sch壁厚等级对照表 公称通径 Nominal Pipe Size 外径 Outside Diameter 公称壁厚T Norminal Wall Thickness NPS BN D SCH5s SCH10s SCH10 SCH20 SHC30 SCH40s STD SCH40 SCH60 SCH80s XS SCH80 SCH100 SCH120 SCH104 SCH160 XXS