Partner Reported Opportunities (PROs) 

### PRO Fact Sheet No. 602 for Reducing Methane Emissions



# Test and Repair Pressure Safety Valves

Technology/Practice Overview

Description
If a pressure surge in a compressor, pipeline, or pressure vessel exceeds the maximum operating pressure for the system, pressure safety valves (PSVs, or pressure relief valves, PRVs) will open and vent excess gas to the atmosphere. Over time, the valve seats wear or become fouled with debris, and will leak gas. Small leaks will grow larger as the leak point erodes or is subject to
corrosion.

Gas STAR Partners fi nd that pipeline valves, connections, compressor valves and open-ended lines are major sources of fugitive methane emissions. A study of fugitive emissions in four gas processing plants found that only 0.4 percent of leaking equipment components were pressure relief valves, yet they contributed 3.5 percent of the total fugitive emissions.

EPA’s Natural Gas Star Partners report a practice of regularly screening PSVs for leakage, and repairing them as needed. A proactive testing and repair program can dramatically reduce fugitive methane losses. Some partners include screening of PSVs in a directed inspection and maintenance (DI&M)

program.

Estimated

Gas Price Annual

Methane Savings Value of

Annual Whole Gas Savings* Estimated Implementation

Cost Incremental Operating Cost Payback (months)

$7.00/Mcf 124 —
2500 Mcf $923 — $18,000 $250 Data not available 3 months —

immediate

$5.00/Mcf 124 —
2500 Mcf $660 — $13,300 $250 Data not available 5 months —

immediate

$3.00/Mcf 124 —
2500 Mcf $395 — $7800 $250 Data not available 8 months —

1 month 

### Economic and Environmental Benefits

Economic Evaluation

 Gas savings and reducing methane emissions

 Improved operational readin ess and equipment safety Additional Benefits: Estimated annual methane emission reductions 124 Mcf – 2,500 Mcf per leaking PSV Methane Savings

* Whole gas savings are calculated using a conversion fa ctor of 94% methane in pipe line quality natural gas. Compressors/Engines

Dehydrators

Directed Inspection &

Maintenance

Pipelines

Pneumatics/Controls

Tanks

Valves

Wells

Other

Applicable Sector(s)

Production

Processing

Transmission

Distribution

Other Related Documents:

Replace Burst Plates with Secondary Relief Valves,

PRO No. 605

Conduct DI&M at Remote Facilities,

PRO No. 901Source: U.S. EPA, Natural Gas STAR Program PRO Fact Sheet No. 602 Continued


### Test and Repair Pressure Safety Valves (Cont’)

Schematic Showing a Pressure Relief Valve on Compressor Piping



### Compressor Drain Valve

Pressure Relief Valve 

### Dehydrator

Controllers

Operating Requirements
While PSVs are in service, screening to locate leaking valves can be accomplished with an organic or toxic vapor analyzer (OVA,TVA), acoustic and ultrasound leak detection, or optical imaging using an infrared camera. If leaks are detected, options available to quantify the leak volume include a high volume sampler, bagging techniques or a rotameter. Additionally, acoustic and
ultrasonic leak detectors often include an estimation algorithm which enables calculation of emission volumes based on the device’s reading. Once quantified, leaks are fixed, or tagged and priori tized for future repair.

Applicability
Partners find that infrared imaging is an efficient approach to identify leaking valves, providing a real time visual image of the leaks. Optical techniques also offer qualitative assessment of leak size for inaccessible areasby simply viewing them. Partners report that the highvolume sampler is often the most effective tool for quantifying leaks and identifying cost-effective repairs. This approach of rapidly screening, evaluating and repairing leaks can be applied to pressure safety valves on all types of equipment in all natural gas industry

sectors. 

### Methane Emissions

The volume of fugitive
methane emissions from PSVs will depend on the age of the equipment, operating pressure and equipment maintenance. An industry study 1 estimated average annual methane emissions from leaking PSVs in gas processing plants to be 844 Mcf per valve; Gas STAR partners report a wide range
of methane emissions depending on their operations.

One partner screened approximately 100 pressure
relief valves and found 25 percent to be leaking. Twenty -five valves were repaired yielding total methane savings of 500 Mcf, approximately 20 Mcf per PSV. A distribution partner repaired 4 pressure safety valves on compressor discharge lines for savings of 124 Mcf per valve. Another distribution partner repaired two compressor discha rge relief valves, saving 467 Mcf per valve. Two gate station pressure safety valves with a history of leaking were replaced, producing total savings of 5000 Mcf.

In high pressure applications, leaking PSVs can be a major source of methane emissions. One partner reported that a leaking one-inch pressure relief valve emitted almost 36,744 Mcf/year. Five man-hours of labor and $125 of material eliminated the leak, producing annualized savings of more than $110,000 at $3.00/Mcf.

The average methane content of na tural gas varies by natural gas industry sector. The Natural Gas STAR Program assumes thefollowing 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

2PRO Fact Sheet No. 602 Continued


### Test and Repair Pressure Safety Valves (Cont’)

Economic Analysis

Basis for Costs and Savings
Typical total repair costs (labor and materials) for leaking PSVs are expected to range from approximately $75 to $250 per valve in current dollars. 2 The cost of complicated repairs that require significant labor will likely be higher. This analysis assumes a range of Partner-reported annual emi ssions savings from 124 Mcf to 2500 Mcf, and the high-end estimated repair cost of

Pressure Relief Valves on Separators at a Production Site

Source: Advanced Res ources International $250 per valve. At gas prices ranging from $3.00 to $7.00, the PSV repairs pay bac k almost immediately for the large leak example (250 0 Mcf), and within 3 to 8 months for the small leak example (124 Mcf).

Discussion
Testing and repair of leaking pressure safety valves provides cost-effective methane savings across a range of leak rates, repair costs, and likely gas prices. Depending on the age, operating pressure, and equipment components of a facility, regular screening and repair of leaking PSVs can be part of the facility’s directed inspection and maintenance (DI&M) program. Emissions from a leaking valve can be substantial for PSVs on high pressure equipment. If no facility DI&M program is in place, a monitoring and repair effort targeting only PSVs
would be cost-effective and could reduce methane losses significantly.

1. Clearstone Engineering, 2002, Identification and Evaluation of Opportunities to Reduce Methane Losses at Four Gas Processing Plants.

2. Ananthakrishna, S. and C. Henderson, 2002, Cost-effective emissions reductions through leak detection and repair, Hydrocarbon Processing , May 2002.

EPA provides the suggested methane emi ssions 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 emis

sion 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.

2011

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