Welding Slip-on flanges to fittings (elbows & Tees...) 4

I am not aware of any prohibitions in B31.3 Process Piping, but it may be a company or customer base prohibition.

I have encountered many instances of prohibitions based on personal opinions rather than code requirements. "I saw it on another project, so I included it on this job."

Best regards

Best regards - Al

K.Beitel,
1. There is no Code restriction against welding a Slip-On (SO) Flange directly to an elbow, a Reducer, a Tee or any other fitting.

2. The Chart ( you have is consistent with others I have used in the past.

3. The main key to welding a SO Flange to a fitting or straight pipe is the "set-back" distance. This is the distance from the face of flange to the end of the fitting (or pipe). Let's call this Dimension "X".
Dim. "X" = the wall thickness of the fitting or pipe plus 1/8' (6mm).
This allows for a 45 degree fillet weld equal to the thickness of the pipe wall plus 1/8" clearance from the "toe" of the weld to the face of the flange.
The 1/8" clearance is to reduce the risk of damage to the gasket sealing surface.

KBeitel,
Before you jump in the job, try to make a scale-up drawing of your slip-on flange joint with the elbow. You'll realise that is almost impossible to get a perpendicular flange face on the elbow centreline, because of the arching of the elbow. That will lead to overstressed fitting/flange in the bolted joint, including the failure of the joint seal and leakage. The slip-on flange presumes the use of straight pipe, where you can weld correctly the flange on the pipe.
Best regards,
gr2vessels

I haven't seen any code restriction against the practice.

As gr2vessels points out, the straight "land" on butt welding elbows and tees is not long enough to permit proper insertion into a slip-on flange at most sizes if you want the flange to end up normal to the axis of the fitting. You usually need to not fully insert the fitting into the flange (i.e. completing the ID fillet weld a little deeper into the flange than the flange is designed for). Even then, you end up with an asymmetrical back fillet weld. But at 150# class, especially for Category D services (where welding both fillet welds on a slip-on is optional per B31.3 anyway), I have done it and would do it again when necessary for fit-up.

I would do it in a pinch, but I would also have to pinch my nose as I did it.

rmw