Gas Utilities Industry Terminology

Advanced Metering Infrastructure (AMI)

A network of smart gas meters, communications, and data systems that provide interval usage reads, two-way communications, and event alarms (e.g., tamper or continuous-flow). Improves forecasting, billing, leak detection analytics, and operations.

Interval usage data used to forecast peak day demand - Remote meter ping and firmware updates - Continuous-flow or tamper alarm triggers field dispatch

American Society of Mechanical Engineers B31.8 (ASME B31.8)

The primary U.S. code for design, construction, testing, operation, and maintenance of gas transmission and distribution piping systems.

Selecting design factor based on class location - Performing hydrostatic pressure tests per code - Qualifying welding procedures for pipeline construction

Billion Cubic Feet (Bcf)

A volumetric unit equal to one billion cubic feet of natural gas. Used to express large-scale supply, demand, storage, and throughput.

Storage inventory reported as 25 Bcf - State annual demand expressed as 1,200 Bcf - Pipeline throughput noted as 3 Bcf/d

British Thermal Unit (Btu)

A standard measure of energy; the amount of heat required to raise one pound of water by one degree Fahrenheit. Gas pricing and billing often use MMBtu (one million Btu).

Furnace rated at 100,000 Btu/hr - Converting 1 therm to 100,000 Btu - Heating value of gas reported in Btu/scf

Cathodic Protection (CP)

A corrosion control technique for buried steel pipe that uses direct current to shift electrochemical potential and prevent external corrosion. Includes impressed current and sacrificial anode systems.

Installing an impressed current rectifier on a steel main - Annual CP survey verifying -0.85 V criterion - Replacing depleted sacrificial anodes on services

Citygate

The physical and commercial delivery point where interstate pipeline gas is transferred to a local distribution company (LDC). Often a pricing location for supply contracts.

LDC receipts scheduled at the citygate meter station - Contracts priced at Chicago Citygate - Basis trades between Henry Hub and SoCal Citygate

Decoupling (Revenue)

A ratemaking mechanism that separates utility revenue from volumetric sales, reducing weather and conservation-related revenue volatility and supporting energy efficiency objectives.

Monthly revenue true-up rider independent of sales volume - Stable earnings following a warm winter - Expanded energy efficiency programs supported by decoupling

Distribution Integrity Management Program (DIMP)

A PHMSA-mandated risk management program (49 CFR Part 192, Subpart P) for gas distribution systems to identify threats, evaluate and rank risks, and implement and monitor risk-mitigation measures.

Threat ranking highlights third-party damage risk - Accelerated replacement of vintage plastic based on risk - Tracking leak rate reduction as a performance measure

Emergency Response Plan (ERP)

Documented procedures and resources for responding to gas emergencies (e.g., leaks, overpressure events), including roles, communications, mutual aid, and coordination with public safety agencies.

Following overpressure event procedures and call-outs - Coordinating with fire department during a main break - Conducting annual emergency drills and mutual aid exercises

Excess Flow Valve (EFV)

A safety device installed in service lines that automatically restricts gas flow if a line is severed or experiences abnormally high flow, helping mitigate hazards from line breaks.

EFV closes when a service line is severed by excavation - Installing EFVs on new residential services - Upgrading to a higher-flow EFV for small commercial loads

Federal Energy Regulatory Commission (FERC)

The U.S. federal agency that regulates interstate natural gas pipelines, storage, and related tariffs and certificates. Distinct from state utility regulators that set LDC retail rates.

Issuing certificates for new interstate pipelines - Reviewing and approving pipeline tariff rate cases - Implementing open-access rules under Order 636

Firm Service

A contracted service level with priority rights that is not subject to routine curtailment, typically used by core customers and backed by capacity entitlements and storage.

Residential core customers served on firm rate - FT contract with a set MDQ and primary path - Curtailment plans prioritize firm over interruptible

Gas Day

The 24-hour scheduling period used for pipeline nominations, flows, and balancing, defined by industry standards (NAESB) and pipeline tariffs.

NAESB gas day from 9:00 a.m. to 9:00 a.m. Central - Submitting Intraday 1 nominations within the gas day - Imbalances calculated over the gas day

Gate Station

The facility where gas transfers from a transmission pipeline to an LDC, typically including metering, pressure regulation, filtration/heating, and odorization equipment.

Metering and pressure regulation at the LDC interconnect - Odorization skid injects TBM at the citygate - Preheaters prevent regulator freeze-off at high drops

General Rate Case (GRC)

A comprehensive regulatory proceeding in which a utility’s revenue requirement, rates, and major cost drivers (CapEx, O&M, depreciation, ROE) are reviewed and approved.

Filing a multi-year GRC to set revenue requirement - Determining ROE and rate base for the test year - Reviewing O&M, depreciation, and capital plans

Henry Hub

The primary U.S. natural gas price benchmark and NYMEX futures delivery point. Used for pricing, hedging, and basis comparisons.

Indexing supply contracts to Henry Hub first-of-month - Hedging with NYMEX HH futures - Managing basis risk between HH and a citygate

High Consequence Area (HCA)

Pipeline segments where a failure could have significant consequences to people or property, defined by regulation (49 CFR Part 192) and used to prioritize integrity assessments and mitigations.

Class 3/4 segments identified as HCAs - Prioritizing ILI assessments on HCA mileage - Installing automated shutoff valves in HCAs

Imbalance (Pipeline)

The difference between scheduled/confirmed quantities and actual physical receipts or deliveries over the gas day or month; subject to tolerance bands and penalties per the tariff.

Monthly long imbalance cashed out per tariff - Charges applied when variance exceeds tolerance band - Trading imbalances with other shippers to net out

Inline Inspection (ILI)

A pipeline integrity assessment method using instrumented pigs (“smart pigs”) to identify anomalies such as corrosion, dents, or cracks in-line without excavation.

Running an MFL tool to detect corrosion - Caliper and geometry tools identify dents and ovality - Excavating anomaly digs to verify ILI indications

Joule-Thomson Effect (J-T Effect)

The temperature change that occurs when a real gas expands across a pressure drop at near-constant enthalpy; in gas systems, can cause cooling, hydrates, or freeze-off at regulators and valves.

Freeze-off observed at a regulator due to J-T cooling - Hydrate formation across a throttling valve - Installing gas preheaters to mitigate J-T cooling

Leak Detection and Repair (LDAR)

Programs and technologies used to detect, quantify, and repair methane leaks, including OGI cameras, mobile analyzers, satellites, and handheld detectors.

OGI camera surveys to find methane leaks - Mobile LiDAR used for system-wide screening - Tracking repair times to meet program targets

Local Distribution Company (LDC)

A regulated utility that distributes natural gas to end-use customers within a defined service territory, distinct from interstate pipelines.

LDC owns and operates distribution mains and services - Residential customers billed by the LDC - LDC procures supply and transportation for core load

Lost and Unaccounted-for Gas (LAUF/UFG)

The difference between metered gas received and delivered, attributable to measurement uncertainty, pressure/temperature differences, theft, and leaks. Managed and often reconciled in fuel cost mechanisms.

Annual UFG target set as percentage of throughput - Adjusting for meter accuracy and thermal factors - Leak surveys and repairs to reduce LAUF

Maximum Allowable Operating Pressure (MAOP)

The highest pressure at which a pipeline segment is allowed to operate, established by design, materials, testing, and records per 49 CFR Part 192.

Establishing MAOP using historical test records - Reconfirming MAOP under 49 CFR 192.624 - Setting relief/regulator setpoints to protect MAOP

Mercaptan (Odorant)

Sulfur-containing compounds (e.g., TBM, THT) added to gas to create a distinct smell for leak detection. Managed via odorization equipment and monitoring.

Adjusting TBM/THT dosing at odorization skid - Field odorometer tests verify detectability - Maintaining odorant tanks and injection pumps

Million British Thermal Units (MMBtu)

An energy unit equal to one million Btu. Standard unit for wholesale gas pricing, hedging, and supply planning.

Wholesale gas priced at $3.25/MMBtu - Converting volume to energy using heating value (MMBtu) - Hedging daily supply of 10,000 MMBtu

Nomination (Gas Scheduling)

The process of scheduling gas receipts and deliveries with pipelines and storage across defined nomination cycles per NAESB and pipeline tariffs.

Submitting Day-Ahead Timely nominations - Making Intraday 2 changes to match load - Confirming receipts and deliveries with operators

Odorization

The process of adding odorant to gas to ensure leak detectability, with dosing control, monitoring, and testing per code requirements.

Controlling injection rate via PLC at citygate - Investigating low-odor alarms and correcting dosing - Periodic verification of odor levels in distribution

Overpressure Protection (OPP)

Devices and schemes (relief valves, monitor/worker regulators, slam-shut valves) that prevent system pressure from exceeding allowable limits (e.g., MAOP).

Monitor/worker regulator configuration at station - Slam-shut valve actuates on high-pressure event - Relief valve sized to protect downstream MAOP

Pipeline and Hazardous Materials Safety Administration (PHMSA)

The U.S. federal agency within DOT that regulates pipeline safety, sets standards (49 CFR Parts 190–199), inspects, and enforces compliance for gas pipelines.

Conducting inspections of operator TIMP/DIMP programs - Issuing Notices of Probable Violation and civil penalties - Finalizing rules on rupture mitigation and valves

Pipeline Class Location

A regulatory categorization (Classes 1–4) based on population density near a pipeline segment, affecting design factors, testing, and MAOP (49 CFR Part 192.5).

Class 1 rural segment with low population density - Class 4 urban segment requires lower design factor - Reclassification after development increases nearby population

Purchased Gas Adjustment (PGA)

A fuel cost pass-through mechanism that reconciles actual commodity and transportation costs with amounts collected from customers, adjusting rates periodically.

Monthly fuel cost adjustment line on customer bills - Annual true-up filing reconciles actual costs - Including hedging gains/losses in PGA calculations

Quantitative Risk Assessment (QRA)

A systematic approach to quantify likelihood and consequence of failures, often using event trees and consequence modeling to inform integrity and investment decisions.

Modeling rupture frequencies and thermal radiation zones - Using event trees to quantify mitigation effectiveness - Prioritizing investments via individual and societal risk contours

Rate Base

The net value of utility assets used to provide service on which the utility earns a return (ROE) through regulated rates; net of accumulated depreciation and adjusted for working capital.

Adding new mains to rate base after in-service - Calculating net plant less accumulated depreciation - Earning allowed ROE on approved rate base

Renewable Natural Gas (RNG)

Pipeline-quality biomethane produced from organic waste (e.g., landfills, wastewater, dairies), conditioned to meet pipeline gas specifications and often accompanied by environmental credits.

Interconnecting a dairy digester RNG project to the LDC - Treating biogas to remove H2S and siloxanes to meet specs - Selling environmental attributes via RINs or LCFS credits

Right-of-Way (ROW)

A legal corridor that grants the utility access to construct, operate, and maintain pipelines and related facilities, with restrictions on third-party activities.

Routine aerial and ground patrols for encroachments - Negotiating easements with landowners - Performing vegetation management within the ROW

Safety Management System (PSMS)

A structured management framework (e.g., API RP 1173) for pipeline safety that emphasizes leadership, risk management, operational controls, learning, and continuous improvement.

Establishing leadership safety policy and objectives - Conducting incident investigations and learning reviews - Performing internal audits and management reviews

Specified Minimum Yield Strength (SMYS)

A material property of steel pipe indicating the minimum stress that will cause yield; used in design and MAOP determinations (e.g., hoop stress calculations).

Calculating hoop stress as a percentage of SMYS - Selecting pipe grade (e.g., X52) based on SMYS requirements - Setting MAOP limits tied to %SMYS thresholds

Supervisory Control and Data Acquisition (SCADA)

A system of sensors, communications, and control software used to monitor and operate gas system assets (pressures, flows, valve status) in real time.

Monitoring pressures and flows at stations in real time - Remote valve operation during an emergency - Alarm management and historian trend analysis

Tariff

The legally approved schedule of rates, terms, and conditions of service for a utility or pipeline, including service classes, riders, and operational rules.

Firm and interruptible rate schedules with terms - Gas quality specifications and measurement rules - Imbalance tolerance bands and penalty provisions

Therm

A billing unit equal to 100,000 Btu. Commonly used for retail customer billing and energy efficiency calculations.

Residential bills show usage in therms - Converting 1 therm to 100,000 Btu for comparisons - EE savings reported as therm reductions

Third-Party Damage (TPD)

Damage to pipelines caused by external parties (e.g., excavation). A leading cause of distribution leaks; mitigated through 811 locate programs, patrols, and public awareness.

Backhoe strikes a service line during excavation - 811 Call Before You Dig public awareness campaign - Increased patrols and markers to reduce TPD risk

Transmission Integrity Management Program (TIMP)

A PHMSA-required program for transmission pipelines that identifies threats, assesses integrity (e.g., ILI, DA, pressure testing), prioritizes repairs, and manages risk, with emphasis on HCA segments.

ILI-based assessment plan for HCA segments - Applying Direct Assessment where ILI is not feasible - Repair criteria and schedules prioritized by risk

Underground Gas Storage (UGS)

Subsurface storage of natural gas (depleted reservoirs, salt caverns, aquifers) used for seasonal balancing, reliability, and price hedging.

Injecting gas in summer and withdrawing in winter - Using salt caverns for high-deliverability storage - Balancing seasonal load and price volatility

Venting and Purging

Controlled removal of gas from piping and replacement with air or inert gas during maintenance or commissioning, performed under strict safety procedures to prevent ignition hazards.

Purging a new main with nitrogen before commissioning - Using a flare or combustor for controlled venting - Following purge procedures after a pipeline repair

Weather Normalization

A ratemaking and analytical adjustment that removes the impact of abnormal temperatures on usage and revenues, stabilizing earnings and improving comparability.

Applying Heating Degree Day adjustments to revenues - WNA rider credits customers after a warm month - Stabilizing earnings by removing abnormal weather effects

Weighted Average Cost of Gas (WACOG)

The average commodity cost per unit of gas delivered, weighted by volumes from various supply sources and periods; often the basis for fuel cost recovery.

Blending monthly purchase costs by volume to compute WACOG - Using WACOG as the basis for PGA rates - Incorporating storage withdrawals into WACOG

Wobbe Index

A fuel gas interchangeability metric equal to heating value divided by the square root of specific gravity; used to assess combustion compatibility across varying gas qualities.

Assessing LNG interchangeability using Wobbe limits - Tuning burners to operate within a target Wobbe range - Rejecting supply that falls outside allowable Wobbe Index

X-Factor (Performance-Based Ratemaking)

A productivity offset in price-cap or performance-based regulation that reduces allowed revenue growth to reflect expected efficiency improvements.

Price-cap formula CPI minus X-factor - Annual allowed revenue growth reduced by 0.5% X - Setting X based on productivity benchmarking

Zonal Rates

Rate structures that vary by geographic or system zones (common in interstate pipelines and sometimes distribution), reflecting distance or cost-of-service differences across zones.

Pipeline tariffs with Zone 1, 2, and 3 distances - Higher charges for long-haul across multiple zones - LDC delivery rates vary by geographic service zones