我(wo)國目(mu)前(qian)還沒有壓力管道設計(ji)(ji)用(yong)鋼(gang)管尺(chi)寸系(xi)列(lie)(lie)（公(gong)(gong)稱直(zhi)徑、外徑、壁(bi)厚(hou)）的國家標(biao)準，只有鋼(gang)管的生(sheng)產標(biao)準尺(chi)寸系(xi)列(lie)(lie)（只有外徑、壁(bi)厚(hou)兩個系(xi)列(lie)(lie)），而現行(xing)壓力管道設計(ji)(ji)用(yong)鋼(gang)管的行(xing)業標(biao)準除(chu)了公(gong)(gong)稱直(zhi)徑外，外徑系(xi)列(lie)(lie)、壁(bi)厚(hou)系(xi)列(lie)(lie)不完全相同。

  公(gong)稱(cheng)(cheng)直(zhi)(zhi)(zhi)徑(jing)(jing)是(shi)用(yong)以表示管(guan)道系統中除用(yong)外(wai)徑(jing)(jing)表示的(de)組成件(jian)(jian)以外(wai)的(de)所有(you)組成件(jian)(jian)通(tong)(tong)(tong)用(yong)的(de)一(yi)個尺(chi)寸(cun)數字(zi)。在(zai)一(yi)般情(qing)況下(xia)，是(shi)一(yi)個完整的(de)數字(zi)，與組成件(jian)(jian)的(de)真實尺(chi)寸(cun)接(jie)(jie)近，但不相等。國(guo)際上通(tong)(tong)(tong)常把鋼管(guan)的(de)公(gong)稱(cheng)(cheng)尺(chi)寸(cun)稱(cheng)(cheng)為(wei)公(gong)稱(cheng)(cheng)直(zhi)(zhi)(zhi)徑(jing)(jing)，而不稱(cheng)(cheng)為(wei)公(gong)稱(cheng)(cheng)通(tong)(tong)(tong)徑(jing)(jing)，主要(yao)是(shi)因為(wei)對(dui)于(yu)(yu)直(zhi)(zhi)(zhi)徑(jing)(jing)大于(yu)(yu)或等于(yu)(yu)350mm（14in）的(de)管(guan)子的(de)公(gong)稱(cheng)(cheng)直(zhi)(zhi)(zhi)徑(jing)(jing)是(shi)指(zhi)其外(wai)徑(jing)(jing)而不是(shi)其內(nei)徑(jing)(jing)。對(dui)于(yu)(yu)螺紋(wen)連(lian)接(jie)(jie)的(de)管(guan)子及管(guan)件(jian)(jian)，因其內(nei)徑(jing)(jing)往往與公(gong)稱(cheng)(cheng)直(zhi)(zhi)(zhi)徑(jing)(jing)接(jie)(jie)近，也可稱(cheng)(cheng)為(wei)公(gong)稱(cheng)(cheng)通(tong)(tong)(tong)徑(jing)(jing)。