大口徑(jing)(jing)(jing)螺旋鋼管(guan)(guan)(guan)(guan)的(de)(de)(de)公(gong)(gong)稱(cheng)通(tong)(tong)徑(jing)(jing)(jing),又(you)稱(cheng)平(ping)均外(wai)徑(jing)(jing)(jing)。這是緣自金(jin)屬管(guan)(guan)(guan)(guan)的(de)(de)(de)管(guan)(guan)(guan)(guan)璧很(hen)薄,管(guan)(guan)(guan)(guan)外(wai)徑(jing)(jing)(jing)與管(guan)(guan)(guan)(guan)內徑(jing)(jing)(jing)相差無(wu)幾,所以取管(guan)(guan)(guan)(guan)的(de)(de)(de)外(wai)徑(jing)(jing)(jing)與管(guan)(guan)(guan)(guan)的(de)(de)(de)內徑(jing)(jing)(jing)之(zhi)平(ping)均值當作管(guan)(guan)(guan)(guan)徑(jing)(jing)(jing)稱(cheng)呼。DN是公(gong)(gong)稱(cheng)通(tong)(tong)徑(jing)(jing)(jing),公(gong)(gong)稱(cheng)通(tong)(tong)徑(jing)(jing)(jing)(或叫公(gong)(gong)稱(cheng)直徑(jing)(jing)(jing)),就(jiu)是各種管(guan)(guan)(guan)(guan)子與管(guan)(guan)(guan)(guan)路附(fu)件的(de)(de)(de)通(tong)(tong)用…