Case of welded truss with unbaked E7018 1

[fcu45]

Hi

Im envolved in a situation where the contractor has done partial penetration fillet welds on MS truss joints with the electrode used is E7018 without any baking.

Having the right to order to redo the weld.
And adopting AWS D1.1.
Would you recommend that? Would there be any possibility for the steel members losing its strength on the grinded welds that has to be redone? We are looking at 40 joints.

Can we avoid redo the weld by conducting package of NDT tests?
The problem here the weld is not full penetration puting limitation in this choice.

My highest priority is not to tolarate for the quality and service life of the structure. Time comes secondary here.
Highly appreciate your inputs

 

[IFRs]

The baking is at least in part to remove water to avoid hydrogen embrittlement of the weld. Is the part subject to loads and/or conditions where such embrittlement is a concern or was 7018 chosen because the welder liked it better than 6010 or some other rod? Was the base metal and joint dry or heated to drive off moisture?

 

[gtaw]

The question will always be "what are the mechanical properties" of the welds deposited with the unbaked electrodes.

The low hydrogen electrodes are specified to mitigate the probability of hydrogen assisted cracking. The covering of a low hydrogen electrode is hygroscopic, thus it will absorb moisture from the air. If you are in a very dry climate or a very cold climate where there is little moisture there is a low probability of moisture in the electrode. As the relative humidity increases, so does the amount of moisture in the flux covering.

The contractor could qualify a WPS using the same electrodes used to weld the truss, but there will always be the question whether or not the electrodes are in exactly the same condition as the welding electrodes used.

Assuming you entertain leaving the welds and using the truss as welded, you could perform NDT, i.e., MT to verify the existing welds are free of cracks. I suggest using wet fluorescent magnetic particles with a black light to detect any small and large cracks that be present. You must recognize only those cracks that have propagated to the surface are likely to be detected. There could be subsurface cracks that could go undetected.

Once a problem has been identified, it is always expensive to correct the welds that it would ha been if the contractor did the job correctly. Some contractors operate with the mind set that if they get away with "it" four times out of five, they've make money. The cost of getting caught and making the corrections is simply the cost of doing business.

Best regards - Al

 

[dhengr]

Fcu45:
Does the truss structure, the steel material used, the details, weld stresses and the welding conditions really require the E7018 electrodes or were they the default electrodes selected. A number of the suggestions above are worth considering. Why not get some of the welding engineers from the electrode supplier involved? They also have a vested interest, and far more knowledge on the matter than you and I, and might take some of the load off your shoulders. I’m not suggesting you should let the contractor off the hook, he should certainly pay for the investigation and any remediation required.

 

[darthsoilsguy2]

not baking alone doesn't seem to be enough cause for redo work. i would think there has to be other conditions involved and documented (which there may be but not posted). A contractor can open a container of 7018's and have his crew burn them away if they are doing a lot of work. the problem is usually if ambient conditions were bad for welding anyway or the substrates were wetted and not preheated back to dry. i could see raising a stink to make a rod oven show up on-site so that the new rods have a good place to hang out until they are used. Usually i would imagine joist structures fabricated in the shop which would be better protected from the elements.

on a different note.... there may be a regional language thing going here, but when i read the phrase "partial penetration fillet welds" i cringed. i think most people refer to full-pen, partial-pen, and fillet welds separately. Partial-pens generally being groove welds that can't be classified full-pen because no backer rod or back-gouging the root, or due to the groove dimension never allowing full penetration. In actuality, there abosolutely is partial penetration occurring in proper fillet welds..... i just wouldn't say it around here or i would get dirty looks from welders.

 

[fcu45]

Thanks dear colleagues.

dhengr
It is box truss for elevated walkway.
The electrode was used because the senior welding supervisor there is used to use it.

The ultimate expected loading stresses in almost all of the truss members does not exceed 30%-50%.

Top chord is 6 inch
Bottom is 8 and bracings are 5.

As I need to take a decision. What do you recommend?

 

[gtaw]

Per AWS D1.1, ASTM A500 does not require low hydrogen electrodes. However, the question is: What are the mechanical properties of the electrodes that were not stored correctly?

Best regards - Al

 

[fcu45]

Thanks Al
Attached picture for Packet of the used electrode.

 

[fcu45]

Attached photo of finished joint.

 

[gtaw]

Based on the photograph, the welds look like they can meet the visual acceptance criteria of D1.1, but there is no way to know what the fit up was, whether the welds are open root (no backing), whether the welders were properly qualified for the position or with or without backing, or whether the WPS was qualified for open root or whether the design calls for CJP or PJP and fillets.

Was there QC involvement during the fabrication? Did QC verify the fit-up conditions, i.e., root opening, groove angles, etc.?

Were the electrodes removed from hermetically sealed containers? Were the electrodes purchased in cardboard boxes with a plastic inner liner? Was the inner liner punctured so that it was no longer hermetically sealed? If the electrodes were contained in hermetically sealed containers, how long were they exposed to ambient conditions?

In an effort to mitigate the potential of costly rework, consider qualifying the WPS using electrodes that have been exposed to conditions similar to those of the electrodes used to fabricate the existing trusses. You and the fabricator will have to agree on certain assumptions to replicate the ambient conditions and exposure conditions of the electrodes.

Nothing in life is a sure bet, so all you can do is take those actions that will put people at ease. The cost of qualifying the WPS is not insignificant, but the cost of removing all the existing welds will be considerably more expensive and there is always a chance that more damage to the members will result by attempting to rework the trusses.

The bottom line is the Engineer and the Owner must be satisfied the structure will meet the design. The other alternative is to scrap the existing trusses and fabricate new replacement trusses. This time place a qualified verification inspector (AWS CWI or SCWI)in the shop to oversee the fabrication and welding.

Best regards - Al

 

[fcu45]

Thanks Al

Tomorrow will conduct fracture test on a joint done under same conditions.

And will conduct as first step NDT for selected joints. If results not satisfactory. Will do for all.

But what would be the most beneficial NDT here?

Regards

 

[gtaw]

I would use wet fluorescent magnetic particle testing after removing the paint from the welded joint and a few inches from each side. The strength of the magnetic field will be reduced slightly by the paint. The thicker the paint, the weaker the magnetic field produced. Since you are interested in finding even the smallest crack, you need to ensure adequate magnetic field strength is developed. That means the legs of the yoke should be in intimate contact with the bare metal surfaces.

Delayed hydrogen cracks, the concern in this case, initiate as very small micro cracks that propagate to interconnect and form larger cracks.

While MT will detects surface breaking cracks, it will tell you nothing of the mechanical properties of the weld.

Best regards - Al

 

[TDIengineer]

Great posts. Good info gtaw. You appear to know your stuff!

 

[berkshire]

The one thing I have not seen in this discussion unless I missed it, was what was the actual condition of the rod to begin with?
If the rod was taken from a new sealed container, either plastic bag or sealed tin. Baking would not have been needed.
If the rods were taken from a half used pack that just happened to be lying around then, Yes baking would be required.
B.E.


You are judged not by what you know, but by what you can do.

 

[berkshire]

I see GTAW did ask the same question in a slightly different form
Were the electrodes removed from hermetically sealed containers? Were the electrodes purchased in cardboard boxes with a plastic inner liner? Was the inner liner punctured so that it was no longer hermetically sealed? If the electrodes were contained in hermetically sealed containers, how long were they exposed to ambient conditions?
The critical part of this question is " How long were they exposed to ambient conditions?"
B.E.


You are judged not by what you know, but by what you can do.

 

[Weldinspect]

If there was not much moisture in your enviroment and the electrodes were not kept out of the plastic protection for more than one hour or even ´till next day the welding should be ok and AWS D1.1 aproved, the welds look ok in the picture. As advised by others take the paint out in a couple of welds and NDT them to check. Next time ask for the welding procedures before allow the welders to start, and never ever allow them to get to the site without an electrode oven, if they do they may not know what they are doing.

 

[fcu45]

Thanks all for your valuable contribution.

The electrodes packet as answered by the senior suprviser is finished in 1.5 to 2 hours from opening. The climate was mild with humidity of 50 or 60%. There was no rain.

Will conduct the tests next week.
Regards

 

[gtaw]

A E7018 electrode can be exposed to the atmospheric conditions for up to four hours if the governing code is AWS D1.1 Structural Welding Code/Steel.

If the supervisor's observation that the electrode container was open for a couple of hours, there should be no problem assuming there were no breaches in the container that would allow moisture to enter the container.

I should make note that if the electrodes were classified as E7018-H4R, they are moisture resistant and can be exposed to ambient conditions for much longer periods of time than the standard E7018. My experience has been that they are very effective in resisting moisture absorption. The structural welding code allows for extended exposure times of about nine hours.

Best regards - Al