Technical Papers:

ABSTRACT: Much has been learned over a short period of time with respect to the corrosion assessment of small medical implant devices. Laboratory testing started with modifications of ASTM G 5 and G 61, which lead to the development of ASTM F 2129, and thence the fine-tuning of that specification to meet the intent of the FDA Guideline for non-clinical tests. The changes in electrochemical testing protocol with time are reviewed. Comparative data is presented addressing test environments, scan rates, statistical replication, alloy response, and acceptance criteria.

The Development of a Laboratory Test to Determine the Mechanisms and Effects of Organic Fluids on Copper Coils

ABSTRACT: Indoor corrosion failures of aluminum-finned copper-tube evaporator coils, and also in some systems without aluminum fins, is a menacing issue in the heating, ventilation, and air conditioning (HVAC) industry. Extensive laboratory testing has verified the development of a reproducible screening method to assess suspected contaminants of producing premature failures of copper tube resulting from a very localized form of corrosion known as "formicary corrosion" [a/k/a "ant nest corrosion"]. This paper provides a historical perspective on formicary corrosion and various mechanisms.

FORMICARY CORROSION [aka ANT NEST CORROSION] An Introduction to Case Studies

ABSTRACT: The phenomenon of ant nest (formicary) corrosion is reviewed. Current theories indicate that attack requires the simultaneous presence of moisture, oxygen and a corrodent, usually an organic acid, such as formic acid. Morphological features are presented using several recent case studies as examples. This paper seeks to create more answers to this less appreciated phenomenon that causes premature corrosion failure in copper tubes used typically for refrigeration or air conditioning applications.

Laboratory Corrosion Testing of Medical Implants

ABSTRACT: Performance evaluation of implantable devices is not new to medical device manufacturers, specifically implant manufacturers. A focus on corrosion resistance of implant devices has prompted members of the medical device industry, along with the United States Food and Drug Administration [USFDA] to set forth a guide for performance testing. Although actual corrosion resistance of a material can only be proven through long-term clinical trials, accelerated laboratory tests can be used to predict certain effects. Because corrosion of metals is an electrochemical process, accepted electrochemical testing techniques are used very effectively in the CPI (Chemical Process Industry) [namely ASTM G5, G61, and G71] have been adopted for use. Inconsistencies among laboratories, employing differing protocols, have resulted in varying interpretations by even the most experienced electrochemists and corrosion scientists. Some of the most widely used standard tests are also the most widely abused and misinterpreted, especially by persons who are less aware of materials properties. Since the USFDA provides no clear direction to testing, a modified electrochemical standard [ASTM F2129] has been adopted to address concerns regarding test environment, voltage scan rate, device configuration, and test protocol. The remaining issue is the establishment of an acceptance criterion.

ABSTRACT: Currently the Ni-Cr-Mo alloys are the leading candidates for the latest design of rad-waste containers for the Yucca Mountain Project. Alloy 22 is the leading candidate whereas alloy 59, an advanced Ni-Cr-Mo alloy, is under consideration as an equal or better alternative. The Nuclear Waste Policy Act of 1982 established an objective of Nuclear Waste disposal in a deep geological repository. This act was later amended in 1987, and established Nevada as the only site to be characterized. In 1994 a technical decision was made for a multipurpose container consisting of an outer barrier of carbon steel, alloy 400 or Cu-Ni 70/30 and an inner barrier of alloy 825. This concept was later modified to require a more corrosion resistant alloy for the inner barrier i.e., an alloy of the Ni-Cr-Mo family, alloy 22 (UNS N06022), titanium or a titanium alloy. Since then many papers (1-6) have been written comparing the corrosion resistant characteristics of various alloys such as alloy 825, 625, C-276 and alloy 22. The design waste package underwent several iterations with one of the latest design called "Enhanced Design Alternative" (EDA) which will consist of 20 mm thick alloy 22 as the outer container barrier. This will be shrunk fit to a 50mm thick inner barrier fabricated of type 316 nuclear grade or standard 316L SS. This waste package was then to be enclosed by a self-supported 20 mm thick Ti-grade 7 mailbox shaped drip shield. This design may be further modified as more comprehensive corrosion characteristics of uniform corrosion, localized corrosion, stress corrosion cracking, thermal stability, microbiological corrosion, galvanic corrosion, intergranular corrosion for both the base metal and more importantly, the weld joints in these waste containers under realistic repository environments are obtained. This paper presents data on a new but well established corrosion resistant alloy 59 (UNS N06059) of the Ni-Cr-Mo family. The alloy appears to have better corrosion resistance, both uniform and localized, better thermal stability and better weldability than alloy 22 as measured in standard ASTM laboratory tests and Modified Varestraint tests for measuring susceptibility to hot cracking. Data from some of these laboratory tests on alloy 59 and 22 along with the various interactions with Lawrence Livermore National Laboratories and the TRW Environmental Safety Systems, Management and Operating Contractor for the waste package design, are discussed. 

ABSTRACT: Construction has started on a facility to immobilize high-level radioactive waste in borosilicate glass at the Department of Energy's Savannah River Plant. Type 304L stainless steels is generally sufficient for supply tankage and service lines. It is used as the reference material in chemical reprocessing of reactor target and fuel tubes. Type 304L, however, has unacceptable stress corrosion cracking resistance in solutions containing formic acid and chloride. Scouting tests were performed on twelve commercial nickel-based alloys in simulated process solutions containing halides, sulfates, nitrates, mercury and formic acid. Mercuric ions and halides interact in acidic environments to increase pitting and crevice attack. Alloys with combined chromium plus molybdenum contents greater than 30%, that also contain greater than 9% molybdenum, were most resistant to pitting and crevice corrosion. Based on this testing, Alloy C-276 has been selected as the reference process equipment material, with Inconel 690 and ALLCORR selected for specialty areas.

Inhibition of Heavy Metal Ion Corrosion on Aluminum in Fresh Water Cooling Systems Using Propylene Glycol Anti-Freeze

ABSTRACT: Electronics cooling and environmental control systems are required in enclosed manned spaces such as the inside of spacecraft or submersibles. Because egress from such spaces may not be possible in a short time frame, coolant leaks must have minimum toxicity. For this reason, propylene glycol coolants are preferred over the traditional ethylene glycol coolants. Corrosion inhibitor formulations are well developed for ethylene glycol coolants, but there is concern that the inhibitor suite for propylene glycol systems may not be as mature. In particular, coolant systems with a mixture of aluminum and copper can develop heavy metal ion corrosion of the aluminum due to precipitation of copper ions from solution onto the aluminum. This type of accelerated corrosion of aluminum does not require electrical contact with copper, as is the case for galvanic corrosion, nor is significant coolant conductivity required for corrosion to occur. This paper presents a study of the ability of a commercial inhibited propylene glycol coolant to prevent heavy metal ion corrosion of aluminum when copper is also present in the coolant system. The inhibited propylene glycol’s performance is compared to that of reagent propylene glycol without inhibitors, a mature ethylene glycol inhibited coolant, and to tap water. The inhibitor suite in the inhibited propylene glycol was found to be as effective in controlling heavy metal ion corrosion as that of the inhibited ethylene glycol coolant, while uninhibited reagent propylene glycol was ineffective in controlling heavy metal ion corrosion. 

CORROSION CONTROL DESIGN CONSIDERATIONS FOR A NEW WELL WATER LINE

ABSTRACT: An impressed current cathodic protection (ICCP) system was recently installed to provide corrosion control protection for approximately 2 miles (3.2 kilometers) of underground, direct buried ductile iron piping at the Savannah River Plant (SRP). The piping system serves well water pumps and delivers the water from two newly installed water wells to the main plant area for potable and domestic water use. 

The route of the piping traverses a variety of soil conditions and for a significant length, is installed in a power line right-of-way with direct buried copper cable counterpoise. The conditions presented a unique challenge for the designers of the corrosion control system, especially considering the safety precautions required. 

Extensive detailed testing was performed along the proposed route of the pipeline. This was required to gather the engineering data necessary to establish soil characteristics and the specific requirements for such a corrosion control system. The results of the testing, the design options which were evaluated, the problems encountered during construction, and the effectiveness of the installed system are discussed. 

PROBLEMS IN UTILIZING ASTM G 48 TO EVALUATE HIGH-ALLOY STAINLESS STEELS

ABSTRACT: The ASTM G 48 test evaluates an alloys resistance to pitting and crevice corrosion using severe test conditions. Unlike most other ASTM standards, which are cut and dry in their test procedures, this standard has loopholes, which allows test-to-test and laboratory-to-laboratory variation, which makes comparison of data difficult. Modifications are often used to improve the standard, but these are not adopted universally. 

This paper identifies the problems associated with using G 48, and the impact these problems have on evaluating high-alloy stainless steels. Recommendations to correct these problems to standardize the test are made. Attention to the use of electrochemical measurement techniques for improved reproducibility are discussed. 

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