我(wo)國(guo)目(mu)前還沒有(you)壓力管(guan)道設計用鋼管(guan)尺寸系(xi)(xi)列(lie)（公(gong)稱直(zhi)徑(jing)、外(wai)徑(jing)、壁(bi)厚）的(de)國(guo)家(jia)標準(zhun)，只有(you)鋼管(guan)的(de)生產標準(zhun)尺寸系(xi)(xi)列(lie)（只有(you)外(wai)徑(jing)、壁(bi)厚兩個系(xi)(xi)列(lie)），而現行(xing)壓力管(guan)道設計用鋼管(guan)的(de)行(xing)業標準(zhun)除了公(gong)稱直(zhi)徑(jing)外(wai)，外(wai)徑(jing)系(xi)(xi)列(lie)、壁(bi)厚系(xi)(xi)列(lie)不完全相同。

  公(gong)稱(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)是(shi)用(yong)以表示管(guan)(guan)道系統中除用(yong)外徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)表示的(de)(de)(de)組成件(jian)(jian)以外的(de)(de)(de)所有組成件(jian)(jian)通(tong)(tong)用(yong)的(de)(de)(de)一(yi)個(ge)尺(chi)寸(cun)數字(zi)。在一(yi)般情(qing)況下，是(shi)一(yi)個(ge)完整的(de)(de)(de)數字(zi)，與組成件(jian)(jian)的(de)(de)(de)真實(shi)尺(chi)寸(cun)接近，但(dan)不相等。國際上通(tong)(tong)常把鋼管(guan)(guan)的(de)(de)(de)公(gong)稱(cheng)(cheng)(cheng)尺(chi)寸(cun)稱(cheng)(cheng)(cheng)為(wei)(wei)公(gong)稱(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)，而(er)(er)不稱(cheng)(cheng)(cheng)為(wei)(wei)公(gong)稱(cheng)(cheng)(cheng)通(tong)(tong)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)，主要是(shi)因為(wei)(wei)對于(yu)直(zhi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)大于(yu)或(huo)等于(yu)350mm（14in）的(de)(de)(de)管(guan)(guan)子的(de)(de)(de)公(gong)稱(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)是(shi)指其外徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)而(er)(er)不是(shi)其內徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)。對于(yu)螺紋連接的(de)(de)(de)管(guan)(guan)子及(ji)管(guan)(guan)件(jian)(jian)，因其內徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)往(wang)往(wang)與公(gong)稱(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)接近，也可稱(cheng)(cheng)(cheng)為(wei)(wei)公(gong)稱(cheng)(cheng)(cheng)通(tong)(tong)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)。