Low ferrite % for A790UNS S31803 during qualification 3

[jazimed]

I'm about to prepare a PQR with a Pipe smls NACE BE 4'' S-40S A790UNS S31803 B36.19. Test coupon: two pup pieces of 150mm butt welded each one to another

The welding process used for qualifcation is as follow:

Root Pass:
- GTAW Process
- Filler metal: ER2209 2.4mm
- shield gas: Argon
- Current: 90A
- Voltage: 9 V
- Heat Input 9.7 Kj/cm

Hot Pass:
- SMAW Process
- Filler metal: ER2209-17 2.5mm
- Current: 50-66A
- Voltage: 21-27V
-Interpass temperature: 150°C
- Heat Input 14 Kj/cm

filling Pass:
- SMAW Process
- Filler metal: ER2209-17 2.5mm
- Current: 44-58A
- Voltage: 21-27V
-Interpass temperature: 150°C
- Heat Input 12 Kj/cm

The problem that I'am facing is having a ferrite percentage very low in the Base metal (37%), the HAZ (30%) and the weld joint (25-20%). the mean used for ferrite measurement is the ferritoscope. at the other hand the material certificate of the pipe is indicating 52% of ferrite according to ASTM E562. I don't know whether there is a problem with the base metal or there is something wrong with the welding process. Any help here?

 

[metengr]

First, the weld parameters look acceptable except the hot pass should be by the GTAW process and not the SMAW process.

Second, have you confirmed by metallographic examination the ferrite volume fraction in the base material, heat affected zone and weld region to compare the Feritscope? Typically, when we have qualified duplex stainless steel weld procedures, we have routinely performed metallographic examination on a sample removed from the weld coupon to verify the volume fraction of ferrite and austenite, and not rely completely on a Feritscope.

 

[jazimed]

metengr, thank you for your quick response.

Do you mean that we cannot trust feritscope at this level and should consider only the metallographic examination to check the exact ferrite amount? what if there is a requirements to check the ferrite% in every production joint? this means there will be a diffrence between PQR and production figures, no?

 

[metengr]

jazimed;
No, not yet. At this point, I think you need to get to the bottom of why the scope is providing low ferrite readings. Once you have confirmed by lab examination that the ferrite levels are acceptable, the next step would be to either obtain a new scope or have this calibrated or repaired. If the lab results confirm the scope is correct, you have bigger problems with the material.

 

[jazimed]

metengr,

In fact, i was preserving the coupon for the remaining inspections to qualify the PQR since the lab examination requires its destruction, that's why I've done one more feritscope inspection with 3rd party and I had almost the same results as the first one. this is not enough to say that there is problem with the base metal?

 

[metengr]

I would conduct the lab examination before proclaiming the material is a problem.

 

[EdStainless]

Do you have duplex cal standards for your Scope? You cannot use the standard readings.
What reading does your Scope give you on the base metal?

In general low ferrite would indicate too high of a temp or too much nitrogen being added. Neither of these looks like your problem. (usually welds are too high in ferrite, that is why 2209 filler is used)
What weld dilution are you getting?

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P.E. Metallurgy, Plymouth Tube

 

[Guest102023]

http://www.imoa.info/download_files/stainless-steel/Duplex_Stainless_Steel_3rd_Edition.pdf

Thanks for posting this question - I discovered this is a new edition of this useful reference.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[jazimed]

EdStainless, thank you for your iterest to my issue,

Please, find attached the third party ferrite test report. Yes indeed there is standard cal used to check he accuracy of the scope before measurement on the BM. Regarding, the the weld metal dillution %, still I didn't make the macrographic examination to determine it.

 

[Guest102023]

I'm with metengr, do a metallographic phase analysis. In fact I would question the ferritscope equipment condition and methodology.

Do not assume that because the base metal FN is low that there is an issue with base metal composition that is in turn negatively affecting weld dilution. FN in the base metal is also a function of prior thermal and mechanical processing (and magnetic measurement technique; see above).

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[Figueredo]

hi all,

I had a similar experience with duplex stainless steels, after analyzing the base material, the heat affected zone and the filler with hundreds of tests it was determined that the problem of high ferrite content lies in the heat imput , gas protection and backup gas .

Please check this constantly. normally 5% N in the shielding gas and 10% in the N backup gas Ar rest. the heat imput should not exceed 10 KJ / cm , I recommend only GTAW.

welders also in many cases this condition does not care because they want is only welded and have money.

the ferritscope is not enough if you want to verify the origin, but for my small experience the problem during execution of the weld.


I hope I can help

 

[jazimed]

brimstoner,

I will do a metallographic examination anyway. but I wonder what will be the utility of the ferritscope (as a method), if it doesn't give accurate figures in regard to the metallographic examination. the material certificate (if we trust it) shows ferrite% 52% as per ASTM E562 and ferritscope % in the BM 37 to 41% according to the above report.

 

[jazimed]

Figueredo,

My concern is about the low ferrite in the 3 zones which are below the requirement 35-65%. Obviously, if the ferrite% is low in the BM, it will be so in the HAZ and in the weld. That's why I believe that the problem is in the material itself and the only way to be sure is to make metallographic examination.

 

[EdStainless]

No, my question is are the ferrite standards for your Scope actually made from duplex stainless?
I don't think so since they show the BM as 35-40%, and it should be 50-55%.
You need duplex ref standards and the calibration must cover the range of 40-60%. The cal points down at 10% are worthless.

Have metallography done. It is only way that you will know.

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P.E. Metallurgy, Plymouth Tube

 

[DekDee]

jazimed,
Strongly recommend you remove the SMAW altogether and weld full GTAW (it is only 6 mm / 1/4" thick).
May make a huge difference in your WM / HAZ readings.
Won't help your BM readings but I am in total agreement with posters above - without metallographic confirmation of BM composition you really have no idea of actual BM composition.
Cheers,
DD

 

[jazimed]

Thank you EdStainless and DekDee,

I will proceed with the metallography and I will let you know about the results.

 

[moltenmetal]

Figueredo: you say heat input must be kept below 10 kJ/cm, but I've also heard people say that inadequate filler metal is a big cause of failure on the ferrite numbers. Aren't these two factors at odds with one another, assuming only GTAW? We haven't even tried high deposition rate processes on this material and the last time we tried, we struggled to meet the requirements with GTAW root/fill. We did not use the 5%/10% N2 shield/backing gas during those tests and that would be the next thing we'd try.

 

[Figueredo]

hello friend moltenmetal

the topic under discussion is on the ferrite content in different areas of welding, once the metallography is made and detect the fault MUST weld again.

the nitrogen is vital in the stabilization of austenite during welding duplex stainless steels , why should not exceed heat imput and using nitrogen gas mixtures help stabilize the austenite and ferrite have less in the HAZ and the weld .

also recommend that when you cut the tube or plate to be tested in the welding process using tools that cut without much heat, plasma cutting is not recommended for their high energy.

I hope can help.

Regards,

 

[EdStainless]

The use of N in the gas and more filler both favor more austenite, because the failure is usually way too much ferrite in the welds.

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P.E. Metallurgy, Plymouth Tube

 

[qcrobert]

Ordered Fischer feritiscope for use on 32205 and have four cal blocks; Base, 9.8 FN 10.9 Fe%, 41.1 FN 36.9 Fe%, 117 FN 81.1 Fe%. Verified base metal mtrs from two different labs for feritiscope comparison. I calibrate using last two blocks and confirm to base metal to be welded.

You can have a base metal of 70% and obtain acceptable 35-60% Fe by controlling cooling rate. Low heat input = higher Fe% and high heat input = lower Fe%. Unlike your process we dealt primarily with fillet welds using GMAW process, 2209 filler metal w/ 90/7/5/2.5 TriMix shielding gas with excellent results.