Porosity welding super duplex 3

[dieselofdog]

I am having an issue with porosity welding super duplex. I have never come across this before. With process of elimination I feel my issue is procedural rather than gas (type or lack of coverage), contaminants, nasty base material or welding consumable, welding machine.

Base Material- UNS S32550
Welding Con - ER2594 1.2mm
Process- GMAW-Pulse and GMAW-Spray
Shielding Gas- Ar78% He20% CO2 2%
Weld type- Build up overlay on round bars ranging from 150-300m OD. 1-2 layers of weld deposited in a 2-4mm deep pre-machined groove.
Pre-Heat- 20deg C
Interpass- 150deg C
Pre-cleaner: Acetone

Welding Parameters
GMAW-Spray 170-180A, 26-27V, Travel 300-350mm/min
GMAW-Pulse 150-160A, 24-25V, Travel 300-350mm/min

The porosity in the weld is not uniformed. If the weld deposit is 4-5mm high the porosity is in the bottom 2mm at the fusion line. The top 3 mm are very clean and defect free. The bar is welded on rollers and weld direction is circumferential. When maching deep into the weld deposit the porosity lines appear to be evenly spaced as the width of the weld bead, looks like it is concentrated in the toe area. The deeper you machine the worse the porosity gets.

I have tried welding with several work shop machines, pulse and spray. All produce the same defect. Tried different brands of consumable. Chemical results of the base metal and welding consumable have showed no abnormalities. The weld looks nice during welding and after.

Is there something obvious that is out of place with the shielding gas type or my parameters etc.

 

[metengr]

What is the flow rate of the gas and dew point? It should be less than 30 cfh. Everything else regarding your essential variables looks good. It could also be technique regarding, because this process is prone to lack of fusion weld defects.

 

[EdStainless]

The supplier recommended CO2 in the weld gas? We use N in the weld gas but never CO2.
Moisture (and oxygen) in the gas is my main concern also. And make sure that you check at the torch and not just at the source. Even hoses that have been in use for some time will be porous enough to impact gas purity.

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P.E. Metallurgy, Plymouth Tube

 

[DVWE]

If you have a qualified WPS, try a gas mixture of 98% Ar and 2% O[sub]2[/sub] or 98% Ar and 2% CO[sub]2[/sub]

 

[EdStainless]

Have your read this?

http://www.nickelinstitute.org/~/Me...ndSuper_DuplexStainlessSteel_14036_.pdf#page=

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P.E. Metallurgy, Plymouth Tube

 

[kjell123898]

hi
Welding of super duplex grades should be made without Co2. Use pure argon or 99,25Ar+0,75N as well as well controll of gas flow and it's turbulens

Kjell Gr°nvold

 

[kjell123898]

hi
Welding of super duplex grades should be made without Co2. Use pure argon or 99,25Ar+0,75N as well as well controll of gas flow and it's turbulens

Kjell Gr°nvold

 

[racookpe1978]

And verify that that Argon itself is "pure" .. We have had a few instances of contaminated Ar causing porosity (not on this particular alloy, mind you), but the porosity stopped when the bottles were swapped on at least 3 job sites the past year.

 

[dieselofdog]

Will the inclusion of CO2 cause porosity?

 

[kjell123898]

hi,recommend you to change the shielding gas to 99.25%Ar + 0.75 Nitrogen (mixgas) which simultaneously stabilizes nitrogen loss during welding (GTAW)
this shielding gas can be supplied by all recognized suppliers of welding gas. The main impurities is water H2O and water concentration shall be kept below 10ppm. (ISO 14175)
by addition of CO2 in the shielding gas can be transmitted hydrocarbons which is not desirable in a austenit / ferrite structure as well as to much activity in the weld bath

Kjell Gr°nvold

 

[gtaw]

I would watch the angle of the gas nozzle relative to the groove and the nozzle to work distance. If the welder has to stop and roll the assembly, he may be "reaching" as he approaches his stop point to roll the assembly and reinitiate the arc. Also, is the welder grinding the starts and stops and between each weld layer to remove the silicon islands that typically collect on the surface of the weld bead.

Changes in the nozzle to work distance, angle of the nozzle, etc. can result in turbulent flow in the shielding gas. Leaking connectors or even old gas hoses can result in air mixed in with the gas by the time it gets to the torch.

Gases provided by the vendor that meets the requirements of AWS A5.32 have very low dew points and very low moisture content ensuring the gas is fine, but the story can change by the time it reaches the gun.

Best regards - Al

 

[qcrobert]

EdStainless,
We have qualified procedures using 90%He/7.5%Ar/2.5%CO2 with GMAW (0.035"dia ER2209) of 2205 with great success. Volume FE% 35%-60% range with joining of 0.125" to 0.125" (butt joints), 0.125" to 0.375" (fillet welds and 0.0625" to 0.375" (fillet welds). GTAW with welding grade Argon.

We are currently conducting in-house testing of 2507 using same TriMix with GMAW (0.035"dia ER2594) and will also be testing other shielding gases. I am open to your suggestions for other shielding gases for 2507 with GMAW and GTAW.

Regards,
Robert

 

[EdStainless]

So you have done A923 testing, both impact and corrosion resistance?
If you haven't done both then you may be in for a suprise.
I would never allow that gas mix on any of my equipment just based on the fact that no stainless maker suggests it.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

For MIG (GMAW) welding of duplex stainless steel using a pulsed current power source, the 2% CO[sub]2[/sub] has been used and recommended by weld wire suppliers.

 

[XL83NL]

Yesterday attended a meeting from Sandvik, mainly focussing on DSS/SDSS/HDSS, the metallurgist mentioned to always use N in the backing/shielding.

http://smt.sandvik.com/contentasset...44f04d0/sav0049_whitepaper_welding_150606.pdf

http://smt.sandvik.com/globalassets...s_downloads/tubular-products/s-120-eng_10.pdf

http://www.stainless-steel-world.net/pdf/SSW_DEC07_fluor_LR.pdf

http://www.techstreet.com/products/1891162

 

[metengr]

For GTAW absolutely yes, for MIG (GMAW), not necessarily. Sandvik has a publication on MIG welding duplex alloys and they have recommended CO[sub]2[/sub] to improve welding characteristics.

 

[qcrobert]

EdStainless,
Yes I had ASTM E562-11 Volume Ferrite Test, ASTM A923-08 Method C Ferric Chloride Corrosion Test, ASTM A923-08 Method B Charpy V-Notch Test, incl. Tensile Pulls Tests and Guided Bend Tests. It is listed as an acceptable gas mixture by some suppliers as long as the CO2 does not exceed 3%. Testing of our gas mixture actually showed the percentage of CO2 around 2.18%.

I copied the independent lab results for your perusal.
Robert

ULTIMATE STRENGTH TEST
Laboratory
Number
Width
(in.)
Thickness
(in.)
Area
(in.2)
Load
(lbs.)
Ultimate Tensile
Strength (ksi)
Fracture
Location
2393-2RTT1 0.753 0.1755 0.1322 15,600 118.0 In Weld 1
2393-2RTT2 0.755 0.1755 0.1325 16,000 120.8 In Weld 1
ASME IX
Req. (Min.) 95
Method(s): ASTM A370-12a
1 Ductile fracture
180° GUIDED BEND TEST
Laboratory
Number Bend Type Thickness Bend Dia. Comments Results
2393-2BND1 Root 0.180” 4T No Cracks Observed Acceptable
2393-2BND2 Face 0.180” 4T No Cracks Observed Acceptable
2393-2BND3 Root 0.180” 4T <1/8” Crack Observed Acceptable
2393-2BND4 Face 0.180” 4T No Cracks Observed Acceptable
ASME IX, QW-163
Requirement --- --- --- No cracks greater
than 1/8” long
Method(s): ASTM E190-92(2008)
(-40°F) CHARPY V-NOTCH IMPACT TEST
Laboratory Number Size (mm) Ft.-Lbs. Notch Location
2393-2CVN1 10 x 2.5 27.0 1 Base Metal
2393-2CVN2 10 x 2.5 24.5 In HAZ
ASTM A923-08, Table 2,
Method B Req. (Min.) 10 2
Laboratory Number Size (mm) Ft.-Lbs. Notch Location
2393-2CVN3 10 x 2.5 16.0 In Weld
ASTM A923-08, Table 2,
Method B Req. (Min.) 6 2
Method(s): ASTM A370-12a
1Unbroken
2 Requirement reduced for sub-sized specimens per ASTM A923-08, Table 2, Note A.
METHOD “C” – FERRIC CHLORIDE CORROSION TEST 1
Laboratory
Number Test Duration Temp °F Corrosion Rate (mdd)
2393-2MET1 24 Hours 72 ± 2 0
ASTM A923-08,
Table 3 Req. (Max.) --- --- 10
Specimen was immersed in a solution of approximately 6% Ferric Chloride in distilled water.
Method(s): ASTM A923-08
1 Method “C” measurements are not A2LA accredited.
% FERRITE (VOLUME FRACTION BY MANUAL 25 POINT COUNT) 1
Laboratory
Number
Average Area
Fraction 2
Standard
Deviation 95% CI Ferrite (%) Location
2393-2MET2
0.43 0.052 6.5 43 ± 6.5 Base
0.58 0.054 6.7 58 ± 6.7 HAZ
0.43 0.033 4.2 43 ± 4.2 Weld
Customer
Req. (Range) 35 – 65
Etchant(s): NaOH + H2O
Magnification(s): 500x
Method(s): ASTM E562-11

 

[metengr]

The above confirms what we discussed regarding pulsed/spray GMAW with less than 2.5% CO[sub]2[/sub].