Locating and Marking of Facilities NGA 21 Book

Some locators provide

"continuous" depth information, but it is only accurate when directly over the line.

High Frequencies range b/t

65kHZ and above.

8000Hz (or 8kHZ)

8000 times per second

Medium Frequencies range b/t

8kHz and 33kHz. 8kHz is most useful for general purpose signals. It is high enough for induction, outside the power frequency interference band and with limited coupling to unwanted lines, but it may not be high enough to impose a strong signal on small diameter lines.

A site survey shall be conducted before you begin locating to ensure

All conditions are acceptable and there is nothing that could negatively impact the locate accuracy. The correct Location. The scope of the work area description is clear.

Steps when using the Conductive Mode

Always check the batteries and keep clean and dry. Do not place grounding rod next to a big metal structure. The field strength reading on your locator should decrease as you get farther away from your transmitter. If the field strength reading on your locator drops off more on one side of the facility that you are locating than it does on the other side, you should check to see if your receiver is picking up interference from an adjacent conductor. If the signal on your locator is not crossing over the adjacent conductor. Bleed off or bleed over is when the signal from a target line jumps to adjacent lines without a direct electrical connection. This condition is more prevalent when using higher frequencies.

Safety Alert Orange

Telecommunication Systems and cable tv. Police and Fire Communications

Safety Pink

Temporary Survey Marks

TC

Terra Cotta

TR

Transite

W/STL

Wired Steel

A circuit is complete when

a ground creates a return path for the signal.

When the pipe is energized with the induced voltage from the transmitter,

a magnetic field is produced in the shape concentric circles which spreads out along the pipe.

Medium Connections

are good at moderate distances.

Electronic Pipe Locators

are the main method used to locate buried metal facilities or locator wires on polyethylene pipe.

High Frequencies

are useful when there is high resistance or grounding is poor.

Energizing (placing the signal on) the water line may cause

bleed off (bleed over), resulting in a faulty locate.

Maintenance

both emergency and scheduled, is extremely important to safe operation of a natural gas system.

Conductor

buried metallic pipe or cable being traced.

Permanent aboveground gas pipeline markers indicate that a pipeline exists in the area,

but they do not always provide the exact location of the pipe.

Distortion

can cause several signal and locating problems.

CAUTION should be used as a

conductive signal energizing both the gas system and the water system can occur through a water heater, if an insulator is not present or is faulty.

3 Ways to Apply an active signal

conductive, close induction, induction

The buried pipe or cable being traced is referred to as a

conductor

Metallic Conductors may be very conductive, such as

copper pipe or energized cable, or less conductive material such as cast iron.

A lack of knowledge or uncertainty about what will be encountered when starting to excavate adds to the

cost and risk of new construction. Therefore, it is important that underground structures in the affected area be located and marked.

A high frequency signal displays better ability to

cross through sources of resistance. However, high frequency can also easily be deflected and jump to a more conductive conductor nearby.

Utility maps must be kept

current and accurate.

Determining the Location of Short Dead End Branch Lines or Stub Ends shows the

current or magnetic field flowing the length of the branch line and decreasing to zero towards the end. This is difficult using conductive coupling methods

A receiver is used to

detect and trace the electromagnetic field induced along the pipe by the transmitter.

Locators

detect electromagnetic signals radiating from the metallic wire or cables and pipes.

The connection may be made with

direct connection, which is preferred, or clamp or induction connections.

Be aware that electromagnetic fields surrounding the line can be

distorted by return currents on other metallic lines

The signal induced on the conductor (or the pipe) is similar to all

electric current; it follows the path of least resistance.

A directional radio type transmitter is used to generate an

electromagnetic field which surrounds and spreads out along the buried metal pipeline or tracer wire.

The Hertz is

equivalent to cycles per second, so 50 Hz means the signal changes 50 times per second.

The effectiveness of different instruments depends upon the ,

frequency of the signal, the type of material used for the conductor, and the soil condition.

The locator receiver contains an antenna array made of copper coils that

generate an electric current when they are exposed to a varying magnetic field.

A dry, sandy, loosely-packed soil provides a

good a high resistivity and poor conductive atmosphere.

A dam, closely packed soil provides a

good conductive medium. However an extremely wet soil will conduct so well that the signal will spread into the large groundbed.

The ability of the conductor to be impressed with the signal is affected by some very important factors, such as

grounding, the frequency of the signal, the type of material used for the conductor, and the soil conditions.

The primary function of the pipe locator is to

impress the signal onto the conductor (or pipe) by the transmitter, and then tuning in the transmitter signal with the receiver to pinpoint the location of the pipe.

Notations are also used to

indicate pipe size, installation dates, and work order numbers.

Long-Range Planning

involving the location of future underground utilities, the location of existing underground structures in the area affected must be determined.

Hand Digging

is any excavation involving nonmechanized tools or equipment.

To protect excavators and private citizens from injury and to help ensure the integrity of buried pipelines and other underground facilities,

operators must follow all company specific procedures and processes to perform locating, marking, and excavation.

Air Coupling

occurs when the transmitter's signal travels through open air and is received directly by the receiver. This causes the receiver to sense the signal from the transmitter instead of the utility line.

Information on the line markers must include the name of the pipeline

operator and the telephone number where the operator can be reached at all times.

The signal from the transmitter always seeks the

path of least resistence.

Inductive Mode

permits locating conductors in areas where a conductive hook-up is impractical or impossible. The inductive mode impresses a signal directly onto the conductive material.

Conductive Mode requires

physically attaching cables from the terminal posts to the conductor and a grounding source.

When the receiver passes over the pipe, the volume generated by the signal may be altered by the

position of the receiver in relation to the direction of the pipe path. Actively locate in PEAK.

When you are close to the transmitter,

the direct signal is much stronger than the signal coming from the utility you are trying to locate. For this reason, YOU SHOULD MAKE SURE YOU DONOT LOCATE WITHIN 30 FT OF THE TRANSMITTER.

Modes of Operation

the equipment used to locate buried metallic conductors can be operated in different combinations depending upon the locating situation.

Maps

the first and most important method of locating underground gas pipes is to refer to a map of the gas system being considered. The system provides various types of information such as size of the pipe, pressure in the pipe, type of pipe coating, material used in pipe, and location of valves, tee's etc.

The locating signal is produced by

the flow of the alternating current (AC) which creates an electromagnetic field. This electomagnetic field radiates from the line and is known as the signal.

The higher the frequency,

the greater the current and the more susceptible to signal loss. It is good for jumping insulated jints

FM

Forced Main

Frequency is measured in

Hertz (Hz).

STL

Steel

SCC

Steel Cylinder Concrete

Electric Power distribution and transmission, and Municipal Electric Systems

Safety Red

Safety Greeen

Sewer and storm drainage systems

Pipe Locator in the Conductive Mode

1. Place transmitter 5 ft away from pipe in a perpendicular direction that is being energized. 2. Connect the positive (red) lead to the pipeline facility or tracer wire. 3. Connect the negative (black) lead to ground. 4. Extend the ground cable from the transmitter to at least 5 ft and set the ground plate or rod vertically into the ground. A damp location is preferred. A good ground connection is essential for the pipe locator to operate properly. Ground plate SHOULD NEVER BE PLACED over another pipeline. 5. Turn on the transmitter and select the mode of operation and begin the sweep.

AC

Asbestos Concrete

Bleed Over issue

Avoid applying signal using the induction; use direct connection or a signal clamp where possible. Use lowest frequency possible for the given method of signal application. Use the minimum power output that can be detected. Avoid Applying the signal in congested areas. Extend the ground stakes as far fr the connection point as possible. Avoid using structures for grounding, as other services may be bonded to them. Use double-ended connections t by-pass the ground return.

The null mode is best for verifying peak mode results over a line if tracing for some distance,

BUT SHOULD NEVER BE USED AS A PRIMARY MODE OF LOCATING!

CI

Cast Iron

Remember when using Inductive Mode

Check batteries and keep clean and dry. There are 2 ways to induce a current onto a target utility (w/ a clamp or coupler or using a coil built into the transmitter). Induction may be less efficient b/c there is no metal-to-metal contact to transfer the current onto the line. Never place the transmitter directly on a metal pipe or valve box as it will cause distortion. If asked to locate an area without a direct-hookup point and/or records, the locators may choose to scan the area using a high frequency to find unknown conductors (ACTIVE SEARCH OR SWEEP). Before using the inductive method, make sure you review company records to determine the accuracy of your locate.

CPR

Copper

Damage Prevention Program Each Operator must provide a written program to prevent damage to that pipeline from excavating activities. Each Pipeline operator must participate in the One-Call System

DOT 192.614

Line Markers for Mains and Transmission Lines Lines must be placed and maintained as close as practical over each buried main and transmission line. The name of the operator and the telephone number where the operator can be reached at all times

DOT 192.707

DI

Ductile Iron

Signal Frequencies

Electromagnetic signals are described by their frequencies. The transmitter is continually flowing and changing direction.

FO

Fiber Optic

Sudden Changes in Signal Tone issue

Increase in tone may be caused by a change in mass of metal (possibly a valve), a decrease in pipe depth, or possible increase in pipe size. Decrease in tone may be caused by an insulated fitting, an increase in pipe depth, or a decrease in pipe size. Confused or interrupted tone may be caused by a cross, tee, or other connection, the crossing of another utility, a short or fault in the system, or a section of badly corroded pipe.

Systems Location Records

Learning to read your company's facility map and the set of mapping symbols is an important skill that you must become familiar with.

To identify signal distortions

Locate the facility using a low frequency and a high frequency and compare the difference between the two locations. Measure t the right and left of the signal center at a 45 degree angle and compare the two measurements. Take one depth measurement at ground level and another with the receiver 12-inches above the ground and check whether the difference is 12-inches. Locate the facility in peak mode and then in null mode and compare the difference between the two locations

Planning for Expansion or Replacement

New underground systems as they become necessary, either to replace or improve facilities or to provide some entirely new service, may have to be installed near existing systems.

High Visibility Safety Yellow

Oil and Gas Distribution and Transmission and dangerous materials

You can use Peak and Null modes to identify a distorted signal/field

On a clean undistorted field the peak and null locate response will match. If distortion is present, the peak and null locate will no longer match. Typically, the greater the distortion, the further apart these locate responses will be.

Active locating of facilities SHOULD BE Always be performed in

PEAK Mode.

The main types of responses for general locating are

Peak and Null

PL

Plastic

PVC

Polyvinyl Chloride

Safety precaution blue

Potable water

The most important reason for accurate and on-time locating is

Public Safety.

Purple

Reclaimed water, slurry, and irrigation facilities

RFC

Reinforced Concrete

Frequency

The rate at which the signal changes direction

Air Coupling in the Inductive Mode

The union of the signal from the transmitter to the receiver in the absence of a conductor is referred to as air coupling.

Transmitter

a voltage is induced on the pipe cable

A low frequency signal provides better

adherence to the conductor than a high frequency signal. However, the low frequency signal because of its penetration is more likely to be stopped by high resistance facilities, such as stubs, fittings, or joints.

Electromagnetic Characteristics

all modern pipe locating equipment operate by inducing an electromagnetic signal on a metallic facility (pipe or wire/cable)

Records of the geographic location of piping and other components of a gas distribution system are

always provided on scale maps of the system. These maps show the locations of the systems components with respect to geographical features, such as streets, rivers, lakes, and railroads.

When using direct connection method for locating and marking mains and services up to the meter,

an acceptable connection location would be valves, pipe, tracing wire, test pipes, the inlet side of the gas meter, or a test station, which is also used to locate coated steel mains.

Map Verification

and updating is an area of operation which is ongoing. In order to be assured of accurate maps, the location of old and new underground pipes and valves must be confirmed and documented according to company policy.

The equipment operator chooses the frequency depending upon the

application, distance from the transmitter, the type of line being located, and the way the signal is applied (direction connection, signal clamp, or induction)

Depth Determination determines the

approximate depth of the pipe by triangulation, starting at the center of the pipe on a vertical axis.

Passive Locating

is generally used to avoid rather than identify buried lines. The passive method uses the receiver only and helps with the ground surveys, locating live power lines, locating unidentified buried lines, and conforming active locates. This should NEVER be used in means of locating a utility line you are marking.

Depth

is measured to the center of the signal.

Conductive Mode

is primarily used in areas where several conductors are located in close proximity to each other. This mode of direct connection allows the operator to energize only the conductor which is being traced. This mode is used because the signal is less likely to jump to other structures than in the inductive mode.

The earth stake or grounding rod

is used to complete the circuit through the ground.

Search method

is used to mark the location of unidentified buried lines before digging. DO NOT USE THIS METHOD TO IDENTIFY OR TRACE "SPECIFIC" LINES

Trace Method

is used to measure the approximate depth of the buried line and to measure the signal current

If signal and record measurements do not match when using the inductive method,

it could indicate signal interference from other facilities.

To understand signal distortion and how it affects the locate,

it is important to first understand that when you are locating a pipeline, you are not actually detecting a pipe, but the electromagnetic field either active or passive, that radiate from them. So, anything that affects this electromagnetic field can affect your locate signal.

The preferred method for placing a signal on the target conductor is by direct connection because

it minimizes signal interference.

If the tracer is too far away from the riser,

it will not likely pick up enough signal to locate appropriately

kHz

k equals 1000 times

Damage Prevention

knowing where all utilities are located in advance is essential to prevent damage to underground facilities caused by excavating activities.This includes notifications to excavators and the general public, location requests and utility locating programs, and correctly marking underground facilities prior to excavating.

Low Frequencies are used to

locate cables and insulated pipes using direct connection. Low Frequencies are useful for long distances because there is less coupling to adjacent lines.

House Connections may be used to

locate the service line from the main to the house at the shut off valve.

It is often a good idea to first select the

lowest power output and lowest frequency when you are about to perform a utility locate.

An excellent conductor is the coated-cooper tracer-wire (polyethylene wrapped) buried with all plastic

mains and services.

Facilities that are adjacent to or in contact with the conductor

may distort, disrupt, or totally impede the signal traveling along the conductor.

Trace Method is the

most preferred method of locating and is utilized when one position of the facility is known or has been located and the actual path of the facility is to be determined

High Frequencies are

most suited to induction method and should be used for shorter distances because they will easily couple to adjacent lines.

Good contacts are

necessary. Rust or paint should be removed from points of contact.

Precise locations are indicated by

notations of distances from property lines, street center lines, or other landmarks.

The location of the metal facility is determined by

observing the strongest reading of electromagnetic field.

Ghost Signal issue

occurs when the signal resonates between 2 conductors and causes a false reading. To determine if you are receiving a ghost signal, the signal strength drops as the receiver is moved toward the ghost.

Under poor soil conditions, several actions can be taken to improve grounding, such as

pouring water around the stake, moving the stake to an area where more moisture is present, or running an extension cable from the the transmitter's ground lead to a nearby road sign or other similar metal object.

White

proposed excavation or construction boundaries

Peak Mode

provides a maximum response over the line. It is best for tracing and pinpointing the line in congested areas.

Null Mode

provides a minimum response over the line.

Grounding

provides the signal with the path of least resistance to complete the circut.

Low Frequencies

range b/t 100Hz and 1kHz.

When performing a locate, the lowest frequency to effectively complete the locate should be selected in order to

reduce risk of coupling to adjacent lines.

Conductive (Direct Connection)

requires one cable connected to the target line and the other to the ground. ALWAYS PREFERRED METHOD.

Therefore, it is generally more successful to locate

stub ends or dead end branch lines by inductive locating.

Using a receiver tuned to the same frequency as the transmitter,

the magnetic field can be used to locate the metal structure (pipe).

The deeper the conductor is buried

the more difficult it is to induce the signal through the soil and onto the conductor.

If a proposed excavation or demolition is planned in such proximity to the underground utility line that the utility line may be destroyed, damaged, dislocated, or disturbed,

the operator shall mark the approximate horizontal location of the underground utility line on the ground to within two feet of either side of the underground utility line by means of stakes, paint, flags, or a combination thereof.

The applied signal is generally less than the the other connection methods because

the signal has to travel through the ground to reach the line. It may also may couple to the other metallic lines and facilities adjacent to the target line.

A larger diameter pipe will cause

the signal to weaken and cover less distance

Procedures Used when Locating a Buried Piping are

the trace method, search method, depth determination method, determining short dead end branch lines or stub ends, and house connectors

If you have a sudden loss of signal while performing a locate on a plastic pipeline,

the tracer wire may be damaged.

Pipe Locators consists of two major components

the transmitter and the receiver.

Search method is utilized when

there is no knowledge or indication of the buried facility. Also a passive location.

High frequencies are easy to apply by induction, but

they also couple very easily to unwanted lines and do not travel far.

This trace method is aka a active location and is used

to trace, identify, and pinpoint a buried line.

An insulator by its nature will

totally stop the signal, whereas, stubs and joints will cause the signal to be reduced.

Soil Conditions is an important factor in the

transmission of the impressed signal.

Maximum efficiency is achieved when the

transmitter and receiver units are vertical and parallel to the buried pipe.

Close Induction

uses a clamp around the line to induce a signal on a pipe without making a direct connection. This method can be used when you cannot connect to a conductor or insulated sheath or for cable identification. This method is not connected or in close proximity to the riser.

Active Locating

uses both the receiver and transmitter. It is used to trace, identify, and pinpoint a buried line. It can also be used to estimate the depth of the buried line and to measure the signal current on the buried line.

Induction

uses the transmitter only. It induces a signal on a pipe by placing the transmitter on the surface over the target line.

Symbols represent pipe accessories such as

valves, insulating fittings, regulators, and corrosion control devices.

The Receiver transforms the

voltage into an optical (visual) signal on the equipment meter and an audio signal in the headphone or built-in speaker of the receiver.

The transmitter ground lead must be connected to the pipe locator's metallic ground plate or rod,

which shall be placed as far away as possible from the connection point.

Using a natural gas system map,

you can establish the approximate pipe location based on such features as the location of utility poles, curb lines, driveways, and similar physical features in relation to the pipeline.

If the tracer wire is broken,

you may need to locate from a different access point, but be sure to notify the appropriate company personnel to make the necessary repairs.

When you cannot electronically locate a facility and maps and records are inaccurate,

you must contact the excavator and your supervisor and appropriate company personnel.

When operating in the inductive mode

you should consider other conductors in close proximity and energized cable or power lines.