Welding Duct Work 1

[MichaelW.]

Good afternoon, I need some assistance with metals, we are a wood conveying facility and sending wood chips through a 88" duct (metal .250 thick) temps range from 140-180 F, duct supplier used stiffing rings about every 4'. problem is duct looks as if its being melted from outside in. I am sending pictures

 

[MintJulep]

Those are crap welds. Looks like many had zero fusion into the duct wall and have already pulled away.

They need to be removed and redone by a better welder than did them originally.

 

[Tmoose]

Are there intermittent/skip/staggered welds on both sides of the stiffening rings ?

If both sides, are the the welds on each side aligned on each side ( called intermittent in AWS 2.4) or offset ( called staggered in AWS 2.41) ?

Those jagged "indications" are mighty interesting.
But the "soot" coming from the welds near the top of the duct in the RH picture in the first pair suggests //maybe// the duct wall is cracked through.

Mostly I'm thinking the indications/cracks are failure of the paint etc on the duct.
I'd go to work with a wire wheel or sanding disk, followed by Dye penetrant inspection
A Dye penetrant inspection kit can be had for less than 50 bux. The kit will have instructions. If followed carefully, civilians can achieve good results.

 

[MichaelW.]

correct, its like metal is slowing being eating(dissolving) away. this duct is about 80ft in the air, if this continues duct will fall. top picture has about 1" gap. I have been told from manufacture that fabricated duct was stiffing ring is acting like a heat sink and condentsation is building around welds and acids from wood chips are what is eating metal. Another fabricator said when you fab duct, you have a preheating metal before you add stiffners. Welded joints are not showing any signs of this, just the rings..

thanks

 

[gtaw]

Few things worse that inspecting and evaluating welds using photograph with low resolution.

Dye penetrant inspection of intermittent fillet welds? On a ferromagnetic material? We're all going to die!

Hire some welding inspectors to inspect the welds. Let them determine if the welds meet the requirements of the design or contract. It would be helpful to know what the material of construction is, what welding standard applies, what does the drawings specify for the welding (size, length, etc.), how long the duct work has been in service. If the duct work is carbon or high strength low alloy steel, magnetic particle testing would probably a better choice that dye penetrant testing. By better, I mean faster, less mess, and less likely to contaminate the material that would interfere with welding should it be necessary to make field repairs.

The welds look "smooth (I don't see any characteristic ripples). Perhaps the system has been in service for a period of time and the welds have been "worn" smooth by the wood chips passing through the duct.


Best regards - Al