Base Metal For Welder Qualification

In this article we shall discuss about the subject of base metal for welder qualification. What grade of base metal, what thickness of base metal should be used for qualifying a welder in accordance with Section IX. What grades and thicknesses of base metals would he be qualified for in production welding – will also be established in this article.

how to choose base metal for welder qualification
Base metal for welding performance qualification

Thickness Of Base Metal For Welder Qualification

What Thickness Should Be Chosen For A Welder Qualification Test Coupon?

For groove joints –

It does not matter what thickness of the base metal you choose. Section IX does not impose any restriction on the base metal thickness. It does, however, in QW 452.1(b), impose restriction on the maximum deposited weld metal thickness. On the lower side, there is no restriction on deposited weld metal thickness either.

If I am qualifying a welder through a groove joint, I would choose around 15 mm thick base metal, and fill it up with a dia 4.0 or lower electrode. A welder thus qualified can deposit ANY thickness of weld metal on a base metal of ANY thickness.

For fillet joints –

For qualifications that had fillet sizes more than 5 mm, there is no restriction on either qualified base metal thickness, or the qualified fillet sizes. A welder, who has been qualified with a fillet size of more than 5 mm in the qualification, is qualified to weld ALL fillet sizes in ALL base material thicknesses. Although the base material thickness should be sufficiently high such that it is not less than the fillet size (QW 462.4(b), QW 462.4(c)).

For fillets of less than 5 mm size, there are some restrictions with respect to the qualified base material thickness and fillet size. See QW 452.5.

So, if I am qualifying a welder through a fillet joint, i would choose around 15 mm thick base metal, and make a fillet of 10 mm size. A welder thus qualified can make a fillet of any size in job.

Interesting Questions Involving Base Metal Thickness

  • A Welder Was Qualified On A 20 mm Thick Carbon Steel Base Material. Can He Weld On A Job That Is 100 mm Thick?

Section IX places no restriction on base material thicknesses as far as welder qualifications are concerned. There is a restriction only on the maximum deposited weld metal thickness, in QW 452.1(b).

If the welder was qualified with a deposition thickness of 13 mm or more, with a minimum of three layers, he can deposit ANY thickness of weld metal in the production welding.

If the welder was qualified with any other deposition thickness ‘t’ (that is, thicknesses lower than 13 mm; and thicknesses higher than 13 mm, but deposited in one or two layers), he is qualified for depositing up to a maximum of 2t deposition thickness on the production weld.

However, in both the above cases, there is no restriction on the base material thickness. He is qualified to weld on absolutely ANY thickness of base material.

  • A Welder Got Qualified By Preparing A 15 mm Thick Test Coupon For A Procedure Qualification. The WPS Used For Preparing This Coupon Is Qualified For Depositing A Maximum Weld Thickness Of 15 mm. Can This Welder Weld On A 50 mm Thick Production Joint?

Yes. However, there must be available a qualified WPS for welding the 50 mm thick production joint.

Although the WPS used for preparing the PQR test coupon can be used for depositing a maximum thickness of 15 mm only, the welder gets qualified for depositing unlimited weld thickness, as per QW 452.1 (b).

Now, if the WPS used in making the PQR test coupon is used for welding on a job, using the same welder as discussed above, the maximum deposited thickness cannot exceed 15 mm, even though the welder is qualified to deposit unlimited thickness.

This is because the essential variables of QW 250 always remain in force. Regardless of the qualifications held by the welder, when you are applying a WPS on any weld, you must satisfy the essential variables of QW 250.

Deposition thickness ‘t’ is an essential variable as per QW 250. So, a WPS qualified for a maximum deposition thickness of 15 mm can be used to deposit a maximum thickness of 15 mm only – in ANY weld, be it a production joint, a welder qualification, or any other.

An Interpretation issued by ASME way back in 1977, attests to this. The Interpretation number is IX-77-19.

  • A WPS Is Qualified For Maximum Deposition Thickness Of 10 mm. Can This WPS Be Used To Qualify A Welder On A 13 mm Thick Test Coupon, Thus Qualifying Him For Unlimited Weld Thickness As Per QW 452.1 (b)?

No. Using a WPS qualified for maximum 10 mm weld thickness on a weld of 13 mm (regardless of whether it is a test weld or a production weld) would violate QW 404.30, which is an essential variable.

An Interpretation (# IX-17-50) was issued by ASME in 2017 on similar lines.

The committee’s answer given in the Interpretation is likewise. This is because the WPS would get violated if it is used to deposit 13 mm thickness.

The matter seems simple enough. Why would anyone ask such a question?

Now, it would not be proper to say the question is silly. After all, the Committee has considered the question worthy enough to merit their consideration and answer. I got similar questions in my mind at the beginning as well.

The question perhaps arises because we generally apply rules of QW 250 to production welds for most of the time. Due to this, one might think that these rules are not applicable for qualification test coupons.

One must understand that regardless of whether you are making a production weld, or a production test coupon, or a welder qualification test coupon, or a Lot qualification coupon, or a temporary weld, or a tack weld – the rules of QW 250 are applicable all the time.

Regarding the question above, I must use some other WPS that is qualified to make a deposit of 13 mm thickness. The welder thus qualified then gets qualified to deposit any weld thickness in any weld.

This shows us that the Section IX considers the PQRs to be sacrosanct. This becomes visible in another example that appears in this article later.

Grade Of Base Metal For Welder Qualifications

What grade of base metal should be chosen for qualifying a welder in accordance with Section IX?

QW 403.18 is listed as an essential variable for most of the welding processes under QW 350. QW 403.18 says that “a change from one P-Number to any other P-Number or to a base metal not listed in Table QW/QB 422, except as permitted in QW 423, and in QW 420.”

The exemptions given in QW 423 (see table below) are far ranging and wide.

Base Metal(s) Used for
Performance Qualification
Base Metals Qualified
P‐No. 1 through P‐No. 15F,
P‐No. 34, or P‐No. 41
through P‐No. 49
P‐No. 1 through P‐No. 15F,
P‐No. 34, and P‐No. 41
through P‐No. 49
P‐No. 21 through P‐No. 26P‐No. 21 through P‐No. 26
P‐No. 51 through P‐No. 53 or
P‐No. 61 or P‐No. 62
P‐No. 51 through P‐No. 53 and
P‐No. 61 and P‐No. 62
Any unassigned metal to the
same unassigned metal
The unassigned metal to itself
Any unassigned metal to any
P-Number metal
The unassigned metal to any
metal assigned to the same
P-Number as the qualified
metal
Any unassigned metal to any
other unassigned metal
The first unassigned metal to
the second unassigned
metal
Table: Base Metals for Welder Qualification

“When a base metal shown in the left column is used for welder qualification, the welder is qualified to weld all combinations of base metals shown in the right column, including unassigned metals of similar chemical composition to these metals.”

The P-No. 1 – P-No.15F includes all steels. So it turns out that a welder qualified on any steel is qualified to weld on every steel.

Many interesting scenarios occur surrounding the question of base metal grade to be used for welder qualification, especially use of unassigned metals. Let us see.

Interesting Questions Involving Grade Of Base Metal

Before we get to some of the questions, note this text that appears in QW 423.2: “A base metal used for welder qualification conforming to national or international standards or specifications may be considered as having the same P‐Number as an assigned metal provided it meets the mechanical and chemical requirements of the assigned metal. The base metal specification and corresponding P‐Number shall be recorded on the qualification record.”

Let us see when QW 423.2 would be useful.

Unassigned Metals For Welder Qualifications

I Have A WPS That Was Qualified Using An Unassigned Metal. While Qualifying A Welder Using This WPS, Can I Use An Assigned Base Metal (of similar composition) For Making The Welder’s Test Coupon?

When a welder is making his Performance Qualification coupon in accordance with a qualified WPS, all variables of QW 250 are applicable. QW 403.11/QW 424 is one of the essential variables. As per QW 424, a Procedure qualified with an unassigned metal can be only used for welding that unassigned metal in the production welding.

So, in order to stay compliant with the qualified WPS, I must use only the unassigned metal (that was used for qualifying the procedure) for making the welder performance test coupon.

For example, 20MnMoNi55 grade material is an extensively used material in my shop. It is an unassigned material of DIN grade; it is however, similar to SA508 Class 3 material, which is an assigned material, having P number 3. A good number of Procedure Qualifications are available with my organization to cater to welding of 20MnMoNi55.

If I want to use such a WPS to qualify my welder, I am permitted to use only 20MnMoNi55 for making the performance qualification test coupon.

If I want to use any other assigned P3 material, I am not permitted to do so, as per rules of Section IX. Because, like I said above, a WPS qualified with an unassigned material can only be used for welding only that unassigned material.

An interpretation (number BPV IX-16-41) to this effect was issued by ASME in 2016.

Now, consider another situation.

I have a WPS that was qualified with an assigned material. Due to some reason, using this WPS – I want to use an unassigned material for making a welder qualification coupon. The unassigned material conforms to national /international standards, and is similar to an assigned metal in chemical and mechanical properties. Am I permitted to do this?

Yes I am. This is where the stipulation given in QW 423.2 comes to the fore.

As long as I stay within the limits of QW 424, for the purpose of welder qualification alone, I can assign same P number to an unassigned base metal (which conforms to national and international specifications) as an assigned metal, provided the unassigned metal conforms to the mechanical and chemical properties of the assigned metal. This is in accordance with QW 423.2.

I can then use such unassigned base material for preparing the test coupon for welder qualification, provided I stay within the limits of QW 424. The P number thus assigned must be recorded on the Performance Qualification Record.

For example, in the situation described above, if the WPS has been qualified with an assigned metal, say a P3 material, then, for the purpose of welder performance qualification alone, I am permitted to use 20MnMoNi55 material for making the welder qualification test coupon, since it is similar in mechanical properties and chemical composition to SA 508 Class 3 material (which is a P3 material).

For the purpose of welder qualification, as per QW 423.2, I can assign P number 3 to 20MnMoNi55 material, and use it for qualifying my welder. I must then record P number 3 on the performance qualification record.

Now, it is also worth bearing in mind that once a welder is qualified with a certain P-Number, as per Section IX, he is permitted to weld on a wide variety of base metals, including unassigned metals of similar chemical composition to these metals.

For example, once a welder is qualified (say, with a P number 3 base material), he is very much permitted to weld on 20MnMoNi55 material, even though it is an unassigned material. This is in line with the last sentence of QW 423.1.

The moral of the story is that ASME Section IX considers Procedure Qualifications as sacrosanct. It frowns upon any violation of QW 250, however small and inconsequential it might be.

My personal opinion on this whole matter is that, as per QW 423.1, a welder qualified with ANY steel qualifies him to weld on EVERY steel. When such liberty has been given, there need not be any restriction on choice of base material used in the welder qualification, as long as it is ‘steel’. 20MnMoNi55, although an unassigned metal, is after all, ‘steel’.

If it was up to me, I would not mind allowing use of a WPS qualified with 20MnMoNi55 for preparing a welder qualification coupon using an assigned base metal of P-No. 3.

So this was all about the subject of base metals for welder qualifications. Would you like to add something? Did you find some of these scenarios discussed above interesting? Do leave your thoughts in the comments section below.

See More:

Welder Performance Qualification FAQs

Leave a Comment