API 671 coupling , hydraulic fit , maximum pressure . 2

[rQuestionEngineering]

Referring to API 671 type coupling , the hub is jammed and cannot be removed.
Would like to know the maximum hub expansion pressure allowed before it will explode ?
Original hydraulic pump supplied is limited to 3000 barG.

https://www.ahrinternational.com/PDF_catalogues/Kop-Flex/MS_Marine_Style_Couplings.pdf

https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/163329/t30pg121.pdf?sequence=1&isAllowed=y

 

[JJPellin]

I would never expect anything to explode. If you keep increasing the pressure, one of three things are likely to happen. The coupling hub will pop off, some fitting in the hydraulic system will fail by leaking, or the o-rings between the hub and the shaft will blow out. I would pump it up to maximum rated pressure and then add heat (steam is better than flame). I would increase the pressure above the maximum rating by 10% if necessary. If it does not pop, you are going to have to cut it off, which is not an easy thing to do.

Johnny Pellin

 

[CouplingGuru]

JJPellin is correct, the hub will not explode. What will happen is it will yield at the weakest point which will compromise its usability when re-installing. If you have a coupling drawing we can provide you the calculation of where this point is. The tough thing about hydraulic fit hubs is that they are very easy to over squeeze on to the shaft during install. This has to do with the ratio of surface area available during install vs during removal. During removal there isn't a gap for the fluid to flow so the pressure required to remove is much greater then what is required to install, if this isn't followed, the hub will be on so tight it will be very difficult to remove with out yielding.

The maximum pressure rating is typically calculated on install (when pressure vs surface area is greatest), so you have much more then that on removal, but it may be difficult to control the pressure once it pops. So you actually yield it after it breaks free when that hydraulic fluid rushes in at a pressure greater then maximum rating.

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