Tapping from Bottom Flat Eccentric Reducer

Is it allowed to take tapping from the bottom flat eccentric reducer? In our plant, we have 24" elbow, 24"x20" eccentric reducer and de-superheater on a steam line (all fitting to fitting - without any pipe piece in between). Now we need to take tapping between the elbow and de-superheater. Consultant has given new design with 24" equal, 24" cap, a pipe piece between reducer and (now tee). New tapping to be taken from the new pipe piece. All this is costing us fortune (fittings, welding RT etc.) Can we take tapping from the bottom flat portion of the eccentric reduer? The tapping size is 6" with weldolet.
Other conditions, Ecc reducer A234-WPB schedule 80, line design pressure 25 bar and temp 360 degree Celcius.

My seniors in stress analysis are of the opinion that it is perfectly all right to take this tapping. But I wanted to take opinion from the learned people of this forum.

Point #1. You will find that there is nothing in any CODE that says you cannot do this.

Point #2. If you can make this same connection from straight pipe, then why can't you make it on the bottom of the bottom flat reducer?

Jop,
Thanks for reply!
Yes, no code disallows this connection.
There seems to be no problem with this connection.
The only limitation that I can see is that the olet size should be such that sufficient space between it and the reducer welding should be there for welding inspection (4t or 50mm whichever is more in this).

Dear Seniors,
Para 304.3.2 of ASME B31.3 states: “It may be assumed without calculation that a branch connection has adequate strength to sustain the internal and external pressure which will be applied to it if (a) the branch connection utilizes a listed fitting in accordance with para. 303.”

Para 303 states: “Components manufactured in accordance with standards listed in Table 326.1 shall be considered suitable for use at pressure-temperature ratings”

And in Table 326.1 we have “Integrally Reinforced Forged Branch Outlet Fittings — Socket Welding, Threaded, and Buttwelding Ends. . . . . . . . . . . MSS SP-97” as a listed item.

Conclusion: Branch reinforcement calculations are not required if we use MSS SP-97 fittings.

Any comment please??

The fitting may be qualified without additional calculation but how about the head?

If you use a proper 'olet type fitting should be OK. I would multiply connection SIF and any reducer SIF together to be extra safe. No extra reinforcement needed.

This 6" tapping is acting as a dripleg for condensate. Dripleg is 450mm long with a cap at the bottom. The line to steam trap from this 6" dripleg is 1".

Shahid,
You wrote:
"The only limitation that I can see is that the olet size should be such that sufficient space between it and the reducer welding should be there for welding inspection (4t or 50mm whichever is more in this)."

The generally accepted dimension for a 24" x 20" Ecc Red is 24"
The OD of the 6" WOL is 8 1/2 " (+/-)
So, if the WOL is centered on the bottom of the reducer then you should have more than 7" (177.8mm) clear from each WOL fillet weld to each of the fitting Butt Welds

That is much more than 4T or 50mm.

agree with Jop

Presumably the eccentric reducer is a B16.9 fitting. This means that it is ‘designed’ by the manufacturer to meet a performance requirement – the allowable pressure rating is to match straight seamless pipe of equivalent material. The manufacturer will often use a heavier wall than the specified ‘nominal’ wall to achieve this pressure rating. In designing a piping system, because it is a B16.9 fitting we need do no further engineering on its pressure rating.

The moment that a hole is cut in this reducer it is no longer a B16.9 fitting, and the manufacturer is not responsible for its pressure rating. The pressure rating needs to be established by the piping designer.

Clearly some engineering judgement needs to be applied to this aspect of ‘modifying’ a B16.9 fitting. If the branch fitting being attached to the NPS 24 fitting is, for example NPS 1, then it is arguable that the impact of the branch on the pressure envelope of the fitting is minor, and that it will have little impact on longitudinal bending stresses in the fitting. At what size does the branch fitting become significant? This is where engineering judgement is required.

For the case discussed above with an NPS 6 weldolet on an NPS 24 x 20 eccentric reducer, the integral reinforcing of the weldolet may be adequate for the pressure envelope, but it cannot be assumed. Remember that the weldolet is sized for reinforcing a specific weight of run pipe wall, and so for this case, at minimum the weldolet would need to be specified for the actual wall thickness of the reducer (not the nominal wall).