我國目前還沒(mei)有(you)(you)壓(ya)力管(guan)(guan)道(dao)設計用鋼(gang)管(guan)(guan)尺寸系(xi)列（公稱(cheng)直(zhi)徑、外(wai)徑、壁厚(hou)）的(de)國家(jia)標(biao)準(zhun)，只(zhi)有(you)(you)鋼(gang)管(guan)(guan)的(de)生產標(biao)準(zhun)尺寸系(xi)列（只(zhi)有(you)(you)外(wai)徑、壁厚(hou)兩個系(xi)列），而現行壓(ya)力管(guan)(guan)道(dao)設計用鋼(gang)管(guan)(guan)的(de)行業標(biao)準(zhun)除了(le)公稱(cheng)直(zhi)徑外(wai)，外(wai)徑系(xi)列、壁厚(hou)系(xi)列不完全相(xiang)同。

  公(gong)(gong)稱(cheng)(cheng)直徑(jing)(jing)是(shi)(shi)用以(yi)表(biao)示(shi)管(guan)(guan)道系統(tong)中除(chu)用外(wai)(wai)徑(jing)(jing)表(biao)示(shi)的(de)(de)(de)組(zu)成(cheng)件(jian)(jian)以(yi)外(wai)(wai)的(de)(de)(de)所有組(zu)成(cheng)件(jian)(jian)通用的(de)(de)(de)一個(ge)尺(chi)寸(cun)數字(zi)。在一般(ban)情(qing)況下(xia)，是(shi)(shi)一個(ge)完整(zheng)的(de)(de)(de)數字(zi)，與(yu)組(zu)成(cheng)件(jian)(jian)的(de)(de)(de)真實尺(chi)寸(cun)接(jie)近，但不(bu)相等。國際(ji)上通常把鋼管(guan)(guan)的(de)(de)(de)公(gong)(gong)稱(cheng)(cheng)尺(chi)寸(cun)稱(cheng)(cheng)為公(gong)(gong)稱(cheng)(cheng)直徑(jing)(jing)，而不(bu)稱(cheng)(cheng)為公(gong)(gong)稱(cheng)(cheng)通徑(jing)(jing)，主要是(shi)(shi)因為對(dui)于(yu)直徑(jing)(jing)大于(yu)或等于(yu)350mm（14in）的(de)(de)(de)管(guan)(guan)子的(de)(de)(de)公(gong)(gong)稱(cheng)(cheng)直徑(jing)(jing)是(shi)(shi)指其外(wai)(wai)徑(jing)(jing)而不(bu)是(shi)(shi)其內(nei)徑(jing)(jing)。對(dui)于(yu)螺紋連(lian)接(jie)的(de)(de)(de)管(guan)(guan)子及(ji)管(guan)(guan)件(jian)(jian)，因其內(nei)徑(jing)(jing)往(wang)往(wang)與(yu)公(gong)(gong)稱(cheng)(cheng)直徑(jing)(jing)接(jie)近，也可稱(cheng)(cheng)為公(gong)(gong)稱(cheng)(cheng)通徑(jing)(jing)。