January 2016, Vol. 243, No. 1

Features

Microbially Induced Corrosion: Silent Killer of Infrastructure

You can’t see them, but microscopic marauders are eating away at the foundations of the oil and gas industry. Corrosion-causing bacteria generate billions of dollars of damage to pipelines and other oil and gas infrastructure each year.

A new rapid field test for microbially induced corrosion (MIC) could help maintenance staff diagnose MIC on the spot and select the right biocide to target the bacteria causing the damage. A joint industry project led by Battelle could soon bring this technology to an oil and gas field near you.  Tiny Cause,

Enormous Consequences

With 185,000 miles of liquid petroleum pipelines, nearly 320,000 miles of gas transmission pipelines, and over 2 million miles of gas distribution pipelines in the United States alone, corrosion is a constant battle for the industry. Left untreated, corrosion can lead to material failure resulting in costly repairs, production delays, business interruption and possibly accidental releases into the environment.

According to the National Association of Corrosion Engineers, the oil and gas industry spends $7 billion annually on direct corrosion control and repair on liquid oil and gas transmission pipelines. The industry spends another $1.4 billion each year to protect or restore production and exploration infrastructure and equipment. Indirect costs – which can include business interruption, environmental cleanup and legal costs – could easily double the financial impact of corrosion.

A significant portion of the damage is directly caused or accelerated by corrosion-causing bacteria. While it’s difficult to determine exact percentages, MIC is believed to be one of the leading causes of corrosion in the oil and gas industry. The more researchers investigate the root causes of corrosion, the more the role of microbes is becoming understood and appreciated.

Pipelines and other oil and gas equipment exposed to soil, freshwater and seawater are especially vulnerable to corrosion-causing bacteria. Other equipment susceptible to MIC includes coiled tubing used in hydraulic fracturing operations and in conventional lateral wells.

While corrosion still occurs over time without the influence of microbes, MIC can be especially dangerous to infrastructure. Unchecked, bacteria can spread and multiply rapidly, quickly turning a small problem into a wide-ranging one. As the bacterial communities grow, the rate of corrosion accelerates as well. For this reason, it is critical to identify and eliminate corrosion-causing microbes before the damage spreads too far.

Understanding MIC

There are several species of bacteria known to cause corrosion in carbon steel, stainless steel, aluminum alloys and copper alloys. These bacteria can be broadly classified as aerobic (requires oxygen to become active) or anaerobic (oxygen is toxic to the bacteria). Different types of bacteria have different mechanisms that lead to corrosion:

• Sulfate-reducing bacteria (SRB) are anaerobic; they are often found in seawater and are responsible for most instances of accelerated corrosion damage to offshore pipelines, oil rigs and other offshore steel structures. Sulfate-reducing bacteria are found in five phylogenetic lineages containing species that can thrive in a range of anaerobic environments, including high-temperature environments found at both conventional and unconventional drilling locations and inside oil and gas pipelines. The damage from SRB primarily comes through production of hydrogen sulfide as a byproduct of their metabolic processes, which causes a chemical reaction with iron that degrades the metal. Some SRB species can also attack metals more directly via withdrawal of electrons from the iron, a process known as electrical microbially influenced corrosion (EMIC).

• Iron-related bacteria (IRB) are frequently associated with accelerated pitting attacks on stainless steel at weld seams in pipelines and other equipment. They often colonize transition zones where de-oxygenated water from an anaerobic environment flows into an aerobic environment. These bacteria use ferrous iron or manganese in their metabolic processes, weakening the metal. Iron-related bacteria can be either metal-reducing or metal-oxidizing.

• Acid-producing bacteria (APB) generate acids such as sulfuric acid, acetic acid, nitric acid and carbonic acid, which corrode the metal. They are found in a wide range of environments and often co-exist with other bacterial species. APBs can sometime be “first colonizers” that make the environment around pipelines and metal components more inviting for other bacterial species.

There are several species of corrosion-causing bacteria within each of these broad categories, along with additional species that do not fit into any of these categories. The mechanism of corrosion and resulting damage depends on the species of bacteria present.

Bacteria often adhere to metal components in large colonies called “biofilms.” These biofilms allow bacteria to stick to each other and to metal surfaces. The colonies often form in areas where there are seams, bends, cracks, rough surfaces, bolts or other features in the metal that provide an initial place to adhere. However, once the colony is established, biofilms allow bacteria to spread to smooth portions of the metal by adhering to each other.

These colonies produce sticky polymers that attract other species to the colonization sites. As they grow, the biofilms form a seal that traps corrosion-causing acids produced by the bacteria against the metal surface. It is this self-perpetuating quality of MIC that makes this type of corrosion so insidious.

Limited Options for MIC Identification

Selecting the right treatment for MIC requires an understanding of the species of bacteria present and mechanisms by which they produce corrosion. Biocides and other antimicrobial treatments vary in their effectiveness against different bacterial species. And, of course, antibacterial treatments will have no effect on corrosion with non-bacterial causes.

When corrosion is detected, inspectors must first determine if bacteria are the root of the problem. If bacteria are present, inspectors must then determine which kind. The mere presence of bacteria does not mean they are the corrosion-inducing type. There are several methods of diagnosing MIC; two specific examples are described below:

• Luminescence-based biomass detection kits can be used to determine total bacteria count. These techniques offer a quick turnaround but are non-specific, meaning they cannot discriminate between bacteria types. These tests will not distinguish between MIC-causing species or even confirm if the bacteria are at the root of the corrosion problem.

• More sophisticated approaches involve extracting bacterial DNA from field samples and sequencing the DNA in the laboratory. Current practice is to use various culture kits and send samples away to a lab for analysis. This yields very specific information on the presence and abundance of a wide variety of bacteria, including MIC-causing bacteria. However, these tests can take up to two weeks to get results, and keeping the organisms alive during shipment can present challenges.

Accurate, rapid and low-cost field-based diagnostic techniques are urgently needed to facilitate detection of MIC-causing bacteria in the oil or gas field. Delayed diagnosis of MIC allows the problem to continue, and incorrect diagnosis may result in needless and wasteful mitigation actions when the true cause of corrosion lies elsewhere.

Rapid identification of bacteria on site would allow maintenance staff to respond more quickly and appropriately to the presence of corrosion-causing bacteria. It would also allow for proactive monitoring and preventive maintenance. Instead of waiting for visible signs of corrosion to be found, maintenance crews could monitor environmental samples for growth of MIC-causing bacteria and apply tailored biocide treatments before significant corrosion damage is done.

New Methods for Detection

Researchers at Battelle are developing a new field detection kit that could allow companies to monitor bacterial growth on pipelines, downhole equipment and other critical infrastructure. Battelle’s rapid field test for MIC will detect genetic markers of a range of MIC-causing bacteria with a simple handheld detection device that can be easily used by non-scientist personnel onsite. Instead of waiting days or weeks to get results, operators will be able to diagnose an MIC problem in the field within a few hours of collecting samples, and start mitigating action right away.

The proprietary MIC detection kit uses field-based methods for purifying DNA from bacteria present in a range of oil and gas industry fluid samples (e.g., source or make-up water, injection water, flowback or produced water, or even product streams). It then amplifies DNA fragments and compares the amplified DNA to known genetic sequences for several MIC-causing bacteria. Test strips change color when MIC-causing bacteria are identified, allowing for rapid and certain diagnosis by field personnel.

The handheld detection kit has performed well in laboratory studies, providing fast and accurate detection and identification of certain common MIC-causing bacteria. Battelle recently used the method for downhole environments in a West Virginia study. Produced water samples taken from a drilling site in West Virginia were analyzed for specific DNA sequences using the new field-based DNA detection system.

Researchers were able to accurately identify targeted bacteria in the produced water samples. This method could provide early warning for developing problems in downhole environments that are difficult to visually inspect. It could also be used for inspection of pipelines and other oil and gas equipment.

Bringing Testing to Market

Battelle is forming a joint industry project (JIP) to complete laboratory and field validation studies and move this promising technology to commercialization. The JIP will expand the range of bacteria groups detected and move into formal field validation studies of the technology with select industry partners.

The objective of the JIP is to fully develop a field-deployable commercial kit for detection of MIC bacteria. To meet this objective, prior to performing the procedures in the field, researchers will first confirm the efficacy of the technology in the laboratory using samples collected from sites known to have MIC.

Once the approach is validated in the laboratory, researchers will move on to in-field validation testing at participating sites. Prototype MIC field kits will then be manufactured and used at selected beta-test sites. Results of observations made during beta testing with industry partners will inform final adjustments to the protocol and test kit prior to commercial manufacturing.

Making this technology available to the oil and gas industry could ultimately save millions of dollars in mitigation costs, infrastructure repair, and business interruptions. Participating JIP partners will be able to provide samples from their sites for testing. They will also receive the data and results from the validation trials and have pre-sale access to the technology. In return, partners will share in the costs of the study. The JIP is open to operating companies as well as field-service companies in the oil and gas industry, and interested companies should contact Battelle for more information.

Written by Craig Bartling,  a principal research scientist,  Battelle Applied Genomics and Biology group. He has over 12 years of laboratory and project management experience and is currently focused on characterization of environmental samples for microbial DNA and proteins.