Abstract: A seal assembly is for a hammer union. The seal assembly comprises: a metal gasket and a pipe comprising a receiving portion arranged to receive the metal gasket internally in the pipe. The receiving portion and the metal gasket are shaped such that a relative rotation between the metal gasket and the pipe results in the metal gasket engaging with the receiving portion, thereby ensuring that the metal gasket is held in the receiving portion independently of the orientation of the pipe. A receiving portion and a metal gasket for use in said seal assembly are described as well. Further, a hammer union including said seal assembly is described.