Weld 2 elbows 90 degree

[a7med217]

what is the minimum allowed distance to assemble 2 elbows 90 degree (bell and spigot), ductile iron, 12", underground, used for fire system, working pressure 10 bar.

 

[LittleInch]

Next to each other.

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[zdas04]

For a long time I had a structure that I'd cut out of a pipe with five 90's welded together. Just cutting that mess out reduced the pressure drop from the wellhead by almost 10 psi.

Two 90's out of plane create a swirl that is still persistent after a mile of Pipe (testing by Elizabeth Laws in the UK in the early 1990's to understand how to eliminate swirl in gas measurement, led to the development of the Laws Plate that worked great but cost $10k each). Dr. Laws found that adding a 5D pup between the 90's prevented the creation of the persistent swirl. Swirl in a flow increases the energy loss per unit length and should be avoided where practical. I've generally found adding a 30 inch pup to a 6-inch line could often be made "practical" (sometimes it just can't be and I accept a higher dP).

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

I fully agree with zdas04 on that - the absolute minimum is zero, but a practical one is more like 5D.

There is though a discrepancy in the title of this post "WELD 2 elbows..." and the text "ductile Iron", "Bell and Spigot" implies push fit connections, not welded.

For a Fire Water system it might not matter so much as the systems Zdas04 was referring to.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.