welding heat exchanger industrial boiler membrane water wall are membrane walls that are made of tubes welded together with or without a strip of metal in between. These walls form the enclosure of the coal combustion chamber. Water wall tubes are also referred to as the evaporator section; they contain water mostly in liquid form which gradually evaporates as it rises in the boiler. The water wall is the main radiation heat surface, arranged inside the boiler chamber and precedes the heat exchange directly with the high temperature flame. The convection tubes are the convection heat surface of the boiler, arranged between the boiler chamber outlet and the end surface and proceed the heat exchange directly with the high temperature fume. The water wall and convection tubes are the main heat surface of the boiler, the tubes diameter for boiler generally used OD51-60mm boiler steel tubes or as the customersâ?? request.