我國(guo)目前還沒有(you)壓力管(guan)道(dao)設(she)計(ji)用鋼(gang)(gang)管(guan)尺(chi)(chi)寸(cun)系(xi)列（公稱(cheng)(cheng)直徑(jing)、外(wai)(wai)徑(jing)、壁厚(hou)）的國(guo)家標準(zhun)，只有(you)鋼(gang)(gang)管(guan)的生產(chan)標準(zhun)尺(chi)(chi)寸(cun)系(xi)列（只有(you)外(wai)(wai)徑(jing)、壁厚(hou)兩個(ge)系(xi)列），而現行(xing)壓力管(guan)道(dao)設(she)計(ji)用鋼(gang)(gang)管(guan)的行(xing)業(ye)標準(zhun)除了公稱(cheng)(cheng)直徑(jing)外(wai)(wai)，外(wai)(wai)徑(jing)系(xi)列、壁厚(hou)系(xi)列不(bu)完全相(xiang)同。

  公(gong)(gong)稱(cheng)(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)是(shi)(shi)用以表示管道系統中除用外(wai)徑(jing)(jing)(jing)(jing)表示的(de)(de)(de)組(zu)成(cheng)件以外(wai)的(de)(de)(de)所有(you)組(zu)成(cheng)件通(tong)用的(de)(de)(de)一(yi)個尺(chi)寸數字。在一(yi)般情況下(xia)，是(shi)(shi)一(yi)個完整的(de)(de)(de)數字，與組(zu)成(cheng)件的(de)(de)(de)真實尺(chi)寸接近(jin)，但不(bu)(bu)相等。國際上通(tong)常把鋼管的(de)(de)(de)公(gong)(gong)稱(cheng)(cheng)(cheng)(cheng)尺(chi)寸稱(cheng)(cheng)(cheng)(cheng)為公(gong)(gong)稱(cheng)(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)，而不(bu)(bu)稱(cheng)(cheng)(cheng)(cheng)為公(gong)(gong)稱(cheng)(cheng)(cheng)(cheng)通(tong)徑(jing)(jing)(jing)(jing)，主要是(shi)(shi)因為對于(yu)直(zhi)徑(jing)(jing)(jing)(jing)大于(yu)或等于(yu)350mm（14in）的(de)(de)(de)管子(zi)的(de)(de)(de)公(gong)(gong)稱(cheng)(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)是(shi)(shi)指其(qi)外(wai)徑(jing)(jing)(jing)(jing)而不(bu)(bu)是(shi)(shi)其(qi)內徑(jing)(jing)(jing)(jing)。對于(yu)螺紋連接的(de)(de)(de)管子(zi)及管件，因其(qi)內徑(jing)(jing)(jing)(jing)往往與公(gong)(gong)稱(cheng)(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)接近(jin)，也可稱(cheng)(cheng)(cheng)(cheng)為公(gong)(gong)稱(cheng)(cheng)(cheng)(cheng)通(tong)徑(jing)(jing)(jing)(jing)。