Tightness and mechanics- Notion of tightness and associated measures

The sealing function is at the heart of current concerns to reduce emission levels (of gas or liquid into the atmosphere) during normal operation ("fugitive emissions"), as well as the risks of accidental leakage, for safety, environmental and economic reasons. In addition, considerations of durability and energy efficiency (especially for dynamic seals [BM 5 419] ) also play a part in sealing performance.

Leak tightness is the result of a set of interdependent and often multi-physical phenomena (geometric, mechanical, thermal, fluidic, physical, chemical, etc.). There is no universal leak measurement methodology, and the choice of a leak measurement technique will involve finding a compromise between the sensitivity of the test required, the properties of the element to be inspected (temperature resistance, chemical compatibility, mechanical resistance, etc.), the cost of the inspection and the time allocated for carrying it out. It is therefore important to be familiar with the different methodologies available, in order to select the technique best suited to the application. A professional certification issued by the COFREND attests to operators' skills and knowledge in carrying out non-destructive tests such as leak testing.

This article deals with current and standardized leak measurement methodologies, as well as some new ones under development. It complements article [BM 5 418] , which deals with sealing at static connections; "dynamic" seals, incorporating rod or shaft movement, are covered in articles [BM 5 419] and [BM 5 420] .

A table of acronyms, notations and symbols is...