2205 machine welding

[ggrindle]

All,

Need some advice. I just visited a shop where we are having some 2205 ductwork fabricated for FGD outlet duct use. I know that termpature and HAZ is important and bead sequence should be watched.

When I got to the shop they used a machine to weld about 70% of the welds. I inquired about the process and it involves butt welding piece of plate together. I asked about the bevel and gap and was told that this machine essential butts up 2 pieces of plate (1/4 inch thick) with square edges (no bevel and no gap) and then welds them together.

The welds are beautiful..prettiest I've ever seen, but the question I have is regarding temperature.

Furthermore 2209 wire is used for the weld material, but I can't imagine very much is used since the plates are square and butted up to one another in this process.

From the standpoint of corrosion, is this process inferior to mig with bevel and gap and proper bead sequence and attention to heat input?

One other thing that got my thinking on this is they used 4' wide plates for the construction because it was cheaper. But of course that means more welds. I didn't specify a size of plate because I assumed the labor savings using larger plates would make it beneficial for any shop to specify 8 or 12' wide plates. But with this machine weld process the welds don't add much labor and so the savings going with less wide plates was greater than the labor to run the weld machine. This is a new one on me.

Advice anyone. Need I be worried?

 

[metengr]

ggrindle;
This is probably automatic gas metal arc welding (MIG), which is common for FGD ductwork. Minimizing the heat input from welding is very important for duplex stainless steel. Considering your stated thickness and presumed automatic weld process, I don't believe heat input is going to be a concern.

My question to you is was the contractor's welding procedure qualified on this base material and joint design????

 

[ggrindle]

Met,

This was not one of the procedures that we approved....which is why it struck me on the shop visit.

 

[metengr]

ggrindle;

If I were you, I would have the contractor immediately run a weld procedure coupon duplicating the shop welding and have this evaluated by a competent met lab. Most have AWS/ASME weld coupon testing capability and I would also have a metallurgical evaluation of the weld cross section and base metal HAZ.

 

[EdStainless]

They should have documentation to show the actual amount of filler used.
You need to look at some micros and run some A923 tests in ferric choride.
My gut feeling is that you should be fine, but nothing beets testing.

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[JamesCKelly]

If they butted 1/4" 2205 plate together and welded without beveling the joint, then one fine day the joint will break apart. Any manner of cyclic loading, mechanical or thermal, can cause that unwelded area to act like a crack and grow out through the weld bead to the surface.
Unlike carbon steel, one cannot get decent penetration in 2205 by just cranking up the heat.

 

[weldtek]

Assuming you stipulated full penetration welds, I'd be concerned with a square edge 0" gap fitup. Like metengr suggests if full pen is req'd, ask for a mockup or have some RT performed to verify your requirement has been met. If they changed procedures on you, ask for a copy of the procedure being used and be sure all of the standard testing is included and acceptable. You didn;t say much about the job requirements you imposed on the fabricator, but, normally, in addition to the standard bends and tensiles, ferrite is verified in the weld and HAZ at the root, mid wall and cap using the manual point count method. (30-65% is common)Additionally, Impact tests at -40F can be a useful quality indicator, and some folks ask for the corrosion test per A923 method C.