Wheep hole on RF pad

[Syahar1975]

Dear experts,

Is there any article or code that we can refer to about the requirement of wheep hole or vent hole on RF pad on the shell plate ?

RF pad for nozzles and manhole always with vent hole. But RF pad for pipe supports or other attachments could be there is or there is not.

What would be the serious impact if there is no vent hole on RF pad of pipe supports or other attachments ?

Some of my welding supervisors explain me the welding method for the RP pad without vent hole to minimize gas trap.

Any comments ?

 

[JStephen]

I have never actually seen anything that says WHY there is a tell-tale hole.
Of course, it allows you to leak-test the fitting welds, and allows you to detect leaks on the interior welds.
And it allows venting of that space.

Uniform pressure inside a cylinder tends to keep it round. If you have a reinforcing pad sealed to the shell, with the space between it and the shell somehow vented to the inside, rather than the outside, that little section of shell plate will have zero net pressure acting on it, and would tend to form into a flat spot, transferring the load to the repad instead of the shell. I've never seen this effect discussed anywhere, never heard it given as a reason for that vent, but it seems to me that it does serve a structural purpose as well.

 

[MJCronin]

Why do you want your tank/vessel to give a low, prolonged whistle ???

Are you perhaps lonely or just enjoy the company of a merry tune ???

https://answers.yahoo.com/question/index?qid=20130418085417AAFVqw1

MJCronin
Sr. Process Engineer

 

[DSB123]

Never ever heard of a wheep hole. However I have heard of a weep - vent - telltale hole. Normally used on re-pad around nozzles and then either plugged or filled with grease after completion of hydrotest. Used to test the re-pad attachment welds and also a secondary benefit by allowing the weld gasses between the shell and the re-pad to vent away which helps in achieving the final section of weld (i.e. no weld gas pressure behind)

 

[Syahar1975]

Yes it is weep hole or vent hole or telltale hole.

I am sorry for misspelling.

But the question still the same. What would be happen if there is no vent hole on the RF pad of pipe supports ?

Is there any significant effect ?

Syah

 

[LittleInch]

Yes there is.

A significant issue behind having a weep hole, as note above, is that the re-pad attachment to the pipe is not designed or tested to be pressure containing. If you get any corrosion hole or other hole developing in the main pipe, you want this to be noticed before the re-pad becomes the pressure containing element, hence the other names - vent hole (gas) or weep hole (liquid) or tell-tale ( either).

The issue over gas blow into the weld is also significant, but the pressure containing bit is the most critical for me.

Welding RF pads for supports sounds a bit old fashioned to me if these are just used for direct contact onto a rubbing bar or similar. Clamp type supports are now much more common in my experience.

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

 

[Duwe6]

Repads are pretty common for big-bore pipe supports on thin - 1/4" , 5/16" - tank walls. A liquid-filled 6NPS or 10NPS line is a substantial load, so spreading it out onto the tank shell is needed.

 

[LittleInch]

Ok, I misread it as a RF pad on the pipe itself. comments still apply to a tank.

Reading API 650 a bit closer shows that the only requirement for non opening attachment requiring a tell tale hole are when you run over a seam weld.

However I still think it's a good idea regardless - 5.8.11.4 applies here. Note requirement for rounded corners.

Makes more sense now why this is in the storage tank forum....

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

 

[IFRs]

LittleInch has it right:
For API 650 new tanks, the only requirement for a tell tale hole are when you run over a seam weld. Otherwise it's a non-issue.