Engineering vs. QA

By gsi

Date 11-17-2005 18:22

Our detailing department recently approached me with a question regarding pipe fabrication of some chilled water line.
They were detailing a standard offset for the shop.
The problem was they were attempting to place a RFSO flange on a 45-degree elbow.
Because the flange did not slip over the pipe enough, I suggested they add small spool pieces of pipe to the run to allow the flange to fit properly.
Providing it did not cause any other problem with the run.
The detailer wanted to make the spool piece about 3” long.
I suggested if it was possible to make it at least 1-x dia or 2-x dia long if possible.
So today the engineer on the project confronted me.
He seamed to be very upset with the decision I had made.
I did ask him if the spool piece caused him some problem.
It apparently did not because he was more interested in how I got this information on the size of the spool piece.
I’m not sure I know were that information came from.
It was something I picked up in a pipe shop some years ago.
So my Question is.
Does any know were I may find some good engineering information that may address this issue in general?

By OSUtigger (**)

Date 11-17-2005 18:31

I am only making a shot in the dark here as I am not fully sure about the setup, but it sounds to me like you are using a rule of thumb concerning tubulent flow in a pipe and sudden contractions of diameter and cross-sections. If this is the case, any fluid dynamics book will reinforce your arguement, but if not disregard this message.

Sorry if I have misunderstood the problem.

gls

By gsi

Date 11-18-2005 12:53

Yes you are correct , it is a rule of thumb I've used in the past. But just not sure the reason for it. I feel that it is more of an appearance issue and the fact that the flange weld would have been right up against the butt joint. Thanks for your comments

By G.S.Crisi (****)

Date 11-18-2005 18:30

Back in my days of erector engineer I've been faced with the same problem a few times.
What we did was to file the flange inner circle maybe one millimeter or two, until it was possible to slip the 45° elbow in it.
So far, I've never heard that those pipings exploded or blew up.
In any case, I havn't anything against what gsi did.
Giovanni S. Crisi
Sao Paulo - Brazil

P.S. The rule of thumb is known also in Brazil and says that no nipple (short piece of pipe) should be shorter that one pipe diameter.
Reason? None, it's just one of those "magic numbers" or "numbers pulled off the air", as Americans say, that we engineers like to use.
Here in Brazil we say "numbers taken off the vest pocket"

By SA-200

Date 11-22-2005 03:33

Why didnt you just use a weld neck flange?

By G.S.Crisi (****)

Date 11-22-2005 12:09

Because the neck flange protrudes a certain length beyond the elbow welding end while the slip on flange does not, and the piping isometric didn't allow such a protrusion for some reason I don't remember now.
Giovanni S. Crisi