Piping Socket Weld Insertion Depth

[sjrfc2]

In an ASME Journal of Pressure Vessel Technology paper (William Koves, Vol 122, August 2000), the author indicates that work was ongoing to develop consistent requirements for fillet welds and the minimum depth of insertion requirements for socket welded joints. I'm specifically interested in minimum insertion depths and the engineering behind the limits. Would anyone know whether this effort was concluded and/or any outcome?

Thanks

 

[JohnBreen]

sjrfc2

We are still working on a standardized approach in the ASME B31 Mechanical Design Committee (MDC) and Dr. Koves is the Chair of this Committee. The fillet weld size issue is focused upon how much effective weld can actually be developed given the size and geometry of the socket weld fittings. Some of the smaller bore ANSI B16.11 socket weld fittings have a very limited amount of area for developing a fillet weld. How does one say "get as much weld on there as you can fit" in Code language?

Currently, the insertion depth is determined by specifying the size of the gap (before welding) where the pipe "bottoms out" in the socket. See B31.3 Figure 328.5.2C. Basically this is saying that the pipe is to be inserted all the way to the bottom of the socket then pulled back 1/16 inch to create the "gap" at the bottom of the socket. Then the fillet weld is made. The idea here is to assure enough "gap" to allow the short inserted piece of pipe (on the socket side of the weld) enough room to expand without "bottoming out" in the socket. When this is done correctly, the expansion of the pipe in the socket will not completely close the gap and result in additional loadings on the fillet weld.

The welder should also look to B31.3 Figure 328.5.2A and the wording there. The fillet welds used for attaching socket weld fittings very often cause "undercut" at the toe of the weld. After the socket weld fitting fillet weld is made, the entire weld should be inspected to look for inadvertent undercut and if undercut is found it should be "smoothed out" by slightly (and "artistically") grinding at the location of the undercut. The idea here is to remove the "stress riser" that the undercut creates so that the fatigue life will not be greatly limited.

Regards, John.

 

[arto]

sometimes they'll scribe a line 1" back on the pipe from the fitting end @ full insertion depth, so that after it's welded they can verify the gap from the outside

 

[sjrfc2]

Thanks John and Arto, I probably didn't explain it well. What I'm concerned about is extremely poor insertion. In this case the pipe would have much more than the 1/16 inch gap from the socket bottom. I'm trying to bound the point where this becomes a concern. From reading the text in the the Journal paper I was thinking that the B31 Codes would be addressing min insertion.

I think there is a stress issue where the unbalanced single fillet weld will drive higher stresses as the insertion is reduced. As the insertion becomes very small it will impact weld quality.

 

[pennpiper]

This is not hard to understand!

For Socket Weld fittings, flanges, valves and other objects the minimum insertion is the same as the maximum insertion.
Shove the pipe, pipe nipple or swege nipple into the socket until it bottoms out. Now scribe or mark a line around the pipe (nipple or swege) at the shoulder of the fitting (object). Next, draw it (the pipe, nipple of swege) back 1/16 of an inch and clamp it. Now tack weld it in place then do the finished Fillet weld.

Do it once! and do it right!