Development of an Aircraft Lap Joint Simulant Environment

Abstract

The aging of aircraft fleet has led to significant concern about the development of corrosion. Occluded regions such as lapsplice joints, which are difficult to inspect, are of particular importance. By analyzing the corrosion products found in these joints, a simulant solution has been developed. The lap joint simulant solution (LJSS) contains 20 mM sodium chloride (NaCl), 4 mM sodium bicarbonate (NaHCO 3 ), 4 mM sodium nitrite (NaNO 2 ), and 2 mM sodium fluoride (NaF) at pH 9. Exposure of AA2024-T3 (UNS A92024) to the LJSS results in a similar corrosion topography to that found on aircraft in the field.

A lap joint simulant laboratory test method of aluminium alloys

“…The proposed LJSC set up provides a straightforward analysis of the controlling effect of mass transport and the location of the electrochemical reactions. This study confirms the previous results of Kelly et al where, in the case of a real lap joint, due to the lack of cathodic reaction on the external surface of the lap joint (oxygen reduction reaction), at long term, the trapped electrolyte becomes alkaline and not acidic.…”

“…the reservoir) promoting higher chloride concentration. In lap joint corrosion, in the absence of an external cathode (external surface often dries significantly) the development of a mildly alkaline occluded solution is observed . The works of Kelly and Ferrer analyse the case of a KC‐135 aircraft lap joint without any external cathode.…”

A study of performance of corrosion prevention compounds on AA2024-T3 with electrochemical impedance spectroscopy

“…The lap joint simulation solution (LJSS) was used as the exposure solution with composition as follows [15]: 20 mM NaCl, 4 mM NaHCO 3 , 4 mM NaNO 2 , 2 mM NaF, adjusted to pH 9. This solution has been shown to mimic that found in isolated occluded regions that are widespread on aircraft.…”

2021 W.R. Whitney Award: The Importance of Local Chemistry and Potential in Localized Corrosion and Stress Corrosion Cracking

“…In collaboration with NASA/Langley and Tinker Air Force Base, over 100 lap joints removed from KC-135 and other aircraft were disassembled, and their occluded solution reconstituted and analyzed with CE. 24 An impressive variety of ionic species was found, 25 in all. One example electropherogram is shown in Figure 2(a).…”