Semi-welded plate heat exchanger is widely used in aggressive media for heating and cooling. One Semi-welded plate cassette is made of two corrugated heat exchanger plates which are mounted in a 180 angle to each other; back to back these are laser welded alongside the sealing groove provided for the gasket, the aggressive media flows through the inlet flow passages, and on the outside, each cassette is sealed with a gasket, when refrigerant passes from one cassette to the other, only two of the four ring gaskets at the apertures get in contact with the media.