http://bitbin.it/giEuawwE/Introduction................................................................................................................................................1
Pipe Materials............................................................................................................................................1
Steel Pipe..............................................................................................................................................1
Plastic Pipe...........................................................................................................................................2
Cast and Ductile Iron Pipe....................................................................................................................3
Service Pipe Materials..........................................................................................................................3
Construction Planning................................................................................................................................4
Route Selection.....................................................................................................................................4
Distance of Possible Routes.................................................................................................................4
Government Regulations......................................................................................................................5
Pipeline Class Location.........................................................................................................................5
Permits..................................................................................................................................................5
Easements............................................................................................................................................6
Pipe Depth............................................................................................................................................6
Joint Trench Installation........................................................................................................................7
Operating Pressures.............................................................................................................................8
Construction Barriers and Obstacles.........................................................................................................8
Construction Costs..................................................................................................................................11
Installation Methods.................................................................................................................................12
Locates................................................................................................................................................13
Excavation Equipment........................................................................................................................13
Trenching............................................................................................................................................13
Plastic Main Installation.......................................................................................................................14
Plowing and Planting Equipment........................................................................................................16
Boring, Tunneling, and Directional Drilling..........................................................................................17
Deep Tunneling...................................................................................................................................19
Pipe Insertion......................................................................................................................................19
Normal Insertion..................................................................................................................................20
Live Insertion.......................................................................................................................................20
Hard Lining..........................................................................................................................................22
Splitting / Bursting...............................................................................................................................23
Pipe Joining Methods..............................................................................................................................24
Plastic Pipe Joining.............................................................................................................................25
Steel Pipe Joining...............................................................................................................................27
Welding Procedure Specifications...........................................................................................................29
Welding Safety Requirements.............................................................................................................29
Compression Fittings...............................................................................................................................30
Hydraulic Compression Couplings......................................................................................................32
Other Couplings..................................................................................................................................33
Pipe Joining Safety Equipment................................................................................................................33
Maintenance............................................................................................................................................34
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Pressure Testing......................................................................................................................................35
Test Parameters..................................................................................................................................35
Pigging.....................................................................................................................................................36
Stopping Operations................................................................................................................................37
Valves.................................................................................................................................................37
Valve Operation..................................................................................................................................38
Valve Inspections................................................................................................................................39
Low-Pressure Bags and Canvas Stoppers..............................................................................................39
Plastic Pipe Squeeze Off.........................................................................................................................39
Tapping and Drilling.................................................................................................................................40
General Practices for Mechanical Stop-Off.............................................................................................41
Stopping Operations................................................................................................................................41
Purging....................................................................................................................................................44
Use of Gases When Purging...............................................................................................................44
Purging Process..................................................................................................................................45
Testing................................................................................................................................................45
Purging Safety.....................................................................................................................................45
Record Keeping.......................................................................................................................................46
Pipe Repair..............................................................................................................................................46
Steel Pipe Repair................................................................................................................................46
Plastic Pipe Repair..............................................................................................................................47
Cast and Ductile Iron Pipe Repair.......................................................................................................47
Pipe Repair Methods...........................................................................................................................47
Preparation..........................................................................................................................................47
Repair Clamps....................................................................................................................................48
Sleeves...............................................................................................................................................49
Cast Iron Joint Sealants......................................................................................................................49
Service Pipe Installation and Repair........................................................................................................50
Multiple or Branch Service Lines.............................................................................................................50
Mobile Home Service Lines................................................................................................................51
Information on Repairs........................................................................................................................53
Restoration..............................................................................................................................................54
Backfill and Compaction......................................................................................................................54
Repaving and Landscaping.................................................................................................................55
Safety.......................................................................................................................................................56
Preventing Accidents..........................................................................................................................57
LIST OF FIGURES
Page
Figure 7-1: Construction Crew..................................................................................................................1
Figure 7-2: Steel Transmission Pipe.........................................................................................................2
CHAPTER 7 ⎯ CONSTRUCTION AND MAINTENANCE 7-iii
Figure 7-3: Coil of Plastic Pipe.................................................................................................................2
Figure 7-4: Scratched Plastic Pipe...........................................................................................................3
Figure 7-5: Cast iron Pipe.........................................................................................................................3
Figure 7-6: Steel Pipe...............................................................................................................................4
Figure 7-7: Copper Pipe...........................................................................................................................4
Figure 7-8: Plastic Pipe.............................................................................................................................4
Figure 7-9: Pipe Depth for Distribution Mains...........................................................................................6
Figure 7-10: Buried Plastic Pipe................................................................................................................7
Figure 7-11: Joint Trench Construction.....................................................................................................7
Figure 7-12: Range of Pipe Pressures......................................................................................................8
Figure 7-13: Pipeline Hung From a Bridge................................................................................................9
Figure 7-14: Pipeline Shoring....................................................................................................................9
Figure 7-15: Shoring Unit.........................................................................................................................10
Figure 7-16: A Shallow Excavation..........................................................................................................10
Figure 7-17: Pump and Well Points.........................................................................................................11
Figure 7-18: Newly Paved Street.............................................................................................................11
Figure 7-19: Tree-lined Street..................................................................................................................11
Figure 7-20: Congested Downtown.........................................................................................................12
Figure 7-21: Rural Area...........................................................................................................................12
Figure 7-22: Installing Pipeline................................................................................................................13
Figure 7-23: Installing Plastic Pipe..........................................................................................................14
Figure 7-24: Tracer Wire..........................................................................................................................14
Figure 7-25: Yellow Warning Tape.........................................................................................................14
Figure 7-26: Backhoe Loader..................................................................................................................15
Figure 7-27: Chain Trencher....................................................................................................................16
Figure 7-28: Plastic Main Plow-in............................................................................................................17
Figure 7-29: Vibratory Plow.....................................................................................................................17
Figure 7-30: Auguring Equipment............................................................................................................18
Figure 7-31: Tunneling Pipe....................................................................................................................18
Figure 7-32: Inserted Plastic Service.......................................................................................................19
Figure 7-33-a : Live Insertion...................................................................................................................20
Figure 7-33-b : Live Insertion...................................................................................................................21
Figure 7-34: Blower and Hose.................................................................................................................21
Figure 7-35: Cured Lining.......................................................................................................................21
Figure 7-36: Hard Slip Lining System......................................................................................................22
Figure 7-37: Pipe Swaging......................................................................................................................22
Figure 7-38: “U” Liner..............................................................................................................................22
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Figure 7-39: Splitting Pipe.......................................................................................................................23
Figure 7-40: Pipe Bursting.......................................................................................................................24
Figure 7-41: Heat Fusion.........................................................................................................................25
Figure 7-42: Transition Fitting..................................................................................................................25
Figure 7-43: Butt Fusion..........................................................................................................................26
Figure 7-44: Sidewall Fusion...................................................................................................................26
Figure 7-45: Electrofusion Control Box and Fittings................................................................................26
Figure 7-46: Socket Fusion......................................................................................................................27
Figure 7-47: Welding...............................................................................................................................28
Figure 7-48: Electric Welding Machine....................................................................................................28
Figure 7-49: Welding Equipment.............................................................................................................29
Figure 7-50: Beveled Pipe.......................................................................................................................30
Figure 7-51: Aligned Pipe........................................................................................................................30
Figure 7-52: Welding Inspection..............................................................................................................30
Figure 7-53: Gasket.................................................................................................................................31
Figure 7-54: Internal Stiffener..................................................................................................................31
Figure 7-55: Cast Iron Pipe Joined..........................................................................................................32
Figure 7-56: Hydraulic Compression Couplings......................................................................................32
Figure 7-57: Flanged Fitting.....................................................................................................................33
Figure 7-58: Bonding Cables...................................................................................................................34
Figure 7-59: Space Required for Maintenance........................................................................................35
Figure 7-60: Pressure Gauge..................................................................................................................36
Figure 7-61: Vault with Valve...................................................................................................................37
Figure 7-62: Gate Valve...........................................................................................................................38
Figure 7-63: Plug Valve...........................................................................................................................38
Figure 7-64: Ball Valve............................................................................................................................38
Figure 7-65: Butterfly Valve.....................................................................................................................38
Figure 7-66: Automated Valve.................................................................................................................38
Figure 7-67: Manual Valve.......................................................................................................................38
Figure 7-68: Gas Stopper Bag.................................................................................................................39
Figure 7-69: Canvas Stoppers.................................................................................................................39
Figure 7-70: Squeeze-off Tool.................................................................................................................40
Figure 7-71: Tapped Pipe........................................................................................................................40
Figure 7-72: Drilling Machine and Equipment..........................................................................................41
Figure 7-73: Pressure Control Fitting.......................................................................................................42
Figure 7-74: Welded................................................................................................................................42
Figure 7-75: Compression.......................................................................................................................42
Figure 7-76: Gate Valve...........................................................................................................................42
CHAPTER 7 ⎯ CONSTRUCTION AND MAINTENANCE 7-v
Figure 7-77: Drilling Machine...................................................................................................................43
Figure 7-78: Stopper Fitting.....................................................................................................................43
Figure 7-79: Stopping Machine................................................................................................................43
Figure 7-80: Hydraulically-operated Squeezer........................................................................................44
Figure 7-81: Vent Stack...........................................................................................................................46
Figure 7-82: Pressure Gauge on Vent Stack...........................................................................................46
Figure 7-83: Damaged Steel Pipe...........................................................................................................47
Figure 7-84: Damaged Plastic Pipe.........................................................................................................47
Figure 7-85: Wrapped Pipe......................................................................................................................48
Figure 7-86: Saddle Clamp......................................................................................................................49
Figure 7-87: Split Sleeve.........................................................................................................................49
Figure 7-88: Compression Coupling........................................................................................................49
Figure 7-89: Pipe Sealant........................................................................................................................50
Figure 7-90: Service Line to a Customer's Home....................................................................................50
Figure 7-91: Branch Service Line............................................................................................................51
Figure 7-92: Mobile Home Service Line and Meter.................................................................................51
Figure 7-93: Service Repair.....................................................................................................................52
Figure 7-94: Shutoff Valve.......................................................................................................................53
Figure 7-95: Tee Cap...............................................................................................................................54
Figure 7-96: Compactor...........................................................................................................................55
Figure 7-97: Pavement Patch..................................................................................................................56
Figure 7-98: Five Factors in the Accident Sequence...............................................................................57
Figure 7-99: Barriers Used to Break the Accident Chain.........................................................................57
CHAPTER 7: CONSTRUCTION AND MAINTENANCE
Introduction
Mains and services transport and deliver natural gas to customers through an extensive piping network. The cost of operating and maintaining a distribution network is a major portion of a utility's total operating expense. A big part of construction and maintenance is the decision of repairing or replacing pipe. New mains are installed to supply additional customers, reinforce pressures, or to replace existing lines in poor condition. Repairs are made on leaking or damaged pipe that is structurally sound, but pipe in poor condition must be replaced.
Another part of construction and maintenance is installation and repair. Installation and repair methods differ, depending on the pipe material, operating pressure pipe location / route, and pipe properties. Proper construction and maintenance of facilities is necessary to ensure safe and reliable gas delivery to customers. This chapter provides a basic knowledge of the operation, construction and maintenance of gas mains and services and includes planning, cost estimation, installation, and facilities operation.
Figure 7-1: Construction Crew
Pipe Materials
The primary pipe materials within a distribution system are steel, plastic, and cast and ductile iron.
Steel Pipe
Steel pipe can be used for all operating pressures within a natural gas system, but today it's used primarily for transmission and distribution lines that operate at high pressures and in areas with heavy loading or stress. High pressure generally refers to 100 psig or greater because this is the highest allowable pressure for plastic pipe.
7-2 GAS DISTRIBUTION SELF-STUDY COURSE
Figure 7-2: Steel Transmission Pipe
The most frequent cause of steel pipe failure is third-party damage. Steel pipe includes low-carbon, high-carbon, and various alloy steels. The biggest disadvantage of steel is that it corrodes and requires coating, wrapping, anodes, test stations, and annual inspections. Damage to steel pipe must be repaired or removed per Federal code 49 CFR 192.309. If external corrosion or damaged coating is found, remedial action must be taken to the extent required by 49 CFR 192.459. Allowable repair on steel pipe is dependent upon the type and depth of damage, pipe specifications and operating pressure, and remaining wall thickness of the pipe.
Plastic Pipe
Plastic pipe is light in weight, easy to handle, fast to install, and has a lower total cost than other pipe materials.
Figure 7-3: Coil of Plastic Pipe
Plastic pipe does not corrode like steel or iron pipe but is softer and much easier to scratch or cut than metallic pipe. Plastic pipe cannot be located with metal detectors, so when it's installed by direct burial a locater wire must be buried in the ditch to detect the pipe location. The maximum operating pressure of plastic pipe is limited by Federal code to 125 psig.
CHAPTER 7 ⎯ CONSTRUCTION AND MAINTENANCE 7-3
If unrestrained, plastic pipe will expand or contract about 10 times as much as steel for a given temperature change; therefore, special practices and anchoring may be required. Plastics include polyethylene, polyvinylchloride, polyamide, and others.
Plastic pipe with scratches or gouges deeper than 10% of the pipe wall must be replaced.
Figure 7-4: Scratched Plastic Pipe
Cast and Ductile Iron Pipe
Cast iron includes pit-cast, centrifugally cast, and ductile and wrought iron. Cast iron and ductile iron pipe do not corrode like steel but can undergo the process of graphitization. Graphitization is a reaction in which iron leaches out of the metal, leaving graphite behind. The pipe surface may appear to be in perfect condition, but the corrosion product is much weaker than the original pipe, leaving it vulnerable to cracking. If a bell joint is exposed, it must be sealed to prevent leakage.
Figure 7-5: Cast iron Pipe
Service Pipe Materials
Gas services are typically steel, copper, or plastic. Precautions regarding proper recognition and the installation of specific materials must be observed, as in the case with mains.
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Figure 7-6: Steel Pipe
Figure 7-7: Copper Pipe
Figure 7-8: Plastic Pipe
Construction Planning
Gas mains are installed to supply new customers, to reinforce supply to an existing system, to relocate an existing facility, for roadway or utility construction, or to replace a facility that is no longer feasible to maintain. Each company will have its own main replacement policy to determine whether a repair or replacement is economically sound. Comprehensive planning must take into account main location, pipe material location of other utilities, soil conditions,permits, applicable specifications, future operations, and method of installation.
Main installations must be planned with sufficient lead-time to allow procurement of materials not on hand. All materials must meet minimum code requirements for the intended service. Materials should be inspected and tested upon receipt to assure compliance with specifications and freedom from damage.
If a line will eventually operate at a pressure higher than its initial service, the future operating pressure must be considered in the design, construction, and testing of the line. Planning also should cover possible future connections or extensions. It is simpler to install a valve or other fitting during initial construction than to make alterations later.
Route Selection
Selecting a pipe route is an important task when designing the installation of new gas mains or services. Route selection may be necessary because of new customers, replacement of pipe in poor condition, street resurfacing, or utility construction.
Planning should consider the distance of possible routes, construction obstacles, government regulations and permits, addition of customers, future maintenance, and cost.
On larger projects, pre-construction and pre-design meetings are held to determine the impact that other utilities may have on pipe route selection. Designers, construction contractors, utility representatives, and other interested parties meet to discuss the scope and timing of intended work, type of equipment involved, nearness of excavation to underground facilities, potential for accidents, and special provisions or requirements.
Distance of Possible Routes
The total length of a pipe route affects the amount of material needed and installation time. Longer routes have a higher overall cost but may be less costly per foot of pipe. Usually, the shortest distance between two points is the most cost-effective route because there is less material, a smaller amount of restoration, and lower construction costs.
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