F Number on WPS & PQR

[perruolo]

Gents I would like to hear your opinions about my statement below mentoned:

We have a corporate PQR-GTAW which was qualified using an electrode ER347, Base metal AISI 304L. We pretend to use this PQR to support our new PQR to be used in different project, but due to cost issues we cannot use the stablished electrode ER347. I proposed to use ER308L

Now, Reviewing ASME Sec IX Essentials variables QW404.15 "A change from one F-Number in table QW-432 to any other F-Number or to any other filler metal, except as permitted in QW-433" I think that I can use same PQR to support my new WPS without requalification because:

Old PQR
Base Metal P No P8 to P8 AISI 304L
F No: F6 AWS 5.9 ER347

New WPS
Base Metal P No P8 to P8 AISI304L
F No: F6 AWS 5.9 ER308L
A No: Not aplicable on stainless steel

However, QC department stated: The assignments (F No) do not imply that filler metals within an F-Number may be indiscriminately substituted, one for another.

I explained them that I ll prepare a new WPS with ER308L to weld 304L base metal supported on my previous PQR but they dont want to accept it.

What do you think???

Thanks

 

[metengr]

The assignments (F No) do not imply that filler metals within an F-Number may be indiscriminately substituted, one for another.

The reason for grouping of electrodes using F-No's is to avoid the cost of having to qualify weld procedures for each electrode. With that said, your QC department cannot reject a WPS using 308L filler metal if the original PQR was qualified with 347 filler metal (based on QW-404.15). Section IX does not endorse or recommend weld consumbales for a particular application. Your QC department has every right to not allow the use of 308L for this application based on design or service issues, but not using Section IX.

 

[perruolo]

Metengr Thanks, Your reply confirm my theory. I dont need to requalify the WPS if I only change the type of electrode but the F-Number remain same.

 

[metengr]

perruolo;
Adminstratively you can do as you suggest. However, I want to warn you that the 308L is low carbon and does not have near the creep strength as stablized grades of stainless (like 347) or high carbon version of 304H.

 

[stanweld]

perruolo,
Your new WPS is supported by the current PQR per ASME IX. Your QC Department is unnecessarily adding costs to the company.

 

[GRoberts]

Your QC department statement is correct (they would have to be since they are basically quoting Section IX), however, they are applying it incorrectly. I would hardly call welding 304L base metal with 308L filler metal indiscriminate since that is what happens every day in thousands of shops around the world, and they are a base/filler combination designed to work together. It is actually the welding of 304L with 347 that is the more unusual situation.

 

[bhollands]

As already stated you are correct in your interpretation as long as impacts are not required. If the base metal requires impact testing the classification is an essential variable. While impact testing 304L is rare I thought it best to include it just in case.

Bob

 

[perruolo]

Sirs Thanks for all your replies.

We also require to prepare a WPS for 316L metal base & ER316L stainless steel electrodes. As we did before, we will support this NEW WPS with the PQR prepared with ER347 (electrode) F-No: 6 & 304 base metal P-No: 8

 

[gtaw]

Just to add a clarification, A numbers apply to all ferrous metal. Since stainless steels are ferrous metals, anything that affects the A number is considered an essential variable.

I doubt the change from a 347 to a 308 filler metal is going to affect the A number, so the substitution is allowed by the code. There is more to the story than the A number alone. Many grades of austenitic stainless can be sensitized when welded without regard to the effects of sustained elevated interpass temperature or the time at temperature when multiple pass welds are deposited. One way to mitigate the ravages of sensitization is to use L grades of austenitic stainless base metal and filler metal. Carbon is the bad actor because it combines with the chrome to form M23C6 compounds, thereby depleting the grain boundaries of their corrosion resistance. Eliminating the carbon component, or at least minimizing carbon, reduces the carbon available to form carbides along the grain boundaries thereby reducing the chance of sensitization.

An alternate to reducing the carbon content of the base metal and the filler metal is to use a stabilized grade of base metal and filler metal. The stabilized grades of stainless use additions of Ti or Cb which have a greater affinity for carbon than the chrome. The Ti or Cb is used to chemically tie up the carbon leaving the chrome intact to provide corrosion resistance. The use of stabilized grades of stainless still retains sufficient carbon to permit higher allowable stresses at elevated temperatures. After all, we add the carbon to steels to gain the strength advantage. The lower carbon in the L grades of base metal and filler metal resist sensitization, but also reduces the allowable stress at elevated temperature.

Just because the code allows you to do something do not mean it is a good idea.


Best regards - Al