Conditions and limit values of the L/D ratio for stainless steel t-pieces - YouTube

Do you know the L over D rule? Sure, you would  say. I'm working since ages in pharmaceutical  

engineering. The question itself is irritating  to me but are you aware about the details  

and the boundary conditions? I will shed some  light into the darkness and take you with me.

In one of our last videos we were talking about  branches in general. Today I would like to follow  

more an academic path considering that  issue. Talking about the L over D rule.  

And L over D means actually the length of a  branch in comparison to the diameter of the branch.

That's very simple. This principle  has first been mentioned in a FDA  

draft in 1972, where this is being considered as  a guidance for dead room free or hygienic design.  

However since then it's been mentioned in numerous  other regulations like world health organization  

papers like the ISPE papers like ASME BPE as well. There are always different numbers been  

given. So some papers talk about 6D some about 2D  some about 3D even 1.5D. So how is that possible that  

such deviations are being mentioned in official  regulations and paperwork? The answer  

is actually pretty simple. People take different  boundary conditions. So some measure really from  

the edge of the main tubing here some measure from  the center of the main tubing so that's something  

that you always have to know while talking about  these values. And the latest ASME BPE release  

it's been given 2D measured from the edge  of the main tube here. And that's I would say  

nowadays the standard. However if you're  considering you're adding a valve  

on top here that would certainly then need  to be measured to the closing edge really  

of the valve as you see in the graphics. But how  about now standard parts such as that one here.  

So here we're considering a one inch  standard equal t-piece and if you measure  

the L over D in this case and consider you are  closing it you probably have this version with a  

clamp and you're putting a blank on top then this  t-piece is even out of spec. So if you have that in  

your system and you're closing it it's considered  a dead leg. As the value L over D is here  

2.5 and not below or equal too. If you're getting  smaller with a diameter such as that one here  

and you're considering a 3/8 of an inch branched  t-piece in this case the value L over D would be  

roughly 7. So totally out of spec. So everything  which is bigger than one inch should be okay  

but everything smaller and one inch itself should  be not okay. However if you're looking towards  

shorter t-pieces or t-pieces like this one with a  clamp on top, you can consider this being pretty  

hygienic when you put a blank on top. This is a  one inch t-piece in this case but let's say coming  

to the edge at roughly half inch and everything  below half inch is also out of spec. So that's  

what we need to consider while talking about  dead room free conditions in standard t-pieces.

That's what I wanted to say and I hope I could  shed some light into the darkness of the history  

of such terms. You basically need to know what  you're talking about. But if you're now asking  

so what about my system? My system itself that  I'm working at or that I'm designing? How is it  

with regard to a WFI-system for example to  an API manufacturing system or what role does  

the flow velocity of my liquid play in that game?  How does it influence the cleanability and  

what are the boundary conditions then? In order to  unveil that I would like to welcome you in one of  

our next videos. So please send us your questions  we would be glad to talk about that with you and  

again take care stay healthy and  see you in one of our next videos. Bye!