Maintenance Predictive Maintenance Reliability

A ‘Natural’ Business Case For PdM

EP Editorial Staff | March 26, 2019

PdM provides significant value in any type of industrial operation, including, if not more so, wherever process safety is a driving issue.

Consider the value that predictive maintenance can bring to your operations in terms of safety, reliability, environmental health, and sustainability.

By Drew D. Troyer, CRE, Contributing Editor

Predictive maintenance (PdM) ticks multiple value-adding boxes for plants, regardless of sector. While this article specifically addresses it in the context of an “all of the above” business case in the natural-gas arena, owner/operators in other industries can adapt—and benefit from—a similar best-practice approach.   


Natural-gas production, distribution, and use are growing rapidly. Between June and December of 2018, production numbers rose from roughly 98.5 to 107.5 billion cubic feet (Bcf) per day, an increase of more than 9% in daily production over a six-month period. From an environmental perspective, these numbers should reflect a feel-good story. But do they?

Methane, the primary component of natural gas, produces about half the amount of CO2 than coal does to generate an equivalent amount of electricity. Without going into significant detail, this is because methane—CH4—has a 4:1 ratio of hydrogen to carbon atoms, as opposed to coal, which has a ratio of about 1:1. Burning hydrogen produces water. Burning carbon produces CO2, solids (soot), and intermediate products. That’s why natural gas is often touted by sustainability experts as a “bridge fuel” that can provide electricity until a true low- or no-emissions energy source becomes available.


Methane is a much-cleaner-burning fuel than coal. That’s the good news. Fugitive methane emissions, however—in the production, processing, and transportation of natural gas—are spoiling the story.

To be clear, methane is a very powerful greenhouse gas (GHG). In the first 20 years after methane is released, it’s about 80 times more powerful a GHG than an equivalent volume of CO2. As it ages, or oxidizes, the methane’s GHG-strength weakens. Most experts agree that, on average, its 100-year GHG multiplier is about 25, meaning it’s 25 times more powerful than CO2 as a climate change-inducing GHG. Because of methane’s efficiency as a GHG, the release of even a small amount of fugitive methane emissions has a big impact.

A relatively recent study conducted by the Environmental Defense Fund (EDF), New York (, in conjunction with researchers from Colorado State Univ., Fort Collins (, found an emissions rate of 2.3% in the Barnett Field in Texas (Zavala-araiza et. al., 2017). The bad news is that 2.3% is much higher than the estimate of about 1.4% provided by the U. S. Environmental Protection Agency, Washington ( Fortunately, according to researchers, a significant portion of those emissions can be traced to a few bad-actor assets that lend themselves to predictive-maintenance (PdM) monitoring, reliability analysis, and asset-performance improvement and management. More on that later, but let’s first look at the true cost of such emissions.

Addressing bad-actor super-emitters in the natural-gas sector is quite pedestrian from a predictive-maintenance and reliability-engineering perspective.


Numbers don’t lie. Fugitive methane emissions are expensive. In terms of dollars and cents, assuming a production rate of 107 Bcf/day (the Dec. 2018 rate, which is rising) at the specified fugitive leak rate of 2.3%, we’re losing about 2.5 Bcf/day (or slightly more than 900 Bcf/yr.). At US$3 per thousand cubic feet (Mcf), fugitive emissions are costing the industry about $2.7 billion in annual lost revenue—money that would go straight to the bottom line if the leaks were contained. Of course, that doesn’t factor in the cost for equipment, energy, equipment maintenance due to wear and tear, labor, overheads, and all the other costs associated with extracting, processing, and transporting the fugitive emissions of natural gas—product that’s literally vanishing into thin air. These losses must be made up for with additional drilling, production, and processing of natural gases to make up for the volume that escapes as fugitive emissions.

The lost revenue is just the tip of the iceberg. The cost to society, or the so-called social cost of carbon (SCC), associated with the release of methane gas is much higher. Environmental analysts evaluate all gaseous releases, including methane, using the carbon-dioxide equivalent (CO2-e) unit. In round numbers, a single Mcf of natural gas weighs about 0.0192 metric tons, which equates to slightly more than 52 Mcf of natural gas per metric ton. However, because the GHG-effect multiplier for methane is 25, each Mcf of it lost to fugitive emissions has a GHG impact, or SCC, that’s equal to about 0.48 tons of CO2. Most experts peg the SCC at between $40 and $50 per metric ton of CO2-e. Consequently, each Mcf of natural gas, which would sell for $3 on the open market if it were contained, carries an environmental cost of $22. If you were doing the math in your head as you read this, you probably concluded the following:

• About 18-million metric tons of methane is lost each year to fugitive emissions, assuming 2018 production levels.

• 18-million metric tons has the GHG impact of 450-million metric tons of carbon dioxide.

• Assuming the generally accepted SCC rate of $45 per metric ton of CO2-e, the price tag to society exceeds $20 billion.

While this massive SCC may not currently be affecting all players in the natural-gas arena, it makes sense for them to plan for the eventual rollout of more comprehensive carbon taxing as concerns about climate change continue to grow and evolve. The bottom line is this: The public is demanding more-sustainable energy solutions, and responsible participants in the natural-gas sector really do want to be sustainable and environmentally conscious. The great thing is that if suppliers eliminate or minimize fugitive emissions, they can make more money by increasing the amount of natural gas they sell and do right by the environment at the same time. That makes the targeting of fugitive methane emissions a very attractive and sustainable proposition. As a bonus, production, distribution, and end-user sites will be safer, given the fact many midstream fires and explosions occur because of these types of emissions.

As is often the case, approaches to problems inherent to one industry sector can be adapted and leveraged by others for use in different applications.

PDM 101

The last thing that a reliability engineer wants to hear is that the opportunity to improve lays within the random many causes of failure. Luckily, that’s not the case here. Researchers who evaluated methane emissions in the Barnett Field in Texas found that a comparatively small number of “super-emitters” represented a disproportionately large percentage of the observed methane emissions, i.e., basically the 80:20 rule, where 80% of the emissions are localized to 20% of the emitting sources. In fact, in a meta study of 18 previous studies, Brandt (2016) found that 50% of the total volume of fugitive methane emissions can be attributed to 5% of the sources. According to the researchers, the “super-emitters” might be persistent or episodic.

Addressing super-emitters in the natural-gas sector, is, candidly, quite pedestrian from a predictive-maintenance and reliability-engineering perspective. Predictive monitoring can be tricky, but it’s doable. Here’s a suggested game plan for those in the natural-gas sector. It’s a basic model that owner/operators in other process sectors can use as well.

1. Survey the operation to identify and quantify leaks employing predictive monitoring and inspection techniques and technologies. Test for leaks using technologies such as infrared (IR) thermography, ultrasonic leak detectors, sniffer technologies, and soapy solution, among others.

Each of these techniques has its own unique strengths and weaknesses. IR provides the best overall macro view. Ultrasonic analysis is the best at localizing and quantifying the emission, assuming a threshold compression pressure value that’s necessary to produce the detectable turbulence. Gas sniffers are relatively effective when applied right on the leak. Application of a soapy solution to find leaks is a tried and true method, but it’s laborious and time-consuming and should probably be limited to localizing leaks.

More recently, a new mid-IR laser detector has been developed and is available in a handy portable package. It delivers excellent detection resolution and can simultaneously detect and differentiate between methane (CH4) and ethane (C2H6), which is a minor component of natural gas.

Since weather and atmospheric conditions can influence the effectiveness of any of these technologies, it is important to always take those environmental conditions into consideration.

2. Tag and catalog the leaks. Catalog details should include an estimate of the leak volume, risks to the organization (which are higher if the methane leak is near an ignition source), cause(s), and corrective action(s). This helps personnel prioritize the game plan for taking corrective action. If the leak is fixed-as-found, it’s important to  note that to maintain complete records.

3. Perform cause analysis on the collected data. In some instances, the problem is clear—so apparent-cause analysis (ACA) is effective and efficient. In other cases, root-cause analysis (RCA) is required to evaluate more serious and/or complex problems.

4. Develop corrective plans. There may be multiple optional solutions for correcting a particular type of leak. Test them for effectiveness and cost-benefit ratio. Prioritize the implementation for addressing each identified leak with an optimized set of test-solution packages. The plan may include one or more of the following:

• redesigning the equipment

• modifying operating context and/or procedures

• employing corrective maintenance to fix the leak

• employing preventive maintenance (PMs) to prevent the recurrence of the leak

• employing predictive monitoring to ensure that corrective measures are effective

• electing to live with the situation (Sometimes nothing is the best option, however, when it comes to leaking flammable gases that have a significant impact on the environment, it’s recommended that operations use this option sparingly.)

• scheduling ongoing testing and monitoring to ensure that corrective actions are effective and implementing continuous improvement. (This is consistent with the Plan-Do-Check-Act [PDCA] cycle, which is specified in the ISO 55000 series of standards for managing physical assets [see chart]).

Targeting fugitive emissions in the natural-gas sector is a very sustainable proposition. Predictive monitoring can be tricky, but it’s quite doable with the approach shown here.


The direct costs associated with leaky midstream natural-gas systems have a significant direct impact on owner/operator profits. Effects on safety, reliability, environmental health, and sustainability are even greater because methane is such a strong greenhouse gas, and fires, which result from natural gas leaks, destroy property, and cause injuries or loss of life. Fortunately, most fugitive methane emissions are caused by bad-actor-asset super-emitters.  

Note that the problems and strategies discussed here aren’t necessarily exclusive to natural-gas operations. Reliability engineers in any sector where process safety is an issue can take dead aim at sources of emissions with predictive-monitoring techniques and, in turn, better manage emissions-related risks and costs to their operations, personnel, and society at large. EP


Brandt, A. (2016). Methane Leaks from “Natural Gas Systems Follow Extreme Distributions.” Environmental Science and Technology, 50(22), 12512-12520.

Zavala-araiza, Alvarez, Lyon, Allen, Marchese, Zimmerle, & Hamburg. (2017). Super-emitters in natural gas infrastructure are caused by abnormal process conditions. Nature Communications, 8, 14012

Drew Troyer is a senior manager with T.A. Cook Consultants Inc., The Woodlands, TX ( Email



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