When Dalian marine parts and components are to be repaired by welding, the number, size and position of the detected defects, as well as the welding repair and heat treatment process procedures shall be submitted to the Classification Society for approval. Carbon steel and carbon manganese steel castings shall be properly preheated before welding; If major defects are repaired by welding, the steel castings shall be subject to grain refining treatment before welding. A boiler that supplies steam to the steam powered machinery of a propulsion ship. The difference between marine boiler and land boiler is that there are strict restrictions on the shape, size and weight. For example, on warships, it is better to sacrifice the thermal efficiency of boilers rather than install air preheaters or even economizers. In order to meet the requirements of light, small and high mobility, heavy oil is widely used. The boiler evaporation capacity is 10 ~ 200t / h, and the steam parameter is slightly lower than the corresponding evaporation capacity. It has been applied to light warships since the beginning of the 20th century. However, the condensed water of the steam engine contained more grease, and the boiler water treatment technology was backward at that time, so it was not widely used in commercial ships. Since the 1920s, due to the gradual promotion of steam turbines on board and the solution of the grease problem in condensate, straight tube boilers have gradually replaced fire tube boilers.
