Lightning currents flow not only in aircraft structures, they can also be conducted through metallic pipework. In particular hydraulic pipes pass through parts of the aircraft that can potentially be exposed to severe lightning events. As with all pipework, there are many joints in aircraft hydraulic systems. All these mechanical joints have to be tested to ensure continued hydraulic pressure integrity after a lightning strike with the objective of improving flight safety. Lightning impulses are applied up to 7.5 kA.