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sowhatso (Mechanical) (OP)
12 Feb 09 8:35
Dear All ,

This question is related to the welded steel pipes that will be used for water project , the sizes of the pipes are 3" , 4" ,  and 6" . In the shop drawings of the pipeline that have the three sizes of  pipes , the profiles are showing Standards bends  used for any change in direction , the standard bends are 22.5 deg , 45 deg , and 90 deg steel elbows . after excavating the trenches of the pipeline and laying the pipes for welding , it has be observed that some changing in direction will require diffrent angles , like 15 deg , 17 deg , 37 deg , etc . According to the technical spcification the maximum deflection in the horizontal line is 50mm and 6mm from the vertical grade.I know that the maximum allowed angle between two connceted pipes is 5 deg.


my question is : can we chamfer and cut both pipes edges to create the required angle with higher deflction rate .

The sizes of pipes that we have is small (3",4"a nd 6") can any one help me in how to fabricate mitered bends for the pipes or can we depnd on the standard bends and chamfering the pipe edjes to make the required angle of deflection ?????

The working pressure for the line is 16 bar and the steel pipe wall thickness is 5/32" , grade B.

 
MTPipeliner (Structural)
12 Feb 09 9:56
I think a better fix is to use a "segmentable" fitting.  A segmentable fitting will have a tighter tolerance on roundness and wall thickness through the body than a "normal".  This allows you to cut the fitting off to any angle you desire and still have an end that is round enough to weld to your pipe.  

If you already have your fittings purchased there is a chance they are round enough to be segmented.  I've seen "normal" 3 and 4 inch fittings successfully segmented.  I don't recall ever doing it with a 6", but if you've got a good fitting I think its possible.  
Apakrat (Civil/Environmental)
12 Feb 09 13:10

Might wanna consider altering a "fitting" to desired angle, by removal of segment of the "fitting" between each factory beveled end.

 

At 74th year working on IR-One2 PhD from UHK  - - -

MJCronin (Mechanical)
12 Feb 09 13:51
You also might wanna consider another field crew with a little more expertise in trenches...

Most of the time the trench is dug to suit the configuration of the piping....not the other way around

-MJC

   

Apakrat (Civil/Environmental)
12 Feb 09 14:35

For consideration, in addition to that of MJCronins' good advice.

Seldom will an "architect" or "catalog engineer" take into account the actual fitting angle change due to slope of piping!
  

At 74th year working on IR-One2 PhD from UHK  - - -

stanier (Mechanical)
12 Feb 09 17:17
You could always get a shop to hot or cold pull a bend to suit the desired angle.

Alternatively use two 90 degree elbows one orientated to the vertical direction and the other orientated to the angle you require.

Helpful Member!  racookpe1978 (Nuclear)
20 Feb 09 20:52
I'd really question your pipe foreman on this one:  He should immediately recommend NOT "beveling (mitering) straight pipe ends to make at simple 17 degree bend.

If he does recommend that, get a different foreman.  8<)

In field installations, this what I have done:

For a 17 degree butt welded turn, take your standard off-the-shelf 22.5 degree or 45 degree pipe elbow, lay it on a piece of plywood so the inlet end of the elbow is at the edge of the plywood.  Full scale (full size) draw the arc of the elbow's centerline bend radius (1.5 nominal diameter of each pipe for long radious elbows - you ARE using long-radius elbows, right?) and the required actual outlet bend angle: 17 degrees, 31, 28.5, or what ever.    

Where the two intersect (where the required angle intersects the centerline bend arc) is where you cut the elbow.  Finish your 37 degree weld prep on the newly cut elbow and you're ready to continue.   

Don't miter:  It creates bad welds, bad pressure drops, inflexible pipes, and future leaks.  The "bend" should be in the elbow, not the pipe.  

Outside contractor bending is possible, but you will likely find it too expensive, and too long for your scedule: it will take a long time for loading, shipping, unloading, bending, re-shipping.  Add in re-unloading crane delays, etc.  Front office contract delays.      

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