Natural Gas Transmission Pipeline Leaks & Repair Criteria

Smart Pig’s Question of the Week – 

A Texas farmer recently contacted us to ask how long could an operator allow a leak from a natural gas transmission line to go without being repaired? He indicated that a leak – identifiable by the soil being sprayed up in the air above the line – had reportedly been visible in a neighboring field for some time, and there had been no apparent effort by the operator to repair it.

Leaving aside all of the reasonable, predictable questions about how that could happen or what an operator’s representative might have said when notified of the leak, here’s what the regulations say about leaks in gas transmission lines. As we suggested in our last post, the regulations vary depending on whether the leak is in a “high consequence area” (HCA) – generally an area of higher population. If you need the details on how gas transmission line operators identify HCAs, you can find them here.

This leak is nowhere near a high consequence area. Not even close. So the leak repair criteria in the gas integrity management rules that would apply in HCAs don’t apply. That means the repair falls under the general gas transmission repair regulations, found at 49 CFR § 192.711, seen in the box below.


§ 192.711 Transmission lines: General requirements for repair procedures.

(a)Temporary repairs.Each operator must take immediate temporary measures to protect the public whenever:
(1)A leak, imperfection, or damage that impairs its serviceability is found in a segment of steel transmission line operating at or above 40 percent of the SMYS; and
(2) It is not feasible to make a permanent repair at the time of discovery.
(b)Permanent repairs.An operator must make permanent repairs on its pipeline system according to the following:
(1) Non integrity management repairs: The operator must make permanent repairs as soon as feasible.
(2) Integrity management repairs: When an operator discovers a condition on a pipeline covered under Subpart O-Gas Transmission Pipeline Integrity Management, the operator must remediate the condition as prescribed by § 192.933(d).
(c) Welded patch.Except as provided in § 192.717(b)(3), no operator may use a welded patch as a means of repair.


To paraphrase, an operator must make immediate temporary repairs to protect the public, but only when lots of qualifiers apply to the situation:

1) the leak/imperfection/damage impairs the serviceability of a pipeline;

2) the line is operating at or above 40% SMYS (specified minimum yield strength, defined in 49 CFR § 192.4); and

3) it is not feasible to make a permanent repair at the time of discovery.

For permanent repairs, none of those qualifiers are necessary: for non-integrity management repairs, meaning like the line in question it is not in a high consequence area, the operator must make permanent repairs “as soon as feasible”. So that begs the question, what does “as soon as feasible” mean? It doesn’t say “immediately,” (presumably because they’ve already made immediate temporary repairs where there is risk to the line or to the public) but it also doesn’t say “as soon as practicable,” or “in the course of ordinary business.” To an ordinary reader, I think “as soon as feasible” would mean “as soon as you can, even if that’s sooner than you want to.”

Unfortunately, the answer could get a bit muddier (or at least more expensive to determine) if one were to look to the rules for repairs on pipes subject to integrity management rules for guidance in determining how soon is “as soon as feasible.” That’s because, as noted in the text box above, repairs on pipes in high consequence areas are required to follow the criteria in 49 CFR 192.933 (d) in remediating a “condition.”  If we assume that a leak qualifies as a “condition,” (and I would argue it does, since “condition” is used in §192.711 interchangeably with “leak, imperfection or damage”) then an operator needs to determine, within 180 days, whether it poses a potential threat to the integrity of the line. Assuming it does pose such a threat, then the operator has to “complete remediation of the condition” within the timeframes included in an industry standard incorporated by reference into the PHMSA regs, but unavailable to mere members of the public unless you either buy them at considerable expense, or trek to the bowels of the Department of Transportation office or the National Archives, both in Washington DC in order to see a copy of them. Once there, you will want to see the schedule in ASMA/ANSI B31.8S, Section 7, figure 4. Unfortunately, this little piggy has not purchased the appropriate set of industry standards, nor am I able to travel to either of these offices, so I am not able to tell you how a leak large enough to blow soil into the air might be classified for repair. The remainder of subsection (d) of the regulation is not of much assistance, either: it names specific types of anomalous conditions on a pipe and indicates whether they are “immediate repair conditions”, “180 day repair conditions”, or a “monitored condition”, which need not be repaired until it gets worse. Leaks are not included in any of those lists.

Bottom line: Leaks on gas transmission lines outside of HCAs need to be repaired as soon as feasible. Leaks inside HCAs: it depends – but only somebody with the industry standards can tell you exactly on what it depends. And I expect there will be continuing conversations about whether it’s okay to make people who live with the consequences of a law pay a private industry organization for a copy of a standard that has been incorporated into that law.

Natural Gas Components, Transmission Line Leaks and Karst Topography

Smart Pig’s Question of the Week –

We were recently contacted by a resident of Virginia who wanted to know whether natural gas transmission lines leak, and particularly about how the methane and other constituents of transported gas might behave if a leak occurred in an aquifer associated with karst topography.

To best respond to his concerns, we’ve divided his questions up into smaller bits:

1) Do gas transmission lines leak?

2) How do we find out what else is in gas transmission lines in addition to methane?

3) How will gas behave when it is released by a leaking transmission line into an aquifer, specifically one in a karst landscape?

1. Do gas transmission lines leak?

Yes, gas transmission lines leak, but because of a variety of factors such as size of leak, weather conditions, how the gas might migrate and/or collect, and available ignition sources, leaks may or may not reach the right mixture with air to ignite. The natural gas in these types of pipelines is primarily methane which is lighter than air, so if there is a leak the gas rises in the atmosphere and dissipates, and is not typically a problem for groundwater contamination like other types of liquid pipelines and pipelines that carry liquid gases (ethane, propane, butane, etc.).

Emissions from all the different types of gas pipelines is a problem that has recently been recognized by the EPA and White House in relation to concerns over climate change. In general “leaks” from gas transmission lines are not the largest source of gas coming from such pipelines. Emissions from compressor stations, blow downs at valves, and releases associated with maintenance programs account for more gas released. If you are interested in the emission concerns that are starting to be highlighted nationally regarding climate change at our recent national conference we had representatives from a variety of groups talking about those issues. You can find video of some of those presentations here.

How long an operator can allow a leak to continue depends on its characteristics and whether it falls into a geographic area known as a “high consequence area” – usually a higher population area – where there are additional safety requirements with which operators must comply. See our next installation for a more detailed discussion of leak repair criteria.

2. How do we find out what else might be in natural gas transmission lines in addition to methane?

Interstate natural gas pipelines will typically only be transporting natural gas that is made up of a high percentage of methane. The specific ratio of gases will be set by the gas ‘quality’ tariffs that the company drafts. A maximum BTU/SCF (British Thermal Unit per standard cubic foot) quality tariff usually sets a maximum on the “richness” of heavier than methane gas components such as ethane, propane etc., that can be in the natural gas. The pipeline company wants to set quality standards for what is included in the natural gas so the end users can use it with the minimal amount of processing, and so it does not contain things that could damage the pipeline. As an example, here is a screenshot of the gas quality measurements from a Williams Transco pipeline that goes through Virginia.

Click for larger version

Click for larger version

You will see that at the Fredricksburg station, the “natural gas” was made up of about 95% methane, with a few other components (predominantly ethane and CO2) also included. You can find this info for the Transco pipeline at  There are buttons on the left hand side of the page that will take you to the “gas quality” section. There you can choose between various tabs to see daily gas quality values and the actual gas quality tariff provisions. Most companies post their tariffs on their websites.

3. How will natural gas behave when it is released by a leaking transmission line into an aquifer, specifically one in a karst landscape?

Karst topography and landforms are created by the action of water on soluble rock types like limestone and gypsum. Karst is typified by sinkholes and caves.  Aquifers in karst topography can transport pollutants much more quickly than other aquifers, simply because there are frequently large cracks and caves through which the water can travel, rather than having to pass through less porous, less permeable rock types. One additional risk incurred by pipelines in these areas is that they must be engineered and maintained accounting for the possibility of rapid changes in the geologic stability of the route, as sinkholes and caverns can collapse quite quickly placing abnormal loads that can cause a pipeline to fail. Another additional risk is that leaked gas could migrate to a pocket in the rock or a cave where it could become trapped and eventually become an explosion hazard if it were to find an ignition source.

The methane being transported in a transmission pipeline will, if released, dissipate as a gas into the atmosphere, making its way through whatever soil or rock type the pipe is buried in. At the low concentrations present in natural gas, the ethane in the gas mixture tends to travel as a gas and not a liquid. If there were to be a transmission line leak, the ethane would release into the atmosphere as a gas, although because it is heavier than air, it will not dissipate as quickly as the methane. If a natural gas line were to leak into groundwater, the small percentage of ethane will tend to be carried with the methane and dissipate as a gas.

New Smart Pig – Question of the Week Series

Hi all,

Today we will be starting a new series on the Smart Pig Blog where we will answer the “Question of the Week.” These will be actual questions we receive from the public, local governments and the media, and will cover a whole range of pipeline subjects. To make this work we need to continue to receive good questions, so please feel free to send your questions to


As time goes on we will be categorizing these questions to create an indexed Frequently Asked Questions (FAQs) section on our website where people can hopefully easily find answers to their question whenever they wish.


On our website we already have a series of 11 briefing papers that cover a variety of general pipeline issues. We will be updating all of those soon. The current briefing papers include:

Natural Gas Pipelines – The Basics

Hazardous Liquid Pipelines – The Basics

The statutes, regulations, consensus standards, and best practices

The Alphabet Soup of Players in Pipeline Safety

Considering Risk

Excavation Damage Prevention

The Need For Better Planning Near Pipelines

Pipeline Routing and Siting Issues

Integrity Management Rules

Cost Benefit Analysis

Emergency Planning


Over the next couple months we would like to add 3-5 more briefing papers to this collection. We really want to produce information that people find helpful, so if you have ideas for new briefing papers please pass them along. Some of the ideas we are kicking around right now are:

• Where to find pipeline information
• How to get an agency to answer your questions
• What do states do regarding pipeline safety and what authority do they have
• Emissions from natural gas pipelines
• How does a good idea become law


Between the new indexed FAQs and the updated and expanded briefing papers we hope people will be able to find what they need to better understand the pipelines that already run through their communities or the ones being proposed.


Let us know if you have ideas or questions.





P.S. – Note on the right we have added a place where you can input your email to subscribe so you will get notices when there are new posts on this Smart Pig Blog