我(wo)國目前還(huan)沒有壓力管(guan)道設(she)計用(yong)鋼管(guan)尺(chi)寸(cun)系(xi)列（公(gong)稱直徑、外徑、壁厚(hou)）的(de)國家標(biao)(biao)準(zhun)，只有鋼管(guan)的(de)生產標(biao)(biao)準(zhun)尺(chi)寸(cun)系(xi)列（只有外徑、壁厚(hou)兩個(ge)系(xi)列），而現行(xing)壓力管(guan)道設(she)計用(yong)鋼管(guan)的(de)行(xing)業標(biao)(biao)準(zhun)除了公(gong)稱直徑外，外徑系(xi)列、壁厚(hou)系(xi)列不完(wan)全相同(tong)。

  公(gong)(gong)稱(cheng)(cheng)(cheng)直徑(jing)(jing)是(shi)(shi)用以表示管(guan)道系統中(zhong)除用外徑(jing)(jing)表示的(de)組成(cheng)(cheng)件(jian)以外的(de)所有組成(cheng)(cheng)件(jian)通(tong)(tong)用的(de)一個尺(chi)寸數字。在一般情況下(xia)，是(shi)(shi)一個完整的(de)數字，與組成(cheng)(cheng)件(jian)的(de)真實尺(chi)寸接(jie)近(jin)，但不相(xiang)等(deng)。國際上通(tong)(tong)常(chang)把鋼管(guan)的(de)公(gong)(gong)稱(cheng)(cheng)(cheng)尺(chi)寸稱(cheng)(cheng)(cheng)為(wei)(wei)公(gong)(gong)稱(cheng)(cheng)(cheng)直徑(jing)(jing)，而(er)不稱(cheng)(cheng)(cheng)為(wei)(wei)公(gong)(gong)稱(cheng)(cheng)(cheng)通(tong)(tong)徑(jing)(jing)，主要是(shi)(shi)因(yin)為(wei)(wei)對(dui)于(yu)(yu)直徑(jing)(jing)大(da)于(yu)(yu)或等(deng)于(yu)(yu)350mm（14in）的(de)管(guan)子的(de)公(gong)(gong)稱(cheng)(cheng)(cheng)直徑(jing)(jing)是(shi)(shi)指(zhi)其外徑(jing)(jing)而(er)不是(shi)(shi)其內徑(jing)(jing)。對(dui)于(yu)(yu)螺紋連(lian)接(jie)的(de)管(guan)子及(ji)管(guan)件(jian)，因(yin)其內徑(jing)(jing)往(wang)往(wang)與公(gong)(gong)稱(cheng)(cheng)(cheng)直徑(jing)(jing)接(jie)近(jin)，也可稱(cheng)(cheng)(cheng)為(wei)(wei)公(gong)(gong)稱(cheng)(cheng)(cheng)通(tong)(tong)徑(jing)(jing)。