Another layer of national standard flanges means: flanges produced in accordance with the dimensions and tolerance ranges required by national standards, which are different from flanges that are not produced in standard sizes, also known as two-standard flanges (some people call non-standard flanges) Is incorrect), usually some unscrupulous merchants will reduce the thickness of the flange and the outer diameter of the two dimensions to achieve the purpose of saving materials, and also use waste steel or scrap steel to process the flange, usually this steel is chemical composition and mechanics Wastes with substandard performance, and even flanges produced by private steelmaking in black steel plants. The old steelmaking technology used in this private steelmaking cannot guarantee mechanical properties and welding performance, and may not be able to be welded to steel pipes during use, or The steel itself has cracks, pores, etc., and will leak after welding. So try to choose the national standard flange when purchasing the flange. If you have limited funds, you must carefully observe and measure the size and material of the flange to avoid being fooled.
