Standard elbows in Crane 1

[Will Qin]

I was confused by the resistance coefficients in Crane.
For standard elbows K=30ft while K=20ft(r/d=1) for flanged or butt-welding 90° elbows.
There is no any note about standard elbows in Crane.
Why there is big difference between standard elbows and others? and what's standard elbow?
Thanks in advance.

 

[casflo]

I don´t know what the Crane Tp-410 says in its last edition about your question, but in the 2010 edition, see the pages 2-7 and 2-8 that can clarify your doubts.

 

[RVAmeche]

Look in Appendix A - a "standard" elbow is a threaded/socket weld, tight radius elbow.

For flanged/welded 90 elbows, such as 1.5R "long radius" elbows typically seen in piping, there's a separate formula (14*fT).

 

[Will Qin]

Thanks casflo and RVAmeche.
I cannot find the definition about standard elbow in Crane Tp-410. Standard elbow is flanged in Figure 2-8, but from picture about standard elbows (see A-30) it is threaded/socket.
Because of the big difference (K=30ft or 20ft), I'd like to make it clear. Thanks.

 

[Will Qin]

I was also confused about K value in Perry's chemical engineer handbook.
K =0.75 for 90° standard elbow (see table 6-4 in Perry's handbook) and there is no definition about standard elbow as Crane TP410.
And K=0.93 for 90° standard-threaded elbow and 0.32 for 90° welded elbow in API 521(see table 9).
What makes the difference? Thanks.

 

[Latexman]

Standard elbows are geometrically dissimilar per Fig. 2-8. Roughly, standard elbows are r/d ~ 1.

I’m pretty sure a threaded joint has more pressure drop than a flanged joint, which has more pressure drop than a butt welded joint.

Good Luck,
Latexman
Pats' Pub's Proprietor

 

[Will Qin]

Thanks Latexman.
K=30ft for 90° standard elbow in many handbooks. There is no definition about 90° standard elbow
and joint type is not classified in these handbooks.
I'm also sure threaded joint has more pressure drop than flanged/butt welded joint.
But all the information got from these handbooks confused me.

 

[RVAmeche]

Note there's a difference between the "K" resistance method and the equivalent length method.

An elbow having equivalent length of 30 ft is not the same thing as K = 1 in a different reference.

 

[Will Qin]

Thanks RVAmeche.

From Table 3-2 Equivalent Length =30 for 90° standard elbow.

There is no definition about standard elbow.

Does that mean equivalent length =30 for 90° standard elbow no mater it is threaded joint or flanged/butt welded joint?

It is not consistent with Crane TP-410.

 

[RVAmeche]

From that table, I would call socket/threaded, or 1.0R short radius elbows, "standard".

In most cases for welded piping systems > 2", long radius elbows are used unless there's a routing issue requiring short radius.

What source is that? It seems odd. Cameron Hydraulic Data has both K factors and and equivalent length table. In the equivalent length table there are multiple values listed by pipe size.

For example, a "standard" elbow ranges from 1.55 to 32.8 ft from 1/2" to 14" pipe size. A long radius elbow varies from 0.83 to 17.5 ft across the same range.

 

[Will Qin]

RVAmeche, thanks for you information, You are very helpful I appreciate it!

 

[jari001]

@RVAmeche
I Googled the table title and Google Books shows this table on page 63 of "Transport Phenomena and Unit Operations A combined Approach" by Richard G. Griskey. Hopefully the OP will confirm/deny.

 

[Will Qin]

@jari001
Thanks. What is your idea about standard elbow in that table from "Transport Phenomena and Unit Operations A combined Approach"?