Repad at Base Ell Support

[KernOily]

Hi guys. It's the evening for dumb questions that fell out of today's even dumber meetings.

Have any of you ever seen a repad at a base ell support?

I have a bunch of large pumps with big inch (sorry BigInch...) sch 10S 90 deg elbows on the suction laterals. The 90's will need some type of reinforcement where the vertical part of the base ell support is welded to the 90 because the vertical member has a guide or a limit stop at its foundation, this being part of the strategy to reduce the thermal loads transmitted to the suction flange. The loads carried by the base ell necessitate a repad on the elbow.

Question: I have never seen this. Is it possible to fabricate a repad that has the proper shape to conform to the compound curves of the outside of the 90? I don't want to generate a fabrication detail for this, only to have the fab shop guys laugh me into the weeds and then suffer the delay while we figure out something else. If necessary we will ditch the 10S 90's and go to std wt or 40S to get the extra meat since I am not pressure-drop critical on the suction. But this is 316L, and every ounce costs $$$ when you are working with 14" and 20" NPS... Thanks guys!!!

 

[BigInch]

No problem, "big inch" pipe was the original inspiration for the handle.

Trying to make a sleeve, or pad to match the curve of an ell would be a bit tough. Most common way to do that would be to use a "dummy leg" support, unless you are using pipeline codes, in which case you will need to weld the dummy leg support to a full encirclement longitudinal full or half-sleeve (sleeve surrounding the main pipe).

From "BigInch's Extremely simple theory of everything."

 

[BigInch]

sketch

From "BigInch's Extremely simple theory of everything."

 

[C2it]

I have seen re-pads on base elbows, usually made by cutting the pad from another donor elbow. Not very economical, so I would recommend a heavy wall fitting in preference.

Also note that if you have a restraint (e.g. guide) to reduce loads acting on a trunnion / elbow support local to a pump nozzle, it is in all probablity a numerical fix only. For such a device to work in reality it would need absolute zero clearance and practically infinite stiffness. Both easily achieved in the CPU, but difficult in the field.

 

[BigInch]

Cold spring, jack screws & epoxy grout.

From "BigInch's Extremely simple theory of everything."

 

[pennpiper]

I like (and would recommend) the idea C2it offered about using a heavier wall elbow at these few spots.

Taper bore the XH ELL ID at the welds to match the Sch 10 pipe wall and then attach the Base Support that BigInch shows in his sketch.

 

[KernOily]

Guys - Thanks for the replies - I appreciate it. Thanks for the sketch BI. THat is the basic arrangement; to that I either need to add the repad or else use a heavier wall elbow.

C2it - Believe me I appreciate your comments. What we have done to try and mitigate that exact situation somewhat is to model the stiffness of the vertical member of the base ell support in all six DOF. We also have specified a gap. That is about the best we can do as regards "sharpening our pencil", besides ensuring the calculated flange reactions are some goodly amount less than the allowables. Not sure what else I can do. Expansion joints are verboten.