Various embodiments include a compressor casing and a method of assembly. The compressor casing comprises a first and an adjacent, second annular casing segments each comprising an annular radially-extending flange with mounting holes; at least one annular recess disposed on at least one annular side mating face of the adjacent flanges of the adjacent segments; at least one set of stress-relief holes disposed through at least one flange of the adjacent segments; and at least one annular leak-resistant plate disposed within the at least one annular recess having at least a third set of mounting holes. All sets of mounting holes are substantially aligned with each other and receive a plurality of respective fasteners, and the at least one annular plate is clamped between the adjacent segments and seals the at least one set of stress-relief holes for preventing leakage therethrough.