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The differential or pressure, usually expressed in terms of the height of a liquid column that the pressure will support. Also, the differential across a primary measuring device in feet of flowing fluid.
Head Up
To tighten the bolts on a hatch cover or manhole plate so that no leakage will occur from or into the vessel when operating.
A pipe or fitting that interconnects a number of branch pipes.
A point at which gas enters the pipeline's main transmission line, either at the interconnection of the gathering system or of a third party transporter. See POOLING POINT.
A formal meeting of interested parties in a rate proceeding before an administrative law judge or regulatory commission to obtain a decision on differences in a filing. Hearing may include written testimony, cross-examination of company witnesses, rebuttal testimony, recross-examination of these witnesses by the company, initial briefs, reply briefs addressing arguments raised by other in the initial briefs, and oral arguments.
Heat Balance
The accounting of the energy output and losses from a system to equal the energy input.
Heat Capacity
Quantity of heat required to raise the temperature of a unit quantity of a substance one degree. Interchangeable with "specific heat" in common usage.
Heat Exchanger, Direct
A heat exchanger in which heat generated in the combustion chamber of the device is transferred directly through walls of the heat exchanger to the heating medium such as air, steam, or water, held in close contact with the combustion-chamber walls. It is a self-contained combustion and heat-transfer device, hence a direct heat-transfer device.
Heat Exchanger, Indirect
A heat exchanger which encloses or contains a heating medium such as air, steam, or water, the heat from which is transferred to another heating medium separately contained in close contact with or directed through the heat exchanger. It is an indirect heat-transfer device.
Heat Fusion Joint
A joint made in thermoplastic piping by heating the parts sufficiently to permit fusion of the materials when the parts are pressed together.
Heat Gain
The amount of heat gained by a space from all sources, including people, lights, machines, sunshine, etc.
Heat Joining
Making a pipe joint by heating the mating surfaces of the parts to be joined so that they fuse and become essentially one piece with or without addition of material. NOTE: Also known as Heat fusion and Fusion.
Heat Liberation Rate
The amount of heat which is liberated per unit time per cubic foot of combustion space.
Heat Loss
The sum cooling effect of a building structure when the outdoor temperature is lower than the desired indoor temperature.
Heat of Combustion
The heat released when a substance is completely burned in oxygen. Compare HEATING VALUE.
Heat of Fusion
The heat lost or gained by a substance in passing from
Heat of Vaporization, Latent
The quantity of heat required to change a unit weight of liquid to vapor with no change in temperature.
Heat Pump
A year-round air-conditioning system employing refrigeration equipment in a manner which enables usable heat to be supplied to a space during the winter period, and by reversing the operation cycle to extract heat from the same space during the summer period. When operating as a heating system, heat is absorbed from an outside medium (either air, water, or the earth) and this heat, together with the heat equivalent of the work of compression, is supplied to space to be heated. When operating on the cooling cycle, heat is absorbed from the space to be cooled and this heat, together with the heat equivalent of the work of compression, is rejected to the outside medium.
Heat Transfer
Flow of heat by radiation, convection, or conduction. This term is sometimes used to mean rate of heat transfer. See CONVECTION; CONDUCTION; RADIATION.
Heat Transfer Coefficient
The quantity of heat transferred through a unit area of a material in a unit time per unit of temperature difference between the two sides of the material.
Heat, Latent
Change in heat content of a substance when its physical state is changed without a change in temperature; i.e., boiling or melting.
Heat, Sensible
That heat which, when added or subtracted, results in a change of temperature, as distinguished from latent heat.
Heat, Specific
The heat required to raise a unit mass of a substance through a degree of temperature difference. Also, the ratio of the thermal capacity of a substance to that of water at 60 degrees F (15.6 degrees C). Interchangeable with "heat capacity" in common usage.
Heater, Construction
A self-contained, unvented, portable heater intended for temporary use during construction, sometimes called a salamander.
Heater, Infra-Red Radiant
A self-contained, vented, or unvented heater used to convert the combustion energy to radiant energy, a substantial portion of which is in the infra-red spectrum, for the purpose of direct heat transfer.
Heater, Make-Up Air
A self-contained, vented, or unvented, gas-fired air heater used only to heat air from the outside to replace air which is leaking, being vented, or being discharged from a heated building. May be direct-fired or indirect-fired.
Heater, Room
A self-contained, free-standing, nonrecessed (except as noted below), gas-burning, air heating appliance intended for installation in the space being heated and not intended for duct connection. This shall not include heating appliances covered by other American Standard Approval or Listing Requirements. It may be of either the gravity or mechanical air circulation type, vented, or unvented. (In some areas, this is referred to as a space heater).
Heater, Unit
High static pressure type is a self-contained, automatically controlled, vented, gas-burning appliance, limited to the heating of nonresidential space.
Heater, Vented Recessed
A self-contained, vented appliance complete with grilles or equivalent, designed for incorporation in or permanent attachment to a wall, floor, ceiling, or partition, and furnishing heated air circulated by gravity or by a fan directly into the space to be heated, through openings in the casing. Such appliances shall not be provided with duct extensions beyond the vertical and horizontal limits of the casing proper, except that boots not to exceed 10 inches beyond the horizontal limits of the casing for extension through walls of nominal thickness may be permitted. Where such boots are provided, they shall be supplied by the manufacturer as an integral part of the appliance and tested as such. This definition shall exclude floor furnaces, unit heaters, and central furnaces.
Heating Degree Day
Heating Season Method
Heating System, High-Pressure Steam
A steam heating system employing steam at pressure above 15 psig.
Heating System, High-Temperature Water
A heating system in which water having supply temperature above 350 degrees Fahrenheit is used as a medium to convey heat from a central boiler, through a piping system, to the heating units.
Heating System, Hot Water
A heating system in which water having supply temperatures less than 250 degrees Fahrenheit is used as medium to convey heat from a central boiler, through a piping system, to the heating units.
Heating System, Low-Pressure Steam
A steam heating system employing steam at pressures below 15 psig.
Heating System, Medium-Temperature Water
A heating system in which water having supply temperatures between 250 and 350 degrees Fahrenheit is used as a medium to convey heat from a central boiler, through a piping system, to the heating units.
Heating System, Steam
A heating system in which heat is transferred from a boiler or other source to the heating units by means of steam.
Heating Value
The amount of heat produced by the complete combustion of a unit quantity of fuel. The gross of higher heating value is that which is obtained when all of the products of combustion are cooled to the temperature existing before combustion, the water vapor formed during combustion is condensed, and all the necessary corrections have been made. The net or lower heating value is obtained by subtracting the latent heat of vaporization of the water vapor, formed by the combustion of the hydrogen in the fuel, from the gross or higher heating value.
Any method of minimizing the risk of price change. Since the movement of cash prices is usually in the same direction and about in the same degree as the movement of the present prices of futures contracts, any loss (or gain) resulting from carrying the actual merchandise is approximately offset by a corresponding gain (or loss) when the contract is liquidated.
Helium (He)
A colorless, odorless, inert gas, specific gravity 0.1368, found in some natural gas.
Henry Hub
A pipeline interchange, located in Vermilion Parish, Louisiana, which serves as the delivery point of natural gas futures contracts.
Herfindahl-Hirschman Index (HHI)
A measure of market concentration. The index is frequently used by the Department of Justice and the Federal Trade Commission to analyze mergers and acquisitions.
Any of 5 isomeric, volatile, liquid, paraffin hydrocarbons C6H14 found in petroleum.
High Btu Gas
A term used to designate fuel gases having heating values of pipeline specification, i.e., greater than about 900 Btus per standard cubic foot.
High Btu Oil-Gas Process
A manufactured gas process in which oil is converted into a fuel gas having a higher heating value than that of coal gas or carbureted water gas. Often called Hi-Btu Gas Process.
High Fire
An expression used for the design maximum rate of fuel input to a burner.
High Pressure Distribution System
High Sulphur No. 6 Oil
Oil with sulphur content of more than 1% by weight.
High Wall
The unexcavated face of exposed over-burden and coal.
High-Density Polyethylene
Type III polyethylene with a density of 0.941 to 0.965 g/cubic centimeters.
High-Priority Customers
Customers with priority in use in utility curtailment
High-Priority Use
The use of gas in a residence, commercial establishment using less than a set volume (i.e., 50,000 cubic feet per day), school, hospital, or similar institution, any use which, if curtailed, would endanger life, health or maintenance of physical property.
Highest Allowed Regulated Rate Clause
A provision in a gas sales contract that specifies that the price paid for the gas would be the highest allowed regulated price.
Hinshaw Amendment
An amendment to the Natural Gas Act which exempts from Federal Energy Regulatory Commission regulation the transportation and sale for resale of natural gas received within the boundaries of a state, provided (1) all such gas is ultimately consumed within the state, and (2) the facilities and rates are regulated by the state. Pipelines qualifying under this amendment are called Hinshaw Pipelines.
Historical Cost
The actual cost of land, buildings, pipelines and other plant items to the company, when used in ratemaking it assumes the company's acquisition costs are prudent. The difference with original cost is the acquisition adjustment. See ORIGINAL COST.
A European term used to describe the surface below the range burner. Sometimes referred to as the burner unit.
Holder, Gas
A gas-tight receptacle or container in which gas is stored for future use. (1) at approximately constant pressure (low pressure containers) in which case the volume of the container changes; and (2) in containers of constant volume (usually high pressure containers) in which case the quantity of gas molecules stored varies with the pressure.
A common term which usually refers to the well bore. Mouse Hole and Rat Hole are shallow bores under the derrick in which the kelly joint and joints of drill pipe are temporarily suspended while making a connection. Rat Hole also refers to a hole of reduced size in the bottom of the regular well bore. Sometimes the driller "rat holes ahead" to facilitate the taking of a drill stem test when it appears that such tests will be desirable.
A discontinuity or break in the anticorrosion protective coating on pipe, tubing, or fitting that leaves the bare metal exposed to corrosive processes.
Holiday Detector
An electronic device for locating discontinuities or breaks in the protective coating on a pipe, tubing, or fitting.
Hoop Stress
The tensile stress, usually in pounds per square inch (psi), acting on the pipe along the circumferential direction of the pipe wall when the pipe contains gas or liquid under pressure.
Horsepower (hp)
A unit of power; equivalent to 33,000 ft-lb per minute, or 550 ft-lb per second (mechanical horsepower), or 0.746 kilowatts.
Horsepower Hour
The equivalent of one horsepower expended for one hour. One horsepower hour equals 1,979,980 foot-pounds.
Horsepower, Boiler (Bhp)
The equivalent evaporation of 34.5 lbs. of water per hour at 212 degrees F and above. This is equal to a heat output of 33,475 Btu per hour.
Horsepower, Brake (bhp)
The power developed by the engine, as measured at the crank shaft or flywheel by the Prony brake or other device.
Horsepower, Compressor
The horsepower rating on the name plate.
Horsepower, Indicated
The horsepower determined from the pressure-volume indicator diagram. This is the power developed within the cylinder of the engine and is more than the power delivered at the driving shaft by the amount of mechanical friction.
Hot Tap
The connection of branch piping to an operating line, and the tapping of the operating line while it is under pressure.
Hot Work
Maintenance or construction work requiring welding, burning, grinding, or drilling.
Hourly Peak
The maximum demand for gas from a transmission or distribution system in a one hour period of time.
House Riser, Gas
The principal vertical pipe which conducts the gas from the meter to the different floors of the building.
A market or supply area pooling/delivery where gas supply transaction point occur that serve to facilitate the movement of gas between and among interstate pipelines. Transactions can include a change in title, a change in transporter, or other similar items.
A mechanical means of increasing the relative humidity by injecting water or water vapor into the air.
A regulating device, actuated by changes in humidity, used for the automatic control of relative humidity.
The entrained weight of water per unit weight of moisture-free gas or air.
Humidity, Relative
The ratio of the weight of water vapor in the atmosphere to the weight the air would hold if completely saturated at that temperature, expressed as a percentage.
HVAC System
A system that provides either collectively or individually the processes of comfort heating, ventilation and/or cooling within or associated with a building.
A copyrighted name of an operation whereby producing formations are fractured by hydraulic pressure to increase productiveness.
A solid ice-like material resulting from the combination of a gas with water under pressure. Of natural gas constituents -- methane, ethane, propane, isobutane, normal butane, and also hydrogen sulfide and carbon dioxide will form hydrates. The greater the pressure in the equipment, the higher the temperature at which the hydrate will form, usually well above freezing. Hydrates can cause restriction or stoppage of flow, and can be controlled by alcohol injection or by dehydration of the gas. Methane hydrates are found in some permafrost regions and beneath portions of the ocean floor and may eventually be a source of methane gas.
A chemical compound composed solely of carbon and hydrogen. The compounds having a small number of carbon and hydrogen atoms in their molecules are usually gaseous; those with a larger number of atoms are liquid, and the compounds with the largest number of atoms are solid.
Hydrocarbon, Saturated
A chemical compound of carbon and hydrogen in which all the valence bonds of the carbon atoms are taken up with hydrogen atoms.
Hydrocarbon, Unsaturated
A chemical compound of carbon and hydrogen in which not all the valence bonds of the carbon atoms are taken up with hydrogen atoms.
A catalytic process for converting high boiling hydrocarbon liquids to lighter, high-quality fractions such as gasoline, diesel fuel, etc., in the presence of hydrogen. Sufficient hydrogen is added such that no coke formation occurs.
Process involving a reaction with hydrogen to remove sulfur compounds from hydrocarbon feedstock.
The gasification of a suitable fuel by reacting it directly with hydrogen.
Hydrogen (H2)
A colorless, odorless, highly flammable gas used in hydrogenation of petroleum and for producing ammonia. Also, an important constituent of manufactured gas.
Hydrogen Sulfide (H2S)
A poisonous, corrosive compound consisting of two atoms of hydrogen and one of sulfur, gaseous in its natural state. It is found in manufactured gas made from coals or oils containing sulphur and must be removed. It is also found to some extent in some natural gas. It is characterized by the odor of rotten eggs.
A process whereby hydrogen atoms are added to an organic molecule to form a new compound; such reactions usually require heat and pressure in the presence of a catalyst.
Heating and/or cooling with circulated water.
A method of effecting the pyrolysis of a fuel by contacting it with hot hydrogen.
Hydrostatic Design Stress
The estimated maximum tensile stress that can act in the wall of the pipe along the circumferential direction due to internal hydrostatic pressure, with a high degree of certainty that failure of the pipe will not occur. See PRESSURE RATING.
Hydrostatic Strength (Quick)
The hoop stress calculated by means of the ISO equation at which the pipe fails due to an internal pressure buildup, usually within 60 to 70 seconds.
Hydrostatic Test
A strength test of equipment (pipe) in which the item is filled with liquid, subjected to suitable pressure, and then shut in, and the pressure monitored. Also a test to determine whether a container will hold a certain pressure.
A coal gasification process developed by the Institute of Gas Technology.
An instrument for determining the relative humidity of air or other gases. Compare PSYCHROMETER.


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