In this article I will discuss the subject of qualified weld thickness for welder qualification. This includes the maximum qualified weld thickness and minimum qualified weld thickness. A small section at the end also addresses the qualified base metal thickness for welder qualification, and qualified weld thickness for welding operators as well.
Thickness Of Weld Metal Qualified
Deposited weld metal thickness ‘t’ is an essential variable for welder performance qualifications as per QW 404.30. This means that if you want to weld a production job that requires a different deposition thickness than the range qualified by the welder’s qualification, then the welder would need a fresh qualification. QW 452.1(b) limits the maximum thickness of the weld metal qualified, in the following manner.
|Thickness of the weld metal deposited in qualification coupon||Thickness of the weld metal which the welder is qualified to deposit in production welds|
|13 mm and over, with a minimum of three layers||Maximum to be welded|
The wording ‘Maximum to be welded’ has been used to indicate that the welder is qualified for unlimited thickness. If anyone ever had any doubt about this, and might have thought the Code is indicating something more subtle and deeper with the ‘max to be welded’ wording, the Committee made it very much clear in Interpretations IX-10-35, IX-89-52, and IX-17-62 (qs 2), that ‘maximum to be welded’ is equivalent to ‘unlimited’.
This means that if the qualification coupon is more than 13 mm thick, and has been welded with at least three layers, then the welder is qualified to deposit unlimited thickness in production jobs. For any other deposited thicknesses, the upper limit of the qualified weld metal thickness has been restricted to 2t.
It is noteworthy that this limitation on the maximum qualified deposition thickness is a liberal one, in comparison to the limits specified in QW 451 for weld metal thickness, for procedure qualifications. If only your welder has been qualified on a coupon that is at least 13 mm thick, and has deposited a minimum of three layers in the welding of the test coupon, he is qualified to deposit absolutely any thickness in the production jobs.
One could not have asked for more.
However, this stipulation throws up interesting scenarios when the deposited weld metal thickness in test coupon is less than 13 mm.
Interesting Scenarios Involving Weld Thickness for Welder Qualification
Consider the following example.
Welding Of Reinforcement Beads
A welder has done his qualification on a 10 mm thick test coupon. This makes him eligible to deposit weld thickness up to 20 mm in production joints.
There is a job that needs to be welded, has a single V groove, the wall thickness is 20 mm thick, and needs to have a weld reinforcement of 2 mm. The welder completes the welding of this joint up to the cover pass. Is a separate welder required to weld the reinforcement?
Should another welder, assuming he is qualified identically to the first welder, be deployed to weld the reinforcement alone? The idea is amusing.
The Section IX does not seem to think that a separate welder is required to weld the reinforcement. Someone asked this question to ASME, and the committee replied in Interpretation IX-83-07 to this effect.
Perhaps the committee thinks that reinforcement thickness is a trivial thing, and a qualified welder – regardless of whether he has used up his quota of eligible-for thickness in the main joint itself – can weld the reinforcement. During the qualification too, Section IX does not take the reinforcement into account for qualification purpose (QW 351). So this stance is understandable.
Multiple Welders Welding On A Single Joint
Now, consider the situation further. There is a production job that is 40 mm thick.
A shop has two welders who are identically qualified in the manner described in the above example. Can one of these welders weld the entire thickness of the job? No, because that directly would violate the essential variable of QW 404.30/QW 452.1 (b).
Can one welder weld 20 mm thickness, while the other welder fills the remaining 20 mm? Section IX has no problem with this. By doing this, no essential variable of Section IX gets violated. When asked questions of similar nature, the committee responded in the affirmative, in Interpretations IX-83-158, IX-15-08 etc.
The following situations form part of conversations with my fellow welding engineers in my company regularly. Debates on such topics with fellow engineers and the authorized inspector serve to establish firmer clarity on the subject. Read on.
In the above example, remember that both welders are identically qualified. How about one welder fills up 20 mm on one day, and comes back the next day to fill the remaining 20 mm? If the second welder is permitted, he is only as good as the first welder!
If the second welder is permitted to fill the remaining 20 mm of thickness on the second day, logically speaking, the first welder should be permitted too!
This, however, is not permitted by Section IX. By doing this, the first welder would end up depositing more than 20 mm in total, thus violating QW 452.1 (b).
Consider another variation of the situation. There is a production job that is 80 mm thick. Can one welder deposit 20 mm on one day, followed by second welder depositing 20 mm the next day, followed by first welder depositing another 20 mm the day after, and the second welder completing the joint by depositing the final 20 mm on the day after that?
This again, is not permitted, because by doing so – the welders would end up depositing more than their qualified thickness in one production joint. This is against the understanding established in Section IX. QW-351 has used the exact wording “…In any given production weldment, welders may not deposit a thickness greater than that permitted by QW 452…”.
This leaves no room for doubt.
The whole scenario is interesting, it must be said. This situation is also observed in double welded joints.
Double Welded Joints
Consider a 30 mm thick double bevel production joint that needs to be welded first from the front side, and then after back grinding/back gouging from the back side to sound metal, needs to be welded from the back side to complete the joint.
Can the welder, having a qualification to deposit 20 mm weld thickness as described in previous example, weld this entire joint? Note that the welder deposits only 15 mm on either side of the joint.
The answer is no. In welding from the front side, the welder deposits 15 mm weld thickness. After grinding to a depth of 2-3 mm to sound metal on the back side, he deposits another approximately 16-17 mm thickness on the backside. In total, he deposits a 31-32 mm thick continuous weld in a single production joint. This results in a violation of QW 350.
In one joint, the welder can only deposit up to 20 mm thickness. The back portion of the weld would need to be welded by another welder (who might be identically qualified to the first welder). The Section IX committee too ruled to this effect, in response to similar questions, in Interpretations IX-83-90 and IX-92-36.
Consider another variation of this. A double bevel 20 mm thick production joint needs to be welded by the welder under discussion in above paragraphs. The thickness of the each bevelled groove is 10 mm.
The welder has to deposit 10 mm on the front side, followed by grinding to a depth of 2-3 mm from the back side to sound metal, and followed by deposition of 12-13 mm from the back side. Is the welder in question qualified to make this joint?
Note that the welder would deposit a total of 22-23 mm thick weld metal in the joint. However, the eventual continuous weld thickness sitting in the joint would be only 20 mm, which is within his qualified deposition thickness. Hence, yes, the welder is qualified to make this joint.
Consider yet another variation of this. There is a 30 mm thick production weld, which is a double bevel groove complete penetration joint, and needs to be welded by GTAW for a few passes at the root (for a thickness of, say 5 mm), and SMAW for the fill passes, on the front side. Then the groove on the second side needs to be filled with SMAW too.
Can a welder described in above paragraphs, qualified for depositing 20 mm weld metal thickness with SMAW, be permitted to weld the entire SMAW portion of the joint? Assume that GTAW has been welded by another suitably qualified welder, for GTAW process.
The welder would need to deposit approximately 25 mm of weld metal in total, 10 mm of it on the front side, followed by 15 mm on the back side. Both the welds are separated by the 5 mm thick GTAW weld. Is the welder permitted for this, as per the rules of Section IX?
One would be tempted to think that both portions should be treated individually, considering they are not a continuous weld metal, being separated by the GTAW weld. Treating them individually would permit the welder to make the weld.
However, the answer to the question is No. The entire joint has to be considered as a single production joint. In any individual joint, the welder is permitted to deposit only 20 mm maximum of weld metal, as per QW 351/QW 452.
A similar question has been addressed by the ASME in Interpretation IX-16-49.
Minimum Qualified Weld Thickness For Welder Qualification
There is no restriction on the minimum deposited weld metal thickness qualified either, for a welder performance qualification. In the earlier editions of Section IX, there was a limit on the minimum qualified thickness too, but somewhere around mid-nineties, this restriction was lifted and only the restriction on the upper limit remained.
Maximum Qualified Weld Thickness For Welding Operators
Moving on, does QW 452 apply to welding operators too?
There isn’t much controversy over this. It is quite clear in Article III of Section IX that only the essential variables specified in QW 360 are applicable to welding operators. QW 452 is not among one of these variables, hence it is not applicable.
If it wasn’t clear enough, ASME made it clearer, in Interpretation IX-13-22.
This means that regardless of what thickness has been deposited in the performance qualification test coupon, a welding operator is eligible to deposit ANY thickness of weld metal in production jobs.
This is not surprising, Section IX at the outset in the Introduction states that for operator qualifications, “…the basic criterion is to determine the ability of the operator to properly operate the equipment to produce a sound joint…”.
Base Metal Thickness For Welder Qualifications
There is no restriction on the base metal thickness, unlike the thickness restriction for base metals in QW 451, for procedure qualifications.
Base Metal thickness has not been included as an essential variable for welding performance qualifications. Hence it is to be disregarded while determining a welder qualification’s applicability for a particular job.
So this was all about the subject of qualified weld metal thickness for welder qualification as per ASME Section IX. Would you like to add something? Did you find some of the scenarios discussed above interesting? Do leave your thoughts in the comments section below.