CJP - Complete Joint Penetration Welds 4

[BSVBD]

In AISC it appears as though the only way to accomplish a CJP / Full-Pen weld is either to weld from both sides or apply a backing (backer?) bar.

In a case where I might specify a Partial-Joint Penetration weld for up to 1/4" material, butt (or square) to 5/16" or thicker, will my "partial" actually produce a "full-pen"?

I have a case where the general contractor frequently repairs PEMB columns after tow-motors (or other) collide with the columns to the extent that necessitates removal of the lower 8' of 0.188" wall intermediate column, and (the G.C. is) replacing it with 0.322" Schedule 40. Therefore, since I'm welding 0.188" Round HSS to Schedule 40 Pipe, I can neither weld from both sides nor install backing.

Again... will my "partial" actually produce a "full-pen"?

I frequently specify a "full-pen" weld, all around weld for HSS Rectangulars when designing stair stringers composed of adjoining, diagonal and horizontal members. Is this wrong?

I realize I need more education in welding.

Thank you!

 

[TLHS]

Yeah, unless you test and qualify the procedure (and get lucky) this isn't going to work. Even if you groove both sides of the weld with a large angle, you'll lose 1/8" of capacity using prequalified welds. Using a more conventional single side groove, you'll lose 1/4"

The first question is, do you actually need capacity there, and if you do can you get it in another way?

Repair is likely near the bottom, max moment is near the top unless it's built as fixed base. Buckling resistance is likely not going to be affected by the discontinuity near the bottom. Axial stress is not going to be an appreciable fraction of the section strength. I'm assuming there aren't seismic detailing requirements.

Alternatively, you could try to groove the larger pipe in such a way that the extra material is backing for the weld. It's not prequalified, but the procedure might test out.

 

[TLHS]

Would a full pen weld even give you full strength? Is the base metal on the pipe strong enough?

 

[j19]

When splicing a pipe column I've seen (actually I haven't seen this but I have heard of it) weld shops cut off a short piece of the pipe (maybe 4" long) and they cut a slit in it (in the 4" direction). Then they fold the piece together until it will fit inside the end of the pipe column. They'll put 2" into the pipe and leave 2" sticking out so that the top piece can fit over it and they have their backing bar.

 

[sandman21]

Typically you can get a pipe smaller size that will fit inside the larger pipe. 3Ø Std. pipe fits into a 3.5Ø pipe, and it will be used a a backer. Modifying a pipe can work provide no gap exists in the material, seems like a lot of work.

 

[Ron]

To get a proper complete penetration weld on a pipe section (or actually any section), there are several things you'll need to do.

First, specify that the welder be qualified in pipe welding (per AWS D1.1 requirements). He/She should be qualified without backing.

Next, design the joint as a pre-qualified joint per AWS.

Next, specify the welding process that is compatible with what you want to achieve. Since these are field welds, I would stay away from either GMAW (Gas Metal Arc Welding....(MIG)) or GTAW (Gas Tungsten Arc Welding....(TIG)) as these are more difficult to control in the field as compared to the shop. Use SMAW (Shielded Metal Arc Welding....common "stick" welding) or FCAW (Flux Core Arc Welding...similar to MIG but does not require shielding gas). Specify that the welding be done with a separate root pass and then filled to complete the penetration.

Next, specify nondestructive testing to determine if the contractor achieved a complete penetration weld. Since these are likely "Tee" joints, radiography will be limited, so ultrasonic flaw detection would be more appropriate.

No...your partial penetration weld will not consistently achieve full penetration requirements.

 

[dik]

Ron:
"I would stay away from either GMAW (Gas Metal Arc Welding....(MIG)) or GTAW (Gas Tungsten Arc Welding....(TIG)) as these are more difficult to control in the field as compared to the shop." ... and even trickier with a light breeze...

There's a really good article on NDT in the Engineering Writer's Guild forum on this site.

Dik

 

[Ingenuity]

FCAW (Flux Core Arc Welding...similar to MIG but does not require shielding gas)

Two types of FCAW: "FCAW-S" (flux only) does NOT use a shielding gas, but "FCAW-G" (dual-shield) does.

 

[hokie66]

These are really light column sections. Why not just replace the whole thing? No matter the welding type or inspection type, I tend to distrust welds on structural pipe without backing bars.

 

[azcats]

Would something like this work? Or is there no room to position the backer bars into place?

 

[dik]

Why not overdesign the pipe a tad (30%+/-) so you can use a partial penetration weld? That's what I usually do.

Dik

 

[BSVBD]

hokie... That is what we were advising from the beginning. We feel this is also a lot less labor.

Thank you all for your replies!