Allowed under ASME Code? Drilling Radial Hole in 150lb flange 2

[zijincheng]

Hello all, I have a piping spool piece with a 150lb flange that is 1" thick and 12" diameter.

I would like to drill a 1/8" pilot hole through the flange (radially) and then add a 1/4" NPT tap at the end for a plug.
Some calcs, the 1/4" NPT tap is approx 7/16" diameter, meaning there is still 9/16" of material left around the tap)

Is this in conflict with ASME code? I briefly looked thruogh B16.5 but couldn't find anything directly relating to this application.

 

[hacksaw]

Orifice Flanges are generally used,
do you search on Orifice Flanges (ASME B16.36)

 

[pennpiper]

zijincheng,
Please tell us why you want (or need) to do this.

Depending on your purpose/reason for doing this, someone out here might be able to suggest options.

Sometimes its possible to do all the right things and still get bad results

 

[XL83NL]

The flange would become a non-compliant B16.5 flange, as B16.5 doesnt describe this is allowed (therefore, there are B16.36 flanges which have similar arrangements - but that standard doesnt cover Cl. 150). Since you mentioned piping spool, I assume youre working under B31.3. If so, the flange, in B31.3 terms, has become an unlisted component, and needs further evaluation per 304.7.2.

 

[zijincheng]

Thanks for all your replies, we have an existing skid and the customer has requested a vent hole drilled into the flange of this specific spool. This hole would be used to vent out air.

We would readily use an orifice flange (e.g. cut off the existing flange and weld on an orifice flange) but none of them are 150lb), and yes we are working under B31.3

However, our shop regularly proof tests spools for CRN so proof testing the drilled flange is no problem for us, I just need to find out if a proof test of the flange itself is enough for the CRN to be registered, or does it need more tests to be done?

 

[moltenmetal]

If the component survives a proof test, it can be approved- as part of the piping system. But what do you mean by a "proof test"?

I'd personally be satisfied to stamp that piping assembly as suitable for the service if the component survived a B31.3 hydrotest at the flange's maximum rating per B16.5. I would not require you to do a true "proof test", which would involve testing the component to failure or to a multiple of MAWP of 4 or 5 times.

You could also analyze the component as an Appendix II flange and de-rate it accordingly. There is nothing in B31.3, nor in CSA B51, which says that a piping assembly has to have an MAWP equal to its flange rating. That is common design practice, but NOT A CODE REQUIREMENT whatsoever. You can design a piece of piping for vacuum and put 150# flanges on it if you like.

You don't need to register a separate CRN for the component (as a Category H fitting for instance) unless you wish to manufacture them and sell them as loose piping components. You simply register the component with the assembly as part of the piping design, and make sure it is tested per the record of inspection and testing (witnessed by your provincial AHJ as required).

I've seen flanges modified in all kinds of ways- orifice taps, venting holes, jack screws to aid disassembly, fixture points welded to them etc. Done properly, none of them is wrong, even if they make the component no longer a standard B16.5 flange. Done wrong, any of them can be a hazard.

 

[pmover]

any possibility of using a bleed ring?

 

[MJCronin]

Why must the piping system vent be EXACTLY on the flange ? ..... Piping venting is not a precise activity

"Because the client says so" is not an acceptable answer .....

What is the problem with a vent ON THE PIPING SYSTEM using a small bore branch connection ?

I don't understand what is accomplished by such a flanged vent ...

MJCronin
Sr. Process Engineer

 

[LittleInch]

The fact you can't get an orifice flange less than class 300 tells you something as well - i.e. the class 150 flange isn't considered thick enough...

But MJC has it nailed.

Drilling holes in flanges is never a good plan IMHO. Bleed rings are a much better alternative. If this is a kid then there is ample room for such a vent on the connecting pipework surely?

Why can't you just drill a hole in the adjacent pipe? That's what weldolets were invented for.

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

 

[zijincheng]

Its complicated as to why we can't drill in the pipe, but our customer has a 2" distance between weld rule that they like to follow, so that eliminates drilling in the pipe spool.
We can't even shorten the pipe spool because its fitting to fitting, and the we have check/gate valves above and below and we can't drill there either.

 

[moltenmetal]

A bleed ring between flanges is another way to solve the problem. You end up with two gaskets instead of one, and longer studs, and another component. But it keeps people from drilling holes in flanges, which if done without proper care and control can become a dangerous thing. You don't end up with any illicitly modified components either- though I'm not sure what standard the bleed rings fall under.

All that said, assuming the flange is appropriately selected for 150# class, the service isn't so hazardous that threads are themselves questionable, and it's not a severely cyclic or vibrating service, I don't personally see a problem with drilling and tapping the hole as suggested.