Abstract: Certain embodiments of the invention may include systems, methods, and apparatus for modifying a turbine casing. According to an example embodiment of the invention, a method is provided for modifying a turbine casing. The method can include providing one or more casing retention pin bores in the turbine casing; inserting a retention pin in the one or more casing retention pin bores; providing one or more patch ring segments configured to be radially constrained by at least a portion of the turbine casing and further configured to slide circumferentially in cooperation with at least a portion of the turbine casing, wherein the one or more patch ring segments comprise at least one retention pin locking bore; installing the one or more patch ring segments in the turbine casing to radially constrain the one or more patch ring segments; and engaging the retention pin in the at least one retention pin locking bore to circumferentially constrain the one or more patch ring segments to the turbine casing.