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Phased Array Ultrasonic Testing (PAUT) of Aluminum Ship Hull Welds for Sensitization of Aluminum

Aluminum Sensitization and Non-destructive Testing

Aluminum alloy ship hulls are utilized on many commercial and military ship platforms. Over their lifetime, they often require non-destructive and destructive testing. Among the common hulls that require such examination include CG 47 Class Cruisers, Littoral Combat Ships (LCS) – both Freedom and Independence variants – as well as Amphibious Assault Ships, Expeditionary Fast Transport, Landing Craft Air Cushions, Ship-to-Shore Connectors, and both CVN 68 Nimitz class and CVN 78 Ford class aircraft carriers. 5XXX series aluminum alloys are commonly used for these assets. They are required to undergo non-destructive testing (NDT) during the material forming, material joining, and in-service. These alloys have the propensity to become sensitized at high temperatures over time, thus driving the need for in-service NDT. While a high Degree of Sensitization (DoS) may not be harmful by itself, high DoS levels make the material more susceptible to intergranular cracking (IGC) and / or stress corrosion cracking (SCC) when exposed to the aggressive environments. Friction Stir Welds (FSW) and Gas Metal Arc Welds (GMAW) may be inspected with phased array ultrasound (PAUT) and full matrix capture / total focus method (FMC/TFM) for welding process and in-service defects. This article discusses some in-service non-destructive testing and destructive testing used for the detection of sensitization, intergranular cracking, and stress corrosion cracking of aluminum ship hulls.

Figure 1: Aluminum sensitization and associated failure mechanisms: Intergranular cracking (IGC) and / or stress corrosion cracking (SCC) may be detected with high frequency phased array ultrasound and non-linear ultrasonic testing.

Figure 2: Sensitized aluminum may evaluated destructively or non-destructively.