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	USAF C-21 aircraft noted to have suffered from pitting corrosion during depaint operations. SwRI engineers were called in to determine the root cause of the pitting and to identify remedial methods to prevent future occurrences.

Corrosion-related failure analyses are conducted for a wide range of clients and industries at Southwest Research Institute (SwRI), including:

• Aerospace

• Barge/shipping

• Pipeline

• Oil and gas drilling equipment

• Pressure vessels

• Valve systems

• Architecture

• Electrical components

• Sporting and utility equipment

The scope of the failure analyses conducted ranges from simple examinations of failed components to determine the root cause of failure to limited-scope experimental studies to validate possible failure modes and mechanisms to identifying and verifying the technical and financial viability of engineering solutions.

Aerospace

USAF C-21 aircraft noted to have suffered from pitting corrosion during depaint operations. SwRI engineers were called in to determine the root cause of the pitting and to identify remedial methods to prevent future occurrences.

Pitting corrosion of a U.S. Air Force C-21 aircraft was noted after paint stripping operations. Concern was raised that the pitting was a result of the paint stripping operation that the aircraft was subjected to. Three main theories were postulated to explain the corrosion observed, and a root cause analysis was performed to establish the conditions leading to pitting on the aircraft and to suggest remediation methods. It was determined that a long stripper dwell time coupled with high concentrations of chloride and sulfate in the rinse water used were the most likely cause of corrosion. Another possibility was that corrosive agents prior to initiation of stripping operations contaminated the aircraft surface.

Based on the work conducted, the following recommendations were made to mitigate the future occurrence of corrosion during depaint operations:

• Subject aircraft to a washdown procedure prior to stripping

• Minimize the stripper dwell time

• Use rinse waters low in dissolved corrosive salts

• Develop an alternative stripping procedure that effectively removes paint but does not remove the chromate conversion coating

For each suggestion, experimental results and procedures were developed to demonstrate the validity of the approach and the benefits of each.
 

Barge/Shipping

SwRI engineers investigated the corrosion of the void space in double-hulled barges and determined that though microbially influenced corrosion may have taken place, the organisms were environmental in origin and could not metabolize the wax paint used.

SwRI engineers investigated the corrosion of the void space in double-hulled barges and determined that though microbially influenced corrosion may have taken place, the organisms were environmental in origin and could not metabolize the wax paint used.

SwRI recently conducted an analysis of double-hulled barges that had been experiencing corrosion in the void spaced between hulls. It was initially suggested that microbially influenced corrosion (MIC) was occurring and that the microbes were utilizing the wax coating used to protect the void space from corrosion as a nutrient source. Using standard microbiology and analytical chemistry methods, SwRI determined that the organisms recovered were environmental in origin and were found to not metabolize the wax paint coating as a nutrient source.

For more information about our corrosion-influenced failure simulation capabilities, or how you can contract with SwRI, please contact Elizabeth Trillo, Ph.D., at etrillo@swri.org or (210) 522-4210.

| Materials Engineering Department | Mechanical Engineering Division | SwRI Home |

Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

January 03, 2013