Air Cooled Heat Exchangers are used mainly in refineries in oil processing and in the processing and transportation of natural gas where the worldwide accepted API (American Petroleum Institute) standard intended for the special requirements of such demanding operations was developed many years ago, according to which almost all clients order such air-cooled heat exchangers. In technical jargon, these heat exchangers are indicated as API-exchangers. They are distinguished by their use at high operating temperatures and pressures, with highly corrosive and flammable media requiring special structures, materials and demanding welding procedures (plug chambers with extraordinary sheet metal thicknesses, duplex steels, etc.). In other industries, the conditions are not so demanding and the technical design of heat exchangers is resolved according to traditions in such industries, according to the specific requirements of customers or our experience, naturally considering the applicable standards for the construction of such pressure facilities.