Bare tube type water wall is composed of ordinary smooth seamless tubes; Membrane water wall is welded on the light tube or directly tied fins, the top of the fins of each tube welded together, the whole water wall is connected as a whole; The pin type water wall is welded on the water wall with many long small round steel as nails, which is mostly used to lay the combustion belt, so that the refractory material can be hung on the pipe. Light tube type water wall is usually used in small capacity medium and low pressure boilers, film type water wall and pin type water wall are usually used in large capacity high temperature and high pressure boilers.