Installation of mains

Installation of MainsInstallation of Mains

DefinitionDefinition

Gas Main: pipes used to carry gas Gas Main: pipes used to carry gas from one pointfrom one point

to another & generally to another & generally carry gas in largecarry gas in large

volume for general or volume for general or collective usecollective use


Common Materials UsedCommon Materials Used

Steel (ST)Steel (ST)

Plastic (PE)Plastic (PE)

*Older materials include: PVC plastic, *Older materials include: PVC plastic, fiberglass and cast iron (CI). The fiberglass and cast iron (CI). The first mains were constructed with first mains were constructed with wood.wood.


Common Sizes & Pressure RatingsCommon Sizes & Pressure Ratings

Sizes range from 11/4” to 24” depending Sizes range from 11/4” to 24” depending on intended use and desired load.on intended use and desired load.

*Pressure limits on plastic(PE) pipe are *Pressure limits on plastic(PE) pipe are commonlycommonly

60 PSIG or less.60 PSIG or less.

*Pressure limits on steel(ST) pipe are *Pressure limits on steel(ST) pipe are commonly between 60 and 1,000 PSIG.commonly between 60 and 1,000 PSIG.


Common Joining MethodsCommon Joining Methods

Steel – welded joints preferred Steel – welded joints preferred Plastic – heat fusion preferred (includes butt, Plastic – heat fusion preferred (includes butt, socket, saddle and electrofusion)socket, saddle and electrofusion)Threaded – above ground and inside Threaded – above ground and inside

buildings buildings onlyonlyMechanical – includes bolt on, compression Mechanical – includes bolt on, compression

and staband stab fittingsfittings


Steel Pipe CoatingsSteel Pipe Coatings

Pipe coatings are used to protect the Pipe coatings are used to protect the underground pipes from corrosion. underground pipes from corrosion. Common coatings include: epoxy, Common coatings include: epoxy, mastic, X-trucoat(yellow wrap) and mastic, X-trucoat(yellow wrap) and coal tar wrap.coal tar wrap.


Material HandlingMaterial Handling

The storing, handling, loading, hauling, The storing, handling, loading, hauling, unloading, unloading,

stringing, and placing of pipe and piping stringing, and placing of pipe and piping materials materials

shall be done in a manner which will shall be done in a manner which will avoid damageavoid damage

to the pipe.to the pipe.


ConstructionConstruction

• Handling and Storage of PipeHandling and Storage of Pipe

Stringing – Stringing – pipe is strung (laid) along pipe is strung (laid) along the routethe route

as close as possible to the as close as possible to the trench sotrench so

that it can be readily installed.that it can be readily installed.


PlanningPlanning

• RouteRoute• Environmental AssessmentEnvironmental Assessment• Locates: Where are other utilities Locates: Where are other utilities

located?located?• Specifications: Company codes and Specifications: Company codes and

standardsstandards


PlanningPlanning

• Multiple Utility Trench Occupancy Multiple Utility Trench Occupancy (Joint (Joint TrenchTrench))

• Materials: Plastic (PE) or Steel (ST)Materials: Plastic (PE) or Steel (ST)• Common Installation Methods: Direct Common Installation Methods: Direct

Burial,Burial,

Plowing, Insertion, and BoringPlowing, Insertion, and Boring• Quality Control/InspectionQuality Control/Inspection


System Pressure DesignSystem Pressure Design

One Way Feed One Way Feed – distribution system has gas – distribution system has gas

pressure supplied from only one pressure supplied from only one directiondirection

Two Way Feed Two Way Feed – distribution system has gas– distribution system has gas

pressure supplied from both directions, pressure supplied from both directions,

also called ‘loop feed’also called ‘loop feed’



• Breaking and Removal of PavementBreaking and Removal of Pavement• Construction/Installation MethodsConstruction/Installation Methods Direct BurialDirect Burial PlowingPlowing InsertionInsertion BoringBoring



Depth of MainDepth of Main

Measured from surface to the top of pipe.Measured from surface to the top of pipe.DOT requires a minimum of 30” of cover.DOT requires a minimum of 30” of cover.

Common depth used by most utilities is Common depth used by most utilities is 36”36”



Clearances for Clearances for ParallelingParalleling or or CrossingCrossing other other

underground facilities or structures.underground facilities or structures.

Should be a minimum of Should be a minimum of 1 foot 1 foot from from otherother

facilities or structures.facilities or structures.

Installation of Installation of MainsMains

Direct BurialDirect Burial

• Backhoe/LoaderBackhoe/Loader

Can dig in all types of soilsCan dig in all types of soils

Effective for larger diameter gas mainsEffective for larger diameter gas mains

Dig out obstacles if neededDig out obstacles if needed

Due to size limited access to some Due to size limited access to some area’sarea’s

Time consuming and costly to backfill Time consuming and costly to backfill and restoreand restore


Direct BurialDirect Burial

• TrenchingTrenching

Can dig in most types of soilCan dig in most types of soil

Effective for smaller size gas mains Effective for smaller size gas mains (2″ or (2″ or smaller)smaller)

Obstacles must be dug out with backhoeObstacles must be dug out with backhoe

Greater accessibility to more area’sGreater accessibility to more area’s

Less time consuming and costly to backfill Less time consuming and costly to backfill and restore and restore


PlowingPlowing

• Vibratory PlowVibratory Plow >Pipe is fed through plow chute and is >Pipe is fed through plow chute and is

laid laid into the ground as plow moves into the ground as plow moves

forward.forward. >Limited to certain soil conditions.>Limited to certain soil conditions. >Limited to smaller size mains>Limited to smaller size mains >Minimal backfill and restoration >Minimal backfill and restoration

neededneeded


PlowingPlowing

• Plug PlowingPlug Plowing

>As plow moves forward the pipe is >As plow moves forward the pipe is pulledpulled

into the earth behind the blade.into the earth behind the blade.

>Limited to certain type soils>Limited to certain type soils

>Weak link must be used with >Weak link must be used with plastic pipe.plastic pipe.


InsertionInsertion

Insert new plastic mains inside older Insert new plastic mains inside older

abandoned steel or cast iron mains.abandoned steel or cast iron mains.

>Requires less excavation and restoration>Requires less excavation and restoration

>Usually includes replacement of gas >Usually includes replacement of gas services at the same time.services at the same time.

>Annular space must be sealed to prevent >Annular space must be sealed to prevent freezing around plastic gas pipe.freezing around plastic gas pipe.


BoringBoring

Various Methods:Various Methods:• Pneumatic Torpedo (Hole Hog/Gopher)Pneumatic Torpedo (Hole Hog/Gopher)• PTO (Mechanically) Driven AugersPTO (Mechanically) Driven Augers• Horizontal Directional Drilling (HDD)Horizontal Directional Drilling (HDD)

>All require >All require potholingpotholing to locate and to locate and avoid otheravoid other

utilities in path of bore.utilities in path of bore.


MAOPMAOP

MMaximumaximum AAllowablellowable OOperatingperating PPressureressure

Note: Plastic (PE) pipelines may not be Note: Plastic (PE) pipelines may not be installed in installed in

systems with MAOP of more than 60 systems with MAOP of more than 60 PSIGPSIG



• Pigging – forcing a mechanical device through Pigging – forcing a mechanical device through with air with air

pressure to clean the interior of the pressure to clean the interior of the pipe.pipe.

A pig catcher must always be installed and no A pig catcher must always be installed and no one is one is

allowed in the vicinity of the pig catcher during allowed in the vicinity of the pig catcher during the the

pigging operation.pigging operation.



• Pressure Testing – all newly installed mains Pressure Testing – all newly installed mains must bemust be

tested for strength and tested for strength and leakage.leakage.

Test pressure commonly is 150% of the MAOP of Test pressure commonly is 150% of the MAOP of the the

installed pipeline. PE pipe test pressure would be installed pipeline. PE pipe test pressure would be a a

minimum of 90 PSIG.minimum of 90 PSIG.

Installation of MainsInstallation of MainsConstructionConstruction

• Pressure Testing – Test MediumsPressure Testing – Test Mediums Air: most common but limited to about 100 PSIGAir: most common but limited to about 100 PSIGNitrogen: used in steel pipelines up to 1,000 PSIG but Nitrogen: used in steel pipelines up to 1,000 PSIG but limited to smaller volumes due to cylinder limited to smaller volumes due to cylinder

sizesizeWater: hydrostatic test commonly used on large Water: hydrostatic test commonly used on large

diameter diameter cross country pipelines which required pigging cross country pipelines which required pigging

toto remove excess waterremove excess water



• Pressure Testing – Test DurationPressure Testing – Test Duration Determined by type ,size and length of Determined by type ,size and length of

installed main.installed main.Minimum commonly is one hour and maximum Minimum commonly is one hour and maximum

is 24is 24 hours. Always refer to the company standards hours. Always refer to the company standards

for the for the specific requirements.specific requirements.


• Pressure Testing – Test Measuring EquipmentPressure Testing – Test Measuring Equipment

Manometer/ U-tube - “W.C. only < 1 PSIGManometer/ U-tube - “W.C. only < 1 PSIG

Pressure Gauges – select proper pressure: “W.C. or Pressure Gauges – select proper pressure: “W.C. or PSIPSI

Recording Chart – provides a permanent record of Recording Chart – provides a permanent record of your pressure test, also select proper pressure levelyour pressure test, also select proper pressure level


• Transition FittingsTransition Fittings

Manufactured fitting that allows you to make theManufactured fitting that allows you to make the transition from steel to plastic for under ground transition from steel to plastic for under ground pipelines. Sizes vary depending on existing pipe and pipelines. Sizes vary depending on existing pipe and

the the specific need required in your distribution system. specific need required in your distribution system. Usually the steel is welded and the plastic is fused Usually the steel is welded and the plastic is fused

for for installation.installation.



• Tie-ins – making physical connection inTie-ins – making physical connection in excavationexcavationThree basic steps:Three basic steps: 1. Controlling the gas pressure at the source 1. Controlling the gas pressure at the source

mainmain 2. Making the physical connection (called a ‘hot 2. Making the physical connection (called a ‘hot

tap’)tap’) 3. Purging gas out of the new main connection, 3. Purging gas out of the new main connection,

along along with a test of the final piping connectionwith a test of the final piping connection



• Bell Hole – an enlarged hole dug in a trench Bell Hole – an enlarged hole dug in a trench to allow to allow

adequate work room for workers to adequate work room for workers to conduct a conduct a

required operation – i.e. install required operation – i.e. install service, make service, make

hot tap, make tie-in, perform hot tap, make tie-in, perform maintenance and maintenance and

repair work, etc.repair work, etc.



• Hot Tap – the process to drill into a ‘live’ Hot Tap – the process to drill into a ‘live’ gas main to gas main to

make a connection for a main make a connection for a main extension, extension,

service line connection, line service line connection, line stopper usage, etc. stopper usage, etc.



Controlling Gas Pressure and/or FlowControlling Gas Pressure and/or Flow

1. Valves: steel or plastic1. Valves: steel or plastic2. Line Stopper (low or high pressure equipment 2. Line Stopper (low or high pressure equipment

& & fittings) steel or cast iron fittings) steel or cast iron

onlyonly3. Squeeze-off (most common is plastic but steel 3. Squeeze-off (most common is plastic but steel

can becan be squeezed off with special squeezed off with special

equipment)equipment)


• Tie-ins – making physical connection inTie-ins – making physical connection in excavationexcavation

• Pressure Testing – all newly installed mains must Pressure Testing – all newly installed mains must bebe

tested for strength and leakage.tested for strength and leakage.

• Pigging – forcing a mechanical device through with Pigging – forcing a mechanical device through with air air

pressure to clean the interior of the pipe.pressure to clean the interior of the pipe.


• Purging – removal of all air and air/gas mixtures Purging – removal of all air and air/gas mixtures fromfrom

pipe prior to customer usagepipe prior to customer usage

Safety Alert: Use of an approved grounding method Safety Alert: Use of an approved grounding method for for

removing static charge is critical at the purge removing static charge is critical at the purge outlet.outlet.

Sources of ignition shall be eliminated from the Sources of ignition shall be eliminated from the proximity of all purging operations. proximity of all purging operations.



• Purging – removal of all air and air/gas Purging – removal of all air and air/gas mixtures frommixtures from


Safety Alert: Use combustible gas indicator Safety Alert: Use combustible gas indicator (CGI) for continuous testing of atmosphere of (CGI) for continuous testing of atmosphere of the pipeline and work area. Never leave the the pipeline and work area. Never leave the purge discharge point unattended. Fire purge discharge point unattended. Fire extinguisher shall be readily available during extinguisher shall be readily available during entire purging process. entire purging process.



• Purging – can also be used for taking a Purging – can also be used for taking a pipeline out of pipeline out of

service to insure all gas is released to service to insure all gas is released to the atmosphere.the atmosphere.

Use your CGI to verify 0 % gas in air to Use your CGI to verify 0 % gas in air to insure that insure that

no combustible gas mixture remains in no combustible gas mixture remains in your pipeline.your pipeline.



• Backfilling and Pavement Restoration – Backfilling and Pavement Restoration – important forimportant for

maintaining good maintaining good customer relationscustomer relations



• As built measurements for company As built measurements for company mapping/records system – critical for mapping/records system – critical for future system protectionfuture system protection


• Purging – removal of all air and air/gas mixtures Purging – removal of all air and air/gas mixtures fromfrom


• Backfilling and Pavement Restoration – important Backfilling and Pavement Restoration – important forfor

maintaining good customer maintaining good customer relationsrelations

• As built measurements for company As built measurements for company mapping/records system – critical for future system mapping/records system – critical for future system protectionprotection

Installation of mains

Education

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