PURGING DISTRIBUTION MAINS AND SERVICE LINES

1
Ohio Gas Association2008 Spring Technical Seminar
PURGING DISTRIBUTION MAINSAND SERVICE LINES
Larry BorderUtility Technologies International
2
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• Goals in Purging
• The gas or air is pushed out escape vents with
  little or no mixing of purge gas and contents
• The area of contact should be small
• Inert gas can be used as a slug
• Use the properties of gas densities to aid in
  purging, ie. Ambient Air 1.0, Natural Gas
  0.6, Propane 1.5

3
PURGING DISTRIBUTION MAINSAND SERVICE LINES
Different Purging Techniques

• Displacement (Preferred) High velocity input
• Short contact surfaces

4
PURGING DISTRIBUTION MAINSAND SERVICE LINES
Different Purging Techniques

• Dilution (Not Preferred)
• Large Amounts of Purge Gas Required
• Large Area of Contact
• Long Period of Contact
• Agitation
• Gravity
• Temperature

5
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• Mechanical Efficiency of Purging
• Avoid interruptions or variations of purge input
• Control input velocity
• Introduce purge gas properly using gas density
• Use large input connections
• Use vents large enough to allow escape of
  displaced gas

6
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• Isolation Devices for Purge Operations
• Valves already in the system
• Blanks or blind plates on flanges
• Physical Disconnects
• Grounded Squeeze-off devices

7
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• Test Purge
• When purged out of service, check for in- leakage
  into the system
• Measure with the CGI unit to zero gas
• When purging in service, check for 100 gas with
  the CGI unit

8
PURGING DISTRIBUTION MAINSAND SERVICE LINES
Safety Precautions The main safety concernin
purging gas lines is toPREVENT
ACCIDENTALIGNITION
9
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• Prevent Accidental Ignition
• Remove any potential ignition sources in the area
• Ground all piping and squeeze-off devices at
  purge points that could be an ignition source
• Monitor gas/air mixtures less than10 L.E.L.
• Have Fire Extinguishers ready

10
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• Valves
• Valves used in the purge must be checked for
  operation
• Valves must be attended or locked/tagged out of
  service during the purging procedure

11
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• Personnel Safety
• Oxygen content must be at least 20 in the purge
  area
• Flame retardant, static retardant clothing must
  be worn by personnel
• Adhere to State Federal safety requirements

12
Purging ScenarioforNew Subdivision
13
Installed Piping
14
Open Valves to Vent Off Air Pressure
15
Three Purge Stacks Are Attached
16
Two Squeeze-offs Installed
17
Squeeze Off Vertical Pipe
18
Open Vent 1
19
Open Valve On Main, Vent to 100 Gas
20
Close Vent 1, Open Vents 2 and 3
21
Open 1 Valve, Vent to 100 Gasand Squeeze Off
Horizontal
22
Close Vent 3,Open Vertical Squeeze-off Tool
23
Open Valve2 and Vent 2 to 100 Gas
24
Close Vent 2 andRemove Squeeze-off Tools
25
Remove Purge Stacks Using Squeeze-off Tools
26
Purge Any Service Lines
27
Completed Purge
28
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• Service Lines
• Purge Outdoors
• Identify Confined Spaces / Excavations
• Identify Potential Ignition Sources
• Test Purge at 100 Gas

29
PURGING DISTRIBUTION MAINSAND SERVICE LINES

• House Lines
• Purge at range burner when possible
• Always control purge with a valve
• Long or larger diameter house lines should be
  purged to the outside atmosphere