All-welded plate heat exchangers are a form of plate heat exchanger capable of withstanding high temperatures and pressures. Maximum temperature was 400°C, with a pressure of 3.5Mpa. Fully welded plate heat exchangers are used in the oil and gas sector, refinery applications, pharmaceutical industry, and chemical/petrochemical industries, depending on application practises. Welded plate heat exchangers provide the following advantages over tubular heat exchangers and gasketed plate heat exchangers: 1) The structure is small and compact. 2) It's light. 3) Low heat loss and high efficiency 4) Gasket maintenance is less expensive and free.