我(wo)國目前還沒有壓(ya)力管(guan)(guan)道(dao)設計(ji)用鋼(gang)管(guan)(guan)尺寸系(xi)列(lie)（公(gong)稱直徑、外(wai)徑、壁厚(hou)）的國家標準(zhun)，只(zhi)有鋼(gang)管(guan)(guan)的生(sheng)產(chan)標準(zhun)尺寸系(xi)列(lie)（只(zhi)有外(wai)徑、壁厚(hou)兩(liang)個系(xi)列(lie)），而(er)現行壓(ya)力管(guan)(guan)道(dao)設計(ji)用鋼(gang)管(guan)(guan)的行業(ye)標準(zhun)除了公(gong)稱直徑外(wai)，外(wai)徑系(xi)列(lie)、壁厚(hou)系(xi)列(lie)不完全相同。

  公(gong)(gong)(gong)稱(cheng)(cheng)(cheng)直(zhi)(zhi)(zhi)徑(jing)是(shi)用(yong)以表(biao)示管道系統中(zhong)除用(yong)外徑(jing)表(biao)示的(de)(de)(de)組成件(jian)以外的(de)(de)(de)所有組成件(jian)通用(yong)的(de)(de)(de)一(yi)個(ge)(ge)尺寸(cun)數(shu)字(zi)。在一(yi)般(ban)情況下(xia)，是(shi)一(yi)個(ge)(ge)完整的(de)(de)(de)數(shu)字(zi)，與組成件(jian)的(de)(de)(de)真(zhen)實尺寸(cun)接(jie)近，但不(bu)相等。國際上(shang)通常把鋼管的(de)(de)(de)公(gong)(gong)(gong)稱(cheng)(cheng)(cheng)尺寸(cun)稱(cheng)(cheng)(cheng)為(wei)公(gong)(gong)(gong)稱(cheng)(cheng)(cheng)直(zhi)(zhi)(zhi)徑(jing)，而不(bu)稱(cheng)(cheng)(cheng)為(wei)公(gong)(gong)(gong)稱(cheng)(cheng)(cheng)通徑(jing)，主要是(shi)因(yin)為(wei)對于直(zhi)(zhi)(zhi)徑(jing)大于或等于350mm（14in）的(de)(de)(de)管子(zi)的(de)(de)(de)公(gong)(gong)(gong)稱(cheng)(cheng)(cheng)直(zhi)(zhi)(zhi)徑(jing)是(shi)指其(qi)外徑(jing)而不(bu)是(shi)其(qi)內徑(jing)。對于螺紋連接(jie)的(de)(de)(de)管子(zi)及管件(jian)，因(yin)其(qi)內徑(jing)往往與公(gong)(gong)(gong)稱(cheng)(cheng)(cheng)直(zhi)(zhi)(zhi)徑(jing)接(jie)近，也可稱(cheng)(cheng)(cheng)為(wei)公(gong)(gong)(gong)稱(cheng)(cheng)(cheng)通徑(jing)。