4　Steel Structures and Metal Parts

4.1　General Provisions

4.1.1　This chapter is applicable to the construction and acceptance of boiler steel structures，the platforms and staircases，the closed seal，sealing elements，combustion equipment，ash and slag chambers and air heaters and other related metal structures.

4.1.2　The main dimension of boiler steel structures and related metal structures shall be measured and inspected with the qualified measuring tools verified by the metrological authorities.When measuring with a steel tape，it shall be tightened with a spring balance，and the tension forces shall be equal when the measuring distance is the same.

4.1.3　Before the erection of boiler steel structures and the related metal structures，the quantity counting shall be carried out according to the goods supply list，the packing list and drawings.The following testing items shall be carried out for the main components:

1　The overall dimensions shall meet the requirement of the drawings，and the allowable deviation shall meet the requirements of Appendix D.

2　The visual examination shall be done to inspect the quality of welding，riveting and bolting connection whether there are defects such as rust，double skin，cracks etc.

3　The type of steels and welding materials used in structure parts and the weld joint quality grade as well as the category and spot-check percentage of nondestructive testing shall conform to the requirement of GB 50205 Code for Acceptance of Construction Quality of Steel Structures.

4　The alloy steel components and parts（excluding Q345 and other low alloy steels）shall be reinspected one by one with PMI.

5　The visual examination on the painting quality of steel framework and related metal structures shall meet the requirements of the technical agreement.

4.1.4　When the correction of boiler steel structures and the related metal structures is carried out，the following items shall be noticed:

1　After the cold correction，there shall be no concave/convex，crack or other damages.When the environment temperature is below 20℃，the hammering shall not be carried out in order to prevent the brittle fracture.

2　For heating correction，the heating temperature of carbon steels shall not exceed the critical temperature Ac3，and that of alloy steels shall be controlled below the steel critical temperature Ac1.The critical temperature of common steels used in power plant erection are shown in Appendix E.

4.1.5　The stacking yard of steel structures and metal structures shall be flat and rigid，and the necessary drainage facility shall be provided.The components shall be stacked firmly and steadily，and the distance of sole timbers shall not result in the deformation of components.