ASME 31.3 - WeldOlet to Blind Flange

[jm2804]

Per ASME B31.3, is welding a 2" Weldolet to a 20" blind flange code compliant? If so, what code discusses this situation. Similar situation is welding a 3" Weldolet to an 8" Blind flange.

 

[LittleInch]

There is plenty on this subject in this site if you search hard enough, but most people point to table 6 of ASME B 16.5 which gives min reducing flange sizes but then also says in note 1 that where a smaller size (your 20" x 2") that they can be made from blind flanges. However your 8" x 3" I would recomend you use a reducing flange or a normal flange and a reducer. There is also somewhere a limit of the hole in blind flange being less than 0.5D.

Note all holes should be in the centreof your blind flange. Any off centre or multiple holes really need this to be considered using ASME VIII.

I would always question what exactly you are connecting this weldolet to. The bigger and heavier it is the more susceptible your small connection is to mechanical damage, fatigue, over stress (e.g.a 2" #1500 valve) without further support.

Take care with these types of connections and use proper components whenever possible.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[jm2804]

I appreciate the response. My understanding is table 6 is referring to welding a pipe or nipple into the blind flange with a fillet weld on the outside and inside (reducing slip-in flange). My question was can you machine a hole into the blind flange and just attach a weld-olet to the outside?

 

[LittleInch]

I can't see any reason why not providing that you fill in the entire weld area of the weldolet. If you can machine in a bevel to have a sit in weldolet then all the better.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[uaepiping]

Littleinch,
This is what we did for one of our projects:
Weldolet required were flat. We had to weld it to blind flange. Received had curvature to match the OD of some pipe. We asked the manufacturer, if we machine the weldolets to remove only the curved portion (matching the radial portion of pipe), will it be compromising strength. Their reply in writing was that there would not be any difference as the smallest part (to fit the axial pipe direction) is the weakest portion to bear the pressure. So machining up to this point will not affect strength.