Vent hole for re-pad inside the vessel

[jtseng123]

All,

I have a situation that re-pad will be required inside the vessel for a beam seat. The re-apd and beam seat with be covered with 4" thick refractory to block heat from catalyst at 1000F so the CS vessel wall will be about 350F.

Do I need to put a vent hole for the re-pad ? My concern is it can trap moisture after hydrotest(this is a 15' dia FCC vessel), water and refractory may get in through vent hole during refractory installation( Note, vessel will be heated up to 1500F to dry out the refractory), and if refractory cracks during operation, catalyst may get in that will pop up the re-pad. Or shall I just plug and seal weld the vent hole after welding re-pad and leave it alone ? If plugged, will the little air or moisture trapped be a concern ?

 

[GenB]

To be the in compliance, You may consider the hole on the outside of the vessel then you can thread and plug as required by Code.

General Blr. CA,USA

 

[r6155]

Can you tell us more information?: thicness of re-pad and dimensions and shell thickness.

Regars
r6155

 

[jtseng123]

GenB, this is just a non pressure part re-pad, a beam seat welded on it to take the packing weight. Your recommendation of punching a hole on pressure part does not sound a good idea which will make the re-pad become pressure part. Also nothing to do with elongation.

Shell 5/8" thk, pad 5/8" thk, pad size about 18" x 30".

 

[SnTMan]

jtseng123, not familiar with your class of work, but I'd be leaning towards tapping the pad, and plugging it immediately after welding it out. Seal welding the plug is probably a good idea as well.

If tapped the pad can be air tested in the future if needed, although seal welding the plug will make this a little more difficult.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Tothesky]

For High Temperature Operation, All Internals' Reinf. Pads have Vent Hole as mandatory.

If you don't make Vent Hole, Reinf. Pad Inside will be sealed perfectly.
During Operation,High Temperature will expand Air inside Reinf. Pad due to Heat.
Finally, The Expanded Air will break Welding between shell & Reinf. pad.

As normal practice, All pad should have vent hole.

Regards,
Moon

 

[JohnGP]

Well, ASME VIII Div 1 only requires tell tale holes on external pads, according to UG-37(h). High temperature could pressure up the space behind a pad, but I don't believe that at 350F there would be sufficient pressure rise to cause any problem with the welds. You need to run the numbers though for whatever maximum temperature is possible.
Regards,
John

 

[r6155]

1) Corrosion between shell and internal pad must be avoided, hence open hole is not allowable in internal pad.

2) Beams should never be welded directly to the vessel wall because of the restraint they would impose on vessel growth.
Use beam sets, clips or support ring when design internal beams, they will allow for the radial expansion of the vessel due to temperature and pressure. Slotted holes in the clip or for the bolting attaching the beam to a beam seat allow for expansion.

See Pressure Vessel Design Manual 4th edition, by Dennis Moss

Regards
r6155