A588 Weathering Steel Electrode Selection/Accelerated Cycles

By yojimbo (***)

Date 04-06-2019 19:33

I've read several archived discussions and looked at D1.1 3.7.3 and Table 3.3 but questions remain. The project application is primarily architectural and falls under AWS D1.1. Some concrete park ramps will be built and some A588 flat bar, 1/4" X 12" will be fastened to the sides of the ramp with concrete screws. There will be 3 different sets of welds to be done, all fillet welds: corner to corner welds where the flat bar needs to transition to a different direction, at the splice points where the 12" flat bar sections meet there will be a 1/4" X 1 1/2" strap to capture the adjoining 12" flat bars and avoid needing to butt weld them, and along the top edge of the 12" flat bar there will be some 1/4" X 2" X 2" squares to act as skateboard deterrents. There are no design requirements from us and the application will obviously not see any loading. The primary considerations here are visual.

Specifications call out material undergoes 5 accelerated cycles prior to being brought on site. This is the second subject in question: Best means of accelerated weathering. Suggestions/answers appreciated.

Regarding electrode selection: reading the archives it seems a 70 series low hydrogen electrode will work if the welds are kept small and this will allow enough base metal chemistry to induce weathering characteristics in the weld pool. We hope to use a GMAW ER 70s6, .030 bare wire and all welds are either 3/16" fillets or 1/2" plug welds. We'll keep it to as welded if that is a pre-qualified WPS- will post heat treat if absolutely required.

In summary the questions are: Electrode selection for color match, means to induce weathering cycles, pre-qualified WPS.

Thank you in advance.

By yojimbo (***)

Date 04-10-2019 00:38

Bumping this in hopes of some input.

By 803056

Date 04-10-2019 02:01

As noted, there must be sufficient dilution to pickup sufficient chemistry from the base metal to produce a weld with weathering characteristics.

The 1/2 inch plug weld is unlikely to produce sufficient dilution.

If the welding process is in the spray transfer mode, sufficient dilution is probable when depositing single pass 3/16-inch fillets. However, pulse or short circuiting transfer is unlikely to produce sufficient dilution.

Al

By yojimbo (***)

Date 04-10-2019 17:01

Thank you Al. We had been planning on a short circuit transfer for the welding. If I understand correctly- the electrode would work in the spray transfer mode. Generally use a 75/25 gas. Would changing to 100% argon get us to spray transfer and would this achieve the dilution? If not, can you recommend a preferred wire electrode?

By 803056

Date 04-10-2019 17:55

I would not recommend 100% argon. A mix of 90% Ar and 10% CO2 should work fine. Some people like 95% Ar and 5% CO2.

75% Ar with 25% CO2 is not what I would recommend. The arc may become unstable and alternate between short circuiting and spray transfer at lower voltages. Its fine for short circuit transfer, but not the best choice for spray transfer.

As for the parameters, use the recommended parameters of the electrode manufacturer. Since this is bare wire, the parameters listed by Lincoln will be pretty much the same as those found on ESAB's web site.

In the case of spray transfer, the contact tip should extend about an 1/8-inch beyond the end of the gas nozzle. Depending on the gun, you may have to buy a shorter gas nozzle or longer contact tips. With a Tweco gun, you can usually slide the gas nozzle on or off a little to provide the proper contact tip extension (opposite of set back). Keep in mind that the electrode extension (CTWD) will be longer than that used for short circuit transfer.

Let me know how it goes.

Al

By Steelslinger (**)

Date 04-10-2019 20:19

We weld a lot of A588(A709-50W and A847) weathering steels using ER80S-Ni1 with 95% Ar / 5% O2 for GMAW and E81T1-Ni1 H4 with 75% Ar / 25% CO2 for FCAW.

As Al said, I wouldn't use 75/25 Ar/CO2 for GMAW for spray mode. Just doesn't cut it.

By TimGary (****)

Date 04-10-2019 19:22

Have you seen the D1.1 : 2015 requirements for weathering steels in section 3.7.3 and Table 3.4?

Attachment: Table3-4.JPG (81k)

By 803056

Date 04-10-2019 20:27 Edited 04-10-2019 20:30

In this case I believe they are trying to utilize the exceptions to clause 3.7.3 by invoking clauses 3.7.3.1 and 3.7.3.2. They also need to look at 3.7.4 with regards to the appropriate shielding gas.

Personally, I would simply use a matching filler metal selected from Table 3.4. Eliminate the concerns with the size of the fillet weld or groove weld, dilutions, etc. However, that wasn't the question.

Al

By yojimbo (***)

Date 04-11-2019 20:51

That is correct Al. As Slinger pointed out there are better wires for our application. The local suplpy guy is checking out a Lincoln .035 wire, a Super Arc LA 75 80 series which is, I believe, the ER 80S-Ni1 Slinger referenced. In order to produce the patina before bringing the steel to site, we are looking at either, wheel abraiding or sand blasting instead or treating it chemically. A different outfit's project showed the A588 developing a deep patina after only a week or so of watering cycles after being sand blasted to remove the mill scale. It would be nice to get rid of any chemical treatment.

By Steelslinger (**)

Date 04-12-2019 12:45

We shot/grit blast all of our structures to one of three SSPC specifications, SP7 for most structures to remove scale and rust so that it patina's evenly, SP6 and SP10 are sometimes required either by general specification or because the structure will be painted.

Being in the upper midwest, we don't perform any watering operation unless specified (often due to the location of installation). I would caution using any chemicals to accelerate the patina as that could affect the corrosion properties of the weathering steel.

Depending on your local (or local to point of use of your product) weather patterns, the patina can develop rapidly. Sitting in our yard during a typical Minnesota Spring/Summer and even fall, within a week or two, it can develop a patina of bright orange on most surfaces (undersides tend to take longer). It can take a several months for the dark brown patina to develop, again the underside would take a bit longer. Arid environments would take much longer to develop the patina.

Lincoln LN-75 is the exact wire we use for GMAW on weathering steels.

By yojimbo (***)

Date 04-12-2019 18:25

Hey Slinger-

Thanks for weighing in- good info. I'll be seeing my sandblast guy today and dropping off a foot of A588 to run a patina test. This is strictly an architectural element in a park so the city's primary concern is visual. The only spec referencing patina is that it's gone through 5 "accelerated weathering cycles". If we bring out nicely rusted sections to hand on their ramps, they're going to be happy. It's designed so any rust runoff should feed into planted locations so if it does at least it shouldn't stain the concrete. I wondered if they'd thought about this before the gave the architect free rein. Good to know the blasted steel patina develops so quickly- will help determine production schedules.