封(feng)(feng)頭(tou)(tou)(tou)是(shi)指用以(yi)封(feng)(feng)閉容器端部使其內外介質隔離(li)的(de)(de)元件，又稱端蓋(gai)。圓(yuan)(yuan)筒形(xing)(xing)(xing)(xing)(xing)容器的(de)(de)封(feng)(feng)頭(tou)(tou)(tou)一般都是(shi)迥轉殼(ke)體。按封(feng)(feng)頭(tou)(tou)(tou)表面(mian)的(de)(de)形(xing)(xing)(xing)(xing)(xing)狀(zhuang)(zhuang)可(ke)分為(wei)凸(tu)形(xing)(xing)(xing)(xing)(xing)、錐形(xing)(xing)(xing)(xing)(xing)、平板形(xing)(xing)(xing)(xing)(xing)和組合(he)形(xing)(xing)(xing)(xing)(xing)。凸(tu)形(xing)(xing)(xing)(xing)(xing)封(feng)(feng)頭(tou)(tou)(tou)是(shi)指外表面(mian)形(xing)(xing)(xing)(xing)(xing)狀(zhuang)(zhuang)為(wei)凸(tu)面(mian)的(de)(de)封(feng)(feng)頭(tou)(tou)(tou)，如半球形(xing)(xing)(xing)(xing)(xing)、橢圓(yuan)(yuan)形(xing)(xing)(xing)(xing)(xing)、碟形(xing)(xing)(xing)(xing)(xing)和無折(zhe)邊球形(xing)(xing)(xing)(xing)(xing)封(feng)(feng)頭(tou)(tou)(tou)等。有(you)的(de)(de)氣瓶采用凸(tu)面(mian)向內的(de)(de)組合(he)形(xing)(xing)(xing)(xing)(xing)底封(feng)(feng)頭(tou)(tou)(tou)，既可(ke)強度(du)，又能滿足安(an)然使用的(de)(de)需求。  

封頭(tou)(tou)(tou)是容(rong)器的一(yi)個部件，是以焊(han)接方式(shi)連(lian)接筒體。（如下(xia)圖）根據幾(ji)何形(xing)(xing)狀的不同，可分(fen)為球形(xing)(xing)、橢圓形(xing)(xing)、碟形(xing)(xing)、球冠形(xing)(xing)、錐殼和(he)平蓋等幾(ji)種，其中球形(xing)(xing)、橢圓形(xing)(xing)、碟形(xing)(xing)、球冠型封頭(tou)(tou)(tou)又統稱為凸形(xing)(xing)封頭(tou)(tou)(tou)。在焊(han)接上分(fen)為對焊(han)封頭(tou)(tou)(tou)，承(cheng)插焊(han)封頭(tou)(tou)(tou)。用(yong)于各種容(rong)器設(she)備，如儲罐(guan)、換熱器、塔(ta)、反應釜、鍋(guo)爐和(he)分(fen)離設(she)備等。材(cai)質有碳鋼（A3、20#、Q235、Q345B、16Mn等）、不銹鋼（304、321、304L、316、316L等）、合(he)金鋼（15Mo315CrMoV35CrMoV45CrMo）、鋁、鈦(tai)、銅(tong)、鎳及鎳合(he)金等。