Why need breathing hole on reinforce nozzle pad, do we have to block it after completion? 1

[Manhnnn]

Why need breathing hole on reinforce nozzle pad, do we have to block it after completion

 

[KevinNZ]

https://www.eng-tips.com/viewthread.cfm?qid=402227

https://www.eng-tips.com/viewthread.cfm?qid=471960

 

[CuMo]

Some plants require these to be plugged with high temperature grease, or if there is insulation, these holes can be threaded and tell tale tubes (1/4" NB or similar) be fitted protruding beyond/outside the insulation.
Check what your plant/client preference normally is.

 

[LittleInch]

Define "block it"? Block it with what?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Krausen]

The breathing/vent hole in repad is typically tapped with threads to do a 15 psig air test on the repad weld. Just plug the tapped vent hole with stiff grease (after painting, if req'd).

 

[Krausen]

Forgot to mention, the reason for this vent hole in repad (in case it isn't clear) is to allow any welding vapors for the repad to vent out & not become trapped within the shell/nozzle area enclosed by the repad

 

[kangomath]

Now NACE require that small hole shall not be plugged..
(NACE SP21534-2024 sect. 4.1.8.).

 

[r6155]

@ Krausen: You are wrong

Please, read the following
1) Vent holes shall not be plugged during heat treatment.
2) Measurement of gap heights between shell and pad shall be taken through vent holes.
3)
Reinforcing Pad Vent Hole Location 
Thread794-402227

See my drawing in 21jan16 16:32

Regards

 

[jt1234]

Krausen, Cumo, both of you are exactly correct. Vent hole is for vapor to escape to avoid hydrogen induced cracking from the welding as well as other harmful particles from the welding process.
The hole is also so call Tale Tell Hole for a reason. I had a Russian project years ago, and client requested all TTH must have a bent threaded tubing beyond insulation and with tubing hole facing ground for leak detection purpose. Though a lot of works and cost for hundreds of vessels, but that makes sense. We had no complaint for compliance.
The TTH also used for 15 psig air testing to ensure no pin holes through welding.
If inspector wants to use TTH to measure the gap, that is their business. Keep in mind, normally only have one TTH and in the very low location. So to use it to judge the gap, I doubt its accuracy.

The substitute of TTH is skip weld at the bottom of the repad, about 1/2" skip weld. This is normally used on the repad for lifting lugs.

 

[DekDee]

This is an interesting subject and there seems to be an awful lot of misinformation out there.
I am currently battling a client who requires 15 psig pneumatic test of trunnion repads.
What on earth for ?
MT/PT will deteck any porosity or cracks in the fillet weld.
I fully understand the requirement for a tell tale or weep hole on nozzles and if crossing weld seams but why for anything else - what are they for.

the reason for this vent hole in repad (in case it isn't clear) is to allow any welding vapors for the repad to vent out & not become trapped within the shell/nozzle area

I totally disagree - look at a slip on flange as an example. Fully weld the outside, fully weld the inside - do you have harmful welding vapours trapped between these two welds ?
Release of heated air during PWHT - yes agree. But if no PWHT - why ?
I have welded literally hundreds of repads and the most you will ever get when tieing in or closing off the weld is a little "pop" which may create a small dimple at the tie in point.

The TTH also used for 15 psig air testing to ensure no pin holes through welding.

Again I disagree - if you are plugging a hole with grease which is non pressure retaining what does the presence of a pinhole matter ?
ASME VIII uses the term vent hole - API uses the term tell tale hole.
I think they are meant to be the same thing but in reality (IMHO) they are two totally different inferences.

 

[Manhnnn]

Thank you team for sharing much of knowledge and opinion. It seems that the vent hole on the pad can be plugged after PWHT and 15 PSI testing.

 

[Krausen]

@r6155

1) Vent holes shall not be plugged during heat treatment.

It's well understood that when you "plug" a repad vent hole/TTH with stiff grease that you're not actually plugging it to retain pressure. The reason you plug/fill the repad vent hole with stiff grease after fabrication is to prevent moisture ingress & local corrosion of the vent hole over time. But feel free to disregard all of this if you'd like & let me know how your vessel repads look after 5-10 years in service.

 

[jt1234]

Sold metal plugs was used in lieu of grease in the past, if any people here old enough to know that. For uninsulated vessel, hey, plug is better than grease. Due to weathering, grease will be gone and who will run the risk of falling to re-grease any vent hole. Think before making your comments.
Asking our principle welding engineer long long time ago who is actually supervising all welding from vendors to site construction, and he is also one of the best welder for site construction storage tanks and any field welding, what I said is his opinion. Take it or leave it.
I have seen an engineering firm or oil company's vessel standard that does ask vent hole for slip-on flanges, even B16.5 does not ask for that. So take it or leave it. Don't immediately object to things that you probably have no experience with.

 

[DekDee]

Sold metal plugs was used in lieu of grease in the past, if any people here old enough to know that. For uninsulated vessel, hey, plug is better than grease. Due to weathering, grease will be gone and who will run the risk of falling to re-grease any vent hole.

ASME VIII Div 1 UG 36 (g)
If the holes are plugged, the plugging material used shall not be capable of sustaining pressure between the reinforcing plate and the vessel wall.

Think before making your comments.

I not only think before commenting I do research before I comment.

If a hole in a re-pad is called a telltale hole (or in the past weep hole) it is obvious what it is for - leakage.
Leakage from the nozzle or the seam weld underneath the pad.
But if a hole in a re-pad is called a vent hole what is it venting ? (hot air during PWHT is an example)
If process fluid is leaking out of a hole in a re-pad is it "venting" ?

Maybe I should not have said there is misinformation out there, maybe I should have said there seems to be confusion.

To get back to my first post, I am battling a Client on a refinery where fabrication is to B31.3 - vent holes on trunnion reinforcing pads are required with 15 psi pneumatic test.

If I do a word search on re-pad in B31.3 I get this.
(g) Reinforcing pads and saddles shall have a good fit
with the parts to which they are attached. A vent hole shall
be provided at the side (not at the crotch) of any pad or
saddle to reveal leakage in the weld between branch and
run and to allow venting during welding and heat treatment.

However, if you go back 3 x pages you will see that this clause is in 328.5.4 Welded Branch Connections.
A trunnion is not a Branch Connection.

 

[r6155]

But feel free to disregard all of this if you'd like & let me know how your vessel repads look after 5-10 years in service.

All pressure vessels shall be inspected frequently in service as determined by the user.

Regards

 

[r6155]

1) NATIONAL BOARD INSPECTION CODE 2023 EDITION DATE OF ISSUE — JULY 1, 2023
PART 2 — INSPECTION

The manhole and reinforcing plates, as well as nozzles or other connections flanged or bolted to the boiler, should be examined for evidence of defects both internally and externally. Whenever possible, observation should be made from both sides, internally and externally, to determine whether connections are properly made.

2)PIP VESV1002 COMPLETE REVISION Design and Fabrication Specification for Vessels January 2019 ASME Code Section VIII, Divisions 1 and 2
4.5.3.4 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 performed before the final hydrostatic or pneumatic test as applicable

NOTE: Obviously the inspector is inside to check the leak, if possible.
I did this test.

Regards