqueous piping in fresh and seawaterapplications have demonstrated thecorrosion resistance of both materials,Ductile Iron having equal or better corrosionresistance than Gray Iron. While the greatmajority of subaqueous installations requireno special consideration with respect tocorrosion, there are instances where bottomsoil conditions will necessitate corrosionprotection. Saltwater installations generallypresent no problem in this regard if thebottom is free of pollutants.

Polyethylene encasement in accord-ance with ANSI/AWWA C105/A21.5 is

the standard method of protectingDuctile Iron pipe from most corrosiveenvironments, based on more than 45years of research and actual fieldexperience. The polyethylene mustremain intact and free from physicaldamage during installation.

The rigors of some of the subaqueousconstruction methods (e.g., pulling thepipeline along the bottom) make thisdifficult to accomplish. However,polyethylene encasement has beensuccessfully employed in underwaterinstallations using the technique oflowering pipe sections from a barge withthe polyethylene in place, sometimesutilizing a strongback so that severallengths of pipe may be wrapped prior toinstallation. Divers then make theconnection to the previously laid pipeand complete the overlap of thepolyethylene at the joint.

For installations where conditions areknown to be corrosive and it is notpractical to employ polyethyleneencasement, other means of corrosionprotection such as cathodic protectionshould be considered.

Above: Polyethyleneencasement can be used insome subaqueous crossings ascorrosion protection for DuctileIron pipe.

9

Project CompletionConnections to the land piping.

Connections to the on-shore line areusually made by use of plain endconnecting pieces and a solid mechanicaljoint sleeve. It is usually good practice tobackfill the underwater line and allow it tosettle for a reasonable period beforemaking the end connections. Where this isnot possible, or where the river bottom isparticularly unstable, connecting pieceswith restrained joints are available and arerecommended.

Inspection and testing. The line maybe hydrostatically tested in accordancewith ANSI/AWWA C600 “Installation ofDuctile Iron Water Mains and TheirAppurtenances,” usually at 1.5 times theoperating pressure, prior to connection tothe land piping. Caps, plugs, and specialclosure pieces are available to seal off theends of the line for this test. These aretapped for line filling and venting. Afterpressure testing, the line may be backfilled.

Trenching and backfilling. In mostcases, subaqueous crossings should be laidin trenches in the river bottom. The trenchprovides protection from damage bynavigation or large anchors (andconversely protects navigation frominterference by the pipeline structure). Italso prevents erosion and obstruction ofriver flow, provides freedom frominstallation obstructions, and furnishesgood bedding for the pipeline.

Trenching is accomplished by dredging,jetting, or digging with a backhoe ordragline. The handling of spoil materialmay be a condition of the Corps ofEngineers permit; it may be stored onshore, in barges, or alongside the trench.Backfill may be dumped or chuted intoposition or allowed to erode into the trenchwhen spoil material is piled upstream.

Crushed stone may be used as basematerial in the trench to form good beddingand also as ballast material for backfill.Careful planning is required in streamswith appreciable current where the pipelaying operation may have to beaccomplished within a short time aftertrenching to prevent erosion of theprepared trench.

SummaryThe combination of joint flexibility,

toughness, and corrosion-resistance ofDuctile Iron ball and socket pipe make itthe ideal material for use in difficultunderwater installations. The versatilityof the pipe allows the installer to deviseinstallation methods as variations of thegeneral methods presented here toaccommodate the particular conditions ofhis job and equipment. As in other typesof construction, proper planning and sitepreparation prior to the actualinstallation provide the fastest and mosteconomical job. Consultation with thepipe manufacturer concerning proposedconstruction methods, safe end pull,buoyancy, and joint capabilities issuggested to the engineer and installerto assure a successful installation.

10

SC/9-01/4MPublished 11-87Revised 2-12

An association of quality producers dedicated to highest pipestandards through a program of continuing research.245 Riverchase Parkway East, Suite OBirmingham, Alabama 35244-1856Telephone 205 402-8700 FAX 205 402-8730http://www.dipra.org

American Cast Iron Pipe CompanyP.O. Box 2727Birmingham, Alabama 35202-2727

Atlantic States Cast Iron Pipe Company183 Sitgreaves StreetPhillipsburg, New Jersey 08865-3000

Canada Pipe Company, Ltd.1757 Burlington Street EastHamilton, Ontario L8N 3R5 Canada

Clow Water Systems CompanyP.O. Box 6001Coshocton, Ohio 43812-6001

Griffin Pipe Products Co.1011 Warrenville RoadLisle, Illinois 60532

McWane Cast Iron Pipe Company1201 Vanderbilt RoadBirmingham, Alabama 35234

Pacific States Cast Iron Pipe CompanyP.O. Box 1219Provo, Utah 84603-1219

United States Pipe and Foundry CompanyP.O. Box 10406Birmingham, Alabama 35202-0406

DIPRAMEMBER COMPANIES

Manufactured from recycled materials.

Copyright © 2001, 1999 by Ductile Iron Pipe Research AssociationThis publication, or parts thereof, may not be reproduced in any formwithout permission of the publishers.