A production string pressure relief system comprising a hollow cylindrical housing with an outer wall, a first relief valve assembly that is mounted on a first support base that is welded to the outer wall of the housing, and a second relief valve assembly that is mounted on a second support base that is welded to the outer wall of the housing directly opposite the first support base. Each of the first and second relief valve assemblies comprises a valve element that is in the shape of a spherical segment with a spherical sealing face, a cylindrical valve seat with a circular sealing face, and a leaf spring. The leaf spring provides a biasing force that pushes the spherical sealing face of the valve element against the circular sealing face of the valve seat to form a fluid-tight seal when the valve is in a normally closed position.