GB/T 25151.2-2010尿素高压设备制造检验方法 第2部分:尿素级超低碳铬镍钼奥氏体不锈钢选择性腐蚀检查和金相检查Fabrication and inspection method for high pressure urea equipment—Part 2:Selective corrosion examination and metallography examination for ultra low-carbon chromated nickel molybdenum austenit