Purging a Pipeline

With the exception of purging service lines,

-Document the existence of a purge plan -

Factors to think about before purging:

-Equipment and/or piping to be purged, and how it should be isolated -The purge medium to be used -How the purge medium is introduced into the equipment and/or piped and vented -Method for testing the completeness of the purge and end point to be attained -Selection and assignment of a responsible project supervisor and operating personnel -

Examples of Source of Ignition

-flames from open lights, matches, lighters, laterns, etc -Sparks and arc from non-approved flashlights , torch igniters, enignes, static electricity, lightning, etc -heated mated materials like glowing metals, cinders, flaments, or electric lights

When purging out of service, the purge is considered complete when the reading is to

0-3% is obtained

Sources of Ignition

accidental ignition is most likely to occur at the outlet of the purge point.

Each small section, if it comes in contact with another dielectric, will

acquire its own local charge and potential.

The slug separates the gas from the

air in the pipeline

If you see a dramatic reduction in gas flow during purging operations,

an activated EFV is most likely the cause

When a vent stack is installed, it should be located in

an area that minimizes the hazards of vented gas

Always follow all relevant company procedures very carefully in order to

avoid hazards during the purging process

It is important that all possible sources of ignition

be eliminated

Whenever a main with attached service lines is to be purged into operation,

be sure that the service is turned off at the meter by making sure that all riser valves are closed

Purging should be performed on any pipeline that is

being taken out of service or placed into service

A facility to be purged is to

blocked or disconnected from the rest of the system

Before severing or disconnecting a pipe, a

bond wire should be attached to the metallic at two points to provide a connection across the proposed severance or disconnection

Before a service is purged, facility records should be reviewed to

check for the presence of Excess Flow Valves (EFV's)

An approved, calibrated combustible gas indicator is required to

check the percentage of gas-in-air during a purge operation and determine when the purge is complete.

If a purge is incomplete,

continue to purge, verify the CGI readings, and evaluate the situation

When purging a pipeline with gas or air, the flow rate should be

continuous over the course of the purge process.

Determining whether an inert gas is required in a purge process consider the

diameter and length of the pipe.

Readings should be done at a vent stack

during the purge and when the purge is complete

Static electricity on materials that are conductors of electricity may be

eliminated by grounding

Static Electricity

gas escaping from a pipeline can ignite in the presence of static electricity, which can lead to disastrous results

The purge velocity in the pipeline should be high enough to limit layering of

gases and create turbulent flow at the interface of the gas in the air

The vent stack should be a designated height above

grade, generally above the workers head

Ensure all machinery, pipes, vent stacks, tools, and other equipment are

grounded when charges may accumulate

Pyrophoric materials that can

ignite spontaneously in the presence of a gas-air mixture

Large Diameter pipes generally require

inert gas when purging into or out of service

Whenever any facility is purged, it is essential to

isolate it from the rest of the system

When purging from combustible gas to air, especially if old piping is being purged,

keep in mind that purging removes only gaseous and volatiale material

Direct communication between the introduction point and the discharge point must be

maintained at all times

The pipes being used should be

metallic, grounded, and properly supported all the time

Maintain the continuous flow rate when purging a pipeline

out of service

Prevent any leakage AFTER the purging operation when the facility is

out of service for inspection, repairs, or demolition.

Continue the operation until no air is

present in that being purged into service

Continue the operation until no combustible gas is

present in the equipment being purged out of service

The purpose for isolating the facility for it to be purged is to

prevent leakage DURING the purging operation

Refer to your company's policies and procedures for

proper handling of liquid or solid combustible material

It is important to make sure that the appropriate flow rate is maintained during

purging operations

Always follow your company's specific

purging procedures

If an EFV is activated during a service line purge,

reset the valve

Natural Gas is often used to purge a

small diameter pipe into service

Air is often used to purge a

small diameter pipe out of service

The vent stack outlet diameter should be

smaller than the pipe diameter

If water is discovered in the line during a purging operation,

stop the purge

If you get a reading of 100% but do not smell gas,

the gas is most likely under-odorized. If this is the case, be sure to contact the appropriate company personnel

It is essential that the combustible gas be diffused into the air without hazard to

the workers, public, or property

Important factors in choosing a vent stack location

wind direction, sources of ignition, building openings, and nearby traffic

During the blow down process, if you determine gas pressure is not dropping as expected,

you should stop the process and investigate

A person who is familiar with the properties and nature of the materials involved and the construction and function of the equipment and/or piping system to be purged

Responsibility and Authority

What can remain in the gas/pipeline after it is purge?

Liquid Combustibles, solid combustible material, and easily oxidized material

The charge cannot be drained by a ground connection

Nonconductor (Dielectric)

Safety Equipment

PPE, Fire Extinguisher

Location of active purge points should be planned to take into consideration

Potential ignition sources and building openings

If a sufficient amount of purging air or gas cannot be supplied to prevent the formation of a hazardous mixture of gas and air, a slug of inert gas must be released into the line first

Purging of Pipelines 192.629

States that the gas and air used to purge a line must be released into one end of the line in a moderately rapid and continuous flow.

192.629 Purging of Pipelines

When purging into service, the purge is considered complete when the reading is to

97-100% gas is obtained

Prior to purging gas mains, it may be necessary to contact company dispatch and/or local emergency officials.

Communication