Is it possible to have ASME rated elbows with non standard angles 3

[Greg80]

Hello

Is it possible to have ASME rated elbows with non standard angles like 25 Deg - 55 Deg - 75 Deg ... for 10 " diameter ?

 

[btrueblood]

Yes.

Now, for a more useful answer, please state which particular ASME standard you want them rated to -- ASME B31.1, B31.3, B31.9 ... ?

 

[Greg80]

B31.3

 

[btrueblood]

Fair enough, look in B31.3 for how you would qualify a part. I'm pretty sure for fittings you follow the same rules as for valves, and qualify by some combination of stress calculations, experimental stress analysis, and/or hydrotesting.

Assuming we are talking steel: You could make the elbow from fabricated (welded) sections, or have a shop bend pipe to form the angles you need. Flanges could be welded on, welding would need to be done by shop with certified welders. Typical fabricated hydrotest pressure for fabricated steel parts is 3x the rated working pressure. If you are talking thousands of these things, you could look into tooling up for castings...

Of all those possibilities, the simplest is to bend the pipe, and subsequently weld on whatever else you need. Per 306.2.1, "Pipe bends made per para's. 332.2.1 and 332.2.2, and verified for pressure design in accordance with para. 304.2.1 are suitable for the same service as the pipe from which it is made". Section 332 talks about allowable flattening of bent sections, and under what temperatures the bending should be done. Section 304 tells you how much wall thinning you are allowed. Bottom line, if the bend radius is large enough, you can bend any pipe you want thru as large an angle as you want...

Section 304 also lists methods for design analysis of mitered and welded corners too.

 

[pennpiper]

Or!
You could take a standard 10" 45 degree ELL and trim off 20 degrees, bevel the end and you would have a 25 degree Ell.

Or take a standard 90 degree ELL and trim off 15 degrees, bevel the end and you would have a 75 degree ELL.

This is done every day and you do not need a bend shop to do it.

 

[BillBirch]

Wrought fittings do not have ratings. The wall thickness (or schedule), diameter and allowable stress determines the maximum allowable operating pressure - independant of the elbow angle.

 

[JohnBreen]

Greg80

As Pennpiper says everybody just trims a B16.9 welding elbow or return and preps the cut end for welding.

Specifically, for Code stated limitations on this you want to look at B31.3 paragraph 328.4.2(b)(6)

"Buttweld fittings manufactured in accordance with ASME B16.9 may be trimmed to produce an angular joint offset in their connections to pipe or to other butt welded fittings without being subject to design qualifications in accordance with para. 304.7.2 PROVIDED the total angular offset produced between the two joined parts does not exceed three degrees".

So, try to make a square cut when you trim.

For P/T design B31.3 paragraph 303 tells you that you can use a "listed component" (listed in Table 326.1) with the P/T rating that is provided by that Standard (no other qualification is needed). Also see paragraph 304.2.2 regarding manufactured elbows that are not in accordance with paragraph 303.

If you have a fab shop bend a piece of pipe you must do the calculations in paragraph 304.2.1. You might also do these calculations if your elbow does not comply with paragraph 303. The thing you will find out about the equations of paragraph 304.2.1 is that a bright new shiny B16.9 welding elbow can be delivered and it will be OK to use it under paragraph 303 BUT if you use the new "as measured" wall thicknesses in the equations of paragraph 304.2.1 it might not comply with the minimum wall requirements of that paragraph(!!?). So what does that mean? You can run into a problem if you have an in-service B16.9 elbow and you try to use the "as measured" (UTT) wall thicknesses with the curved pipe equations of paragraph 304.2.1 to qualify it for fitness for continued service. Been there done that.

The "catch-all paragraph' for qualifying unlisted piping components for P/T design is paragraph 304.7.2 and it give you very good motivation to work with "listed components".

Regards, John.