March 2017, Vol. 244, No. 3

Features

Corrosion Threats for the Oil and Gas Industry

The oil and gas industry plays a major role in generating the energy we use every day, representing an important part of today’s global economy. To keep up with increasing energy consumption, the industry has led deepwater and other explorations. The pace of exploration is expected to rise to meet this demand.

The machinery used in onshore and offshore exploration is constructed of metals and alloys, including steel. These machines have to function in demanding environments where they are exposed to saltwater, high pressure, and extreme and fluctuating temperatures. Consequently, the steel components of the machinery often become corroded.

Corrosion Problem

Corrosion is a serious issue in terms of cost, injury and loss of life. It’s one of the significant threats to onshore transmission of gas and hazardous liquids pipelines, gas distribution services, and oil/gas gathering systems. The effects of corrosion are measured in terms of negative effect on capital and operational expenditures, health, safety, and the environment.

In a 2008 report, the U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA) revealed in the 20-year period from 1988 through 2008, corrosion was responsible for 18% of the significant onshore and offshore incidents. During the same time period, excavation damage was responsible for 26% of significant incidents. Other causes were human error (5.3%), material failure (15.4%), natural force damage (8.5%), other outside force damage (3.9%), and other causes (22.9%).

PHMSA identifies specific criteria to determine significant incidents:

• A fatality or injury requiring in-patient hospitalization.

• Cost of $50,000 or more (measured in 1984 dollars).

• Five barrels of highly volatile liquid or 50 barrels or more of another other type of liquid released.

• A liquid release that causes a fire or explosion.

Frequency of Incidents

Looking again at the 20-year period from 1988 through 2008, there were 40-65 significant corrosion incidents per year, with an average of 52 each year. At least half of all incidents involved onshore liquid pipelines, with the next highest number of incidents occurring with onshore gas transmission pipelines.

While the infrastructure during this period of time has aged, the number of incidents has remained relatively steady, which can be attributed to effective corrosion-control efforts.

Liquid vs. Gas Incidents

Corrosion failures show as leaks or ruptures, with leaks more common. Leaks from gas pipelines don’t typically cause property damage because the escaping gas is dispersed into the air. Liquid leaks are more problematic due to the possibility of soil, groundwater or surface water contamination. On the other hand, gas pipeline ruptures are more apt to cause injuries and fatalities due to explosion and fire.

Most liquid pipeline corrosion incidents occur in onshore lines. The few incidents that took place on offshore lines didn’t cause injuries or fatalities, in part because of the low likelihood of individuals being present during this type of incident occurs.

The Toll

Of the 1,074 significant incidents during the same period, there were 30 fatalities, 100 injuries and $551 million in property damage, compared to 1,552 significant incidents associated with damage from excavation. The latter resulted in 147 fatalities, 619 injuries, and $518 million in property damage.

The global financial impact of corrosion is massive, with an annual cost worldwide of $2.2 trillion. In the United States, the annual cost of corrosion comes to $423 billion – $276 billion specifically for carbon steel corrosion. While steel corrosion in air, soil and water is natural, if the correct methods were used to protect against corrosion, it is estimated 25-30% of the damage could be prevented or slowed.

Despite the fact that the science of corrosion is well-known, pipeline failures due to corrosion still occur regularly. While we may understand the behavior of metals such as steel when placed in saltwater, a buried pipeline presents a more complicated scenario.

Factors that affect corrosion include:

• Unknown chemical properties of the environment making contact with a buried pipeline.

• Varying concentrations of oxygen and moisture as well as the differences in the soil along the length of the pipe and from the top to the bottom.

• Variations in oxygen and moisture over time.

• Variations in coating quality.

• Disbonded coatings causing groundwater to come into contact with the steel and shielding it from cathodic protection currents.

• Disbonded coating preventing aboveground detections of corrosion.

• Variations in composition of soil and gaps affecting distribution of cathodic protection current.

• Necessity of excavation to visually inspect the pipe and coating.

• Stray current from nearby buried structures interfering with the pipeline’s cathodic protection system.

As is plain to see, pipeline engineers must deal with the difficulties involved in preventing corrosion in pipelines and machinery where the chemical and physical properties of the environment are unknown. Often, engineers don’t have the ability to observe most of the structure.

Addressing the Problem

In order to prevent corrosion and mitigate the financial and health toll they create, oil and gas companies use equipment made from corrosion-resistant alloys (CRAs). This has led to an increased demand for stainless steels, alloy steels and nickel alloys to be used in upstream operations.

Because it’s highly susceptible to corrosion, iron is unsuitable for use in oilfields. Steel, which is created by mixing iron and carbon, is stronger than iron and is used in machinery. Other metals can be added to iron to lower its susceptibility to corrosion. Formulating CRAs generates a strong corrosion-resistant oxide film on the surface of the metal.

The following are some of the methods used to prevent or reduce corrosion:

• Coatings: The metal can be coated with a layer of protective paint. The coating must be thick enough to completely protect the metal from the surrounding environment.

• CRAs: Temperature and the presence of chemicals in the environment are important variables that determine the effectiveness of CRAs. In addition, the availability of capital as well as short- and long-term operating costs must be taken into consideration.

• Corrosion inhibitors: These work to shield the metals and alloys to minimize the effects of corrosion from water, oil and gas.

• Cathodic protection: This is an electrochemical process to control corrosion that keeps the metal strong and increases its longevity.

Corrosion is a continuing problem, costing the oil and gas industry tens of billions of dollars annually in lost revenue and treatment costs. Solving the problem requires using a combination of many scientific disciplines.

In the end, there is no single solution for the problems associated with corrosion. Each case and installation must be considered fully in order to determine the best materials to use for mitigating corrosion.

Author: Merrick Alpert is president of EonCoat. Prior to that he served in executive positions at R&D Altanova, Colt’s Manufacturing Company, Turbine Generator Maintenance, Eceptionist, Enron Energy Services, Pacific Gas & Electric and Smith Cogeneration International.