1、1976 CFR 212规范为6D,指主管道中心到支管阀门中心的距离应小于支管直径的6倍。
4、ASME BPE为2D,指主管内壁到阀门密封点的长度应小于支管直径的2倍。
5、WHO 建议为1.5D,应避免大于分支管径1.5倍的盲管。6、2010版中国GMP指南:
为了避免将来造成混乱,本指南建议死角长度从管的外壁来考虑。我们建议避免对于最大可允许的死角做硬性规定。
TheTruth about the 3D/6D Rule
The installation of pipework leads to recurrent discussions about how deadlegs can be prevented and about the maximum length outgoing pipes/pipe tees mayhave for the sensor. There is less throughflow in dead legs. Hence, it isharder to clean them and during thermal sanitisation it takes longer until these'branches' have also reached the required temperature. In calls fortender and tests the 3D/6D rule is often used for the specification, but notalways in the completely correct way. In order to further explain this, pleaseread following the history of this rule.
But how does it work in practice? Is one rule more binding or better thanthe others?
但在实践中要怎么应用呢?是否有一个规则比其它的更具有法规效力呢?
One has to know that the 3D and the 6D rule cannot be compared directlybecause they have a different reference point. In the case of the 3D rule thelength L of the dead leg is measured from the pipe wall of the main pipe andput in relation to the diameter of the parting pipe. The initial 6D rulemeasures the length L beginning in the centre of the main pipe.
我们必须知道3D和6D规则并不能直接进行比较,因为它们有不同的测量点。采用3D规则时,死管的长度是从主管的管壁开始测量的,与支管的直径进行比较;而6D规则是从主管的中心线开始测量的。零死角阀门
现在,零死角阀门(0D 阀门)已有生产,当然成本会更高一些。各个厂商所设计的零死角阀门可能会有点不一样。下图是一种类型的零死角阀门,红色线为主管流向,粉色线为支管流向,阀门密封点直接在主管管壁上(即L=0D)。
建议:
1、在使用点采用零死角阀门,减少使用点形成菌膜、污染的风险。
2、管道设计应该基于风险的原则进行评估采用哪种方式防止死角造成微生物污染的风险,如:在纯蒸汽管道的非使用端,可能6D原则就足够了。
3、如果是不可避免的情况下,实行特别的规定进行说明来防止死角是非常重要的。考虑的因素包括操作温度、流速和使用频率(如果死角是一个使用点)。
4、应该认识到如果不经常冲洗或消毒,任何系统都能会存在死角。
联系客服