Rebar "Weldability" 3

[EIT2]

The only reference to rebar weldability that I have is the "ACI DETAILING MANUAL - 1988". There it states that all standard bar specifications, A615, A616, and A617, specifically note that "The weldability of the steel is not part of this specification." Further, "it is recommended that bars conforming to ASTM A706, ... be used ... wherever important or extensive welding is required."

Contractors that I have dealt with, do not want to hear anything about rebar not being weldable ... they have been doing it for years ...

Am I outdated with my references?

Is A615 still not weldable?

Have the specifications for A615 been updated?

Any commments?

Thank you!

 

[amokhta]

You should indicate on the project drawings/specifications that "the welding of reinforcing bars shall conform to the ANSI/AWS D1.4 Welding Code." ANSI/AWS D1.4 requires the Contractor to prepare written welding procedure specifications conforming to the requirements of the Welding Code.


Reinforcing bars conforming to the ASTM A706 specification are intended for welding. The ASTM A615 specification includes a statement concerning welding: " ... Welding of material in this specification should be approached with caution since no specific provisions have been included to enhance its weldability. When the steel is to be welded, a welding procedure suitable for the chemical composition and intended use or service should be used." The specification then recommends use of ANSI/AWS D1.4 for welding of reinforcing bars. The "carbon equivalent" formula in ANSI/AWS D1.4 for A615 bar is: C.E. = %C + %Mn/6.


In either case, the bar producer should be required to report material properties so that the Contractor will have the C.E. available for the bars to be welded.

I hope this helps.

 

[Koz]

Hi all,

Welding of reinforcing steel, including A615, has been done successfully for years. There are several other considerations that must be made but most significantly, the higher the CE, the higher the preheat needed before welding. Contractor's don't want to hear this either, but it is crucial to a successful weld in this kind of material. It is also an easy place to cheat, when no one is looking .

AWS D1.4 is an excellent document. It requires destructive tests to validate the welding procedure. It also sets preheat and filler metal requirements. Your contactors' methods will be safe if they follow the requirments of the Code. Unfortunately, I have found that there is a steep learning curve among reinforcing steel contractors. They haven't used this Code even though it has been around for years.

Require your contractors submit welding procedures, procedure qualification records noting the successful acceptance of the tests, and the qualifications of the welders. Regardless of the reinforcing steel used, if the welding procedure has been proven by test, I am inclined to accept the weld, unless D1.4 prohibits the welding of that type of steel. I am 85% sure, however, you will find your contractors procedures or personnel qualifications don't meet Code for the joint configuration you are trying to accomplish. D1.4 Code testing gets real expensive, real fast!

Rebar tests per D1.4 are required even when welding reinforcing steel to structural members!!!

D1.4 also establishes allowable joint designs and stresses. If you are designing reinforcing steel, you must have this welding standard. It costs less than $100 and will reduce your errors and liability. Don't just quote it in your specs, use it in your design.
Koz

 

[CWIC]

In addition to the very good comments already provided, check out the following thread on this subject:
thread507-55969

 

[jheidt2543]

The July 2003 issue of Concrete International, published by ACI, has an article that covers some of the above topics and clarifies a number of terms regarding rebar welding. The article is "Thermex-Processed Reinforcing Bars - Heat treatment increases ductility and weldability of steel", pages 85 - 88.

 

[Koz]

Hi all,

I just waded through the thread that CWIC referenced. Boy, that thread goes far afield. Here are my comments.

Hats off to dik for his code information. It is right on.

It doesn't take a "good" welder to weld reinforcing steel. A commonly certified welder will do. The techniques used are taught in the 1st year of a 2-yr welding program at any technical college or union trades program. It takes a conscientious welder to preheat the reinforcing steel in accordance with the tested welding procedure parameters.

It takes someone with welding technology or welding engineering skills to develop a good welding procedure. This step cannot be left to the common craftsman performing the work. These skills are not being taught in welding programs and are not being taught in civil engineering classes.

The stainless to carbon welds talked about in the thread are completely beyond the scope of AWS D1.4. While I am hearing about this connection more and more, it leaves D1.4 in the dust. AWS D1.6, Structural Stainless, appears to have provisions for this combination.

Previously, I said I would be inclined to accept "any" welding procedure that survived mechanical testing. In light of this thread, I have to retract that statement. Welding reinforcing steel to 300 series stainless with E308L is bad practice. I agree with the manufacturer that the qualifying group responsible for the welding procedure "lucked out". E308L will work for small sections if there is not much dilution from the reinforcing steel base metal. But it is not normally the "right" decision. I bite my tongue to say use the more common E309L. We need to know the joint configuration and the service conditions i.e. temperature and cycles before we can stand behind E309L. This rod is built for joining carbon to stainless base metals and will work in most cases. But it has it's limits. I would say make sure you stay within the electrode manufacturer's recommendations for filler metal and electrical parameters. Allow excursions only from top-notch welding technology/engineering groups and then make them prove it to you the hard way.

There was also some discussion regarding the quadruple certification of A36,A572 gr 50, A992 (wide flanges), and A709. It is all the same material. I have answered this question before. A careful read of the above specs shows that they all cross-qualify and there is no difference. A992 has a mechanical limit that the others don't have, so it may not qualify in some instances. And with the exception of some angles and round bar and heavy plate, you can't get A36 with 36 ksi yield any more. Check your certs. That is why we use low-hydrogen type electrodes on virtually all structural steel anymore. Again, we can't leave this decision up to the craftsman. It must come from welding engineering.

Fun!
Koz

 

[CWIC]

The original post by EIT2 inquired about the weldability of:
A 615, A 616 & A 617 vs. A 706 (known to be weldable).

All of the above materials (depending on the grade used) are weldable and are listed in Table 5.1 of the AWS D1.4-98. As I noted in another thread, these and any other materials welded in accordance with the D1.4 code require procedure qualification, there are no prequalified joints, welds or processes.

I have inspected countless rebar welds over the years, here in the US and in several other continents. I respectfully disagree with "A commonly certified welder will do." Commonly certified welders often repairs many of their own welds even though they have been certified/qualified to perform these welds for a number of years. Not all of these welders have gone through an apprenticeship program or any other formal training. Even the ones who have training (ironworkers, pilebutts, millwrights, etc.) often ignore what they know to be code and SOP throw most of that knowledge out the window in the name of production. All of the rebar welding performed at the now famous "Orange Crush" in CA was performed by trained, experienced, journeyman trademan. I guess they knew what they were doing - despite the taxpayers having to foot the bill to repair about 70% of these joints (replaced by mechanical couplers). I have only been on a few jobs (just a few) in the last 12 years where the welders did EXACTLY what they were required to do with rebar.



While the topic reinforcing steel to stainless steel is slightly off from EIT2's original post, naturally I have a few comments on this subject as well:
thread330-65649

If dissimilar metals are joined, overlapping codes occur or the weld does not fall within the scope of any code whatsoever, I often use the AWS B2.1 Specification for Welding Procedure and Performance Qualification. This spec. is widely accepted by the designers who send their "unusual projects" to my office. For most of my projects that involve "nonstandard" welding procedures, we typically perform full scale mock-up tests in addition to the procedural mechanical, nondestructive and metallurgical testing.

 

[Koz]

Hi all,

Interesting. Most of the welds in reinforcing steel are fillet welds or their indirect cousins the flare-bevel groove. At times we see direct butt joints that require complete penetration and chisel-point tees. Most joints are lap joints, indirect butt joints, or common tee joints. Very simple, very easy. Fillet welds are taught in the "Basic Welding" courses of welding programs, a little after beads on a pad. AWS QC-10, a national training program for welders, has fillet welds very early in the sequence. Union apprenticeship programs follow similar formats. Strength of the electrode is not an essential variable for the welder. It doesn't take a good welder to weld a fillet weld. An average welder will do, if he can follow a good welding procedure.

The reinforcing steel, itself, welds no differently under the arc than any other carbon steel. The product form, however, is significantly difficult for the direct butt joint qualification. Radiusing around the diameter of the bar takes a lot of skill by the welder. That is why D1.4 has the welder qualify on the smallest diameter for which they'll be qualified. Beyond the rod manipulation, if the welder follows a proven welding procedure the welds will be acceptable.

Now are we teaching our welding students to inspect their own work? I don't think so. Code-based training is only recently being promoted in QC-10 programs or AWS S.E.N.S.E schools. All of the Ironworker Apprenticeship Training Labs have AWS CWI's running their programs. I am confident that these students are learning code-based welding and are capable of evaluating their welds, good student bad students aside. We have bad students in our civil engineering programs and nondestructive examination schools.

Until we establish a national training program, we can't expect that all welding instructors are teaching skills relevant to today's demanding designs. Many are still teaching how to weld a "good bead". A lot of welders don't know how to measure their welds so many rejectable welds result because we have not adequately conveyed what is required. It's like working with adults who haven't learned how to read. We all suffer from their personal handicap. We all should be promoting quality welding education as recommended by AWS and the trade unions. Our country's infrastructure depends upon this committment. That costs money, however, and remember the US is a service society or so we are told.

But I have seen many good welders lay down shoddy welds because they are being instructed to do so by their foremen and supervisors. I was told early on, if you want to keep your job, never argue with the boss. That still holds true. So if the boss tells me not to worry about the preheat and he is the one controlling the weed-burner and my paycheck what am I, as a welder, to do? And after looking at what happened with Arthur Anderson and Enron, it seems most Americans know where this is coming from. Responsibility must come from those of us at the top of the decision making chain.

Low bid doesn't mean low cost as evidenced by the high repairs you note. So engineers and their eyes on the project, the inspector, have to hold the erectors and shop fabricators hands to the fire. Sorry, but that is the way it is when we have welding illiterate management. Make welders do the work the way the specs require. That gets me back to my early statement to EIT2. Buy a copy of the Code and use it. Don't just quote it in your specs. And I would add enforce it.
Koz