Analysis of the factors involved in failure of a brass sleeve mounted on an electro-valve

Several electro-valves have failed because of the fracture occurred on the internal sleeve made in a typical free cutting leaded brass CW614 N (UNS 36000). The morphology of the observed fracture surface clearly indicates that the failure phenomenon has been ruled by a stress corrosion cracking mechanism. On the other hand, all the electro-valves operate in an environment featured by potable water that does not justify an alchaline concentration able to induce the SCC phenomenon. The analysis of the observed surface and the comparison of the stress that can induce SCC clearly point out that the failure has been induced by the application of excessive torque on the threaded sleeves to grant their fixing. The performed investigation allows us to indicate the correct procedure in order to avoid the failure of the sleeves and also the change of the applied alloy or an excessive increase of the resistant thickness of such a component.