俺来帮大家理解一下什么是velocity exempt materials： 1. 定义：（参见 http:///fileadmin/docs_pubs/doc%2013%2002%20e.pdf ） exempt materials are engineering alloys, which are exempt from any oxygen velocity limitations within defined limits of pressure, material thickness and oxygen purity. only those materials, which demonstrate combustion resistance, when subjected to particle impact and/or promoted ignition tests conducted in oxygen enriched atmospheres can be qualified as exempt. 2. velocity exempt materials = 允许免除氧气流速限制的管材 如果在系统设计压力的条件下，合金材料可以阻燃，就不需要对氧气流速有限制。这种材料就是velocity exempt materials 例子：不锈钢管或铜基合金管 （参考 http:///viewnews.jsp?newsid=4628 和 http:///view/29068a3567ec102de2bd895e.html ）
