interpreting bend angles on Isometrics and inspecting them

[QCJT]

Hello

Could someone help me to understand how do I interpret these bend angles and the projections under them? What does fitter actually do with these figures when laying this line? And from inspection point of view - how can I check in field that this bend angle is actually correct?
Another question is about the elbows. I have seen in field that when they are fabricating the elbows for such bends (with 80 or 88.3 degree) they cut one end of the elbow to make it shorter and thus reduce the angle. But how can I actually check if they achieved this angle? Luckily, I have an app on my phone that shows me the angle when I lay it on a surface but I don't want to rely on that app only. Any conventional methods?

Any references for more reading are also welcome.

Thanks
JT

 

[europipe]

Why do You want to know the exact angle ?, when the pipe is connecting A to B then it's ok.
when fabricating this elbow they use a levelinstument with angle adjustment, then they can draw the right cut angle on the elbow, when it is installed it's harder to determine the angle.

 

[LittleInch]

The solid black lines represent horizontal level, i.e. you could attach a string and generate a horizontal level then measure either 1516 vertically or 781 vertically respectively.

How anyone can accurately cut 1.7 degrees off an elbow is having a laugh. I would think they would build this from either end as 80 degrees is a bit more of a chunk and then just mark of on the elbow where it needs a bit of trimming.

all depends on the size of pipe - what is this? 450?

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

 

[11echo]

My experience when your dealing with pipe fabrication your shooting for around 0.125" accuracy, and that's "tight"! You need to remember (or learn) that most pipe construction is done out in the field, not in some machine shop where you have the luxury of chasing everything to a the thousandths of an inch. I think europipe explained it pretty well ...You connect one end of the pipe at point "A" and run it per the drawings that layouts the routing, and ending at point "B" ...end of story.

 

[racookpe1978]

Well, in power industries (steam piping) they DO inspect fitups for butt welds looking for 1/8 inch gaps around the periphery of the elbows - even those at slightly odd-angles.

But. If the root is a little below 1/8 (0.125) at the botton and slightly larger than 0.125 at the top, it not always certain the weld inspector would require re-grinding the root. (Nukes a different story). But pipe angles for drainage and for freeze and water hammer prevention DO matter, and I DO inspect with a digital angle finder for oil drain pipes, oil control and supply pipes, steam pipes, condensate, etc. Right-left angles not so much, because those you can normally "get the vertical fitup right, then rotate it about the vertical face of the lower elbow to fit under the next vertical elbow."

A good engineer can make even a bad fitter's job acceptable.
A good welder can make any fitter look good.
A good fitter can make even a bad welder look good.
A great grinder can make anybody look good.

 

[Ziggypump]

My experience with isometrics, as I draw them, is for clarification of the system. Look at the floor plans and compare them with the isometric, and that should help a great deal in determining the angles you need.

I create isometrics for hydronic and domestic water systems, so my angles are at 45 or 90 degrees, with a 22.5 rarely used. Using isometrics to determine angles should not work, as depending on the view point, a 90 degree angle is drawn at 60 or 30 degrees. If the drawings want something that isn't a standard angle, I would think that drawings should call this out.

Is there a call for lots of weird angles when dealing with fluids?

 

[europipe]

Ziggy, ever involved with conveying systems ?

 

[Ziggypump]

Nope, that's why I'm asking on the elbow deflections.

 

[saplanti]

The first think you need to do is ask for the piping specification. It must include all the requirements.

In case you produce the elbow by cutting the standard elbow, you will realize that the cut geometry is not going to be circular any more.

Welding a non-circular to a circular has some consequences in welding, check the code requirements for welding tolerances. Some codes allow large tolerances while other codes don't.

In case, as manufacturer, you are not sure about geometry the problems will accumulate. The Murphy's rule.

There were some spreadsheets or acrobat files on the internet that show how to calculate unknown from other dimensions in the pipe runs which have bends. You may be able to calculate the angle (if this is the concern) from one bend to another. If you need this spreadsheet I might be able to find mine.

 

[DekDee]

QCJT,
Are you new to this game ? - seems like you are getting overly concerned with something you shouldn't be.
As europipe has stated the only thing you worry about are points A & B - how the fabricator gets between those two points is not your concern.
When you get to the "tie- in" points at A & B - that is where you earn your money.
If the angles given on the isometric have not been fully complied with then there is a strong possibility that the piping will need mechanical means to pull it in to line with the equipment or piping it ties in to.
If it requires mechanical means to bring it in to line - bring it to the attention of the piping designer.
They are the ones who ultimately sign off on the system - not the inspector.
Cheers,
DD

 

[Gator]

"In case you produce the elbow by cutting the standard elbow, you will realize that the cut geometry is not going to be circular any more."

That's true if the person doing the cutting doesn't know what they're doing.

 

[europipe]

Yes Gator, You are right, put a clamp on the right place.

 

[KevinNZ]

The cut elbows are there to put slope into the lines. Measure the angle of the pipe to check the piping is meeting the design requirements. No need to check the elbow directly.

 

[powerbouy]

I think you can go with what europipe said, more important is clashfree pipe from point A to point B as per isometrics and the required slope has been given to the pipe.

 

[racookpe1978]

That required slope should be explicitly defined on the iso as a slope (or as a delta height from end workpoint to end workpoint, not implied by the bend angle of the end elbows. The fitter will cut the elbows as needed to fit the welds at both ends of the elbows to form the required slope.