Infamous Tack Welds

Date 08-18-2011 14:57

You didn't say, but it sounds like you are working to AWS D1.1.
Assuming that you are, Table 6.1 item#1 has some specific language regarding the cracks(doesn't matter where they are).
Also take note of Clause 5.18....lots of talk about tacks.

By FabsForLife (*)

Date 08-18-2011 15:09

Thanks for the reply John,
Yes we are inspecting to D1.1 and Clause 5.18 does nothing but confuse the heck out of me. Clause 5.18.1 (2) states tack welds that shall not be incorporated in final weld shall meet visual weld requirements. So doest that mean if they are incorporated they (tacks) do not need to meet visual weld requirements?

By jwright650 (*****)

Date 08-18-2011 15:28

>Clause 5.18.1 (2) states tack welds that shall not be incorporated in final weld shall meet visual weld requirements. So doest that mean if they are incorporated they (tacks) do not need to meet visual weld requirements?

right.

I try to get my guys to make sure they tack where they can incorporate them(ie. bent plate used as pour stop that is shop welded with intermittant fillet welds).....just clean them good before depositing the final weld over them, and make sure they are not so big as to not be remelted. IOW, thin them with a grinder before depositing over them.

By FabsForLife (*)

Date 08-18-2011 16:23

So what about the cracked ones? They should fall under table 6.1 even if they are incorporated? Also should heavy sections be preheated per clause 3 prior to tack placement if they are incorporated? This is just real grey to me for some reason. Lastly, should WPS's be written for final welds where tacked using GMAW and welded using FCAW be qualified? or am I thinking too much?

By jwright650 (*****)

Date 08-18-2011 16:48

>So what about the cracked ones?

They really need to be removed or really thinned so to be certain that they get remelted completely.

>Also should heavy sections be preheated per clause 3 prior to tack placement if they are incorporated?

My take is on this is no, as long as it is remelted and incorporated.
Although, the reason for the preheat is to prevent cracking because of that huge heat sink that quenches the weld metal creating a hard, brittle spot. I have pictures of an arc strike test that we did and you would be surprised at how it cracked everywhere those little arc strikes were.

>Lastly, should WPS's be written for final welds where tacked using GMAW and welded using FCAW be qualified? or am I thinking too much?

I'm not certain about writing a procedure and having to qualify it because of mixing processes like that...although, we have used SMAW to tack with and FCAW to weld. I'm thinking that you could have a WPS for tacking with GMAW, and a seperate WPS for the FCAW final weld.

Maybe others will chime in with thier opinions.

By FabsForLife (*)

Date 08-18-2011 17:06

Thanks alot John for the input I appreciate it. I'd like to see them arc strike test pictures some day sounds interesting.

By jwright650 (*****)

Date 08-18-2011 17:19

http://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=140333

I think this was the thread...may have to scoll down, but the pics were in there.

By 99205

Date 08-19-2011 00:38 Edited 08-19-2011 00:40

"Lastly, should WPS's be written for final welds where tacked using GMAW and welded using FCAW be qualified? or am I thinking too much?"

2010-D1.1, Clause 5.18.4(1) gives a little guidance on that.

By jwright650 (*****)

Date 08-18-2011 15:07

The info that I was referring to is in the 2010 edition of D1.1.

Clause 5.18 was revised in the 2008 edition and carries into the 2010. I applaude the AWS D1 committee for adding some clarification to tack welds...previously it was left up to the imagination and lots of people had different ideas about what you could do and couldn't do with regards to tack welding.

By raptor34 (**)

Date 08-18-2011 20:48

When I was just out of high school I worked in a fab shop and all the tacks that were made by non certified welders were required to be removed prior to making the final welds. We would fit the joints and tack them in place, when the welder came to finish the weld he would make his own tacks and remove ours before beginning his welds. My opinion on this issue is if any of your weld material will be in the final weld then you will need a WPS and a certified welder.

By 803056

Date 08-18-2011 22:20 Edited 08-18-2011 22:40

D1.1-2010
Clause 5.18.1 (1) Tack welds and construction aid welds shall be made with a qualified or prequalified WPS and by qualified welders.
(2) Tack welds that are not incorporated in final welds and construction aid welds that are not removed shall meet visual inspection requirements before a member is accepted.

My take is that any tack weld must be in accordance with a WPS, that includes preheat, filler metal, etc. The issue of making tack welds without preheat violates 5.18.1 (2) unless the tack weld is incorporated into the final weld by SAW per clause 5.18.5(1).

Clause 6.9: All welds shall be visually inspected and shall be acceptable if the criteria of table 6.1 are satisfied.

No distinction between a tack weld and a completed weld is made, therefore all welds must meet the requirements of table 6.1, i.e., no cracks permitted.

The welders are operating under the assumption they are remelting the tack welds, that is an assumption that can be easily disproven. Have the welders tack weld a T-joint together with the tack welds located on the joint where they will deposit a single pass fillet weld. Break the tack welds to simulate cracked tack welds and refit the plates together without any root opening, i.e., a tight fit between the butting and nonbutting members. Have the welders deposit a single pass fillet weld on the same side of the joint as the broken tack welds. Once the single pass fillet is deposited, break the weld.

I will buy you lunch if they deposit a single pass fillet and completely remelt the tack welds. I am willing to bet the broken tack welds will still be clearly evident. As a matter of fact, if they deposit a single pass fillet weld with 5/16 inch legs, they will have incomplete fusion for most of the length of the welds, i.e., the edge of the plate will still be visually evident.

I'll buy you lunch at FabTech if they succeed in producing welds that meet the visual criteria of clause 4.9.1.2. You bring the welded samples, I'll buy the lunch. You read it here folks!

Best regards - Al

By waccobird (****)

Date 08-18-2011 22:31

Al

Thank You

That is my take on it also.

Marshall

By Lawrence (*****)

Date 08-18-2011 23:13

Just because Al stirrs the pot on every other post.. I'll stir here

Al says
"Clause 6.9: All welds shall be visually inspected and shall be acceptable if the criteria of table 6.1 are satisfied.

No distinction between a tack weld and a completed weld is made, therefore all welds must meet the requirements of table 6.1, i.e., no cracks permitted.

The tack becomes part of the "weld" in this case.. Think about a multi pass weld.. It's not 3 fillets, but one fillet consisting of 3 passes.

If the tack ( and the crack in the tack) are consumed during a production weld pass over the offending tack, and then inspected to 6.1 and found to be crack free, whats the beef according to the letter of the law? There can be undercut or any number of issues in multi pass welds that get repaired as the process of making the "weld" continues.

I'm not addressing preheat... Just the cracked tack.

This senerio sounds sloppy as blazes... But is it a violation of the code?

By 803056

Date 08-19-2011 03:55

Is this a case of selective reading?

Clause 5.24, addressing weld profile, states that all welds shall meet the visual criteria of Table 6.1 and shall be free from cracks, overlaps, and the unacceptable profile discontinuities exhibited in Figure 5.4, Table 5.9, and Table 5.10, except as otherwise allowed in 5.24.1, 5.24,2, and 5.24.3. Since there is no distinction between a tack weld and the final production weld, the criteria is equally applicable to the tack weld, each weld bead if making a multipass weld, as well as the final weld.

There are no provisions limiting the visual criteria to the final weld, quite the contrary, clause 6.5.2 states "The inspector shall, at suitable intervals, observe joint preparation, assembly practice, the welding techniques, and performance of each welder, welding operator, and tack welder to ensure that the applicable requirements of this code are meet."

I see no text that would allow a reasonable person to interpret the requirements of D1.1 to permit welding over cracked tack welds, slag inclusions, individual weld beads, or other weld defects and state the requirements of D1.1 are met if the final weld surface meets the criteria listed in Table 6.1. Clause 6.5.2 is in line with the credo that visual inspection must be performed "before, during, and after welding to be effective.

Best regards - Al :roll:

By Lawrence (*****)

Date 08-19-2011 04:09

Gold Star

By FabsForLife (*)

Date 09-29-2011 19:17

**Cracked Tack Weld Update!**
Ok I noticed in D1.5 tack welds were a little more note worthy. But I have finally found the answer I was looking for and I knew had to exsist.
The New AISC 14th Edition in the 360-10 specifications in the new QC chapter N Table N5.4-2 one of the tasks to observe in "NO welding over cracked tack welds." There is a Welding Inspector God after all.

By Tyrone

Date 09-30-2011 11:15

I'm glad you found it!
Seems a little crazy that you need ammunition from a code to justify the obvious.
Saving time, not removing the cracked tacks, or being lazy are not good reasons to reduce quality.
Tyrone

By 803056

Date 09-30-2011 13:36

I typically fall back on the show and tell methodology when I have a question of whether a technique or procedure will produce expected results. Simply weld a sample and test it.

I believe I proposed a simple demonstration previously in this post or one that came before it; tack weld a T-joint consisting of two 1/2-inch thick plates measuring 4 x 8-inches. The tack welds should be on one side only. The tack welds should replicate the typical tack welds used for production. Break the tacks as you would in the standard Fillet weld break test. Reassemble the T-joint and weld it as you would in production, i.e., use the same process, welding parameters, technique, etc. Then, once again, break the T-joint as you would any fillet weld break test and evaluate the root to see if the initial tack welds were completely consumed or if there is evidence of the broken tacks remaining. The demonstration is quick and relatively inexpensive. It provides clear evidence indicating the cracked tack welds can be completely consumed or that they are not consumed and must be removed completely before welding the joint.

My supposition is that the tack welds will still be evident for GTAW, SMAW, GMAW, or FCAW processes. My experience is that welders get a fraction of the depth of fusion they assume they are able to achieve. In support of my hypothesis is that so many back gouged welds fail to pass ultrasonic or radiographic examination because welders do not excavate the weld to sound metal, i.e., they leave traces of the unfused root in belief they can “melt it out” with their next pass. Test results would indicate otherwise.

Best regards – Al

By Metarinka (****)

Date 09-30-2011 16:42

I'll mirror the "show and tell" method, I've now switched 3 shops I've worked in from 75/25 to 85/15 . "why would I change the gas, we've been using it for X years without a problem and 85/15 costs more" Simply setup 2 machines or a manifold between the two bottles and let the welders trial each one. Most are sold in a few seconds.

Don't have any comment on this particular problem as I don't work in the D codes, we always retacked cracked tacks (we would also preheat for fitup and distortion reasons). Most of our welds were mechanized so I had a better idea of where the penetration would be... I would be worried about crack tacks on fillet welds.