我國目(mu)前還沒有(you)壓力(li)管(guan)道設計(ji)用鋼(gang)管(guan)尺(chi)寸(cun)系(xi)列（公(gong)(gong)稱直(zhi)徑(jing)、外(wai)(wai)徑(jing)、壁厚(hou)）的國家標(biao)(biao)準(zhun)，只有(you)鋼(gang)管(guan)的生產標(biao)(biao)準(zhun)尺(chi)寸(cun)系(xi)列（只有(you)外(wai)(wai)徑(jing)、壁厚(hou)兩(liang)個系(xi)列），而現行壓力(li)管(guan)道設計(ji)用鋼(gang)管(guan)的行業(ye)標(biao)(biao)準(zhun)除了公(gong)(gong)稱直(zhi)徑(jing)外(wai)(wai)，外(wai)(wai)徑(jing)系(xi)列、壁厚(hou)系(xi)列不(bu)完全相同。

  公(gong)稱(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)(jing)是(shi)用(yong)以(yi)表(biao)示(shi)管(guan)道系(xi)統中除用(yong)外(wai)徑(jing)(jing)(jing)(jing)(jing)表(biao)示(shi)的(de)組(zu)成(cheng)件(jian)以(yi)外(wai)的(de)所有組(zu)成(cheng)件(jian)通(tong)(tong)用(yong)的(de)一(yi)個尺寸數(shu)字。在一(yi)般情況下，是(shi)一(yi)個完整的(de)數(shu)字，與組(zu)成(cheng)件(jian)的(de)真實尺寸接近(jin)，但不(bu)相等。國際上通(tong)(tong)常(chang)把鋼管(guan)的(de)公(gong)稱(cheng)(cheng)(cheng)尺寸稱(cheng)(cheng)(cheng)為公(gong)稱(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)(jing)，而不(bu)稱(cheng)(cheng)(cheng)為公(gong)稱(cheng)(cheng)(cheng)通(tong)(tong)徑(jing)(jing)(jing)(jing)(jing)，主要是(shi)因為對(dui)于(yu)(yu)直(zhi)徑(jing)(jing)(jing)(jing)(jing)大(da)于(yu)(yu)或等于(yu)(yu)350mm（14in）的(de)管(guan)子的(de)公(gong)稱(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)(jing)是(shi)指(zhi)其外(wai)徑(jing)(jing)(jing)(jing)(jing)而不(bu)是(shi)其內(nei)徑(jing)(jing)(jing)(jing)(jing)。對(dui)于(yu)(yu)螺紋(wen)連(lian)接的(de)管(guan)子及管(guan)件(jian)，因其內(nei)徑(jing)(jing)(jing)(jing)(jing)往往與公(gong)稱(cheng)(cheng)(cheng)直(zhi)徑(jing)(jing)(jing)(jing)(jing)接近(jin)，也可稱(cheng)(cheng)(cheng)為公(gong)稱(cheng)(cheng)(cheng)通(tong)(tong)徑(jing)(jing)(jing)(jing)(jing)。