法蘭接頭是由法蘭、密封墊片(pian)及連接螺栓三種元件組成的一個承壓管道連接件。在法蘭密封接頭中，墊片是最主要的密封元件。對于非金屬墊片來說，法蘭接頭的密封是通過擰緊螺栓，使法蘭與墊片接觸表面及其墊片內部造成較大的壓緊應力，從而一方面使墊片表面與法蘭表面緊密貼合以填滿法蘭表面的微間隙，另一方面減小墊片材料的孔隙率，即減小被密封流體的泄漏通道，從而實現法蘭接頭的密封。由于任何制造或加工方法都不可能形成絕對光滑的理想表面，也不可能實現密封面間的完全嵌合以及密封件本身孔隙的完全阻塞，所以在相互接觸的密封面間和密封墊片內部總是存在著微小的間隙或通道。因而，對墊片密封來說，泄漏總是不可避免的。當介質以一定的壓力通過螺栓法蘭連接時，總會在密封點處出現泄漏。

  法蘭接頭的密封(feng)失效形式主要(yao)表現為泄(xie)漏。泄(xie)漏輕則造成能源(yuan)、原材料的大量(liang)浪(lang)費(fei)，重則導致(zhi)設備報廢、停工停產、人員傷亡和嚴重的環境污染。隨著現代石油、化(hua)工、原子(zi)能、航(hang)天及深(shen)海技術(shu)的迅速發展，對管(guan)道(dao)及其裝置的密封(feng)提(ti)出了更(geng)嚴格的要(yao)求，因(yin)而密封(feng)墊片(pian)的地(di)位更(geng)加(jia)重要(yao)。

  在(zai)墊(dian)片密(mi)封(feng)的(de)(de)法蘭(lan)接頭中，雖(sui)然泄漏(lou)無(wu)法避免(mian)，但可以控制(zhi)在(zai)一定的(de)(de)范圍內。墊(dian)片密(mi)封(feng)的(de)(de)可靠(kao)性與連接結構(gou)的(de)(de)形式(shi)、介質(zhi)特(te)性、工況(kuang)條件(jian)等諸多因素有關，而且最主要的(de)(de)是與所采用的(de)(de)密(mi)封(feng)墊(dian)片材料和其結構(gou)有關。影響墊(dian)片密(mi)封(feng)的(de)(de)因素很(hen)多，至今(jin)還是一個未能(neng)定量的(de)(de)問題(ti)，因此研究墊(dian)片密(mi)封(feng)的(de)(de)工作，至今(jin)仍然是工業界(jie)普遍關注的(de)(de)問題(ti)。

  本篇就墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)基(ji)礎知識、墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)結(jie)(jie)構(gou)(gou)及(ji)其標準進行描述，共4章(zhang)組成，內(nei)容包(bao)括墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)的一般結(jie)(jie)構(gou)(gou)型(xing)式(shi)、種類、參數和(he)設(she)計選用(yong)；非(fei)金(jin)(jin)(jin)屬(shu)平墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)（含(han)(han)(han)非(fei)金(jin)(jin)(jin)屬(shu)軟墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)及(ji)聚四氟乙烯包(bao)覆墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)）；金(jin)(jin)(jin)屬(shu)復合(he)墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)（含(han)(han)(han)纏繞式(shi)墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)、金(jin)(jin)(jin)屬(shu)包(bao)覆墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)、金(jin)(jin)(jin)屬(shu)沖齒(chi)板柔性石墨復合(he)墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)、柔性石墨金(jin)(jin)(jin)屬(shu)波齒(chi)復合(he)墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)）及(ji)金(jin)(jin)(jin)屬(shu)墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)（含(han)(han)(han)金(jin)(jin)(jin)屬(shu)環形(xing)墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)、金(jin)(jin)(jin)屬(shu)齒(chi)形(xing)墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)片(pian)(pian)(pian)及(ji)R型(xing)、RX型(xing)及(ji)BX型(xing)專用(yong)自(zi)緊密(mi)封金(jin)(jin)(jin)屬(shu)環墊(dian)(dian)(dian)(dian)(dian)(dian)(dian)）等。