Valves......................................................................................................................................................27
Valve Classifications...........................................................................................................................27
Valve Categories.................................................................................................................................28
Valve Types........................................................................................................................................28
Valve Inspection and Testing..............................................................................................................30
Valve Costs.........................................................................................................................................31
Additional Gas Stop-off Methods........................................................................................................31
Plant Location Records............................................................................................................................32
Easements..........................................................................................................................................34
Pipe Repair or Replacement Decisions...................................................................................................35
Transmission Lines.............................................................................................................................35
Distribution Lines.................................................................................................................................35
Plastic Pipe.........................................................................................................................................36
Repair or Replacement Strategy.........................................................................................................36
Computer Modeling.............................................................................................................................40
Uprating of Facilities................................................................................................................................41
Factors to Investigate Before Uprating................................................................................................41
Construction Preparations for Uprating...............................................................................................43
Uprating Records................................................................................................................................43
Benefits of a Sectionalizing Program..................................................................................................43
LIST OF TABLES
Page
Table 6-1: Specified Minimum Yield Strength of Common Gas Distribution Main Materials..................10
Table 6-2: Cost of Valves for Varying Designs and Sizes......................................................................31
Table 6-3: Cost Benefit Analysis Example Data.....................................................................................38
Table 6-4: Risk Factors...........................................................................................................................39
LIST OF FIGURES
Page
Figure 6-1: Cast Iron Pipe.........................................................................................................................5
Figure 6-2: Corroded Cast Iron.................................................................................................................5
Figure 6-3: Installing Plastic Pipe.............................................................................................................6
Figure 6-4: Coils of Plastic Pipe................................................................................................................7
Figure 6-5: Three Types of Stress (F = Force).........................................................................................9
Figure 6-6: Stress Strain Diagram for Tensile Stress in Steel..................................................................9
Chapter 6 ⎯ ENGINEERING 6-iii
Figure 6-7: Manufacturing Steel Pipe.....................................................................................................16
Figure 6-8: Edge Forming System..........................................................................................................17
Figure 6-9: Plastic Pipe Manufacturing...................................................................................................17
Figure 6-10: Fittings.................................................................................................................................19
Figure 6-11: Compression Fitting............................................................................................................20
Figure 6-12: Steel Band Clamp...............................................................................................................21
Figure 6-13: Stiffener...............................................................................................................................21
Figure 6-14: U-bolt...................................................................................................................................21
Figure 6-15: Pipe Blocking.......................................................................................................................22
Figure 6-16: Butt Fusion..........................................................................................................................22
Figure 6-17: Saddle/Sidewall Fusion.......................................................................................................22
Figure 6-18: Electro Fusion.....................................................................................................................23
Figure 6-19: Pipe Welding.......................................................................................................................23
Figure 6-20: Electric Arc Welding............................................................................................................24
Figure 6-21: Oxy Acetylene Welding Equipment.....................................................................................24
Figure 6-22: Bolted Flange Joint..............................................................................................................25
Figure 6-23: Hydraulic Installed Couplings..............................................................................................25
Figure 6-24: Scratched Plastic Pipe........................................................................................................27
Figure 6-25: Valve Basin.........................................................................................................................28
Figure 6-26: Valve Box............................................................................................................................28
Figure 6-27: Gate Valve...........................................................................................................................29
Figure 6-28: Plug Valve...........................................................................................................................29
Figure 6-29: Ball Valve............................................................................................................................29
Figure 6-30: Butterfly Valve.....................................................................................................................29
Figure 6-31: Bypass Valve.......................................................................................................................30
Figure 6-32: Above Ground and Underground Valves............................................................................30
Figure 6-33: Low Pressure Bag...............................................................................................................31
Figure 6-34: Squeeze-off Tool.................................................................................................................31
Figure 6-35: Sample Main Location Map (Atlas) With Dimensions.........................................................33
Figure 6-36: Sample Map........................................................................................................................34
Figure 6-37: Damaged Plastic Pipe.........................................................................................................36
Figure 6-38: Corroded Distribution Line...................................................................................................36
CHAPTER 6: ENGINEERING
Introduction
The engineering function of a gas company is very important because it designs major additions and revisions to a company’s gas system and structures. Engineering staff develop construction and material standards and are the primary resource for information regarding system design, code interpretation, material requirements, and environmental issues. Engineering functions typically involve the largest expenditure of company operating and maintenance dollars.
A typical gas distribution company’s engineering department includes the following specialized functions:
• System Planning
• System Design
• Station Design
• Codes and Standards
• Environmental Affairs
• Drafting
Smaller companies may have a single engineer responsible for multiple functions. In larger companies, each of these functions may be in a separate area of the engineering department.
System Planning
System Planning is responsible for determining the effects of changing load patterns on the piping network and proposing methods to assure adequate distribution system capacity. All significant additions of gas load such as new residential subdivisions or increased industrial loads should be evaluated by System Planning to:
• Verify that the existing system can handle the proposed load
• Determine optimal methods to expand the system and reinforce pressures in an area, as required.
A close relationship should be maintained between system planning and the sales and marketing areas of the company so that future growth of the distribution system can be handled in the most economical way. When proposed gas loads exceed the capacity of an existing distribution system, System Planning engineers may propose the installation of new mains or an additional regulator station. System Planning will also arrange for annual pressure surveys (normally taken at or near the peak flow day) to study the system's ability to handle present and future loads. The flow analysis of a larger area or an entire system is normally solved by computer. Although these systems can be expensive, the initial cost can easily be recovered by enabling decisions to be made in the most economical manner.
System Design
System Design is responsible for project planning to replace piping in poor condition, respond to public improvement, and address needs identified by system planners. System Design engineers produce
6-2 GAS DISTRIBUTION SELF-STUDY COURSE
detailed drawings, specifications, and bills of material from which construction can take place. Small projects, such as simple main extensions and small subdivisions, can normally be handled by the operating areas utilizing standards previously developed for such projects.
Major projects can originate from the following 4 sources:
1) New business: piping required to supply new customers
2) System improvements: new mains required to improve gas supply and pressure to an area
3) System replacement: installation of piping to replace existing main or services in poor condition
4) Public improvement: main replacement or relocation due to roadway or utility construction.
System design may also be responsible for the design of pressure reducing facilities as well as large specially designed industrial meter sets. Another function of system design is participation in pre-construction or pre-design meetings. These meetings are a common practice on larger projects and require that system designers, construction contractors, utility representatives, and other interested parties of the project 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.
Station Design
Station Design is responsible for designing large, non-standard facilities such as city gate stations, flow control regulators, odorizers, field heaters, and other buildings needed for the supply network. Station design may also be involved with the design of gas storage facilities, peakshaving plants, and telecommunication instruments.
Codes and Standards
Codes and Standards is responsible for material and construction standards for the company. This area reviews new and proposed regulations to determine the impact on gas operations. Construction specifications are checked for code compliance, material standards, and safety. As new material comes into the gas industry and is approved for general use, this area is responsible for designing the standards for these materials.
The 3 primary codes and standards groups that apply to the gas industry include⎯
5) Department of Transportation (DOT)
6) Occupational Safety and Health Administration (OSHA)
7) Environmental Protection Agency (EPA).
Department of Transportation (DOT)
The United States DOT is required by law to develop and enforce minimum safety regulations for the transportation of gas by pipeline, natural gas systems and operators. The safety regulations are published in Title 49 of the Code of Federal Regulations (CFR), Parts 190, 191, 192, and 199. These DOT safety regulations are also published online.
Chapter 6 ⎯ ENGINEERING 6-3
Pipeline safety regulations require gas companies to:
• Deliver gas safely and reliably to customers
• Provide training and written instruction for employees
• Establish written procedures to minimize the hazards resulting from natural gas pipeline emergencies
• Maintain records of inspection and testing
• Report significant incidents and conditions as specified in Part 191.
Additionally, operators of all natural gas systems, except master meter systems, must test employees in safety-sensitive positions for prohibited drugs and alcohol and provide an employee assistance program. State agencies may also enforce pipeline safety regulations and are allowed to adopt more stringent safety regulations if certified by the Office of Pipeline Safety (OPS).
Occupational Safety and Health Administration (OSHA)
Many gas distribution company safety rules and required personal protective equipment are based on OSHA standards. For example, OSHA standards specify that a “competent person” must be on location whenever an excavation is 5 feet or more in depth or examination of the ground indicates unstable or soft material. A competent person is one who has successfully completed OSHA training and is capable of identifying existing and predictable hazards and taking prompt corrective measures.
An additional example of OSHA regulations involves confined space entry procedures. This is especially critical to gas distribution companies because the air in manholes, regulator vaults, and other confined spaces can have an oxygen deficiency and result in asphyxiation. If employees must enter a confined space, trained personnel and monitoring equipment must be present.
Environmental Protection Agency (EPA)
The EPA specifies requirements for control and handling of hazardous material spills and other environmental problems. Water used for hydrostatic⎯or pressure⎯testing of natural gas lines or residue discovered in gas piping must be treated as if hazardous according to the EPA.
Additional Information
Requirements for customers piping beyond the meter are contained within the “National Fuel Gas Code,” NFPA 54/ANSI Z223.1 and other local codes and ordinances.*
Each state is required to adopt the Federal Standards as a minimum if they expect federal grants to help fund the operation of their own Public Service Commission (usual title). Some east coast states have agreements in which they depend on the Federal Department of Transportation to enforce violations observed and documented by state PSC staff. A few western states have withdrawn from any agreement leaving Federal DOT staff responsible for inspection and enforcement in those states, as they are in the District of Columbia and in Puerto Rico.
* Although the National Fuel Gas code is national in scope, there are 4 or 5 regional and specialized codes that include gas house piping. Each of some 1400 local jurisdictions in the U.S. can choose among these and add variations of its own.
6-4 GAS DISTRIBUTION SELF-STUDY COURSE
A variation to be aware of is that some states do not include municipal gas systems in their jurisdiction. Another variation in some states involves piping beyond a master meter, such as in mobile home courts (trailer parks) or apartment buildings. As the Federal regulations apply to both of these categories of gas systems, here again DOT must pick up the responsibility when the state does not.
Environmental Affairs
Environmental Affairs reviews new and existing environmental regulations to verify that materials, construction specifications, and operations comply with the Environmental Protection Agency (EPA
