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Up Topic Welding Industry / ASME Codes / A-Numbers Again: What & Why ?
- - By tom cooper (**) Date 12-28-2017 13:39
I don't usually have the opportunity to cross into the ASME world but now I do and am looking for any insight on an ASME Section IX PQR requirement that applies to deposited weld metal:    The A-number is an essential variable for most of the common welding processes and is described in QW-404.5 as the "...chemical composition of the weld deposit...";  I presume the purpose is to account for chemistry after dilution with the base metal and any molecular effects due to the shielding gas but cannot find any definitive explanation of this in my literature or AWS Forum searches.  If dilution and shielding gas effects were the concern of interest, then why does Section IX not recognize that dilution varies considerably throughout the cross-section and length of any welded joint and provide a more precise explanation of where the chemistry composition should be sampled from. If dilution control was the goal of maintaining an A-number classification then heat input control would seem to be a superior essential variable for this purpose, yet heat input is often only a supplemental.  To make the issue more confusing, QW-404.5(b) seems to allow deriving an A-number from the filler metal specification or from a manufacturers CoC, neither of which may represent the actual PQR configuration. Furthermore, the AWS A5.18 filler specification chemical analysis pad shown in Fig 3 is designed to minimize dilution with the base metal, so I am thoroughly confused.      WHAT IS AND WHY DOES ASME PLACE ANY ESSENTIAL VALUE ON A-NUMBERS ?  

Thanks for any thoughts or referrals on this and Happy New Year to all who read this.
Tom C
Parent - - By 803056 (*****) Date 12-29-2017 05:24
I don't sit on the Section IX committee, so I could be way off base here, but this is my take on the subject.

ASME lists the minimum requirements for the qualification of a WPS. The contractor is suppose to hire people that are competent in their area of expertise. Thus, if the individual tasked with qualifying the WPS feels it is prudent to go beyond the minimum code requirements, it is perfectly acceptable.

Generally, for most fabrication, the material of choice is a ferrous metal and for the most part, one is welding similar base metals together. If the job involves welding carbon steel to carbon steel the filler metal is most likely a carbon steel with mechanical properties similar to the base metal. This is verified when the WPS is qualified by testing and the assembly is subjected to mechanical tests.

The A number can be based on the chemistry determined when the manufacturer qualified the WPS. Usually, the deposited chemistry is listed in the product literature for a given set of conditions and made available from the manufactures sales literature. As long as the chemistry is similar, the mechanical properties are not going to vary substanially. So, it really doesn't matter if the carbon steel is welded with E6010 or E6011, the deposited chemistry is not going to be altered and the mechanical properties will not be affected.

Even the joint design is going to have little affect on the mechanical properties as long as the chemistry of the deposited weld is not changed substantially. Once again the assumption is that matching filler metals are used, the F number isn't altered, etc.

Everything changes if one is welding dissimilar metals and the filler metal doe not matching either base metal. Consider 316 stainless welded to A36 carbon steel using 309 filler metal. The weld is a single pass weld in a square groove. There would be substantial dilution of the filler metal with both the 316 and the A36. The deposited chemistry of the weld would be much different if the groove detail was changed to a groove with a 90 degree groove angle. The weld deposit chemistry would change and most likely likely the A number would be affected.

One must consider all the variable and how they are going to affect the chemistry of the deposited weld metal. So, while the groove detail is a nonessential variable, it may affect the chemistry of the deposited weld metal. One has a choice of using the chemistry of the deposited weld metal based on the manufacturer's literature (maybe not the wisest choice in the case of joining dissimilar metals) or sending out a sample of the weld for chemical analysis (better choice in my opinion). The person tasked with qualifying the WPS must have sufficient background to understand what should be done to meet the code, but also protect the employers best interests. The code doesn't tell you how or why. The contractor is responsible to ensure the person assigned to the task has the knowledge and experience to make those decisions.

The dilution is not as much of a concern if the base metal is thick and deposited as a multipass weld. If the A number of the filler metal is unchanged, the mechanical properties are probably unaffected. Thus, the manufacturer can switch from a 309 to a 310 and there end result will probably be fine if the A number of both filler metals is the same (I didn't check the A numbers or 309 versus 310, this is simply an  example).

This isn't to say the corrosion resistance of both 309 and 310 are the same, nor is it saying the two filler metals will perform at elevated temperature the same. Once again, it is the contractor's responsibility to verify these additional operating parameters can be met before one filler metal can be substituted for another.

One must also consider the other essential variables to see how they interact and affect the properties of the completed weld.

Just my ramblings on the subject.

Happy New Year - Al
Parent - - By tom cooper (**) Date 01-02-2018 14:00
Thanks for your thoughts on the matter Al, your insights are always highly valued.

The notion of A-number as an essential variable really disturbs me because "deposited chemistry"  is the result of other essential variables such as choice of welding rod, heat input, possibly change of shielding gas, etc.     What use is an pseudo essential variable if the Code allows me to copy the chem composition results out of the electrode specification, even though the electrode specification method of test bears no resemblance to my actual PQR procedure?    The 70S-6 chemistry that was fully discussed a few years back may or may not meet the A-No. 1 classification based on the % of Si or Mn but if either element was a smidgeon more than the A-no. 1 allowed or even if it was 2x a smidgeon more than A-No. 1 allowed, would it make a difference in my machine settings or technique?  No.
Will the extra 2x smidgeons make a difference in my tensiles or impacts? No.
Do the AWS construction Codes D1.1 or D1.5 or any of the myriad of military weld specs have an analogous "deposited chemistry" essential variable? No.
What then is the logic or reason for it's essentiality in the ASME world?  
Your mention of A-number chemistry being very relevant and important to SS-CS dissimilar welds is a good point but the point is good only because ASME allows stainless electrodes and fillers to co-exist in the same F-number groups as carbon steel electrodes and fillers (which I also find to be bizarre).  So in this case only would the A-number chemistry serve a useful purpose of preventing weld procedure cross qualification with a wrongful electrode selection, a circumstance that could not possibly occur in any other welding Code.

Anyway Al,  I thank you again for helping me think this thing through.
Best regards and a happy, prosperous new year to you.
Tom C
Parent - - By 803056 (*****) Date 01-02-2018 15:55
Hello Tom;

One must consider that D1.1 is intended for carbon steels or high strength low alloy steels joined to the same. Likewise, D1.6 is intended for stainless to stainless. Dissimilar base metal combinations, they are a tiger of a different stripe.

ASME has a different philosophy from AWS. Whereas AWS codes typically endorse the concept of prequalification, ASME has the philosophy of "show me it will work."

ASME operates under the presumption the person making the decisions is knowledgeable and familiar with the technology and processes they are using. AWS, not so much.

The A number is an additional constraint that comes into play when welding similar base metals, but involved additional complications when dissimilar metals.

Not only do you see A numbers in ASME, but you used to see the weld deposit chemistry as an essential variable in the old MIL-STD-8604 for welding aluminum alloys. The reason was due to the exact factors you mentioned.

AWS B2.1 used to have different F numbers for all the ferrous filler metals differentiated by the welding processes. It wasn’t until AWS tried to harmonize B2.1 with ASME Section IX that the multitude of ferrous F numbers were combined into the F6 grouping. That was a mistake from my point of view.

It has been my longstanding view that ASME is one of the few codes that allow the unwary to write a code compliant WPS that simply will not work. In that respect, I believe the AWS structural codes are more relevant and more conducive to developing a “workable” document the welder can actually implement.

I always write a WPS with the welder in mind, something ASME seems ignores. That shouldn’t surprise anyone familiar with welding, few of the people on ASME’s committees have ever struck an arc. An engineer’s perspective on welding is different from a welder’s perspective. The engineer is interested in the mechanical properties and whether the weld will perform as expected. They expect the welder to be trained, skilled, and knowledgeable. Those attributes that are skill related are not usually addressed by the ASME WPS in sufficient detail. Why, because many of the engineer tasked writing the WPS are clueless about those aspects of welding. Actually, I see AWS structural welding codes drifting in that direction as well.

All that being said, I find the A number, if properly used, a valuable means of ensuring the wrong filler metal isn’t substituted for the production weld. And for many of the reasons you’ve noted, the person tasked with writing or implementing the WPS must know when a chemical analysis of the deposited weld metal is more relevant than the chemistry provided by the manufacturer.

In reality, some of the element you mentioned, i.e., silicon, does affect the mechanical properties. Silicon and manganese are effective deoxidizers and are added to filler metals for that reason as well as others. With a change in shielding gas, i.e., CO2 to ArCO2 for example, those elements are not utilized as deoxidizers and they become alloying constituents. As such, the tensile strength and yield strength goes up at the expense of ductility. The change in weld deposit chemistry may result. Am I going to blindly use the A number provided by the manufacturer that qualified the filler metal using CO2  or as the engineer in charge consider the chemistry of the deposited weld metal?

One must also consider the fact that ASME Section IX also considers the shielding gas to be an essential variable. A change for one gas to another is something that must be considered and usually requires a supporting PQR to demonstrate the resulting weld will still provide the properties required. 

Section IX considers the groove detail to be a nonessential variable. However, when welding dissimilar base metal combinations, the amount of dilution can change the deposit chemistry. So, should one blindly use the A number determined by the manufacturer when qualifying the filler metal on matching base metals, or base the A number on the actual deposited weld metal chemistry? Where should the sample be taken; from the center of a multipass groove weld, from the weld interface, if the weld interface, which one? Things can get pretty complicated very quickly. The point really is whether the groove detail has an affect on the deposited weld chemistry. I believe you and I agree that it does if the amount of dilution is substantially different based on thickness, and groove detail. That’s really when the A number shines. If the dilution substantially affects the resulting chemistry of the deposited weld metal, a change in A number results and a new supporting PQR is in order.

Much of this is beyond the purvey of many CWIs, so while a CWI may be able to write a simple prequalified WPS, additional education and training may be warranted for someone tasked with developing WPSs for combinations of dissimilar metals. 

Just my ramblings and my opinion on the subject. I expect there will be blowback from some that work with ASME Section IX, but this is how I view the requirements of A number. Simply put, it attempts to prevent the mindless substitution of filler metals simply because they are from the same F number group. Consider that an ER70S-3 belongs to the same F group as ER309. Just because they are from the same F number grouping, we can agree that the chemistry, thus A numbers are going to be different. It is the A number that keeps us from substituting ER70S-2 in place of ER309 when welding carbon steel to stainless steel.

What about substituting ER308 in place of ER309 in the case of a single pass weld joint 1/8-inch carbon steel to austenitic stainless steel? Would the A number be affected?

Let’s assume the Cr and Ni are reduced by dilution so that only 60% of the Cr and Ni are contained by the fully mixed deposit, that’s an assumption, but reasonable for a square groove with no root opening.   The ER308 has roughly 19% Cr and 9% Ni. The ER309 has roughly 23% Cr and 13.5% Ni. Both filler metals are grouped as being A-8. The chemistry of the weld deposit is going to be roughly 10% Cr and 6 Ni using ER308. The chemistry of the deposited weld is roughly 13% Cr and 7% Ni using ER309. The resulting weld deposit chemistries are sufficiently different that the A numbers would be different, Thus if the WPS was qualified using ER309, one could not substitute ER308 and expect the same A number. One would have to qualify a new WPS before making the substitution. If one blindly uses the A number derived by the manufacturer, the results would not be so favorable. This conclusion is bourn out if a solution is derived using the WRC diagram or the WRC diagram as modified by Kotecki and Liphold. The metallurgy of the deposited weld would not have the necessary Ferrite and the morphology would be unfavorable if one was to use the ER308 filler metal in place of the ER309.

Best regards - Al
Parent - - By tom cooper (**) Date 01-02-2018 21:13
It's amazing how you spew this stuff out so fast.  This post is very good treatise on A-numbers and was a good learning exercise for me, thanks again.
Parent - By 803056 (*****) Date 01-03-2018 00:25
Once upon a time, long, long ago, I saw it in a book that had lots of pictures.

Parent - - By 46.00 (****) Date 01-02-2018 21:18
These are the reasons I keep coming back to this forum! The opinions keep me thinking! I most likely will spend a week absorbing this info!
Parent - - By 803056 (*****) Date 01-03-2018 00:33
It isn't as sanitary as the "members only" site, but this is a lot more fun. It is rare that I respond to inquiries posted on the "members only" forum. I don't particularly care for big brother sanitizing or censoring my responses, thank you.

Parent - By welderbrent (*****) Date 01-03-2018 17:42
Don't let him fool you, he just uses intermediaries to respond on the other forum. 

No matter how often we cover A numbers, probably once every year or two, it is always an interesting discussion to me.  I don't generally use them in my world but the concept is an interesting one depending upon the need of the job.

He Is In Control, Have a Great Day,  Brent
Parent - - By kcd616 (***) Date 01-04-2018 10:52
thank you for putting things in order
and saving me a lot of typing:eek::evil::twisted::wink:
maybe someday we can find the time and place close to me to go over things like this more in depth
have some questions and things to bounce of you 
maybe you might like my ideas:eek: doubt it:wink:
as far as the members only forum
it is more of inspectors and engineers
and everyone knows how I feel about them and there ideas and thoughts:evil::twisted::yell:
learn to be a welder and weld for a living (ie a paycheck)
and then they may know something and go from there
just my thoughts
Parent - - By 803056 (*****) Date 01-04-2018 15:54
Aw, come on Ken. You're being too hard on us inspectors and engineers. You might bruise my feelings and I would have to sulk in the corner for a day or two.

Send me an email, my address in listed in my profile. If I'm ever in your area I would love to share a meal with you and discuss the finer points of our chosen field of interest.

Best regards - Al
Parent - - By kcd616 (***) Date 01-06-2018 04:51
i heard that the new members forum has a safe space:evil::twisted::wink::yell::eek:
And would most enjoy have a meal with you:smile:
think I would learn something also, thank you
BTW: anyone else hear about the new nuke plant in Ga? and get job offer?
Parent - - By 803056 (*****) Date 01-07-2018 04:06
Are you referring to Vogtle?

I have a couple of friends working on it.

Parent - - By kcd616 (***) Date 01-07-2018 14:12
for some reason got an offer:wink::twisted::evil::cool::eek:
from MAJOR contractors for me to
sub-contract for them:eek:
my heath limits me on travel
so not my cup of tea
my best to your friends and all
always my best to you and your family
Parent - By 803056 (*****) Date 01-07-2018 23:22
Sorry to hear you are not up to the travel and work due to health issues. You have to take care of yourself first. The contractors aren't going to care.

I hope you feel better shortly my friend.

Up Topic Welding Industry / ASME Codes / A-Numbers Again: What & Why ?

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