Corroded steel surface prep for welding.

[MacGruber22]

Is it appropriate to specify SSPC SP-10 for preparing corroded structural steel for welding? After reading the SP-10 specification, it seems that there still could be a problem with deep corrosion pits and delamination. I know it is not the most rigorous surface preparation, but I figured that once that level of prep is complete, additional spot prep could be performed to remove deeper defects. I couldn't find anything in the AWS standards I have.

The application is fairly critical, as there is no redundancy if the welds fail.

 

[gtaw]

Grinding is the most frequently method used to prepare surfaces for welding. As you noted, deep pits must be ground to remove the imbedded corrosion. Since the areas have to be blended (faired) in with the adjacent surfaces, little is gained by grit blasting unless the corrosion is relatively light.

Best regards - Al

 

[Tmoose]

SP-10 supposedly looks like this -

http://blastal.com/index_files/sp10pix.html

depending upon what you are really doing, some of the maintenance SMAW electrodes would make a pretty sound weld with that level of prep.

http://www.lincolnelectric.com/en-us/support/welding-solutions/Pages/welding-rusty-steel-detail.aspx

As always, There is more to success than weld quality.

http://img.photobucket.com/albums/v315/erikas/DSC00399.jpg

 

[MacGruber22]

Thanks, gtaw.

Tmoose, there is an additional complication to this weld. The existing steel is about 80-years old. Now, it is most likely ASTM A-9 Gr.30 or better, but I know they did not have carbon limitations in the A-9 spec, so weldability could be suspect. I have drawing notes that provide that information and say that the ultimate weldability and electrode/process selection is the responsible of the contractor. Is that sufficient, or do I put notes that call for composition testing? Also, in lieu of the composition testing, I thought there was a in-situ test where you weld lugs on the existing steel and perform a shear or pull test?

Thanks for the photos, Tmoose.

 

[metengr]

Yes, there is an in-situ test where you can fillet weld a lug and stike it with a hammer. If the lug fractures at the fillet weld instead of bending, the weldability of the steel is in question and would require a small sample removal for chemical analysis.

 

[gtaw]

Like anything else, not all contractors are created equal. If you don't ask for it, you won't get it.

Carbon isn't the only potential problem. The early steel specifications typically didn't have to worry about sulfur or phosphorus, both very major concerns when welding is used as the joining method.

Consider the fact that your organization will be on the firing line if anything goes wrong and legal action is taken by the Owner. Anything you can do to demonstrate due diligence will mitigate liability in the even something goes wrong. the cost of performing the chemical test and feasibility assessment is to everyone's advantage.

Best regards - Al

 

[yaschief]

Having done repairs on Structural Steel that dates to the early 1900's, I can state that a chemical/coupon test is the minimum due diligence that should be applied. If possible a section should be test welded to see which electrode will achieve the required result. As gtaw has stated , phosphorous can and will be an issue, and where it does it is a nasty one.

 

[Tmoose]

what are you attaching to this octogenarian steel? and where?

I was just thinking maybe it is some flavor of what was called " wrought iron " ?

http://www.twi-global.com/technical.../faq-can-wrought-iron-be-repaired-by-welding/

 

[MacGruber22]

gtaw: I agree

yaschief: Unfortunately, couponing is not going to happen. They won't pay for it. We are requiring an inspection agency to oversee the lug test in addition to IBC special inspections. If the lug test fails, the next step is UT. That is what our senior engineers have agreed on. We are going to use 6010 or 6011 electrodes as recommended by a welding specialist, who said that low-hydrogen electrodes (7018) are overkill for this application. It does concern me that this differs from everything else I have read (Link) but I have to go with what the senior guys want.

Tmoose: They are doubler plates on channels and S-shapes that have significant web corrosion. The members are part of a suspended canopy system. The doubler plates will be welded to the flanges, not the webs. It is definitely steel, not an Iron alloy, as their profiles conform to structural steel shapes listed in the AISC historic steel database.

 

[gtaw]

The lug test described by one of the other posters was described by an engineer from Berlin Steel about twenty years ago in an article published by AISC if I remember correctly. It is a practical approach to a problem the is well known.

The results of the test will confirm the steel member tested is "weldable" if it does not produce a centerline crack while welding (high sulfur or phosphorus) or tear out of the base metal because of high carbon and high hardenability. It provides no information about the mechanical properties, nor does it verify the rest of the steel is equally weldable. Different heats will have different chemistry. There is little likelihood all the steel came from the same heat or even the same mill.

One must consider how highly stressed the member is, whether the design has redundancy so alternate load paths are available should the weld fail.

If the members are critical to the stability of the structure, bolted connections may be the best choice.

Best regards - Al

 

[MacGruber22]

gtaw, I wanted to use bolted connections, but it would require removing a great deal of roofing elements, which nobody wanted.

The only member redundancy is what steel is remaining in the webs (there are no holes through the members) to transfer the shear. These repairs are realistically somewhere in between "belt and suspenders" and carrying all of the load. Calculations indicate that the remainder of the steel section is OK for shear, but we are concerned that defects may be deeper into the steel than what is apparent.

The lug test "Fillet Weld Break Test" is recommended by AISC in the link I provided in my previous response. The test procedures and acceptance criteria are described in the AWS D1.1. I agree that it provides no information about the mechanical properties, but based on our conversation with the welding specialist they believe that is an acceptable lower bound based on where and how we are performing it. The test will be performed on each member on the flanges where the final welding will be performed - that should take care of the rolled steel temperature differences you mention. In addition, the "Macroetch" test will be performed on the flange of the shapes.

Thank for your input!