reinforcement pad for nozzle inner side of wall or shell 9

[Zubir MMHE]

Dear all,

I am looking for design that can be my reference for nozzle reinforcement pad design inner side of wall for pressure vessels or tanks. Based on ASME VIII, UG-37 not specifically mentioned reinforcement pad (repad) must locate outside but the schematic showing it in common, repad is place outside. Is there anyone of us has had experience weld the repad inner side of wall?

thank you

Zubir

 

[r6155]

Read UG-37 again and continue to the end of UW.

Regards

 

[SnTMan]

Zubir MMHE, re-pad inside the shell is permitted, see Fig UW-16.1 (a-2), (a-3). I personally have never seen it done. The presence of an un-vented space between shell and pad would bother me.

May make sense for some classes of work I guess...

Regards,

Mike

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

 

[MJCronin]

I cannot imagine the circumstance where an internal repad would be any sort of an advantage.

I can, however imagine and understand the problems that would occur in fabrication inspection and testing.

Never have I seen one in the field.

MJCronin
Sr. Process Engineer

 

[Zubir MMHE]

Dear SnTMan,
Thanks for advise. Yes I do refer to Fig UW-16.1 as u mentioned but in reality, i agreed with MJCronin that me too not seen it field. Since the code has provision for that (repad inner side), then i would appreciate if any expert that has had experience to share with us.

 

[SnTMan]

Zubir MMHE, yeah, well, best of luck finding one

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

 

[r6155]

In UG-37 (g)” Reinforcing plates and saddles of nozzles attached to the outside of a vessel shall be provided with at least one vent hole….. STOP HERE. This means that when attached to the inside, the vent hole is not required.

See Pressure Vessel Design Manuak 4th ed, by Moss
5. Forming.
Reinforcing pads should be formed as closely to the contour of the vessel as possible. While normally
put on the outside of the vessel, re-pads can also be put inside providing they do not interfere with the vessel’s operation

I have a client that requires a special aesthetic appearance for their stainless steel pressure vessels, therefore the reinforcing pad for manhole is placed inside.

No special test is required when Reinforcing pad is placed inside. On the contrary. some inspectors forget to do the leak test on the outer reinforcing pads.

Regards

 

[0707]

In my point of view it is not comum practice to repad from inside of a vessel. What normally is done is to install a cast peace with the proper thickness to avoid excess of tensions and welding on the nozzle.

luis

 

[Zubir MMHE]

Hi r6155,

agreed with you that vent hole is not required for repad installed inside vessel. This is typically same concept with deflector plate at head for the application of inlet nozzle device.
Dennis Moss manual mentioned also about internal repad, I noticed that too.

Just in case any of us having the actual experience on field.

thanks

 

[DriveMeNuts]

I have never seen an internal Re-Pad, however I think it would have some similarities to a wear plate or support doubler pad welded to the inside of a vessel which a bracket is then welded to.
If the vessel is in liquid cryo service, a hole is required for an inside double plate.
If it is in corrosive service, a hole should be avoided, or if a hole is mandatory I don't see why it couldn't be drilled through the main shell.
It really depends on the service.

 

[Don56]

Internal repads are very common on DOT LPG NQT vessels in the rear head.

 

[Zubir MMHE]

Hi Don56,

Could u share how it (reinforcement pad inside) commonly done in DOT LPG NQY vessels

 

[r6155]

I think someone is confused.
1)Vent hole shall remain open during welding and/or post-weld heat treatment.

2) Vent hole may be tapped for a preliminary compressed air and soapsuds test for tightness of welds that seal off the inside of the vessel. This was deleted from UG-37(g)in 2015.

But Good Engineering Practice is: “Reinforcing pad attachment welds and accessible surfaces of inside nozzle to vessel wall welds shall be tested for the absence of leaks with a gauge pressure of 15 psig (100 kPa) dry air or nitrogen and bubble forming solution. This test shall be prior to the final hydrostatic or pneumatic test as applicable”
A responsible manufacturer does this test.

Regards

 

[Zubir MMHE]

Dear Experts,

hope everyone well and in good health.
I still need some input for my reference

Thanks all

 

[212197]

Zubir MMHE (Mechanical)(OP)

What is the reason of providing rf pad inside?

 

[Zubir MMHE]

Hi 212197,

the reason of providing repad inside due to potential clashing between repad outside with stiffener ring & saddle weir plate at the nozzle vicinity.

 

[TGS4]

Is the service in the vessel susceptible to crevice corrosion? If so, then your corrosion and materials engineer should reject this request out-of-hand.

If this is a benign service, then I would look to exhaust every possible avenue (including moving the nozzle, using a self-reinforced nozzle, moving the stiffener ring, etc) before proceeding with an internal repad.

I would also consider how you will inspect this in the future. How will you detect corrosion, check for cracks, etc? The burden that you are placing the operating facility's inspectors is significant, and it may even affect the run time between shutdowns.

 

[r6155]

Zubir MMHE.
Your reasons are out of good engineering practice. I suggest change the design and use external pad.

Regards

 

[Zubir MMHE]

Hi TGS4 and e6155,

Thanks for advise. I am aware about the inspection perspective but out of engineering practice sometimes new knowledge can be inspired like the building of Stephenson bridge, there is no tubular bridge was build before it.

Just happy if somebody can share their experience with repad inner shell

 

[r6155]

Zubir MMHE: I repeat my reply on 12 Apr 20 14:38

I have a client that requires a special aesthetic appearance for their stainless steel pressure vessels, therefore the reinforcing pad for manhole is placed inside.

No special test is required when Reinforcing pad is placed inside. On the contrary. Some inspectors forget to do the leak test on the outer reinforcing pads.

Didn't you read it?

Regards