外徑表明代數學正（zhèng）當中有（yǒu）關直徑。通常也用繁體（tǐ）字d來表明。外徑和內徑是比較而言的. 就進行諸如關於一根焊管,外層的那一個更加最大圓的（de）有關直徑是外徑,管裏邊那一個圓的有關直徑（jìng）是（shì）內徑. 它的（de）外徑=內徑（jìng）+2*焊管的厚薄 就（jiù）是說關於（yú）兩個齊心圓,外徑是焊管大圓的有關直徑,內徑是焊管小圓的有關直徑. 外徑和內徑都進行（háng）所在有關直徑,可（kě）以各自又有特指.
The outer diameter represents the diameter in mathematics. The letter D is also commonly used. For example, in a welded pipe, the outer diameter of the largest circle is the outer diameter, and the inner diameter of the circle is the inner diameter. Its outer diameter = the inner diameter + 2* is two concentric circles, the outer diameter is the diameter of the larger circle of the welded pipe, and the inner diameter is the diameter of the smaller circle of the welded pipe. 見下文說下直縫焊管的（de）新式外徑（jìng）規（guī）範標準（zhǔn）形式參數進行介紹
Following is the introduction of the latest external diameter standard parameters of longitudinal welded pipe
DN600- ф 630mm
DN15- ф 22mm DN20- ф 27mm
DN25- ф 34mm DN32- ф 42mm
DN40- ф 48mm DN50- ф 60mm
DN65- ф 76 73 mm DN80- ф 89mm
DN100- ф 114mm DN125- ф 140mm
DN150- ф 168mm DN200- ф 219mm
DN250- ф 273mm DN300- ф 324mm
DN350- ф 360mm DN400- ф 406mm
DN450- ф 457mm DN500- ф 508mm
在這當中DN表明（míng）有名無實有關直徑（jìng）： DN是有（yǒu）名無實通徑，有名（míng）無實通徑(或叫有名無實有關（guān）直徑（jìng）),就是說多種管材（cái）與管路備件的（de）參加（jiā）標準。相同有（yǒu）名無實有關直徑的管（guǎn）材（cái）與管路備（bèi）件均能相互之間包括，具備貿（mào）易性.它並非真實情況重要性上的（de）彈道外徑或內徑，盡管其（qí）實測值跟彈道（dào）內徑較比好像或（huò）認為； ф表明外徑（jìng）。
Among them, DN denotes nominal diameter: DN is nominal diameter, nominal diameter (or nominal diameter), which is the general diameter of all kinds of pipes and pipeline accessories. Pipes and pipe accessories of the same nominal diameter can be interconnected and interchangeable. It is not the actual outside diameter or inside diameter of the pipeline, although its numerical value is close or equal to the inside diameter of the pipeline; indicates the outside diameter.
