Slip-on Flange Weld Detailing 1

[JStephen]

I'm just curious how other people detail welds on slip-on flanges. Specifically, with reference to Fig UW-21(1) in ASME B&PV Code Section VIII Div 1.

Suppose you have a 4" Sch 80 pipe and need a 0.337" fillet weld on the inside. Do you show a decimal dimension for weld size? Show it as "full"? Show 5/16" or 11/32"? The difference between flange ID and pipe ID is slightly less than 3/8", so theoretically, it can't be 3/8".

On the back side, the fillet weld size is limited by the hub thickness, but per the flange catalog, the hub "may" be tapered up to 7 degrees, and only the untapered diameter is shown in the flange dimensions. So do you assume it's tapered, assume it's not, show it as "full" or what? That taper, or lack thereof, makes a 0.17" difference in the weld size on a 24" 150# flange.

 

[david339933]

The weld on the inside only needs to be 1/4" max. according to UW-21. The weld symbol should indicate 1/4". The outside is 1.4 x .337 = .4718". If you indicate 1/2" the and the hub is not 1/2" thick, a good welder will weld it out to the thickness of the hub.

 

[JStephen]

I was assuming that inside weld would have corrosion allowance added to the throat dimension, which makes the tn the limiting thickness.

 

[SnTMan]

JStephen, inside fillet, as david339933 says, is required to be 1/4" min. However, it is not clear whether this is in the corroded condition, as is so common elsewhere in the Code, or not. However a 1/4" plus corrosion fillet dimension is obviously not achievable in the thinner walls.

So, my practice is to add the corrosion to the 1/4" inside fillet when the pipe neck allows, and to not do so when it doesn't.

For the outside fillet, my practice at my most recent employer, due to an overly legalistic frame of mind by QC, is to refer to a note at the fillet symbol. Note states something like "Minimum of 1/2" or hub small end thickness". 1/2" being an example of course of the calculated thickness required by UW-21. Again, not clear if the "tn" used as the basis is in the corroded condition or not. I never dimension welds in increments smaller than 1/16".

Yuk. Miss the old days when it was just neck x neck.

Really good reason to just use weld necks, IMO

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Duwe6]

Theoretically, SO's are cheaper than WN's; sez so in the catalog. Right up until you have to pay to weld them onto a pipe and meet Code. Then it's time to educate your purchasing agent. An 8"NPS Sch 80 SO Flg requires 3/4" fillet weld, about a full day's welding if the pipe is horizontal and cannot be rotated. The butt-weld for a WN flg should take a decent welder half that time.

 

[LawEngineering]

JStephen,

I agree with the 1/4" minimum fillet weld on the ID. For the OD, I typically dimension the calculated value and specify that it is the minimum and let the welder use their judgement on the actual or maximum dimension considering hub thickness. I like to let the welder know what is required per code rather than just some nominal size.

 

[r6155]

Welder must comply with shop drawings / welding symbols. All weld dimensions shall be indicated in drawings, no judgement from the welder.

Regards
r6155

 

[gtaw]

Few welders have ever seen a code, never mind read the specific code applicable to the job he's working on. Only a small percentage of those welders have any formal welding training, and those that do, the training consist of how to deposit a sound weld. Code requirements are not something typical included in a welder training program.

The welder only knows what is provided by the drawings, more than that, is wishful thinking.

Rarely have I been on a project where the welder or anyone on the field crew even knew what pressure piping code they were welding to. "Its just pipe." is the response I usually hear.

Best regards - Al