【Daily Question】Utilities - Mechanical & Electrical - 20200712

B The joints of the metal protective layer can be designed using lap, interlock, insertion, or embedding methods. The protective layer should be installed in close contact with the insulation layer or moisture barrier. The longitudinal joints of the metal protective layer can be joined by lapping or interlocking ； The circumferential joint can be made by butting or lapping. For the indoor external protective layer structure, a lapped configuration is recommended. Metal protection refers to the measures taken to avoid or reduce metal corrosion and extend its service life. These measures include the selection of corrosion-resistant metal materials, structural anti-corrosion design, treatment of corrosive media, and surface protection. Generally, metal protection can be divided into two main categories: the first category achieves corrosion prevention by altering the corrosion process itself ； The second type achieves corrosion resistance by forming a protective layer on the surface to prevent the metal material from coming into direct contact with corrosive agents. In the early days, the former type was called active protection, while the latter type was called passive protection. Therefore, among the following joint types, the butt joint is not used in the construction of the metal protective layer for insulation work.

Among the following joint types, which one is not used in the construction of the metal protective layer for insulation projects? A. Lap joint type B. Butt joint type