The evening news may leave many of us feeling war-weary, but one ASTM International technical committee has been successful in conflict of a different sort. It’s a commonplace but epic struggle between the natural and civilized worlds — the fight against metal corrosion.
For the past half-century, the weapon of choice of ASTM Committee G01 on Corrosion of Metals has been its nearly 100 standards. They promote research, the collection of engineering data, and methods and tests for detecting, monitoring, measuring and preventing metal corrosion. While some battles have been won, it’s a sure bet that committee work will continue for many more years.
“Corrosion is a part of life,” says Daniel Crabtree, G01 committee chairman and senior project manager, Corrpro Companies Inc., Birmingham, Alabama. “It’s always going to be here.”
We all experience everyday corrosion skirmishes with old, rusting garden tools, overzealously cleaned griddles, bicycles that have never seen the inside of a garage, and cars that have encountered too much melting snow and road salt. More deadly corrosion disasters can involve the failure of power plants, bridges, buildings, silos, vessels, pipes and other infrastructure. In addition to human loss, corrosion can cause environmental harm, contamination, mechanical damage and deterioration of surface properties, like electrical conductivity.
The costs are staggering. According to Robert Baboian, veteran ASTM member and corrosion consultant, Greenville, Rhode Island, a 1976 study by the National Bureau of Standards (now the National Institute of Standards and Technology) determined that the economic effects of corrosion totaled $70 billion annually. By 2002, the U.S. Highway Administration had bumped that figure to $276 billion. NACE International (formerly the National Association of Corrosion Engineers) estimated that the annual cost of corrosion in the United States in 2013 would significantly exceed that amount.1
A Tactical Approach
With a few exceptions, like gold, most metals do not occur naturally. We process them from ores. As soon as they’re used in an environment with oxygen (usually from the atmosphere) and an electrolyte (usually water and/or soil), they strive to break down and return to their elemental form. In a spontaneous and electrochemically biased process, metals behave like deteriorating anodes, employing 15 different types of corrosion as allies.
Meanwhile, we counterattack by modifying their environment or using alloys. We provide cathodic protection with galvanic anodes (like zinc) that sacrifice themselves to protect underlying metals or are protected themselves via electrical current. Or we introduce corrosion inhibitors, like coatings or platings.
“The corrosion process is an insidious one, which is often difficult to recognize until extensive deterioration has occurred. In some cases, this leads to catastrophic failure,” notes Baboian.
Committing to Combat
As early as 1900, ASTM members were concerned about corrosion. Railroads wanted reliable track. Steel’s ability to withstand corrosion versus wrought iron was a popular subject of debate. In 1932 and 1937, ASTM sponsored a lecture and a symposium, respectively, on corrosion.
By mid-century — with increased use of galvanized and stainless steel, plus nonferrous metals like aluminum, nickel and copper — dozens of ASTM subcommittees were formed to consider corrosion. But it was Frances L. LaQue, president of ASTM from 1959 to 1960 and director of marketing at International Nickel Company, who was instrumental in establishing ASTM Committee G01 in 1964. The intent was to reduce duplication of effort, centralize corrosion standards development in one technical committee and acknowledge the growing needs of several industrial sectors.
According to Sheldon Dean, Dean Corrosion Technology, Glen Mills, Pennsylvania, by the mid-1960s, the automobile industry was struggling with pitting and peeling chrome bumpers and corroded painted auto body steel where stainless steel was attached to it. The nuclear power industry needed ways to test for stress corrosion cracking. The chemical industry required solutions for localized corrosion at welds in pipelines. The defense industry wanted to test for the alloys’ tendency to peel off the surfaces of military aircraft. Additionally, with the expansion of the aluminum industry, standard methods were needed to determine the corrosion resistance of aluminum alloys.
With the profusion of industries and applications affected by corrosion, ASTM Committee G01 continued to expand. Today, it has more than 600 members representing 32 countries, and 12 subcommittees with jurisdiction over close to 100 standards used throughout the world.
The committee initially acquired four existing ASTM standards and focused on atmospheric and laboratory tests, plus corrosion in natural water, soils, and industrial and high temperature environments. In recent years, it has published more industry-specific standards geared to the development of new alloys and materials systems for specific environments, notes Baboian.
G01 standards address:
- Localized corrosion — including stress corrosion cracking (such as the kind that might occur in aircraft landing gear, automobile axles and springs, or stainless steel fasteners for bridge decks);
- Galvanic corrosion;
- Pitting and crevice corrosion;
- Intergranular corrosion where the boundaries of microscopic crystals, or grains, are more susceptible to corrosion than their insides due to local depletion of the corrosion-inhibiting elements in normally corrosion-resistant alloys; and
- Electrochemical techniques for corrosion testing and evaluation.
ASTM Committee G01’s signature standard is B117, Practice for Operating Salt Spray (Fog) Apparatus. It’s used most frequently for quality control testing of various coatings, including paint systems, on metals. Originally published in 1939, it’s consistently among the top 10 best-selling ASTM standards and the most valuable and widely used corrosion standard in the world, says Baboian. It’s also an integral part of a practical, hands-on ASTM training course about using corrosion tests that includes demonstrations of how to mix corrosive solutions, clean coupons and samples, and evaluate samples and results.
Other ASTM Committee G01 standards may not be as famous, but they’re equally significant to the industrial sectors they impact. For instance, another inherited standard, ASTM C876, Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete, is used worldwide to electrochemically evaluate the corrosion performance of steel in concrete. Likewise, G57, Test Method for Field Measurement of Soil Resistivity Using the Wenner Four Electrode Method, “is used by everyone involved with corrosion control in the oil and gas industry or any industry with buried infrastructure,” says Crabtree. “Soil resistivity is imperative in determining how corrosive the environment is and how to effectively protect underground infrastructure.”
Robert Kain, a LaQue Center for Corrosion Technology retiree and Wilmington, North Carolina-based consultant, specifically cites ASTM G50, Practice for Conducting Atmospheric Corrosion Tests on Metals, and G52, Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater, as among significant standards emerging from years of research. “ASTM Subcommittee G01.04 on Atmospheric Corrosion (and its predecessor) sponsored long-term atmospheric exposures in rural, industrial and coastal settings, some lasting as long as 20 years,” he says. “Likewise, Subcommittee G01.09 on Corrosion in Natural Waters conducted a five-year, worldwide seawater corrosivity study encompassing 14 locations in North America, Europe and Asia.”
Key to the certification of aluminum marine alloys for the boat- and shipbuilding industry is yet another standard developed by ASTM Committee G01, explains Thomas Summerson, a Kaiser Aluminum retiree who lives in Spokane, Washington. That’s ASTM G67, Test Method for Determining the Susceptibility to Intergranular Corrosion of 5XXX Series Aluminum Alloys by Mass Loss After Exposure to Nitric Acid (NAMLT) Test. It’s also an essential component of a standard developed by ASTM Committee B07 on Light Metals and Alloys: B928/B928M, Specification for High Magnesium Aluminum Alloy Sheet and Plate for Marine Service and Similar Environments. That document affects U.S. Coast Guard patrol boats, fishing boats, off-shore oil crew boats, high speed ferry boats and even the U.S. Navy’s new series of littoral combat ships.
According to John Grubb, manager of product technology, Allegheny Technologies Inc., Flat Rolled Products, Natrona Heights, Pennsylvania, a tried and true standard that all other standards must aspire to is G36, Practice for Evaluating Stress Corrosion Cracking Resistance of Metals and Alloys in a Boiling Magnesium Chloride Solution. Another standard, G48, Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution, “is used in labs all the time,” Grubb says. “It really explains how to do the procedures and provides an answer in a short time to what actually happens in seawater over a long period of time.”
Some of the most significant standards developed since the 1960s have involved electrochemical testing, says Dean. In simplest terms, electrochemical corrosion testing provides initial data on the corrosion behavior of materials by generating electrical energy from chemical reactions or producing chemical reactions by introducing electrical energy.
In addition to conducting symposia and publishing articles and books, ASTM Committee G01 has developed a long list of highly technical electrochemical standards addressing:
- Potentiostatic and potentiodynamic polarization (which use electrical potential, or voltage, to allow corrosion reactions to be monitored or driven at the surface of metal samples);2
- The measurement of potentials;3
- Polarization resistance measurement (enabling the estimation of a corrosion rate);4
- Electrochemical impedance spectroscopy (to measure and evaluate corrosion);5
- Electrochemical repassivation (to evaluate the breakdown of corrosion resistance in corrosion-resistant alloys);6 and
- Electrochemical noise measurement (to evaluate the corrosion behavior of metals with minimal environmental changes).7
ASTM Committee G01 is especially distinguished by its long-standing adherence to round robin testing. “It can take us a long time to develop a test, but the intent has always been to enhance and improve reliability and predictability,” says Summerson. He adds that collegiality has also been characteristic of committee members despite loyalties to different organizations. “We could be commercially competitive, developing an alloy, but that wasn’t a concern when we were developing a corrosion test.”
Crabtree also notes that the committee has a history of working with other standards organizations such as NACE International and the Institute of Electrical and Electronics Engineers, as well as other ASTM committees. “We don’t want to duplicate standards people are already using when we can work together to strengthen or complement those standards.”
Besides developing standards, ASTM Committee G01 has continued to sponsor symposia and publish scientific and technical papers on corrosion science.
But what particularly impresses John Snodgrass, an Alcoa Aluminum retiree residing in Pittsburgh, Pennsylvania, is “the core of people who’ve been associated with the committee for so many years and the stability and direction they’ve given it.”
Dean and Snodgrass have served on ASTM’s board of directors, along with LaQue, Baboian, Wayne France, and Harvey Hack, who all went on to become chairmen of the board.
Many more years of work remain for ASTM Committee G01. Existing standards continually require revision to keep up with new materials and technology. And new standards are under development. One is in response to requests from auto, truck and vehicle parts manufacturers, and the U.S. Department of Transportation, for more accurate corrosion testing of calcium chloride and magnesium chloride, de-icers used as alternatives to more common road salt, or sodium chloride.8 Future standards may address nonmetallics, such as carbon and composite materials, or corrosion in electronic products, electric cars, wind generators, solar panels or medical products, including stents and joint replacements.
“We often have issues that we won’t be aware of until we reflect back to things that are very basic,” says Grubb. For example, when the high pressure fuel rails on engines in automotive fuel injection systems sometimes failed, manufacturers switched from reinforced polymers to stainless steel, which corroded. “By using cyclic polarization (a method of measuring the susceptibility of metals to localized corrosion),9 we eventually determined that the general effect of electricity on corrosion was what was causing the fuel rails to corrode.”
Dean concurs that “very little in the corrosion field is new. We simply aren’t always using the available information to deal with it.”
That fact remains part of the endless struggle against corrosion.
“Corrosion control needs to be addressed up front,” says Crabtree. “We’ve made great strides in educating the public and industry about corrosion and maintaining infrastructure, but we’ve still got a long way to go.” And the development of standards will continue to be an effective and essential strategy.