Trimmed / Small angle elbow welding difficulties

[nikolastrojman]

Hi!

I would like to hear your thoughts/opinions on the subject matter stated in the title. Do you know what is the minimum angle of an elbow for a given NPS of pipe acceptable by the welder/pipe fitter to be used on site?

We are currently designing piping route on a sleeper way located on a sloppy terrain which sometimes requires to use trimmed/small angle elbows (i.e. 12° or 8°).

On the other hand, the client insists on avoiding this kind of elbows because it requires a lot of cutting/welding effort on site and it is also more expensive and time-consuming.

The code of design/construction of the piping in this project is ASME B31.3, so may question is also is there an angle in the code which defines a limit for using trimmed elbows?

 

[pennpiper]

nikolastrojman,
There are three ways to make a change in direction for a pipeline.
- Fitting
- Miter
- Bend
All of these are allowed in the B31.3 Code

- As you have already found with the Fitting you reach a point where the angle and the trimmed fitting leaves you with too little material for the proper weld.

- If you consider using a "Miter" weld for this application you do not have the problem of destroying an expensive fitting for one change in direction. Why, you can make small changes in direction and you end up with only one weld and to NDE.

- With the Bend you do not have any of the problems with either the Fitting method or the Miter method for the change in direction. No cutting of the pipe, no cutting on a fitting and no welding. Just heat the pipe to the proper temperature to bend the pipe and let it cool in angle.

 

[LittleInch]

Officially in B 31.3 a miter bend below 3 degrees doesn't need any calculations.

There are sections in B 31.3 which deals with the impact of a miter bend (304.2 & 306.3), type of fluid, design pressure at different angles etc. At 8-12 degrees it could easily be you best option.

However for bends less than about 15 degrees you could just cold bend the pipe to some agreeable radius ( say 20 or 40D) and do the wall thinning calculations as per the code.

What is practical and suitable depends on how many of these bends you have, size and wt of the pipes and where you can get the bending done.

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

 

[nikolastrojman]

Tnx for the help. I also think that the best way to tackle this problem is to bend pipes on site, but the problem is that we are dealing here with pipes of NPS 6" and 12" so I'm afraid that these piping sizes are maybe difficult to bend. I thought that maybe miter bends can be of help in this situation.

I would also like to have a sort of table with minimum elbow angle specified for the different pipe sizes which are acceptable for welding (i.e. for NPS 2" minimum angle is 22.5° or maybe even bigger).

 

[LittleInch]

Six and twelve inch pipes should be easy to bend, but you do need the right equipment and experience.

Depends how many you have, but it may be best to send a set of pipes to a fab shop and have them bend a bunch of them rather than hire a pipe bender for a few bends.

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