Lessons Learned 

from Natural Gas STAR Partners 

Reducing Methane Emissions From 

Compressor Rod Packing Systems 

Executive Summary 

More than 51,000 reciprocating compressors are operating 

in the U.S. natural gas industry, each with an average of

four cylinders, representing over 200,000 piston rod

packing systems in service. These systems contribute over

72.4 Bcf per year of methane emissions to the atmosphere,

one of the largest sources of emissions at natural gas 

compressor stations. 

All packing systems leak under normal conditions, the

amount of which depends on cylinder pressure, fitting and

alignment of the packing parts, and amount of wear on the

rings and rod shaft. A new packing system, properly 

aligned and fitted, may lose approximately 11 to 12 

standard cubic feet per hour (scfh). As the system ages,

however, leak rates will increase from wear on the packing

rings and piston rod. One Natural Gas STAR Partner 

reported measuring emissions of 900 scfh on one 

compressor rod. 

By using company-specific financial objectives and 

monitoring data, Partners can determine emission levels 

at which it is cost-effective to replace rings and rods. 

Benefits of calculating and utilizing this “economic 

replacement threshold” include methane emission 

reductions and cost savings. Using this approach, one 

Natural Gas STAR Partner achieves savings of over 

$233,000 annually at 2006 gas prices. An economic 

replacement threshold approach also results in operational

benefits, including a longer life for existing equipment,

improvements in operating efficiencies, and long-term 

savings. 

Technology Background 

Reciprocating compressors in the natural gas industry leak

natural gas during normal operation. Areas of high leak

frequency include flanges, valves, and fittings located on 

compressors. The highest volume of gas loss, however, is

associated with piston rod packing systems. 

Packing systems are used to maintain a tight seal around 

the piston rod, preventing the gas compressed to high

pressure in the compressor cylinder from leaking, while

allowing the rod to move freely. Exhibit 1 shows a typical 

compressor rod packing system. 

Compressor rod packing consists of a series of flexible

rings that fit around the shaft to create a seal against

leakage. The packing rings are lubricated with circulating 

oil to reduce wear, help seal the unit, and draw off heat. 

Other cooling methods include air cooling, water jacketing, 

and circulating coolants inside the packing box. Packing 

rings are held in place by a set of packing cups, normally 

one for each pair of rings, and kept tight against the shaft

by a surrounding spring. The number of cups and rings

will vary depending on the compression chamber 

pressures. A “nose gasket” on the end of the packing case

prevents leaks around the packing cups. 

Under the best conditions, new packing systems properly

installed on a smooth, well-aligned shaft can be expected

to leak a minimum of 11.5 scfh. Higher leak rates are a 

consequence of fit, alignment of the packing parts, and 

wear. Leakage typically occurs from four areas: 

Method for Reducing 

Natural Gas Losses 

Volume of 

Natural Gas 

Savings (Mcf/ 

year) 

Value of Natural Gas Savings ($/ 

year) Implementation 

Cost ($) 

Payback (Months) 

$3 per 

Mcf 

$5 per 

Mcf 

$7 per 

Mcf 

$3 per 

Mcf 

$5 per 

Mcf 

$7 per 

Mcf 

Economic replacement of 

rings and rods in 

compressor rod packing 

865a $2,595 $4,325 $6,055 $540b 3 2 

General Assumptions: 

a Pipeline Research Committee International (1999). 

b $1,620 cost of ring replacement every three years rather than four years (industry average). 

1 

Economic and Environmental Benefits 

1 
 

Reducing Methane Emissions From Compressor Rod Packing Systems 

(Cont’d) 

Exhibit 1: Typical Compressor Rod Packing System 

Around the packing case through the nose gasket. 

Between the packing cups, which are typically 

mounted metal-to-metal against each other. 

Around the rings from slight movement in the cup 

groove as the rod moves back and forth. 

Between the rings and shaft. 

Leaking gases are vented to the atmosphere through 

packing vents on the flange. Leakage can be reduced

through proper monitoring and a cost-effective schedule for 

replacing packing rings and piston rods. New ring

materials and new designs for packing cases are emerging 

that should reduce emissions in the future. 

Economic and Environmental Benefits 

Monitoring and replacing compressor rod packing systems 

on a regular basis can greatly reduce methane emissions to 

the atmosphere and save money. For instance, 

conventional bronze-metallic packing rings wear out and 

need to be replaced every three to five years. However, as 

packing deteriorates, leak rates can increase to the level at 

which replacing packing rings more frequently can be 

economically justified. In addition, more frequent ring 

replacement might actually extend the life of the 

compressor rod. Partners who institute a program of 

monitoring and cost-effective replacement are able to 

achieve several benefits: 

Reduced methane emissions. 

Gas savings from lower leakage rates. 

Extended service life of compressor rods. 

Decision Process 

Companies can determine a cost-effective replacement 

schedule by following five simple steps. 

2 
 

 

 

Reducing Methane Emissions From Compressor Rod Packing Systems 

(Cont’d) 

Step 1: Monitor and record baseline packing leakage 

and piston rod wear. 

Establishing baseline leakage rates and monitoring piston 

rod wear allows Natural Gas STAR Partners to track 

increases in leakage and evaluate the economics of 

replacing packing rings and piston rods. 

The vent port on the packing case flange provides a means 

for gas leakage to escape to the atmosphere. However, gas

can also flow along the rod and/or from the gasket at the 

end of the packing case, thus bypassing the packing cup 

vent and entering the distance piece. Consequently, where 

possible, measurements should encompass emissions from

both the packing cup vent and distance piece. Some 

systems vent the packing cup into the distance piece, while

others have separate vents. 

Gas leakage can be measured with either a hand held or 

an installed measuring device. Before measurements are 

initiated, a check of the packing vent system should be

undertaken. Failure to account for emissions escaping into

the distance piece may result in an underestimation of

packing-related emissions by up to 40 percent, which could 

impact the economics of the decision process. 

It is important to take measurements immediately after

installing new seals (or new rods and seals). This 

measurement becomes the baseline for the new packing

and can serve as a suitable default baseline for other 

cylinders and compressors of similar type, size, pressure,

and age of rods. After installation of rings, Partners 

should routinely monitor and record leakage rates and 

related operating conditions (pressure, lubrication, 

temperatures) over the entire life of the packing rings,

usually on a monthly or quarterly basis. 

Rods can be monitored periodically during ring

replacements by documenting shaft dimensions and 

surface roughness where the rod contacts the packing 

rings. Piston rods wear more slowly than packing rings,

having a life of about 10 years. Rods wear “out-of-round” 

or taper when poorly aligned, which affects the fit of 

Five Steps to Economic Packing and Piston Rod Replacement: 

 Step 1: Monitor and record baseline packing leakage and piston rod wear. 

 Step 2: Compare current leak rate to initial leak rate to determine leak 

reduction expected. 

 Step 3: Assess costs of replacements. 

 Step 4: Determine economic replacement threshold. 

 Step 5: Replace packing and rods when cost-effective. 

packing rings against the shaft (and therefore the 

tightness of the seal) and the rate of ring wear. An out-ofround shaft not only seals poorly, allowing more leakage, 

but also causes uneven wear on the seals, thereby 

shortening the life of the piston rod and the packing seal.

The leakage attributable to rod wear is determined by the 

change in the baseline leakage rate after each successive 

ring replacement (assuming same operating conditions and 

ring type). This increase in baseline leakage can be used

to establish an economic threshold for replacing the piston

rod (see Step 4). 

Step 2: Compare current leak rate to initial leak rate 

to determine leak reduction expected. 

Using the monitoring data obtained in Step 1, the baseline 

emission measurement should be compared to the current

leak rate to determine whether the current leak signals a 

need for packing or rod replacement. Exhibit 2 

demonstrates how a comparison can be made. 

Exhibit 2: Comparing Current versus Initial 

Leak Rates 

Given: 

IL = Initial leak rate at the last packing ring rod replacement 

CL = Current leak rate 

LRE = Leak reduction expected 

Calculate: 

LRE = CL - IL 

For example, if the leak rate of a packing ring is currently measured at 100 standard cubic feet per hour (scfh), and the same component was measured at 11.5 scfh after the last replacement, then 

the leak reduction that can be expected is: 

LRE = 100 scfh - 11.5 scfh 

LRE = 88.5 scfh 

For accurate analysis, Partners should calculate the “leak

reduction expected” (LRE), which is the savings that will 

occur from installing new equipment separately for 

packing seals and piston rods. When determining the LRE 

for the installation of new rings only, assume all of the

leakage increase since the last ring replacement is 

attributable to ring wear. When determining the LRE for 

replacing the piston rod and rings (note that new rings are 

always installed with a new rod), use the initial leakage

measured immediately after the last rod replacement on

this compressor. Where historical data may not be 

3 
 

 

 

 

 

Reducing Methane Emissions From Compressor Rod Packing Systems 

(Cont’d) 

The 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 

available on individual compressors, data from other 

similar compressors with similar operating conditions can 

be used to establish baseline (initial leak) values. 

Step 3: Assess costs of replacements. 

Costs of replacing packing rings and piston rods vary 

between compressors. For packing ring replacements, 

variables include the number of compressor cylinders and 

the type of replacement ring. A Natural Gas STAR 

Partner reported that costs for a typical Teflon or molybased, 8 to10 cup ring set for a three-inch rod will range 

from $135 to $170 per cup, or about $1,350 to $1,700 total. 

Another source stated that a set of rings may vary between

$675 and $1,080, or $2,025 to $3,375 if the cups and cases 

are included. Factors affecting equipment costs for rod 

replacements include rod dimension and type of rod. 

Estimates of the costs of rods can range from $2,430 to 

$4,725. Special coatings, such as ceramic, tungsten

carbide, or chromium, can increase costs by $1,350 or 

more—the cost of some rods may be as high as $12,150 to 

$13,500. 

Installation costs vary as well, depending on site location

and difficulties encountered during replacement. Both 

Partners and manufacturers estimate that installation 

costs are roughly equal to equipment costs. One Partner 

spent an average of $1,420 per packing ring set for 

purchase and installation. Partners have found that 

monitoring and leak measurement costs are insignificant 

on a per-packing basis relative to the labor costs to install

rings or rods. 

Step 4: Determine economic replacement threshold. 

With the information obtained from Steps 1 through 3,

Partners can develop an “economic replacement threshold”

that defines the specific point at which it is cost-effective to

replace rings and rods. Partners have identified several 

methods for calculating this threshold, relying on company 

investment evaluation criteria and site-specific 

characteristics. 

A simple approach is to use discounted cash flow principles 

to calculate an economic replacement threshold. Partners

can calculate their economic replacement threshold for

both packing seals and rods by using the following 

equation: 

CR * DF *1,000 Economic Replacement Threshold (scfh) = H * GP

Where: 

CR = Cost of replacement ($)

DF = Discount factor (%) 

H = Hours of compressor operation per year

GP = Gas price ($/Mcf) 

The discount factor is the term used for capital recovery for

equal annual revenues and is calculated from the following

formula: 

i(1 i)

n

DF  (1 i)

n 1 

Where i equals the discount rate or company hurdle rate

expressed as a decimal and n equals the payback period 

selected. Using this formula, a 10 percent discount rate (i 

= 0.10) and a one-year payback (n = 1) yield a discount 

factor of 1.10; for a two-year payback (n = 2), the discount 

factor is 0.576, etc. 

Exhibit 3 presents an example for discounted payback.

This table was constructed to show the LRE necessary to 

pay back the investment in a new ring packing set in one

year, two years, and so on. Exhibit 3 shows that the 

$1,620 cost for packing ring replacement can be paid back

in one year with a leak reduction of 55 scfh, in two years 

with a leak reduction of 29 scfh; etc. (with future leak

savings discounted at 10 percent). Thus, if a Partner's 

Exhibit 3: Economic Replacement Threshold for 

Packing Rings 

Leak Reduction Expected (scfh) Payback Perioda (months) 

55 7 

29 12 

20 18 

16 22 

13 27 

a Assumes packing ring replacement costs of $1,620, $7.00/Mcf gas, and 8,000 operating 

hours/year. 

4 
 

Reducing Methane Emissions From Compressor Rod Packing Systems 

(Cont’d) 

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. 

internal investment criterion is a two-year payback, the 

Partner should establish an economic replacement 

threshold for ring replacement at 29 scfh. In other words, 

when the LRE of a ring replacement reaches 29 scfh, the

Partner should replace ring packing. 

Similar to rings, economic replacement threshold can be

determined for rod replacement by establishing the leak

reduction needed in order to justify the investment in a 

new rod assembly. Follow the same steps above, but 

substitute rod capital costs for cost of replacement (CR) to 

determine the economic replacement threshold. 

After determining the economic replacement threshold, 

Partners should determine the amount of methane 

emissions attributable to the replacement. Current 

leakage (CL) measurements do not distinguish between 

contribution from worn rings and rod wear. However, over 

time, the initial leakage (IL) measurements will show a

gradual increase in the baseline leak rate, indicating rod 

wear. Partners should measure and track the change in IL 

to determine the amount of emissions attributable to the 

aging rod. Partners need to establish a baseline by which

to compare piston rod-related leakage. This can be 

accomplished by taking measurements when the rod is

first installed or by comparing measurements from similar 

facilities that have new rods and packing. Once this 

baseline is established, Partners can conduct a discounted 

cash flow to determine the amount of rod-related leakage

that signals the need for replacement. 

Exhibit 4 uses the same approach as Exhibit 3 to provide

the LRE economic replacement thresholds for replacing 

Exhibit 4: Economic Replacement Threshold for 

Rods & Rings 

Leak Reduction Expected 

(scfh) Payback Perioda

 (months) 

376 7 

197 13 

137 18 

108 22 

90 27 

a Assumes packing ring replacement costs of $1,620, rod replacement costs of $9,451, 

$7.00/Mcf gas, and 8,000 operating hours/year. 

rings and rods. This example is based on a cost of $11,701

to replace both the rod and packing rings. The table shows 

that companies desiring a payback of one year require a

LRE of 376 scfh, while a company satisfied with a threeyear payback should replace rods and seals when the LRE

is 137 scfh (with future savings discounted at 10 percent). 

One note of caution: a poorly aligned rod or poorly fitted 

rings can result in a high current leakage measurement, 

and hence a high LRE, that might not indicate the need to 

replace the rod, but rather a need to refit rings or realign

the rod. Monitoring rod dimensions (i.e., tapering, out-ofround, scratches, and surface roughness) is necessary in

determining that the increase in IL over the baseline is in

fact attributable to general rod wear. 

Step 5: Replace packing and rods when cost-effective. 

Monitoring emissions and replacing worn rods and packing 

rings at the economic replacement threshold will result in 

an immediate reduction in emissions and compressor fuel 

costs. Partners should compare compressor station data to

the replacement thresholds. Partners should replace 

One Partner’s Experience 

Consumers Energy replaced worn compressor rod 

packing rings on 15 compressor units with total 

estimated savings from reduced gas leakage of $49,000 

(based on leakage reductions of 7,000 Mcf per year, and 

assuming a gas price of $7 per Mcf). The costs of 

replacing all the packing rings, including materials and 

labor, was $23,000, resulting in a payback period of six 

months at 2006 costs. 

5 
 

 

 

Reducing Methane Emissions From Compressor Rod Packing Systems 

(Cont’d) 

packing rings and rods when actual LREs are equal to or 

exceed the economic replacement thresholds. Partners are 

also encouraged to select economic replacement thresholds

that maximize the methane reduction. 

Additional Options 

Partners in the Natural Gas STAR Program have not 

reached a consensus on standard emission reductions that 

can be achieved by changing compressor rod packing.

Many variables are cited as affecting potential savings, 

including cylinder pressure, fit and alignment of packing 

parts, and amount of wear on the rings and rod shaft, as 

well as company-internal decision criteria. However, 

Partners agree that identifying a replacement threshold

for replacing packing rings and piston rods is a practical 

method to reduce methane emissions from reciprocating 

compressors. 

New materials can improve the life and performance of

certain equipment and provide Partners with additional 

savings through reducing leakage and repair and 

replacement costs. 

Options for rings. Carbon-impregnated Teflon is 

gradually replacing bronze metallic rings. One 

vendor claims that the price is about the same, with 

Teflon expected to last about one year longer than 

the conventional bronze rings. However, other 

factors—including proper installation, cooling, and 

lubrication—might play a greater role in the service

life of a ring. 

Upgraded piston rods. New or existing compressor

rods coated with tungsten carbide have proven to 

increase service life for rods by reducing wear, as well 

as making them effective for “static-seal” 

installations (see Lessons Learned study, “Reducing 

Emissions When Taking Compressors Off-Line”).

Coating each piston rod with tungsten carbide would 

cost an additional $1,350 to $2,700. Chrome coating 

is also used to reduce wear. 

Three-ring rod packing. A three-ring rod packing 

system shown in Exhibit 5 is becoming more 

widespread. The rings are typically installed in one 

of the last two cups. The primary benefit of this 

Exhibit 5: Three-Ring Fugitive Emission Rod Packing Assembly 

6 
 

Reducing Methane Emissions From Compressor Rod Packing Systems 

(Cont’d) 

arrangement is that this design can usually be 

installed without any replacement or modification of

the packing case cup. 

Lessons Learned 

Partners have found that providing compressor station

personnel with simple guidelines for economic replacement

of reciprocating compressor piston rods and rod packing 

will greatly reduce methane emissions. This natural gas

savings pays back the costs for more frequent

replacements. The principal lessons learned are: 

Develop a system for regularly measuring and

monitoring leakage from piston rod packing cases. 

Regularly monitor lubrication and cooling to help 

reduce wear on packing rings. Poor heat conductivity 

at very high operating temperatures can be a 

significant factor in ring deterioration. 

Establish baseline initial leakage (IL) rates for new 

rods and new packing rings, categorized by operating 

conditions and compressor types and sizes. 

Share baseline initial leakage rate data with other

stations to provide substitute data where specific 

data may not be available for all stations. 

Establish a company-specific emission threshold for 

each compressor to serve as a useful tool for knowing

when to replace packing rings and piston rods 

economically. 

Upgrade piston rods where economically justified.

The upgrades will result in fewer emissions over the 

life of the rod. 

New packing ring materials, types, and entirely new

packing systems are available and becoming more 

common where product values or environmental 

factors offset the higher costs. 

For additional information, consult the Lessons 

Learned study entitled Reducing Emissions When 

Taking Compressors Off-Line. 

When changing out packing rings and rods, record 

methane emissions reductions in Natural Gas STAR 

Program annual reports. 

References 

Alastair J. Campbell, Bently Nevada Corporation, Houston, Texas. Optical 

Alignment of Reciprocating Compressors. 

Borders, Robert, C. Lee Cook, Louisville, Kentucky, personal contact. 

France Compressor Products. Mechanical Packing—Design and Theory of 

Operation, Bulletin 691. 

Miniot, Joe, Compressor Engineering Corporation, Houston, Texas, 

personal contact. 

Parr, Robert, TF Hudgins, Houston, Texas, personal contact. 

Pipeline & Gas Journal, “Compressor Shutdown Leakage,” December 

1985. 

Pipeline Research Committee International, Cost-Effective Leak Mitigation 

at Natural Gas Transmission Compressor Stations, PR-246-9526, 

August 1999. 

Schroeder, David M., France Compressor Products, Newtown, 

Pennsylvania, personal contact. 

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

7 
Reducing Methane Emissions From Compressor Rod Packing Systems 

(Cont’d) 

United States 

Environmental Protection Agency 

Air and Radiation (6202J) 

1200 Pennsylvania Ave., NW 

Washington, DC 20460 

October 2006 

EPA provides the suggested methane emissions estimating methods contained in this document as a tool to develop basic methane emissions estimates only. As 

regulatory reporting demands a higher-level of accuracy, the methane emission estimating methods and terminology contained in this document may not conform to 

the Greenhouse Gas Reporting Rule, 40 CFR Part 98, Subpart W methods or those in other EPA regulations. 

8