This post may contain affiliate links. Which means I will make a commission at no extra cost to you should you click through and make a purchase. Read the full disclosure here.
ASME Section IX considers that depositing corrosion resistant overlay requires a different skill than the skill required to weld on groove welds, fillet welds, build ups, etc. Thus, in QW 381, Section IX provides for the stipulations governing the welding performance qualifications for corrosion-resistant weld metal overlays. In this article, we shall discuss various aspects related to welder qualification for corrosion resistant overlay.
Before proceeding further, please note that the terms ‘cladding’ and ‘corrosion resistant overlay’ have been used interchangeably in this article.
Thickness Of Corrosion Resistant Overlay For Welder Qualification
As per QW 381.1 (c), there is no limit on the maximum thickness of cladding that may be deposited by a qualified welder. This is clearly specified.
Is there a limit on the minimum qualified deposition thickness?
For welding performance qualifications, there isn’t directly specified any minimum qualified deposition thickness for corrosion resistant overlays.
For procedure qualification of corrosion resistant overlays, the minimum qualified cladding thickness is the one at which the WPS-required chemical composition has been achieved. This thickness is the value that gets specified on the qualified WPS.
If you are using such WPS for making your welder qualification test coupon, or for production for that matter, you are not permitted to deposit a thickness lower than the minimum qualified thickness specified on the WPS. This is as per QW 402.16.
So, in preparation of the test coupon for performance qualification, the welder must deposit at least the minimum qualified cladding thickness, specified on the WPS. The coupon thus prepared must then undergo the testing specified in QW 453. In production jobs too, the welder must deposit at least this minimum thickness, to satisfy the WPS requirement.
This is all well and good as long as there is only one WPS used for both the performance qualification and the production welding. However, what about when they are different?
Now, say, the welder is qualified by depositing 7 mm thickness on a corrosion resistant overlay performance qualification test coupon, using a qualified WPS. There exists another WPS which is qualified for depositing 5 mm thickness. Can the welder qualified with the first WPS weld with the second one, assuming all other essential variables are satisfied?
The answer is, yes. QW 381.1 (c) indicates that “…the essential variables of QW 350 shall apply for welders…” (for welders qualified for corrosion resistant overlays). This means that QW 404.30 is applicable. As per QW 404.30, there is no restriction on minimum qualified deposition thickness.
Any minimum thickness can be deposited by a qualified welder as long as a qualified WPS is available to support it. Hence, the welder qualified with the first WPS can weld on production jobs with the second WPS too.
Is there a minimum qualified deposition thickness when there is no chemical analysis specified on the WPS?
No. When the WPS does not require any specific chemical composition on the weld metal, there is no restriction on the minimum qualified thickness. This has been made clear in an Interpretation too. The Interpretation number is IX-10-11.
Can A Welder Qualified With A Groove Weld On Cladding?
There is one particular component in my shop that has, among others, two different joints in it. One is a corrosion resistant over lay cladding, for which there is a chemistry requirement specified by the WPS. The other joint is a buttering.
Both look identical. Same electrode, same PWHT condition, almost same thickness of the deposit, all other variables are same as well.
I have a few welders in my shop that are qualified on a groove weld, of 25 mm thickness, with the same electrode that is required on the above described job.
I deploy these welders for doing the buttering joint. Section IX demands no separate kind of test coupon for buttering. A welder qualified on a groove weld is considered good enough to weld buttering and build ups too.
However, the authorised inspector stationed in the factory does not permit me to deploy these welders for welding on the cladding.
Both the buttering and the cladding look exactly the same. The skill required to weld both seems to be the same too.
To qualify my welder for cladding, I must make him weld a cladding coupon, and do bend tests on it in accordance with QW 453. This is because QW 381.1 (b) requires that only a welder qualified for corrosion-resistant weld metal over cladding is qualified for depositing corrosion resistant weld metal overlays.
What if the job WPS does not have a chemistry requirement specified on it?
HOWEVER, if the cladding is such that the WPS does not require a chemical composition, then a welder qualified on groove weld is also qualified to deposit cladding, provided that the bend specimens removed from the groove weld coupon meet the acceptance criteria for cladding, as defined in QW 163. This is permitted in QW 381.3.
The interesting thing is that it is not even required to check chemical composition of the thus welded cladding coupon (to satisfy QW 381.1 (b)) for the welder qualification.
There is no difference in physical appearance between buttering and cladding. Yet, the methodology for qualifying a welder differs.
What about the reverse? Can a welder qualified on a cladding coupon weld on a groove weld?
No. To weld on a groove weld, a welder must be qualified on a groove weld described in QW 304.
To summarise, a welder qualified with cladding does not make him eligible to weld on groove. Also, a welder qualified with a groove coupon can weld on cladding, provided there is no chemistry requirement in the WPS, and provided the bend tests taken from the groove weld test coupon met the acceptance criteria for cladding, described in QW 163.
If there is a chemistry requirement specified on the WPS, the welder must be qualified by making a cladding coupon, as described in QW 381.
What about renewal?
Validity Of Corrosion Resistant Overlay Performance Qualification
A Welder Is Qualified For Both Cladding And Groove Welds. In The Six Months Following The Qualification, The Welder Welds Only On Groove Welds. Does This Extend The Validity Of His Cladding Qualifications Too?
The situation described in the question occurs across a large number of companies, including in mine. The jobs in my shop are a mix of both cladding and groove welds. And as described above, the cladding in my jobs comes with chemistry requirements.
So a good number of welders in my shop are qualified for both cladding and groove welds. However, it so happens that the cladding joints come in a torrent. And once these joints have been completed, the next set might take 8-10 months to come again. In the interim, the shop engineer is able to engage these welders only on groove joints, fillet joints, and buttering.
Which makes the situation described in the question arise.
Can the validity of a welder’s cladding qualifications be extended for six months based on his engagement on groove welds, with the same process? Note that the cladding in question has a chemistry requirement specified on the WPS.
What about vice versa? If the welder engages only in cladding welding for six months, does that extend the validity of his groove welds too?
The answer is quite uncomplicated. QW 322.1 (1) unambiguously states that welder should have welded with that ‘process’. As long as the welder’s cladding qualification and groove weld qualifications have been done with the same process (say, both are with SMAW), welding on one kind of joints extends the welder’s Performance Qualifications’ validity for the other kind as well.
The ASME has issued several Interpretations to establish the above understanding. A few of them are – IX-17-26, IX-86-82 (Q2) and IX-92-22 (Q1).
Likewise, say, the validity of one or more qualifications described above has expired. In order to renew the validity of expired qualifications, a welder need not make separate test coupons. A groove weld test coupon made in accordance with QW 322.2 would renew the validity of his cladding qualifications too.
Occasionally, in my shop, it so happens that a welder possesses only a groove weld qualification. Due to some reason, the validity of his qualification expires. Due to production requirement, it is now required to qualify him for cladding. The welder passes all acceptance criteria in the cladding test coupon. Does this renew his groove weld qualification too?
Yes it does. Doing so meets the requirements of QW 322.2 (a), and so, why not? There is an Interpretation validating this understanding. Addressing a similar question in IX-86-50, the reply given by ASME was in the affirmative.
Corrosion-Resistant Overlay: Pipe vs Plate
Is A Welder Qualified For Cladding On A Plate Test Coupon Eligible For Cladding On A Pipe?
If you do cladding on the production pipe in the axial direction, that is – the direction of welding is parallel to the axis of pipe, then, it is akin to welding on a plate. In such case, a welder qualified by cladding on a plate test coupon is very much eligible to weld on a pipe, irrespective of the diameter of the pipe.
If you have to do cladding on the pipe in the circumferential direction, that is – along the circumference of the pipe, in such case too the welder (qualified on plate) is eligible to deposit cladding on the pipe, but with the position and diameter restrictions enshrined in QW 461.9.
This understanding appears obliquely in QW 381.1 (c). A hint is also available in figures of QW 462.5 (b) and QW 462.5 (c). The cladding shown on the pipes is indicated in the circumferential manner, which gives us a hint that if the cladding was required to be deposited in an axial manner, a qualification utilising a plate test coupon would be good enough.
This understanding has been given the seal of confirmation by ASME, through an Interpretation issued by ASME. The Interpretation number is IX-92-72 (qs 1).
Cladding With Machine Welding
If a performance qualification for a corrosion resistant overlay is done with machine welding, would the essential variables of QW 381, which is the governing clause for performance qualifications for corrosion resistant overlays, come into play?
Or instead, would the qualification be governed by QW 360, which is applicable for welding operators for machine welding?
A similar question that throws light on this matter has been answered by ASME through an Interpretation, IX-98-17. The answer given in the Interpretation is yes. This means that the thickness limitations and required tests given in QW 453 are applicable for corrosion resistant overlay performance qualifications for both manual welding and machine welding.
So, this was all about welder qualification for corrosion resistant overlay. Please do let know your thoughts on the subject in the comments section below.