Hey All- Ready for a long question? (Research included!)
As with any new position, the difference of terms here tend to be quite bother some. So a nit-picky question that I look to you, the educated and experienced, to help me sort out.
The Plant Manager here tends to flare up any time he hears the word 'backing'. Specifically, we deal with SAW. Two beveled plates are brought together to make a double V groove, 'tacked' into place, and then a SAW pass is ran on both sides, consuming/remelting the 'tacks' entirely, producing CJP.
The issue is, on the shop floor this tack is often called 'backing'. However, the P.M. first called this a 'continual tack', and now in his last polite discussion called it a seal pass.
With as much confusion as I've seen around here, I fear they may have investigated this topic when the company first started and have been cherry-picking what works best for them ever since.
What I know comes from D1.1:
5.18.1 General Requirements
(1) Tack welds and construction aid welds shall be made with a qualified or prequalified WPS and by qualified personnel.
(2) Tack welds that are not incorporated in the final welds, and construction aid welds that are not removed, shall meet visual inspection requirements before a member is accepted.
5.18.2 Exclusion Tack welds and constriction aid welds are permitted except that:
(1) in tension zones of cyclically loaded structures, there shall be no tack welds not incorporated into the final weld except as permitted by 2.16.2, nor construction aid welds. Location more than 1/6 of depth of the web from tension flanges of beams or grinders are considered outside the tension zone.
(2) On members made of quenched and tempered steel with specified yield strength grater than 70ksi [485 MPa], tack welds outside the final weld and construction aid welds shall require the approval of the Engineer.
5.18.3 Removal At locations other than in 5.18.2, tack welds and construction aid welds, not incorporated into the final welds, shall be removed when required by the Engineer.
5.18.4 Additional Tack Weld Requirements
(1) Tack welds incorporated into final welds shall be made with electrodes meeting the requirements of the final welds. These welds shall be cleaned prior to incorporation.
(2) Multipass tack welds shall have cascaded ends or be otherwise prepared for incorporation into the final weld.
(3) Tack welds incorporated into the final welds that are qualified with notch toughness or are required to be made with filler metal classified with notch toughness shall be made with compatible filler metals.
5.18.5 Additional Requirements for Tack Welds incorporated into SAW Welds. The following shall apply in addition to 5.18.4 requirements.
(1) Preheat is not required for single pass tack welds remelted by continuous SAW welds. This is an exception to the qualification requirements of 5.18.1
(2) Fillet tack welds shall not exceed 3/8 in [10 mm] and shall not produce objectionable changes in the appearance of the weld surface.
(3) tack welds in the roots of joints requiring specific root penetration shall not result in decreased penetration.
(4) tack welds not conforming to the requirements of (2) and (3) shall be removed or reduced in size by any suitable means before welding.
(5) Tack welds in the root of a joint with steel backing less than 5/16 [8 mm] thick shall be removed or made continuous for the full length of the joint using SMAW with low-hydrogen electrodes, GMAW, or FCAW-G
Walking my way through all of that...
-From my perspective, we match 5.18.1 (1), part (2) doesn't apply to us here.
-Our finished product here isn't made of quenched or tempered steel, though while our product is cyclically loaded, I don't know of any tension zone, so I believe 5.18.2 doesn't apply here.
-Our tacks are consumed or remelted in the SAW passes, so 5.18.3 doesn't apply here.
-Our tacks are made with electrodes meeting the requirements of the final weld, and we clean them before welding on them...so we meet 5.18.4 (1).
-The tacks aren't multi pass, so 5.18.4(2) doesn't apply.
-All of our PQR's go through a CVN, and our GMAW is commpatable with our SAW.
-This is a single pass tack weld that is remelted by the following SAW pass, so no preheat is required.
-We're welding a CJP double V groove joint, so 5.18.5 doesn't apply.
-Our tacks are in the root and CJP is required, our tacks haven't decrease the penetration (all welds are inspected with UT). So we're good here.
-Our tacks meet (2) and (3), so (4) doesn't apply.
-We don't have steel backing, so (5) doesn't apply here.
In AWS A3.0M/A3.0:2010 backing is defined as:
A material or device placed against the back side of the joint adjacent to the joint root, or at both sides of a joint in electroslag and electrogas welding, to support and shield molten weld metal. The material may be partially fused or remain unfused during welding and may be either metal or nonmetal. See Figures B.8(D), B.12, and B.37.
tack weld is defined as:
A weld made to hold the parts of a weldment in proper alignment until the final welds are made.
root pass is defined as:
A weld pass made to produce a root bead.
and because that definition included another term...
root bead is defined as
A weld bead extending into or including part or all of the joint root.
Figure B.8(D) is a single V-groove, Figure B.12 is Split Pipe Backing, and B.37 depicts Electroslag Welding.
I haven't found anything about a 'continual tack' or a 'seal pass', are these older terms, or just made up terms?
Looking at all of this I'm inclined to say that our GMAW pass is a 'single pass tack weld'. Specifically, from my perspective, the tack that we put in doesn't penetrate the root, it leaves a tiny gap, that when viewed from the edge, one can see. Though with that said, I'm sure that root has had fusion made by this tack.
So...what are your thoughts on this topic?
Thank you for reading this far though, this community has been most helpful!
I'll conclude by saying that I am a novice CWI and am worried to being 'led astray'.
Ex. Trying to convince my employer that, 'Hey, the WPS that we operate under specify checking the preheat and interpass temperature with a contact polymer only...and we don't have any in house.' was a struggle. Only after some documentation and explanation (Instead of wanting to purchase the tempilstiks, the P.M. blamed improperly written WPSs...and found they were written and signed off by him...it wouldn't be bad if he wasn't also a CWI).
Hello Bowler_Hat,
First, let me compliment you on posting such a thorough and previously researched question.
Second, I need to state that I don't have my D1.1 with me at the moment, so my reply is opinion based only, so don't take it to the bank until you get the several replies I assume this will generate.
Assuming that by continuous tack and seal pass, you mean that this GMAW "tack weld" is continuous from one end of the joint to the other.
Also assuming that the reason for this is to prevent the first SAW pass from blowing through the joint root.
Opinions -
1. This is not a tack, it is a root pass.
2. This is not a backing weld as it is inside a double V groove.
3. The reason it's being called anything other than a root pass is a loose interpretation of this comment copied from your post:
"5.18.5 Additional Requirements for Tack Welds incorporated into SAW Welds. The following shall apply in addition to 5.18.4 requirements.
(1) Preheat is not required for single pass tack welds remelted by continuous SAW welds. This is an exception to the qualification requirements of 5.18.1"
which is a means of not having to go through the expense of preheating for a root pass, as required.
4. The reason joints receiving a root pass need to be preheated, when material conditions require, is to help prevent it from cracking, which if said crack is welded over, may remain in the joint and cause failure.
5. That these welds are UT'd is good, and provides a little bit of warm fuzzy feeling, but is every such joint UT'd? Also we need to keep in mind that UT is not infallible.
6. This is a typical method of a contractor or manufacturer to reduce costs by cutting corners on quality because if or when this practice causes a failure, it will be long after the project is done and has been paid for.
Some what cynically,
Tim
Bowler Hat,
I’ve never heard of “continual tack” or “seal pass” and to the best of my knowledge neither one is recognized by A3.0, and therefore non-standard terms. If it’s continuous and it’s intended to serve as backing, then it’s a “backing weld”, which is defined in A3.0 as backing, in the form of a weld.
You indicated that “two beveled plates are brought together to make a double V groove, 'tacked' into place, and then a SAW pass is ran on both sides, consuming/remelting the 'tacks' entirely, producing CJP.
Prequalified joint designations for a CJP double bevel groove for the SAW process are either going to be a B-U3a-S, or a B-U3c-S, which both require backgouging.
If you’re using this “continual tack” as backing and as you say, “consuming/remelting the 'tacks' entirely, producing CJP”, then D1.1 does not recognize this as being a prequalified joint because the backgouging has been eliminated. Furthermore, there is no prequalified double V groove joint with backing. So, unless the WPS was generated from a qualified PQR, showing a “backing weld” and as you put it… "subsequent consuming/remelting the 'tacks' and entirely, producing CJP", then the WPS is not valid.
Bowler Hat,
Question well put. I also don't have D1.1 with me so I'm shooting from the hip.
I've actually had a similar situation in which "single pass tack" was misinterpreted (due to the word "pass") as opposed to the term being contrasted with, and related to, "multiple pass tack." But, in that scenario it was just a single weld from a well-intentioned welder and it was an easy fix. In your case the terminology is integrated into your welding program and needs to addressed.
With this being an initial full-length pass in a groove weld and incorporated into the final weld it would take a strong argument to convince me that it's anything other than a root pass. But, other than a terminology disagreement what's at stake? Is this "continuous tack" term being used in conjunction with 5.18.5 to justify not preheating the joint prior to 'tacking,' as TimGary suggests? If that's the case, and if your WPS doesn't reflect the situation, then your procedure needs to be brought into alignment with your welding conditions, or vice versa. If the procedure is properly qualified then the only ramification is having to deal with an obstinate plant manager. I don't think you'll find any code violations in their method as long as the procedure is valid. It's simply a root pass and not a tack weld. Make sure your WPS clarifies it as such.
Do they use actual tack welds to secure the plates prior to the "continuous tack"? That would be annoying.
Terminology isn't always as straight-forward as it seems on the surface. Language in general is fascinating. Sometimes during disputes with production fellas I can't help but wonder if we're both reading the same thing even though I know we are. And sometimes people are just being willfully ignorant to exert an agenda.
As an example, and thought exercise, I could make a pretty good argument that a GMAW pass that bridged the root of a double-V and didn't fuse any root could be considered a backing weld in function and intent. But does it cease to be a backing weld when it's subsequently filled and capped? Could I be right and wrong at the same time? Things like this keep it interesting.
While the correct designation is 'seal weld' it is most definitely in A3.0 Terms and Defs.
It is often referenced in the tail of the welding symbol as either of the above to indicate a weld pass intended to seal any leakage generally in applications with some form of liquid involved.
But, I have seen it used to form the 'root' for SAW and other welding procedures.
Now, it is in no way a 'tack' weld. Not by the application. While I know D1.1 says a tack weld shall be made continuous for certain applications, a TACK weld is not a weld that is continuous in a joint. This is misleading as once you add any dimension to it beyond the strength required to hold everything in place to continue with the welding procedure it is no longer a TACK weld. When used thus it is either a seal weld or most properly a weld pass in the root.
For instance, if it is a 'tack' weld then a person qualified as a 'tack' welder could weld it right? So, why not just qualify all my welders as tack welders using the 2" long test and then claim they were only tack welding even though they were utilizing multi-pass tacks and full length tacks?
There does need to be some clarification on this in my opinion and I will check through previous official interpretations but I don't remember seeing anything in this area.
It could actually be considered a 'backing' weld as it is performing in many ways the definition of such, a weld used for backing. That would be more accurate than a seal weld as it is not really sealing anything unless the root is so wide that it is keeping the flux from falling through prior to the welding operation.
Just my two tin pennies worth.
He Is In Control, Have a Great Day, Brent
