Eccentric reducer_thickness calculation reference

[GD_P]

Hello,

Can anybody tell, how to calculate the thickness of an eccentric reducer?
Any reference (standard / handbook)?

I understand that, it sound weird of calculating thickness of eccentric reducer, but I have to qualify the reducer as per B16.9 using design calculations instead of proof test.

Any help will be appreciated.



GD_P

 

[LittleInch]

Why?

Just buy one to b16.9

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

 

[GD_P]

I apologies for delayed response LittleInch.

Actually we were thinking of the possibility to make available the reducers when we are only couple of reducer short and the delivery of time of standard item is long (for eg., MOC - 316 Ti). I will look whether Sec VIII div I gives any method for eccentric cones.


GD_P

 

[robyengIT]

If I remember well, for eccentric reducer, the min length is Lmin = 8 * (D-d) (the min length should be bigger 8 times the difference of the max and min diameter). After that the thickness calculation

 

[LittleInch]

Measure one of the ones you have already got?

B16.9 is rather vague on the whole design thing...

So it sounds like FEA to me is needed.

How are you thinking of making these?

2.2 Design of Fittings
The design of fittings shall be established by mathematical
analyses (e.g.,ASMEB16.49 for bends) contained
in nationally recognized pressure vessel or piping codes,
or at the manufacturer’s option by proof testing in accordance
with section 9 of this Standard. In order to meet
design or manufacturing requirements, it is expected
that some portion of formed fittings may have to be
thicker than the pipe wall with which the fitting is
intended to be used. The mathematical analyses, if used,
may take into account such thicker sections. Records of
mathematical analysis and/or successful proof test data
shall be available at the manufacturer ’s facility for
inspection by the purchaser.

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

 

[racookpe1978]

For a straight pipe, calculated thickness is greater for a larger diameter (basic hoop stress theory) than for a small diameter at the same pressure; so realistically, a reducer should be the same wall thickness at the larger end as at the small end (if rolled from a plate) or forged.

If investment cast or 3D modeled (cast at all for ? pressure piping? or for Ti alloys?) you could cast or model darn near anything of any varying wall thickness. But grain structure and fracture toughness? Only testing could tell you if it would work, and cyclical failure requires looooooong test periods.

 

[GD_P]

Thank you experts for your response.

Sec VIII Div 1, UG-36(g)does allow the design of oblique /eccentric reducer (max cone angle equl to or less than 30, Isn't it enough to prove 2.2 of B16.9?

@robyengIT
This does not match for standard reducers as per B16.9.

@LittleInch
I am thinking to make them by machining from heat treated (HT) forged rod. This is allowed as per SA 403 & as the rod used is HT, no further HT is required after machining.

@racookpe1978
That makes sense. Thank you.
As the rod is forged, I dont think the cyclic testing is required.



GD_P

 

[HP.E]

If you want to use a butt-welded fitting like a reducer in a line, the wall thickness of each side needs to be matched with the corresponded pipe on that side because they are going to weld to each other. so, you can use the pipe wall thickness for your fittings. It means in reality you need to specify two wall thicknesses for a reducer corresponding to large and small diameters.

Please see the Para 2.1 of ASME B16.9:

“The allowable pressure ratings for fittings designed in accordance with this Standard may be calculated as for straight seamless pipe of equivalent material (as shown by comparison of composition and mechanical properties in the respective material specifications) in accordance with the rules established in the applicable sections of ASME B31, Code for Pressure Piping. For the calculation, applicable data for the pipe size, wall thickness, and material that is equivalent to that of the fitting shall be used. Pipe size, wall thickness (or schedule number), and material identity on the fittings are in lieu of pressure rating markings.”