Low-Hydrogen FCAW Electrodes

Date 05-28-2003 22:29

Check out the Annex to AWS/ASME A/SFA 5.20. Paragraph A8.2.2 says "Flux cored arc welding is generally considered to be a low-hydrogen welding process. However......" It then goes on in that paragraph and for another 1 1/4 pages about hydrogen & its precautions/testing in FCAW welding.

By DGXL

Date 05-29-2003 00:26

CHG:
This is probably NOT what you are looking for, but just my 3 cents worth. Hope it is not too inappropriate in reply.

*There are low hydrogen electrodes (SMAW) and processes which will provide a low hydrogen weld metal deposit (as required by the specific electrode specification/classification). The latter would include most of the common arc welding processes such as GMAW, FCAW, SAW and GTAW. Comment: CHG, as you already know (by your previous posts), shielding composition has lot's to do with the as-welded deposit.
*AWS A5.01-93 (filler metal guidelines) uses the term "low-hydrogen" in example 2 and notes the "...moisture content of the covering..." for SMAW electrodes.
*The term "low-hydrogen" was originally intended for SMAW electrodes (IMHO). I have a letter from the previous AWS senior engineer and D1.1 chair who [adamantly] states the term low-hy and any process other than SMAW to be incorrect. Basically we are in agreement. The letter was issued in response to statements made in FEMA 353. I asked the SAC committee (formally) to provide a qualifier for these statements, but no response. We did get responses to other issues though...

Now for my (non-cents):
1.) In the D1.1:2002, A572 Gr. 65 requires a low alloy (A5.29) FCAW electrode per Table 3.1. An E71T-1 electrode would require additional designator(s) to comply with a low-alloy classification. It gets more confusing: Table 3.2 (preheat) does not list the FCAW process for A572 Gr. 65, but notes the SMAW, GTAW, GMAW and SAW processes. I do not have any errata to resolve this.

2.) I don't know what your project specs. denote for impact, but E71T-1 has a 20 ft-lbs @ 0 degrees. 20 @ -20 is the flavour of the month in CA for any structural welds.

3.) A5.20 denotes an E71T-1 as having a rutile-based slag system, to my knowledge this component is not low-hy in composition (but, the weld metal deposit is).

Personally, I think this weld and the materials to be joined are not at all problamatic, but I don't have specific info on the service, location, type of environment, etc. of the duct. So it would be easy to say "go for it".

Are FCAW electrodes low-hydrogen?
This is a question that (to my knowledge) has not been defined by the powers that be. When you find out, let us know so we can all get some sleep and put the issue to bed.

By Fred Alvarez Date 05-29-2003 06:27

This is probably not as difinative as you would like, but Lincoln's Procedure Handbook, Page 6.5-1 and 6.5-2 states:

"In the gas shielded flux-cored arc welding process the shielding gas protects the molten metal being transferred across the arc from atmospheric oxygen and nitrogen by forming a protective envelope around the arc and weld pool. There is little need to denitrify the weld metal with the flux because most of the nitrogen is excluded by the gas shield."

By rpoche

Date 05-29-2003 08:22

CH,

Try this article from Lincoln -

http://www.lincolnelectric.com/knowledge/articles/content/fillermetals.asp

Robert

By jwright650 (*****)

Date 05-29-2003 16:55

Good article, Robert.
John Wright

By billvanderhoof (****)

Date 05-30-2003 03:29

Ditto
Bill

By CHGuilford (****)

Date 05-29-2003 16:08

Thanks for the help everyone.
I had missed the Annex to A5.20 but the article Robert provided the link to will probably work out the best in this case.

DXGL, I did see A572 Gr 65 in category C of Table 3.2 but I had not noticed FCAW not being mentioned until you noted it.
Impact strength is not specified in this case. This is just an air handling system that might see a little vibration but nothing major. Grade 65 material was not the original material specified but was found by our purchasers in sizes and prices that make good sense to try to use. The engineer rightfully questioned the weldability to A992 or A572-50, so I'm researching the code issues of that. But, basically, the A572-65 would be used as the ducting, which is bordered on the exterior by structural steel. A lot of the welding is stitched, so I don't think there should be much of a problem.

As far as the FCAW being low-hydrogen question, the article Robert pointed to sums it up as well as I think we'll see.

Again, thanks to everyone.
Chet Guilford

By billvanderhoof (****)

Date 05-30-2003 03:36

Since the flux is inside the tube it would seem (without science to back me up) that the flux is well enough protected without oven storage. I guess a truely anal person would clip of a few inches from the end of the wire at the start.
Bill

By PhilThomas (**)

Date 05-30-2003 13:20

Yes and no. The ability for a tubular wire to pick up moisture is largely dependent on the seam construction. Lap and butt seams are the most common constructions, but both can allow moisture pick up. There are some FCAW wires (Nippon and Thermal Arc are two that I know of) that use seamless construction which essentially eliminates this variable.

The other thing to consider is "how hygroscopic are the core ingredients?" and what steps are taken to prevent them from absorbing moisture....particularly during manufacturing the wire?

::plink, plink::

Phil

By amarlowe444 Date 05-31-2003 21:55

Forgive me for intruding in your conversation but I heard that low H2 FCAw s not only should be exempt of H2 content but should also clear from this element the surrounding welding area (includimg HAZ) because if not the effect is lost.
Also I hear that elements active in true lowH2 do that.
Have you heard something about it?

By PhilThomas (**)

Date 06-01-2003 01:26

That is true. The measurement most commonly used is "diffusible hydrogen" which is of the scale ml/100g of weld metal. The FCAW (or SMAW rod, for that matter) must provide sufficient shielding and/or scavenging - and contain a low enough level of hydrogen - to keep the amount of diffusible hydrogen in the deposit below the certified level.

By sayeeprasad (*)

Date 06-03-2003 11:47

If I remember correctly, most manufacturers make FCAW wires with seams. Oerlikon is the pioneer and in fact has a patent(Again I can't confirm this immediately) for making seamless wires where the flux is filled up into the semaless tube by using vibrations(The density of the flux in the core should be even all along the length) and then the tube is extruded to the final required diameter.

By Niekie3 (***)

Date 06-03-2003 17:09

Hi

I may be mistaken, but I was under the impression that Lincoln pioneered both the FCAW process and the seamless wire.

Regards
Niekie Jooste

By jwright650 (*****)

Date 05-30-2003 13:26

I have seen ovens that you store 60# coils of wire in. I think it was FEMA that requires FCAW exposure limits just like a SMAW LOW-HY rod. Oh, I better quote the paragraph cuz I might screw it up:)

Excerpt from FEMA 353 Part I 3.3.3 Electrode Storage and Exposure Limits

FCAW electrodes shall be received and stored in the original, undamaged manufacturer packaging, until ready for use. Electrodes in packages that have had the external plastic wrapping damaged shall not be used for welds in Seismic Weld Demand Catagory A or B...................

...........In lieu of testing, when welding is suspended for more than 8 hrs., electrodes shall be removed from the machines and stored in an electrode wire oven maintained at a temperature between 250F and 550F, or as recommended by the mfg. Electrodes not consumed within 24hrs of accumulated exposure outside closed or heated storage shall not be used for welds in Seismic Weld Demand Catagory A or B. Electrode spools shall be identified to facilitate monitoring of total atmostpheric exposure time. FCAW electrodes that have been exposed for periods exceeding an accumulated 24hrs. may be dried if mfg's testing and recommendations show that drying is effective at removing moisture and restoring electrodes to their designed diffusible hydrogen level.

Also in paragraph 2.4.1.2 Hydrogen Level

It states that "For welded joints as Seismic Weld Demand Catagory A or B, the filler metals, as supplied by the mfg, shall meet the requirements for H16 (16 ml diffusible hydrogen per 100 grams of deposited weld metal)....."

just for more info on the subject,
John Wright

By billvanderhoof (****)

Date 05-31-2003 02:11

A day when you don't learn something new is a poor day indeed.
Thanks
Bill

By DGXL

Date 05-31-2003 18:28

CHG:
Kinda waiting to hear what turned out with your original post. This is always an interesting topic.

By CHGuilford (****)

Date 06-01-2003 12:10

DXGL,
I haven't heard anything yet. I forwarded copies of applicable D1.1 Tables, A5.20-Annex 8.2.2, and the article from Robert's link. I will post a follow up as soon as I hear.
Chet Guilford

By CHGuilford (****)

Date 06-16-2003 20:48

DXGL and Other Interested Parties,

I promised an update so here it is: The customer's engineer wasn't comfortable with welding A572-65 to A572-50 and he requested that a PQR be run. The project manager, who had initiated the substitution request, decided that the cost savings would be eaten up in the testing. So the request was withdrawn and he has ordered the material as originally specified. [I promised a follow-up; I didn't promise it would be a good one :) ]

Thanks to everyone who responded. Even though it turned out to be an exercise in academics, I still learned from it.

Chet Guilford

By DGXL

Date 06-16-2003 23:30

CHG:
First, let me say thanks for being a forum user who actually posts the outcome of his/her query.

My intial response (above) seems to be somewhat of a pain in the butt to most of the clients I do business with. They usually don't like what I have to say on this subject. Scott Funderburks article (in the link posted by Mr. Poche) appears to be in line with my way of thinking as well. The article also paralles what is stated as low-hydrogen in the A5.01 guidline. There are actually a number of papers and references on the subject, all with the same opinion, low hydrogen is a term used for SMAW electrodes (their covering actually).

A low hydrogen weld metal deposit is attainable from the commonly used processes. A low hydrogen process(?), that still has me kinda confused as the definition of this term changes from project to project depending on the [welding] knowledge of those who make decisions on our behalf.

So where does this leave all of us welders, consultants, designers, forum users, managers, etc? Until one of the industry authorities or organizations steps up to the plate and formally defines these terms with regards to each variation (low hydrogen electrode, low hydrogen process, low hydrogen weld metal, etc.), it will always result in a misunderstanding by those who make decisions on our behalf.

While discussing this issue on a recent project, the RDP simply stated: "Use low hydrogen electrodes..." When I asked which one, he got somewhat upset, because he did not have an answer for this question even though he put it into the specs. The same appllies to the FEMA stuff or Section XI of the D1.1. If your going to spec it, you better know what your getting into, most do not. Misunderstanding welding terminology, the use of a particular code, all can be costly to those who fabricate or erect structures.

How did my post turn into an understanding of weld terminology? I received a set of drawings last Friday that states: "...use low-hydrogen electrodes..."

Thanks once again CHG.

By rhoople47 (**)

Date 06-17-2003 15:49

Anyone; I have a question that's a little off this target with FCAW, but isn't a GMAW soild wire a low HY. also? No flux No HY, right? I think I read somewhere that it was, am I wrong? Kind of a dumb question, but when they say low HY, couldn't you use a solid wire GMAW process? OR, does it have to be a FCAW or SMAW?

Rick