Ideal Gas Law
The ideal gas law is the combination of the volume, temperature, and pressure relationships of Boyle's and Charles' laws resulting in the relationship PV=RT. Real gases deviate by varying amounts from the ideal gas law. See SUPERCOMPRESSIBILITY FACTOR and LAWS.
Ignition Temperature
The temperature at which a substance, such as gas, will ignite and continue burning with adequate air supply.
Ignition, Automatic
A means which provides for automatic lighting of gas at the burner when the gas valve controlling flow is turned on and will effect relighting if the flame on the burner has been extinguished by means other than closing the gas burner valve.
Ignition, Continuous
Ignition by an energy source which is continuously maintained through the time the burner is in service, whether the main burner is firing or not.
Ignition, Intermittent
Ignition by an energy source which is continuously maintained through the time the burner is firing.
Ignition, Interrupted
Ignition by an energy source which is automatically energized each time the main burner is fired and subsequently is automatically shut off during the firing cycle.
Ignition, Manual
Ignition by an energy source which is manually energized and where the fuel to the pilot is lighted automatically when the ignition system is energized.
The group of unsaturated or heavy hydrocarbons in a manufactured gas, such as ethylene and benzene, which burn with a luminous flame.
When a party receives or delivers a quantity of natural gas, then delivers or redelivers a larger or smaller quantity of natural gas to another party.
Immersion Length
The length from the free end of a thermometer bulb or well to the point of immersion in the medium, the temperature of which is being measured.
Impact Evaluation
Examination of the effects of a DSM program, including quantitative documentation of a program's costs and benefits, program participation and measure adoption, performance of technologies, and energy impacts.
Impact Resistance
Energy required to break a specimen by a sudden blow.
Impact, Izod
A specific type of impact test made with a pendulum-type machine. The specimens are molded or extruded with a machine notch. See ASTM D 256.
Impact, Tup
A falling weight (tup) impact test developed specifically for pipe and fittings. There are several variables that can be selected. See ASTM D 2444.
Any formation that prohibits the passage of fluid or gas through it.
Impounding Area
An area which is defined through the use of berms,
Imputed Capitalization
A method to adjust a projected capital structure for accumulated deferred income taxes.
In Situ Coal Gasification
Gasification of coal underground by introduction of air or oxygen into the coal seam.
In DSM, a cash or non-cash award that is offered to encourage participation in a utility-sponsored DSM program.
Incentive or Industrial Sales Programs (ISP)
Special marketing programs that make gas available at more competitive prices, usually accomplished by reducing gas costs rather than redistributing fixed costs from one customer group to another.
Incentive Program
A DSM program in which an incentive is offered to encourage participation and adoption of the recommended measure.
Incentive Rate of Return (IROR)
A variable regulatory rate that reduces the allowed return in the event of cost overruns.
Inch of Mercury
A pressure unit representing the pressure required to support a column of mercury one inch high at a specified temperature; 2.036 inches of mercury (at 32 degrees F and standard gravity of 32.174 ft/sec2) is equal to a gauge pressure of one pound per square inch.
Inch of Water
A pressure unit representing the pressure required to support a column of water one inch high. Usually reported as inches W.C. (water column) at a specified temperature; 27.707 inches of water (at 60o and standard gravity of 32.174 ft/sec2) is equal to a gauge pressure of one pound per square inch.
The process of reducing refuse material to ash.
The trade name of an instrument used to determine whether or not the well bore is proceeding in a vertical orientation at any point. In most drilling operations, either government bodies or contract stipulations or both, provide a maximum deviation of the well bore from the vertical; commonly, this maximum is three degrees. When deviation is in excess of the allowable, it is necessary to modify drilling procedures to bring it back in line.
Incremental Cost
The additional costs incurred from the production or delivery of an additional number of units of gas, usually the minimum capacity or production that can be added. The additional cost divided by the additional capacity or output is defined as the incremental cost. Also, in DSM, the difference in costs between an efficient technology or measure and the alternative standard technology.
Incremental Pricing
A pricing mechanism established by the Natural Gas Policy Act of 1978. It is the passing through of certain costs of acquiring new gas by way of a surcharge and applying the surcharge to certain end uses by certain industrial facilities. In 1987, Title II, incremental pricing, of the NGPA of 1978 was repealed.
Indefinite Price Clauses
Contract clauses that cause the price of natural gas to increase. Usually of two types - favored nation clauses and oil related clauses. Favored nation clauses place
As used in the oil industry, usually refers to a nonintegrated producing company. The integrated company usually operates production, transportation, refining, and marketing facilities. Generally, the independent producer has operations only in the field of petroleum production.
Independent Petroleum Association of America (IPAA
A trade group representing independent oil and gas producers.
Independent Power Producer (IPP)
Wholesale electric producer unaffiliated with the franchised utility in the area in which it is selling power.
A general term for a measure; also applied to the mechanism, composed of gears, dials, and dial face, that indicates the quantity of gas passing through a meter.
Index, Constant-Pressure Compensating
An index used to indicate a gas volume converted to a constant base pressure when used in conjunction with a gas meter operated at a constant pressure other than the contract base pressure.
Index, Meter
The mechanism which displays the volume of gas that has passed through the meter. Indexes consist of two general types: The circular dial type employs a pointer which sweeps through a circle marked with numerals indicating volume registered. The direct reading (digital or counter type) type employs a display marked with numerals indicating volume registered.
Index, Temperature Compensating
A meter index display used to correct volume under flowing gas conditions to a base temperature, commonly 60oF.
Tying the commodity price in a contract to other published prices, such as spot prices for gas or alternate fuels, or general indexes like the Consumer Price Index or Producer Price Index.
Indicator, Demand
A device that indicates on a scale, chart, or tape the maximum volume metered during a predetermined period of time.
Indicator, Engine
A mechanical device connected to an engine to draw a chart of cylinder pressure versus piston position from which the relation of the energy input and energy output of the engine may be computed.
Indicator, Volume
A component of a auxiliary device designed to indicate on a scale or chart, or both, the volume of gas passing through a meter in relation to time, temperature, pressure, or any combination thereof.
Indirect Oven Thermostat System
A control system of two or more integrated automatic devices to maintain a selected oven temperature. That portion of the system responsive to oven temperature causes operation of another portion of the system to turn on or shut off the gas supply to the oven burner.
A heater in which combustion products do not come in contact with the material to be heated; heating of the material is accomplished by radiation or conduction from the heated surfaced. Compare DIRECT-FIRED.
Industrial and Railroad Generating Stations
Electric generating stations operated by industrial establishments and railroads to supply all or part of their own power requirements.
Industrial Fuel Switching
Switching from natural gas to alternate fuels such as residual or clarified oil by large industrial customers, primarily motivated by the relative fuel prices.
Industrial Service
A material not acted upon chemically by the surrounding environment. Nitrogen and carbon dioxide are examples of inert constituents of natural gases; they dilute the gas and do not burn, and thus add no heating value.
Infield Exchange Agreement
Contract specifying the terms and conditions for the exchange of wellhead gas production between different companies usually within the same producing field.
Infill Drilling
Drilling between existing well locations to extract pockets of gas that might otherwise be missed, or to increase deliverability from a production or storage field.
Infill Well
Any well drilled on a closer than normal well spacing pattern or requirement. Also, any well drilled between existing wells producing from the same reservoir.
The air entering a space through a wall, crack, doors, and other openings.
Infra-Red Radiation
A chemical agent which slows or reduces chemical action. Inhibitors are used principally in liquid coolants to reduce corrosion of metal parts of the system and in well drilling fluids to reduce corrosion of metals in piping of equipment used in well drilling operations.
Initial Delivery
The first gas to flow under an agreement at a new facility or for a new contract.
Injected Gas
Injection Molding
The process of forming a material by forcing it, under pressure, from a heated cylinder through a sprue (runner, gate) into the cavity of a closed mold. Fittings are usually made by this process.
Injury/Illness Incidence Rate, Disabling
The number of disabling occupational injuries and illnesses per 200,000 employee hours of exposure. This is computed by multiplying the number of disabling injuries and illnesses by 200,000 and dividing by the number of employee-hours worked. The hours worked should not include any non-work time such as holidays, vacations, and sick leave.
Injury/Illness, Disabling
An occupational injury or illness that results in a fatality or one or more days away from work.
Input Rate
The rate at which gas is supplied to an appliance. It may be expressed in Btu per hour (Btuh), thousands of Btu per hour (MBtuh); in cubic feet per hour (cfh); or thousands of cubic feet per hour (Mcfh); in therms (th) or dekatherms (Dth) per hour.
Input Rating
The gas-burning capacity of an appliance in Btu per hour as specified by the manufacturer. Appliance input ratings are based on sea level operation and need not be changed for operation up to 2,000 feet.
Plastic, copper, etc., tubing inserted into a run of existing pipe, thereby eliminating the need for a new trench.
Instantaneous Technical Potential
An estimate of energy savings based on the assumption that all existing appliances, equipment, building-shell measures, and industrial processes are instantly replaced with the most efficient commercially available units.
Instrument Piping
All piping, valves, and fittings used to connect instruments to main piping, other instruments and apparatus, or measuring equipment.
Insulation (Thermal)
A material having a relatively high resistance to heat transfer.
Intangible Plant
Organization, Franchises and Consents, Patent Rights, Licenses, Privileges, and other intangible property necessary or valuable in the conduct of the utility's operations.
Integrated Company
A company which obtains a significant portion of its gas operating revenues from the operations of both a retail gas distribution system and gas transmission system.
Integrated Gasification Combined Cycle
A system to convert coal to clean combustible gas which fuels a combustible turbine generator.
Integrated Resource Planning
A utility planning method whereby alternative resource mixes, including demand-side and supply-side options, are evaluated in order to determine which resource plan minimizes the overall cost of service, subject to reliability and various other constraints.
Integrating Device
A mechanism designed to automatically correct a gas-volume-related input to some predetermined base conditions.
Integrating Pressure-And-Temperature Instrument
The integrating pressure-and-temperature instrument registers, on a counter, the total quantity of gas passed through the meter, reduced to standard cubic feet at a definite base pressure and base temperature. Each increment of volume is multiplied by a temperature-factor corresponding to the line-temperature and base-temperature. It is then multiplied by the pressure-multiplier corresponding to the line pressure and base pressure. The product is totaled on a counter index. A supplementary index is furnished which reads the total quantity passed at line conditions.
Integrating Pressure-Instrument
The integrating pressure-instrument registers the total volume of gas metered in cubic feet at a specified base pressure. This instrument is equipped with a second register which records the total volume at the flowing pressure. Each unit of volume flowing through the meter causes the integrating mechanism to make one cycle and apply the correct pressure multiplier for that unit. The summation of these products is registered on a counter index indicating the displaced volume at base pressure.
Interactive Effects
The effects that a change in one end-use's consumption in a given structure has on another end-use's consumption in that structure.
A measure of the degree to which combustion characteristics of one gas are compatible with those of another gas. Two gases are said to be interchangeable when one gas may be substituted for the other gas without interfering with the operation of gas burning appliances or equipment.
Interconnection, System
A connection between two utility systems permitting the transfer of gas in either direction.
Interest Charged to Construction-Credit
Interested Parties
In a rate case, interested parties are the pipeline company, its customers, the FERC Staff, and "others". The "others" are commonly known as intervenors, and they include such groups as state regulatory agencies, consumer groups, competing pipeline companies, and customers of customers.
In ratemaking intergeneration refers to costs that are incurred by more than one generation of rate payers (e.g., depreciation). Section 9 of the Natural Gas Act requires a separate just and reasonable finding on any intergeneration costs even in Settlements.
Interim Bill
Interim Relief
Relief granted by the Commission in response to an applicant's claim that a regulation would cause irreparable injury, special hardship or inequity to himself or the public.
Interior Zones
The portions of a building which do not have significant amounts of exterior surfaces. Such zones have heating or cooling needs largely dependent upon internal factors such as lighting. Compare EXTERIOR ZONES.
A control to prove the physical state of a required condition, and to furnish that proof to the primary safety control circuit.
Internal Combustion
Pertains to any engine in which the heat or pressure necessary to produce power is developed in the engine cylinder by the combustion of a fuel.
Interruptible Service
Low priority service offered to customers under schedules or contracts which anticipate and permit interruption on short notice, generally in peak-load seasons, by reason of the claim of firm service customers and higher priority users. Gas is available at any time of the year if the supply is sufficient and the supply system is adequate.
Interruptible Transportation Service (ITS)
Low priority service offered to customers under schedules or contracts which anticipate and permit interruption on short notice, generally in peak-load seasons, by reason of the claim of firm service customers and higher priority users.
With respect to natural gas companies, the transporting and sale of gas for resale across state lines.
Interstate Gas
Gas transported in interstate pipelines to be sold and consumed in states other than that state in which the gas was produced.
Interstate Natural Gas Association of America (ING
Trade group representing the interstate pipelines.
A person, business entity, or public body that is granted the right to participate in a rate case or hearing.
With respect to natural gas companies, the transporting and sale of gas for resale within the boundaries of a state.
Intrastate Gas
Gas sold and consumed in the state where it is produced and not transported in interstate pipelines.
An electrical device for conversion of direct current to alternating current.
Investment Tax Credit (ITC)
The credit against federal income taxes provided by the Revenue Act for qualified depreciable assets after December 31, 1961, except for suspension periods October 10, 1966 to March 9, 1967, and April 18, 1969 to August 15, 1971. Tax Reform Act of 1986 repeals regular ITC for property placed in service after December 31, 1985.
Investment Tax Credit Adjustments, Net
The income account used by those companies which do not apply the entire benefit of the investment tax credit to income in the year in which such credit is realized. This account is used to record the charges for the current year's investment tax credit less the current year's amortization of the accumulated investment tax credits under a plan which spreads over the useful life of the qualified property additions or some shorter period the investment tax credit benefits applicable to that property.
ISO Equation
An equation showing the interrelations between stress, pressure and dimensions in pipe, namely: P(ID + t), P(OD - t), S = 2t or 2t, where: S = hoop stress, P = pressure, ID = average inside diameter, OD = average outside diameter, t = minimum wall thickness
Isobutane (C4H10)
A hydrocarbon of the same chemical formula as butane but different molecular structure, resulting in different physical properties, notably lower boiling point. Gross heating value 3261 Btu/cu. ft. gas.

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