Knock: malleable iron pipe fittings is a tough casting product. If it is knocked by external force, the surface of the pipe is notched or a small amount of deformation is not cracked, then its material properties are still acceptable.
Two see: look at the length of thread, the general shoddy product thread length is always very short. Second, galvanizing, ASME B16.3-1995 provisions of the galvanizing are better corrosion resistance of hot-dip galvanizing, its process is hot-dip galvanizing before processing threads, and then thread processing, so there is no zinc layer on the surface of the thread. The fake and inferior products after the processing of threads and then electroplating zinc or other coating treatment, the surface of its threads zinc layer (coating), its low cost, poor corrosion resistance, installed in the pipeline, yellow water (rusty water) will appear.