Filler Metal On A WPS

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This article some of the issues related to the subject of filler metal on a WPS. The entire discussion is done in the context of ASME Section IX, and might not be relevant to other codes. The article focuses special attention on use of unassigned filler metals on a WPS, and also rules regarding filler metals when toughness is a consideration.

filler metals for procedure qualification
Filler Metals As Per ASME Section IX

In my workplace, we get to see extensive usage of E7018-1 electrode and E9018-B9 electrode. In my early days as a welding engineer, this question would trouble me frequently: when a PQR has been qualified with E7018 electrode, can we use the WPS written with the support of this PQR but use E9018-B9 electrode?

Conversely, can we use E7018 electrode in production while taking support of a PQR qualified with E9018-B9 electrode?

Can we make any substitution of filler metal at all, over the one used in qualification? How do we go about making that decision?

Of course, an overall engineering judgement must guide such a change; however, Section IX thankfully lays down a few rules that make it easier for the welding engineer to decide on the choice.

A few other related questions come to mind. As long as use AWS grade electrodes, we have Section IX to seek guidance from. However, if we use electrodes not classified in ASME Section II Part C, which are therefore not assigned any F number in QW 432 of Section IX, how do we go about judging questions of the nature of the one described in above paragraph?

Does changing brand name of an unassigned filler metal require re-qualification? Is it alright to use in production a filler that produces weld that matches the chemical composition of the weld produced by the unassigned filler used in procedure qualification test coupon? This article tries to answer some of these questions.

Change Of F-Number Is An Essential Variable

QW 404.4, which appears as an essential variable for most processes under QW 250, states that a change from one F-Number in QW 432 to any other F number or to any other filler not listed in QW 432 will require re-qualification.

The first part is quite clear. The same F-Number filler only must be used in production as the one used in procedure qualification.

What QW 404.4 also implicitly indicates is that a PQR qualified with a filler classified in Section II Part C can be used only with fillers classified in Section II Part C. Using such a PQR, one cannot use an unassigned filler metal conforming to national or international specifications, even if the filler metal is similar/same in composition to the AWS grade.

Note that QW 404.4 does not require a requalification on change of trade name of the consumable, and only requires requalification on change of F number. This has been further attested to, by Section IX Committee, through an Interpretation IX-80-71. 

Unassigned Filler Metals

Section IX is not so forthcoming about the rules that need to be followed while using unassigned filler metals.

It is noteworthy that in case of P numbers, Section IX in QW 424 neatly defines the method of judgement if an unassigned metal has been used in procedure qualification. Also, it is clearly understood from QW 424 how to qualify your procedure qualification if the production job is with an unassigned metal.

Likewise for welder qualification, in QW 423, it has been enunciated clearly how to judge the applicability of a welder’s qualification for a production job if the qualification has been done with an unassigned metal (but the production job is a defined P number metal).

It has also been provided therein how to judge a welder qualification’s applicability if the qualification has been done with a defined P number (but the production job is an unassigned metal).

However, lack of such clarity for F-Numbers is noticeable in Section IX. It is not much clear in what all places a PQR qualified with an unassigned filler can be used.

If you must use a non-AWS grade filler (that is, unassigned filler) in your production welds, you must first qualify a procedure qualification using the same unassigned filler. And the procedure qualified with such an unassigned filler metal can be used to support production welds with only that unassigned filler (of same trade name? Keep reading!).

Indiscriminate Substitution Of Filler Metals Is Not Permitted

Now, consider QW 404.4 again. It permits us to use other fillers too vis-a-vis the filler used in procedure qualification, provided they have the same F-Number assigned in QW 432. Does this mean we can use any other filler, as long as it has the same F-Number as the one used in procedure qualification?

No, engineering judgement must be applied before making such a substitution.

In fact, QW 431, which introduces the F-Numbers table of QW 432, is forthright in saying that the grouping of F numbers in QW 432 does not imply that filler metals “within a group may be indiscriminately substituted for a metal that was used in the qualification test without consideration of the compatibility of the base and filler metals from the standpoint of metallurgical properties, post-weld heat treatment (,) design and service requirements, and mechanical properties.”

Change In A-Number Is Also An Essential Variable

If you require using a different filler metal than the one used in qualification test, besides the QW 404.4 – you also need to satisfy QW 404.5. The QW 404.5, that deals with A-Number, also appears as an essential variable for most processes in QW 250. So, A-Number also helps us in avoiding an erroneous substitution of filler metal.

QW 404.5 states that “a change in the chemical composition of the weld deposit from one A-Number to any other A-Number in Table QW-442” is an essential variable (and will therefore require requalification). Also, “Qualification with A-No. 1 shall qualify for A-No. 2 and vice versa.”

This means that the alternate filler metal that you are thinking to use (instead of the one used in qualification test) must also, besides being of same F-Number, produce a weld that is nominally similar in chemical composition to the one produced by filler metal used in qualification.

It is to be noted that QW 404.5 is applicable only for ferrous metals.

At all times, whether it is for ferrous metals or for non-ferrous ones, if it is required to use a different filler metal over the one used in procedure qualification, the judgement must be guided by the metallurgical compatibility, PWHT requirements and mechanical properties of the weld produced by the proposed alternate filler metal.

Change In Trade Name Of Filler Metal

There is another variable in QW 250 that appears in the Tables for most of the processes. QW 404.33 has been listed as a non-essential variable, in majority of the processes under QW 250. It must be said that, unusually, QW 404.33 is not very clear in its intent and meaning.

QW 404.33 goes like this: “A change in the filler metal classification within an SFA specification, or, if not conforming to a filler metal classification within an SFA specification, a change in the manufacturer’s trade name for the filler metal” is a non-essential variable.

Let us see what this means. The first line means that it is alright to change (since QW 404.33 is a non-essential variable) filler metal grades as long as they are classified under the same SFA specification (provided of course they are of same F-Number and produce weld metal of same A-Number).

Note: This makes one ask: Is it not alright to change to a filler metal outside of the SFA specification? Perhaps, it ought to be reworded as: “A change in the filler metal classification within SFA specifications…” is a non-essential variable.

The second line conveys that for those filler metals that are not classified under any SFA specification, a change in the manufacturer’s trade name is a non-essential variable. This part is clear enough.

What is implied here, though not stated explicitly, is that for those filler metals too that are classified under one of the SFA specifications – change in brand name is a non-essential variable.

The paragraph goes on to say that: “When optional supplemental designators, such as those which indicate moisture resistance (i.e., XXXXR), diffusible hydrogen (i.e., XXXX H16, H8, etc.), and supplemental toughness testing (i.e., XXXX‐1 or EXXXXM), are specified on the WPS, only filler metals which conform to the classification with the optional supplemental designator(s) specified on the WPS shall be used.” This part is self explanatory.

Apparently, QW 404.33 has been worded as a counter balance to QW 404.12. When read independently, QW 404.33 isn’t a very transparent paragraph. Perhaps the authors could have worded it a bit more smartly.

Filler Metal For WPS Having Toughness Requirement

The foregoing discussion holds good only for WPSs that do not have a toughness requirement. When toughness is a consideration, the supplementary essential variables specified in QW 250 also become activated.

QW 404.12 is a prominent supplementary essential variable. Let us see what it is all about?

It begins with “A change in the filler metal classification within an SFA specification,…” is a supplementary essential variable. This is clear enough.

Ordinarily, QW 404.33 permits us to use other classifications available in the various SFA specifications (provided F number and A number considerations of QW 404.4 and QW 404.5 are satisfied). However, when toughness is a requirement, this kind of change is not permitted, as per QW 404.12.

In essence, when toughness is a consideration, in production welds – we cannot generally substitute the filler metal (used in procedure qualification) with ANY other filler metal even if it has same F-Number, same A-Number, same SFA specification etc. Basically, Code wants us to use the same filler as that used in the procedure qualification.

This understanding has been firmly established by QW 404.12, and further reinforced through the Committee’s replies to questions in Interpretations IX-13-19, IX-17-32, IX-17-33, IX-18-14, 15-2223 (Record No.) etc.

QW 404.12 continues further, “or for a filler metal not covered by an SFA specification or a filler metal with a “G” suffix within an SFA specification, a change in the trade designation of the filler metal” is a supplementary essential variable.

This means that when toughness is a consideration, and when a filler not covered under any of the SFA specifications, or one classified under an SFA specification but having a suffix “G” in its designation, has been used in qualification of procedure, then a change in trade name of the electrode to be used in production (compared to the one used in qualification of procedure) will require requalification of procedure.

For such cases, the trade name of the filler metal used in test coupon must be recorded on the PQR, and filler of same trade name then must be used in the production welds too.

What is implied here, though not stated explicitly, is that for those filler metals too that are classified under one of the SFA specifications – change in brand name is not an essential variable. For such cases, trade name of the filler metal used in test coupon need not be recorded in PQR (this finds affirmation in Interpretation IX-20-27 as well).

The essence is that if a filler metal has been classified under one of the SFA specifications, regardless of whether toughness is a requirement or not, change of trade name is not a big deal, and is permitted. This is with the exception of the grades that have a “G” in their suffix.

And if an unassigned filler metal (not classified under one of the SFA specifications) is used, change of trade name IS a big deal (and is not permitted), albeit only when toughness is a consideration.

Another noticeable thing in QW 404.12 is the use of the word “or” in second line of the paragraph. This “or” in this place is a redundant entity, and serves no meaning. A full stop in its place would have been better.

Trade Name Vs Trade Designation

Are the terms “trade name” and “trade designation” same thing, are they interchangeable? Yes they are. Section IX used to deploy “trade designation” till about 2015 edition. Since then, the “trade name” has been used in subsequent editions. However, both mean the same thing. This has also been affirmed through an Interpretation issued by ASME BPVC Committee, the Interpretation number is IX-17-47.

Exemptions to QW 404.12

The QW 404.12 continues further to give some exemptions on the restrictions imposed by the first couple of sentences. These exemptions are self-explanatory, and require no re-production here.

Multiple Filler Metal Sizes In WPS

Can we use multiple filler metal sizes in the procedure qualification? And when that is done, does the production weld have to have a replication of the same?

There is nothing in Section IX that prevents us from using multiple electrode sizes while preparing the procedure qualification test coupon. Filler metal size is a non-essential variable for most processes, as per QW 404.6.

This means that we can prepare the procedure qualification test coupon with any size of the electrode. In production welding, we are permitted to use any other size of electrode, or multiple sizes, in any sequence. The sequence followed in procedure qualification is not required to be replicated in production welding.

However, when toughness is a consideration, the supplementary essential variables become additional essential variables, and the choice of electrode size is not so liberal for such cases. See below paragraphs.

Use Of Higher Electrode Diameter Is Not Permitted

Note that electrode size per se does not appear as a supplementary essential variable. However, heat input is a supplementary essential variable, as defined in QW 409.1. If we use a higher electrode size in production (as compared to the one used in procedure qualification), it would entail using higher current and voltage, and therefore a higher input. This would violate QW 409.1.

So, when toughness is a requirement – increase in electrode size is not permitted, since we would end up violating QW 409.1. However, decreasing the electrode size would present no such problem.

This means: say you have qualified your procedure with a diameter 5 mm electrode, then, with the support of this PQR, you can use diameter 5 mm and all lesser diameters in production. It is not permitted to use diameter 6 mm electrode, since using dia. 6 mm would entail higher heat input, which is not permitted.

Interestingly, till the 2019 edition of Section IX, QW 404.7 was also listed as one of the supplementary essential variables. The QW 404.7 says that “a change in the nominal diameter of the electrode to over ¼ in. (6 mm).”

It restricts using electrode sizes of diameter more than 6 mm in production when the procedure qualification has been done with a lower electrode size. The discussion in above paragraph tells us that increasing the electrode size is not permitted anyway, regardless of QW 404.7.

Perhaps recognizing the redundancy of this variable, QW 404.7 has been removed as a supplementary essential variable from QW 253, in 2021 edition of Section IX.

The above discussion teaches us that when one goes about qualifying a procedure, one should choose using a higher diameter of the electrode for preparing the test coupon. This would allow one to choose from a wider range of electrode sizes during production welding.

Some Other Common Questions About Filler Metals On A WPS

  1. Can multiple fillers of different F numbers be used in the same PQR?

Yes. Section IX permits us to use multiple fillers of different F-Number in one test coupon.

In fact, not just multiple fillers, we can even use multiple combinations of other variables (like process, electrode size etc.) too in one test coupon. It only needs to be ensured that the approximate thickness of weld metal deposited is recorded for each set of essential variables, and when required, supplementary essential variables (this has also been expressly indicated in QW 483 – the PQR format, under QW 402).

The weld metal deposited for each set of variables has to be then included in the mechanical test specimens. This has been enshrined in QW 200.2.

When above is ensured, each set of variables gets qualified, and can be treated as an individual qualification, which can then be used as a singly, or in combination with others.

So, this was all about the subject of filler metal on a WPS. Would you like to add some of your own observations? Please do leave your thoughts in the comments section below.

See More:

Weld Repairs And Build-ups As Per ASME Section IX

WPS Qualification For Pressure Retaining Fillet Welds

A-Number On A WPS

P-Number As Per ASME Section IX

PWHT In Procedure Qualification

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