Bleeder Valve on Concentric Reducer 4

[Chance17]

I am evaluating safety valve inlet pipe with tight space constraints for branch bleed valve.
It is proposed to bore a hole on a 3" x 4" concentric reducer and then weld a 1/2" NPT half coupling for bleeder valve.
The pipe is 150# flange carbon steel.
The proposal is for full x-ray of trhe weld and full hydrotest of the installation.
Can anyone advise the cons for this design?

 

[pennpiper]

An alternate you might want to consider is the use of a "Bleed Ring" with a 1/2" tap either between the 3" flanges or the 4" flanges which ever is more appropriate.
A Bleed Ring only takes 1 1/2" face to face (see

http://qps-orifice.com/Bleed Rings/RF BLEED RING.pdf)

Also see:

http://www.mac-weld.com/FlushRing-BleedRing/FR-BR-BleedRing.html

 

[Berndt]

Hi Chance17,

Your proposal falls within a bit of a grey area. Modifying a code standard item ensures that that item no longer complies with the specified code and is therefore considered unlisted. Approval of an unlisted item can be done by several means, but the most common methods used for approval include FEM or by proving a good service history, assuming that a similar set-up has successfully operated somewhere in your client's plant.

Apart from the above, I would suggest using a weldolet/threadolet instead of a half coupling should you decide to stick with your proposal and not follow pennpiper's advice.

 

[MJCronin]

Kreig....

The weldolet/treadolet contour is not suited for a concentric reducer.

 

[Berndt]

MJCronin,

My view is that since the OP will most likely have to perform FEM to get approval, a shaped to suit non-standard weldoelt should not cost significantly more and will most likely result in longer component lifetime.

 

[Jmoore1]

Cronin, you can have a weldolet to fit reduceres.

 

[Duwe6]

Concur with Jmoore1: Use an O'let. Half-cplg may or may not have adequate reinforcement to fully reinforce the hole you put in the reducer.

If you were thinking of using half of a 3000# series socket-weld coupling, that would work, ASSUMING that the cplg was beveled such that there was a full-penn weld between it and the reducer, and that there was sufficient weld reinforcement for properly 'fair' it in to the reducer without making any stress-risers [like right-angle corners].

Cheaper/easier to use an O'let.

 

[CRG]

Chance17,

You made no mention of the relevant pipe code if any.

ASME B31.3

304.3.2 ~ It may be assumed without calculation that a branch connection has adequate strength to sustain the internal and external pressure which will be applied to it if
(b) the branch connection is made by welding a threaded or socket welding coupling or half coupling directly to the run in accordance with para. 328.5.4, provided the size of the branch does not exceed DN 50 (NPS 2) nor one-fourth the nominal size of the run. …

NOTE: Within the B31.3 piping code, I do not believe that the term "run" is defined; however, when referencing pipe the code uses "run pipe." As such, I would interpret the term "run" to include the reducer you have described.

 

[DLite30]

Personally I wouldn't recommend this, not because it wouldn't work, just that if anyone asked you about what standard you followed to do that, it would be hard to justify it, without coming off kind of shady.

I would agree with pennpiper on using a bleed ring.

If space really is that tight, another off-the-shelf option could be a tapped flange (intended for a measurment orfice).

 

[Chance17]

All of your answers are very good and professional. Thank You