Lessons Learned 

from Natural Gas STAR Partners 

Directed Inspection and Maintenance 

at Gate Stations and Surface Facilities 

Executive Summary 

In 2001, fugitive methane emissions from gate stations

and surface facilities in the United States totaled about 27 

million cubic feet (MMcf) from leaking meters and

regulating equipment. Implementing a directed inspection

and maintenance (DI&M) program is a proven, costeffective way to detect, measure, prioritize, and repair 

equipment leaks to reduce methane emissions. 

A DI&M program begins with a baseline survey to identify 

and quantify leaks. Repairs that are cost-effective to fix 

are then made to the leaking components. Subsequent

surveys are based on data from previous surveys, allowing

operators to concentrate on the components that are most

likely to leak and are profitable to repair. This Lessons

Learned study focuses on maximizing the savings that can 

be achieved by implementing DI&M programs at gate

stations and surface facilities. 

Natural Gas STAR distribution partners have reported 

significant savings and methane emissions reductions by 

implementing DI&M. Based on partner data, 

implementing DI&M at gate stations and surface facilities

can result in gas savings worth up to $1,800 per year, at a 

cost of between $20 and $1,200. 

Introduction 

Gate stations (or ‘city gates’) are metering and pressure

regulating facilities located at the custody transfer points 

where natural gas is delivered from transmission pipelines 

into the high-pressure lines of a local distribution 

company. Gate stations typically contain metering runs as 

well as pressure regulators, which reduce the transmission

line pressure from several hundred pounds per square inch

gauge (psig) to a suitable pressure for the distribution

system (usually less than 300 psig). Other surface facilities

within a distribution system include heaters to replace the

heat lost from gas expansion, and downstream pressure

regulators, which further reduce gas pressure so that gas

can be delivered safely to customers. Exhibit 1 is a

schematic illustration of a gas distribution system showing 

a gate station and pressure regulating facilities. 

Exhibit 1: Distribution System Schematic Showing 

Gate Station and Pressure Regulators 

Gate stations and surface facilities contain equipment

components such as pipes, valves, flanges, fittings, openended lines, meters, and pneumatic controllers to monitor

and control gas flow. Over time, these components can

develop leaks in response to temperature fluctuations, 

pressure, corrosion and wear. In general, the size of the 

Method for Reducing 

Natural Gas Losses 

Volume of 

Natural Gas 

Savings (Mcf) 1 

Value of Natural Gas Savings ($) Implementation 

Cost ($) 2 

Payback (Months) 

$3 per 

Mcf 

$5 per 

Mcf 

$7 per 

Mcf 

$3 per 

Mcf 

$5 per 

Mcf 

$7 per 

Mcf 

Locating and 

Repairing Leaks 600 per site $1,800 $3,000 $4,200 $20 – $1,200 1 – 8 1 – 5 1 – 4 

1

 Savings are modeled as 600 Mcf per site. Typical estimates for leaking facilities tend to range between 30 and 200 Mcf per site. 2

 The implementation cost will vary depending on facility size and types of repairs. 

Economic and Environmental Benefits 

1 
 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

facility and the facility leak rate correspond to the inlet or

upstream gas pressure; the higher the inlet pressure, the

larger the gate station and the greater the number of

equipment components that may develop leaks. 

Technology Background 

DI&M is a cost-effective way to reduce natural gas losses

from equipment leaks. A DI&M program begins with a 

comprehensive baseline survey of all the gate stations and 

surface facilities in the distribution system. Operators 

identify, measure, and evaluate all leaking components

and use the results to direct subsequent inspection and 

maintenance efforts. 

The following sections describe various leak screening and 

measurement techniques that can be cost-effective at gate

stations and pressure regulating facilities. The 

appropriateness of the various screening and 

measurement techniques will depend upon the 

configuration and operating characteristics of individual

distribution system facilities. 

Leak Screening Techniques 

Leak screening in a DI&M program may include all 

components in a comprehensive baseline survey, or may be 

focused only on the components that are likely to develop 

significant leaks. Several leak screening techniques can be

used: 

Soap Bubble Screening is a fast, easy, and very 

low-cost leak screening technique. Soap bubble 

screening involves spraying a soap solution on small,

accessible components such as threaded connections. 

Soaping is effective for locating loose fittings and 

connections, which can be tightened on the spot to fix 

the leak, and for quickly checking 

the tightness of a repair. Operators

can screen about 100 components

per hour by soaping. 

Electronic Screening using small

handheld gas detectors or “sniffing”

devices provides another fast and 

convenient way to detect accessible 

leaks. Electronic gas detectors are 

equipped with catalytic oxidation
 

and thermal conductivity sensors

designed to detect the presence of

specific gases. Electronic gas

detectors can be used on larger
 

openings that cannot be screened by soaping.

Electronic screening is not as fast as soap screening

(averaging 50 components per hour), and pinpointing 

leaks can be difficult in areas with high ambient

concentrations of hydrocarbon gases. 

Organic Vapor Analyzers (OVAs) and Toxic 

Vapor Analyzers (TVAs) are portable hydrocarbon 

detectors that can also be used to identify leaks. An

OVA is a flame ionization detector (FID), which 

measures the concentration of organic vapors over a 

range of 9 to 10,000 parts per million (ppm). A TVA 

combines both an FID and a photoionization detector

(PID) and can measure organic vapors at 

concentrations exceeding 10,000 ppm. TVAs and 

OVAs measure the concentration of methane in the 

area around a leak. 

Screening is accomplished by placing a probe inlet at 

an opening where leakage can occur. Concentration

measurements are observed as the probe is slowly

moved along the interface or opening, until a 

maximum concentration reading is obtained. The 

maximum concentration is recorded as the leak 

screening value. Screening with TVAs is somewhat 

slow—approximately 40 components per hour—and

the instruments require frequent calibration. 

Acoustic Leak Detection uses portable acoustic 

screening devices designed to detect the acoustic 

signal that results when pressurized gas escapes 

through an orifice. As gas moves from a highpressure to a low-pressure environment across a leak

opening, turbulent flow produces an acoustic signal,

which is detected by a handheld sensor or probe, and

read as intensity increments on a meter. Although 

acoustic detectors do not measure leak rates, they

provide a relative indication of leak size— 

a high intensity or “loud” signal 

corresponds to a greater leak rate. 

Acoustic screening devices are designed

to detect either high frequency or low

frequency signals. 

High Frequency Acoustic Detection is best 

applied in noisy environments where the 

leaking components are accessible to a 

handheld sensor. As shown in Exhibit 2, 

an acoustic sensor is placed directly on 

the equipment orifice to detect the signal. 

Alternatively, Ultrasound Leak Detection 

is an acoustic screening method that

detects airborne ultrasonic signals in the 

Exhibit 2: Acoustic Leak 

Detection 

Source: Physical Acoustics Corp. 

2 
 

 

 

 

 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

frequency range of 20 kHz to 100 kHz. Ultrasound 

detectors are equipped with a handheld acoustic

probe or scanner that is aimed at a potential leak 

source from a distance up to 100 feet. Leaks are 

pinpointed by listening for an increase in sound 

intensity through headphones. Ultrasound detectors 

can be sensitive to background noise, although most

detectors typically provide frequency tuning

capabilities so that the probe can be tuned to a 

specific leak in a noisy environment. 

Infrared Cameras work according to the principle 

that hydrocarbon emissions absorb infrared light in a 

certain wavelength. Infrared (IR) cameras use this

characteristic to detect the presence of gas emissions

from equipment by converting the scanned area into 

a moving image in real time such that the gas plumes 

are visible due their absorption of the IR light. 

Because of this, an IR camera is able to screen 

hundreds of components per hour. An additional 

advantage is the ability to screen inaccessible 

equipment: components in confined spaces or in 

elevated locations can be screened remotely from an 

accessible location within viewing distance. In 

addition, IR cameras can be hand-held for walking 

surveys of individual components, mounted on trucks 

and other vehicles for close-range inspection over 

moderate distances, or mounted on aircraft for aerial 

inspection to locate major leaks and vents over long

distances. While it may not be able to pinpoint 

individual leaking components with low leak rates,

aerial inspection is useful to screen many miles of 

transmissions pipelines or dispersed equipment to 

detect plumes from large emissions sources. 

Leak Measurement Techniques 

An essential component of a DI&M program is 

measurement of the mass emissions rate or leak volume of 

identified leaks, so that manpower and resources are 

allocated only to the significant leaks that are costThe average methane content of natural gas varies by natural gas 

industry sector. The Natural Gas STAR Program assumes the 

following methane content of natural gas when estimating 

methane savings for Partner Reported Opportunities. 

Production 79 % 

Processing 87 % 

Transmission and Distribution 94 % 

Methane Content of Natural Gas 

Nelson Price Indexes 

In order to account for inflation in equipment and 

operating & maintenance costs, Nelson-Farrar 

Quarterly Cost Indexes (available in the first issue of 

each quarter in the Oil and Gas Journal) are used to 

update costs in the Lessons Learned documents. 

The “Refinery Operation Index” is used to revise

operating costs while the “Machinery: Oilfield Itemized 

Refining Cost Index” is used to update equipment 

costs. 

To use these indexes in the future, simply look up the 

most current Nelson-Farrar index number, divide by 

the February 2006 Nelson-Farrar index number, and, 

finally multiply by the appropriate costs in the Lessons 

Learned. 

effective to repair. Four leak measurement techniques can 

be used: conversion of TVA and OVA screening 

concentrations using general correlation equations; 

bagging techniques; high volume samplers; and 

rotameters. 

Data available for total fugitive emissions rates from gate

stations and surface facilities indicates that the leak rate 

for many components is relatively small. For most gate

stations, DI&M will only be cost-effective using the lowest 

cost measurement technique, which is likely to be 

conversion of TVA/OVA screening values using EPA

correlation equations and TVA or OVA instruments that 

may already be at hand. 

OVAs and TVAs can be used to estimate mass leak 

rate. The screening concentration detected at a leak

opening is not a direct measurement of the mass 

emissions of the leak. However, the screening 

concentration in ppm is converted to a mass 

emissions rate by using EPA correlation equations. 

The EPA correlation equations can be used to 

estimate emissions rates for the entire range of

screening concentrations, from the detection limit of 

the instrument to the “pegged” screening

concentration, which represents the upper limit of

the instrument. If the upper measurement limit of

the TVA is 10,000 ppm, a dilution probe can be used

to detect screening concentrations up to 100,000 ppm. 

OVAs and TVAs must be calibrated using a reference

gas containing a known compound at a known 

concentration. Methane in air is a frequently used 

3 
 

 

 

 

 

 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

reference compound. The calibration process also 

determines a response factor for the instrument, 

which is used to correct the observed screening 

concentration to match the actual concentration of 

the leaking compound. For example, a response 

factor of “one” means that the screening 

concentration read by the TVA equals the actual

concentration at the leak. 

the carrier gas. Leak rate measurement using 

bagging techniques is accurate (within ± 10 to 15 

percent) but, slow and labor intensive (only two or 

three samples per hour). Bagging techniques can be 

expensive due to the labor involved to perform the

measurement, as well as the cost for sample analysis. 

High Volume Samplers capture all of the emissions 

from a leaking component to accurately quantify leak 

Screening concentrations detected for individual 

components are corrected using the response factor 

(if necessary) and are entered into EPA correlation 

equations to extrapolate a leak rate measurement for 

the component. Exhibit 3 lists the EPA correlation 

equations for equipment components at oil and gas 

industry facilities. 

Exhibit 4 provides a table based on the above EPA 

correlation equations for TVAs and OVAs. This can 

be used to estimate mass leak rate from the 

screening concentrations detected at leaking

components at gate stations and surface facilities. 

Bagging Techniques are commonly used to 

measure mass emissions from equipment leaks. The

leaking component or leak opening is enclosed in a 

“bag” or tent. An inert carrier gas such as nitrogen is 

Exhibit 4: Example Screening Concentration/Leak 

Rate Correlations 

Screening 

Concentration 

(ppmv) 

Estimated Mass Leak Rate (Mcf/yr) 

Valves Pump 

Seals 

Connectors Flanges 

OpenEnded 

Lines 

Other1 

1 0.001 0.023 0.001 0.002 0.001 0.006 

10 0.006 0.093 0.004 0.011 0.005 0.024 

100 0.032 0.380 0.021 0.053 0.026 0.093 

1,000 0.180 1.547 0.112 0.269 0.130 0.362 

10,000 1.004 6.301 0.606 1.360 0.655 1.404 

100,000 5.593 25.669 3.293 6.864 3.313 5.450 

Screening value 

pegged at 

>10,000 

29.109 33.657 12.735 38.660 13.645 33.203 

conveyed through the bag at a known flow rate. Once 

the carrier gas attains equilibrium, a gas sample is

collected from the bag and the methane concentration 

of the sample is measured. The mass emissions rate 

is calculated from the measured methane 

concentration of the bag sample and the flow rate of 

Screening value 

pegged at 

>100,000 

63.676 72.773 13.645 38.206 35.931 50.031 

1

 “Other” equipment components include: instruments, loading arms, pressure 

relief valves, stuffing boxes, and vents. Apply to any equipment component 

other than connectors, flanges, open-ended lines, pumps, or valves. 

Source: U.S. EPA, 1995, Protocol for Equipment Leak Emission Estimates. 

Exhibit 3: U.S. EPA Leak Rate/Screening Value Correlation Equations for Equipment Components in 

the Oil and Gas Industry 

Equipment Component 

EPA Leak Rate/Screening 

Value Correlation 

(kg/hr/source) 

Leak Rate Correlation (kg/hr) for 

“Pegged” Screening Value >10,000 ppm 

Leak Rate Correlation (kg/hr) for “Pegged” 

Screening Value >100,000 ppm 

Valves 2.29 E-06 x (SV)0.746 0.064 0.140 

Pump Seals 5.03 E-05 x (SV)0.610 0.074 0.160 

Open-Ended Lines 2.20 E-06 x (SV)0.704 0.030 0.079 

Other Components 

(instruments, pressure 

relief, vents, all others) 

1.36 E-05 x (SV)0.589 0.073 0.110 

Flanges 4.61 E-06 x (SV)0.703 0.085 0.084 

Connectors 1.53 E-06 x (SV)0.735 0.028 0.030 

The correlations presented are revised petroleum industry correlations. Correlations predict total organic compound emissions rates. 

Correlation factors for methane: 1 kg methane = 51.92 scf; 1kg/hr = 1.246 Mcfd 

Source: U.S. EPA, 1995, Protocol for Equipment Leak Emission Estimates. 

4 
 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

emissions rates. Leak emissions, plus a large volume

sample of the air around the leaking component, are 

pulled into the instrument through a vacuum 

sampling hose. Sample measurements are corrected

for the ambient hydrocarbon concentration, and mass 

leak rate is calculated by multiplying the flow rate of 

the measured sample by the difference between the 

ambient gas concentration and the gas concentration 

in the measured sample. High volume samplers

measure leak rates up to 8 cubic feet per minute 

(scfm), a rate equivalent to 11.5 thousand cubic feet 

(Mcf) per day. Two operators can measure 30 

components per hour using a high volume sampler, 

compared with two to three measurements per hour

using bagging techniques. High volume samplers can 

cost approximately $10,000 to purchase. 

Alternatively, contractors can provide leak 

measurement services at a rate that ranges from

$1.00 to more than $2.50 per component measured. 

Rotameters and other flow meters are used to 

measure extremely large leaks that would overwhelm 

other instruments. Flow meters typically channel gas 

flow from a leak source through a calibrated tube. 

The flow lifts a “float bob” within the tube, indicating

the leak rate. Because rotameters are bulky, these 

instruments work best for open-ended lines and 

similar components, where the entire flow can be 

channeled through the meter. Rotameters and other

flow metering devices can supplement measurements

made using bagging or high volume samplers. 

Decision Points 

A DI&M program can be implemented in four steps: (1) 

conduct a baseline survey; (2) record the results and 

identify candidates for cost-effective repair; (3) analyze the

data, make the repairs, and estimate methane savings; 

component the mass leak rate is estimated using one of the

techniques described above. In the distribution sector, the 

emissions from leaking equipment components at gate

stations and surface facilities may be one or more orders of

magnitude less than emissions from leaks at compressor 

stations. For DI&M to be cost-effective at gate stations and

surface facilities, the baseline survey costs must be 

minimal. 

Some distribution sector partners elect to conduct leak

screening only, using very low cost and rapid leak 

detection techniques, which are incorporated into ongoing 

maintenance operations. In these cases, all of the leaks 

that are identified are repaired. A baseline survey that 

focuses only on leak screening is substantially less 

expensive. However, leak screening alone does not 

quantify leak rate or potential gas savings, each of which

is critical information needed to make cost-effective repair

decisions in cases where partners do not have the 

resources to repair all leaks. 

Step 2: Record Results and Identify Candidates for 

Repair. 

Leak measurements collected in Step 1 must be recorded 

to pinpoint the leaking components that are cost-effective

to repair. As leaks are identified and measured, operators

should record the baseline leak data so that future surveys 

can focus on the most significant leaking components. The 

results of the DI&M survey can be tracked using any

convenient method or format. The information that 

operators may choose to collect includes: (1) an identifier 

for each leaking component; (2) the component type (e.g., 

gate valve); (3) the measured leak rate; (4) the survey date; 

(5) the estimated annual gas loss; and (6) the estimated

repair cost. This information will direct subsequent

emissions surveys, prioritize future repairs, and track the 

methane savings and cost-effectiveness of the DI&M 

program. 

Decision Steps for DI&M: 

1. Conduct baseline survey. 

2. Record results and identify candidates for repair. 

3. Analyze data and estimate savings. 

4. Develop a survey plan for future DI&M. 

and (4) develop a survey plan for future inspections and 

follow-up monitoring of leak-prone equipment. 

Step 1: Conduct Baseline Survey. 

A DI&M program typically begins with baseline screening 

to identify leaking components. For each leaking 

Natural Gas STAR partners report that the most common

leaks at gate stations and surface facilities are pinhole

leaks and component flaws, loose connections, and loose or 

worn valve stem seals. High frequency leak locations 

identified by partners include: orifice plate/fittings, plugs 

installed on test points, grease fittings on valves, multiple

or large diameter meter runs, couplings, valve stem 

packing, and flanges. The largest leaks are generally 

located at pressure relief valves, open-ended lines, flanges, 

gate valves, and gate valve stem packing. Leaks are 

prioritized by comparing the value of the natural gas lost 

with the estimated cost in parts, labor, and equipment

downtime to fix the leak. 

5 
 

 

 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

Gate stations and surface facilities vary significantly in

size and pressure capacity depending upon the size and

complexity of the distribution system. As a result, there

can be substantial variation in fugitive methane emissions

9 from such facilities. A 1994 field study sponsored by EPA 

and the Gas Research Institute (GRI—now GTI, the Gas

Technology Institute) used a tracer gas technique to 

measure total facility methane emissions at 40 gate

stations and 55 district pressure regulators. This study 

found that average annual methane emissions ranged from

1,575 Mcf per year for gate stations with inlet pressures

greater than 300 psig to less than 1 Mcf per year for 

district regulators with inlet pressures less than 40 psig.

Average annual facility emissions, based on all 95 sample 

facilities were 425 Mcf. This study estimated that a large 

component of total site emissions are contributed by 

pneumatic controllers, which are designed to bleed gas to 

the atmosphere. 

In 1998, EPA, GRI, and the American Gas Association 

Pipeline Research Committee International (PRCI) 

conducted a second study of methane emissions from 

equipment components at 16 natural gas metering and 

regulating facilities in transmission and distribution. Four

of the facilities studied were distribution system gate

stations. This analysis included component counts for each 

site, and leak screening and measurement of individual

component leaks using a high volume sampler. As in the

earlier study, pneumatic controllers were found to 

contribute most of the total site emissions (more than 95 

percent). Because pneumatic devices are designed to bleed

gas during normal operation, these emissions are not 

considered leaks. Pneumatic controllers provide a 

significant opportunity to reduce methane emissions from

gate stations and surface facilities, which is the subject of 

Lessons Learned: Convert Gas Pneumatic Controls to 

Instrument Air and Options for Reducing Methane 

Emissions from Pneumatic Devices in the Natural Gas 

Industry. 

Exhibit 5 summarizes average component emissions 

factors obtained during the 1998 field study.

Approximately 5 percent of the 2,261 total components

screened were found to be leaking. 

Exhibit 5 shows that pressure relief valves were found to

be the largest leak source, followed by gate valves and

control valves. The smallest leaks were found at 

connectors, flanges, and ball/plug valves. Exhibit 5 

indicates that the typical leak to be expected at gate state 

stations and surface facilities is relatively small, and the

number of components to be surveyed at each facility is 

Exhibit 5: Average Emissions Factors for 

Equipment Leaks at Sixteen Metering and 

Regulating Facilities 

Component 

Emissions 

Factor 

(Mcf/yr/ 

component) 

Total Number of 

Components 

Screened 

Average Number 

of Components 

per Site 

Ball/Plug Valve 0.21 248 18 

Control Valve 0.46 17 1 

Flange 0.13 525 38 

Gate Valve 0.79 146 10 

Pneumatic Vent 134.3 40 1 

Pressure Relief 

Valve 4.84 5 1 

Connectors 0.11 1,280 91 

TOTAL 2,261 162 

Source: Indaco Air Quality Services, 1998. 

over 100. 

Based on the leak measurements of individual equipment 

components, the 1998 study determined the average total 

gas emissions from metering and regulating facilities to be

409 Mcf per year. Excluding the total facility emissions

contributed by pneumatic controllers, the average total 

emissions contributed by equipment leaks was in the 

range of 20 to 40 Mcf per site, although substantial leaks 

in the range of 60 to 100 Mcf per year were reported for

some of the sites. 

The 1998 field study reinforces the point made in Step 1,

that a cost-effective DI&M program at gate stations and

surface facilities must rely upon very low cost and rapid 

screening techniques. Otherwise, the cost of finding the 

leaks might not outweigh the savings gained from fixing

the leaks. 

Step 3: Analyze Data and Estimate Savings. 

Cost-effective repair is a critical part of successful DI&M 

programs because the greatest savings are achieved by 

targeting only those leaks that are profitable to repair. 

6 
 

 

 

 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

Some leaks can be fixed on the spot, for example, by simply

tightening a valve stem packing-gland. Other repairs are 

more complicated and require equipment downtime or new

parts. For these repairs, operators may choose to attach 

identification markers, so that the leaks can be fixed later. 

Easy repairs should be done on the spot, as soon as the

leaks are found. In all cases, the value of the gas saved

should exceed the cost to find and fix the leak. Partners 

have found that an effective way to analyze baseline 

survey results is to create a table listing all leaks with

their associated repair cost, expected gas savings, and 

expected life of the repair. Using this information, 

economic criteria such as payback period can be easily

calculated for each leak repair. Partners can then decide 

which leaking components are economic to repair. 

Exhibit 6 provides an example of this type of repair cost 

analysis, which summarizes the repair costs, total gas

savings, and the estimated net savings for the anticipated

repairs. The leak and repair data featured in Exhibit 6 are 

from the 1998 EPA/GRI/PRCI field study, during which

leak repairs were evaluated for two of the sixteen facilities

included in the study. 

Because of safety concerns, some partners repair all leaks

found at gate stations and meter stations. In this case, a 

DI&M program may be useful for improving the costeffectiveness of ongoing inspection and maintenance 

operations by prioritizing repairs—the major leaks are

identified and repaired first, or inspection and 

maintenance is conducted more frequently at facilities 

with the greatest leak frequency. 

As leaks are identified, measured, and repaired, operators 

should record baseline data so that future surveys can 

focus on the most significant leaking components. This 

information will direct subsequent emissions surveys,

prioritize future repairs, and track the methane savings 

and cost-effectiveness of the DI&M program. 

Step 4: Develop a Survey Plan for Future DI&M. 

The final step in a DI&M program is to develop a survey 

plan that uses the results of the initial baseline survey to

direct future inspection and maintenance practices. The 

DI&M program should be tailored to the needs and 

existing maintenance practices of the facility. An effective 

DI&M survey plan should include the following elements: 

A list of components to be screened and tested, as 

Exhibit 6: Example of Repair Costs and Net Savings for Selected Equipment Components 

Component 

Descriptions Type of Repair 

Repair Cost1 

(includes labor & 

material) 

Total Number of 

Components Fixed 

at Two Sites 

Total Gas Savings 

(Mcf/yr) 

Estimated Net 

Savings2

 ($/yr) 

Repair Payback 

Period (years) 

Ball Valve Re-grease $13 5 60 Mcf $115 0.4 

Gate Valve Replace valve stem 

packing $3 5 67 Mcf $36 0.8 

Gate Valve Replace valve stem 

packing $3 1 92 Mcf $243 0.1 

Connectors Tighten Threaded 

Fittings $3 4 11 Mcf $21 0.4 

Sr. Daniel Orifice 

Meter Tighten Fittings $33 1 68 Mcf $171 0.2 

Flange3 Tighten 

(estimated) $40 5 99 Mcf $97 0.7 

1

 Average repair costs are in 2002 dollars. 

2

 Assumes gas price of $3/Mcf. 

3

 Repair cost not reported in original study. Flange repair cost estimated based on similar 1997 data on leak repair cost of “off-compressor” flanges at 

compressor stations. 

Source: Indaco Air Quality Services, 1998, Trends in Leak Rates at Metering and Regulating Facilities and the Effectiveness of Leak Detection and Repair (LDAR) 

Programs, Draft Report. 

7 
 

 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

well as the equipment components to be excluded 

from the survey. 

Leak screening and measurement tools and 

procedures for collecting, recording, and accessing 

DI&M data. 

A schedule for leak screening and measurement. 

Economic guidelines for leak repair. 

Results and analysis of previous inspection and 

maintenance efforts which will direct the next DI&M 

survey. 

Operators should develop a DI&M survey schedule that

achieves maximum cost-effective gas savings yet also suits 

the unique characteristics of the facility—for example, the

age, size, and configuration of the facility and the inlet

pressure. Some partners schedule DI&M surveys based on 

the anticipated life of repairs made during the previous

survey. Other partners base the frequency of follow-up 

surveys on maintenance cycles or the availability of

resources. Since a DI&M program is flexible, if subsequent

surveys show numerous large or recurring leaks, the 

operator can increase the frequency of the DI&M follow-up

surveys. Follow-up surveys may focus on components 

repaired during previous surveys, or on the classes of

components identified as most likely to leak. Over time, 

operators can continue to fine-tune the scope and 

frequency of surveys as leak patterns emerge. 

Estimated Savings 

Savings achieved by Natural Gas STAR partners 

implementing DI&M programs at gate stations and

surface facilities vary widely. Factors affecting results 

include the number of stations in the DI&M program, the 

stage of program development (i.e., new versus mature

program), and the level of implementation and repair

costs. Costs differ between facilities because of the type of 

screening and measurement equipment used, frequency of

surveys, and number and type of staff conducting the 

surveys. 

Exhibit 7 provides a hypothetical example of the costs and

benefits of implementing DI&M at three gate stations. The

leak rates and number of leaking components in this 

example are based on actual leak rates reported for three 

sites in the 1998 EPA/GRI/PRCI study. Exhibit 7 

illustrates the type of calculations that distribution 

partners should make to evaluate whether DI&M could be 

cost-effective for their operations. 

Exhibit 7 illustrates that although the costs of finding and 

fixing leaks may not be recovered by the value of the gas 

saved at each and every site, if multiple sites are included

in the DI&M program, the overall program can still be

profitable. For the hypothetical example in Exhibit 7,

DI&M is not cost-effective at Site 2, although DI&M is

profitable for the three sites considered as a whole. In this 

case, the operator would use the experience gained from

the baseline survey of Site 2 to direct subsequent surveys; 

possibly excluding Site 2 from subsequent surveys,

screening Site 2 less frequently, or screening only a 

selected group of components. 

Partner Experience 

From 1995 to 2000, 18 Natural Gas STAR partners

reported gas savings from implementing DI&M at gate

stations and surface facilities. 

One Partner’s Experience: Company A 

During 2000, this company surveyed 86 facilities and found leaks at 48 

sites. A total of 105 leaks were identified, and 66 leaks (63 percent) were 

repaired. The total cost to find and fix the leaks was $2,453, an average 

of $29 per facility surveyed. Total gas savings were 1,519 Mcf per year, 

worth $6,557 at $3 per Mcf. Total savings from DI&M was $4,104. Net 

savings were approximately $50 per facility surveyed. 

Total Gas Savings $6,557

 Total Survey Costs $1,700 

Total Cost of Repairs $753 

Net Savings $4,104 

One Partner’s Experience: Company B 

Eighteen facilities were surveyed in 1997 for a total cost of $1,080. Fifteen 

small leaks were identified including 1 flange, 2 swage lock fittings, and 12 

small valves. The average leak rate was 17.5 Mcf per year. The 15 leaks 

were repaired for a total cost of $380, which resulted in gas savings of 

263 Mcf per year. At $3 per Mcf, the value of the gas saved was $789. 

The total cost of the leak survey and repairs, $1,460, was not recovered in 

the first year. The average survey and repair cost was $60 per facility 

surveyed. 

Total Gas Savings $789

 Total Survey Costs $1,080 

Total Cost of Repairs $380 

Net Savings $(671) 

8 
 

 

 

 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

Exhibit 7: Example of Estimating the Savings from Implementing DI&M at Gate Stations and Surface 

Facilities 

General Assumptions: 

Leak Screening by soaping; 80 components per hour 2 hours x $/hour labor cost 

Leak measurement using TVA correlations 1 hour x $/hour labor cost 

Hourly labor rate $50/hour 

TVA capital cost $0 (assume already owned by partner) 1 

Estimated repair life 12 months 

Site 1 

Number of leaks 20 leaks (six valves repaired —2 x 30 Mcf/yr; 2 x 10 Mcf/yr; 2 x 1 Mcf/yr) 

Hypothetical repair cost Assume 3 repairs x $10 and 3 repairs at $3 

Total gas savings 82 Mcf 

Site 2 

Number of leaks (assume fewer leaks to measure) 8 leaks (2 x 10 Mcf/yr; 6 x 2 Mcf/yr) 

Hypothetical repair cost Assume 2 repairs x $5; 6 repairs at no cost 

Total gas savings 32 Mcf 

Site 3 

Number of leaks 16 leaks (1 x 60 Mcf/yr; 2 x 30 Mcf/yr; 1 x 15 Mcf/yr; 6 x 10 Mcf/yr; 6 x 1 Mcf/yr) 

Hypothetical repair cost Assume 1 repair x $33; 2 repair x $15; 5 repair x $3; remaining repairs at no cost 

Total gas savings 201 Mcf 

Total 

Survey Cost 

Total 

Repair Cost 

Value of Gas Saved Payback Period (months) 

$3 per Mcf $5 per Mcf $7 per Mcf $3 per Mcf $5 per Mcf $7 per Mcf 

Site 1 $150 $39 $246 $410 $574 10 Months 6 Months 4 Months 

Site 2 $125 $10 $96 $160 $224 17 Months 11 Months 8 Months 

Site 3 $150 $78 $603 $1,005 $1,407 5 Months 3 Months 2 Months 

Total $425 $127 $945 $1,575 $2,205 7 months 5 Months 3 Months 

1

 TVAs can cost up to $2,000. Savings from avoided emissions may not support purchasing a TVA. 

9 
 

 

Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

The number of facilities included in partners’ DI&M

programs ranged from less than 20 facilities to more than

2,100 facilities. Leaks were found at 50 percent of facilities, 

and an average of two leaks were found per leaking facility.

The average emissions saved per leak repair was 100 Mcf 

per leak. 

Partner-reported survey and repair costs varied 

substantially. Incremental costs for DI&M surveys ranged 

from “negligible” for partners with ongoing leak inspection

programs already in place, to more than $1,200 per facility. 

The highest DI&M survey costs were reported for large 

distribution systems in urban areas where labor costs are 

higher, and the gate stations are presumed to be larger and

to have more components. Reported repair costs similarly 

ranged from negligible for simple repairs made on the spot, 

to more than $500 per repair. 

Lessons Learned 

DI&M programs can reduce survey costs and enhance 

profitable leak repair. Targeting problem stations and 

components saves time and money needed for future

surveys, and helps identify priorities for a leak repair

schedule. The principal lessons learned from Natural Gas

STAR partners are: 

To be cost-effective, DI&M at gate stations and 

surface facilities must use the most low cost and rapid

screening and measurement techniques. Soaping,

listening for audible leaks, portable gas “sniffers,” and 

TVAs/OVAs are recommended for leak screening.

TVA screening concentrations and EPA’s correlation

equations are recommended as a cost-effective 

method for estimating mass leak rate, especially if a 

One Partner’s Experience: Company C 

This company surveyed 306 facilities and identified and repaired 824 

leaks. Four leaks were described as “large”, seven were described as 

“medium”, and the remaining leaks were described as “small”, meaning 

that an electronic detector or soaping was required to locate the leak. 

Total survey and repair costs were approximately $16,500, an average of 

$54 per site surveyed. Total gas savings were 117,800 Mcf, an average of 

143 Mcf per leak. Net savings were approximately $1,100 per facility 

surveyed (at $3 per Mcf). 

Total Gas Savings $353,430 

Total Cost of Surveys $16,500

 and Repairs
 

Net Savings $336,930 

TVA or OVA is already available at the facility. 

A small number of large leaks contribute to most of a 

facility’s fugitive methane emissions. Partners should

focus on finding leaks at equipment components that 

are cost-effective to repair. One of the most costeffective repairs is simply to tighten valve packings or

loose connections at the time the leak is detected. 

Partners have found it useful to look for trends, 

asking questions such as “Do gate valves leak more

than ball valves?” 

Partners have also found that some sites are more 

leak-prone than others. Tracking of DI&M results 

may show that some facilities may need more 

frequent follow-up surveys. 

Institute a “quick fix” step that involves making 

simple repairs to simple problems (e.g., loose nut,

valve not fully closed) during the survey process. 

Re-screen leaking components after repairs are made 

to confirm the effectiveness of the repair. A quick way

to check the effectiveness of a repair is to use the soap

screening method. 

Frequent surveying (e.g., quarterly or twice yearly)

during the first year of a DI&M program helps 

identify components and facilities with the highest

leak rates and leak recurrence, and builds the 

information base necessary to direct less frequent

surveying in subsequent years. 

Record methane emissions reductions for each gate 

station and/or other surface facilities and include 

annualized reductions in Natural Gas STAR Program 

reports. 

References 

Bascom-Turner Instruments, personal communication. 

Foxboro Environmental Products, personal communication. 

Gas Technology Institute (formerly the Gas Research Institute), personal 

communication. 

Henderson, Carolyn, U.S. EPA Natural Gas STAR Program, personal 

communication. 

Indaco Air Quality Services, Inc., 1995, A High Flow Rate Sampling System 

for Measuring Leak Rates at Natural Gas Facilities. Report No. GRI94/0257.38. Gas Technology Institute (formerly Gas Research 

10 
Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

Institute), Chicago, IL. 

Indaco Air Quality Services, Inc., 1998, Trends in Leak Rates at Metering 

and Regulating Facilities and the Effectiveness of Leak Detection and 

Repair (LDAR) Programs, Draft Report prepared for PRC International, 

Gas Research Institute, and the U.S. Environmental Protection 

Agency. 

Radian International, 1996, Methane Emissions from the Natural Gas 

Industry, Volume 2, Technical Report, Report No. GRI-94/0257.1. Gas 

Technology Institute (formerly Gas Research Institute), Chicago, IL. 

Radian International, 1996, Methane Emissions from the Natural Gas 

Industry, Volume 10, Metering and Pressure Regulating Stations in 

Natural Gas Transmission and Distribution, Report No. EPA600-R-96-

080j. 

Tingley, Kevin, U.S. EPA Natural Gas STAR Program, personal 

communication. 

U.S. Environmental Protection Agency, 1994–2001, Natural Gas STAR 

Program, Partner Annual Reports. 

U.S. Environmental Protection Agency, 1995, Natural Gas STAR Program 

Summary and Implementation Guide for Transmission and Distribution 

Partners. 

U.S. Environmental Protection Agency, 1995, Protocol for Equipment Leak 

Emission Estimates, Office of Air Quality Planning and Standards, 

EPA453-R-95-017, November 1995. 

U.S. Environmental Protection Agency, 2001, Lessons Learned: Convert 

Gas Pneumatic Controls to Instrument Air, EPA430-B-01-002. 

U.S. Environmental Protection Agency, 2003, Lessons Learned: Options for 

Reducing Methane Emissions from Pneumatic Devices in the Natural 

Gas Industry, EPA430-B-03-004. 

11 
Directed Inspection and Maintenance at Gate Stations and Surface Facilities 

(Cont’d) 

United States 

Environmental Protection Agency 

Air and Radiation (6202J) 

1200 Pennsylvania Ave., NW 

Washington, DC 20460 

EPA430-B-03-007 

October 2003 

12