Hanre,
I got your PM today and so far, this is what I've been able to come up with... Now keep in mind that I'm not aware off the top of my head whether one or more of the welding codes or standards require a specific percentage of N in the shielding gas mix and below are mostly recommendations from various DSS producers... There may be someone else who may chime in with some reference to a code or standard where there is some specific amount of N to be used in the shielding & backing gases when welding 2205 DSS...
Cleaning the base metal prior to welding should be done properly and carefully... Scotch bite pads, or abrasive wheels are not recommended, or anything else which may leave a thin layer of any type of unknown residue for that matter... Any discs that were used on Carbon steel must not be used as the iron/iron oxide residue will contaminate & degrade the corrosion resistance... So use only dedicated grinding & surface cleaning discs/medium for Stainless steels and keep them clean!
Gas purity & Dew point are also important factors to consider in both the shielding & backing gases as well as gas flow from the torch (Gas diffuser should be used), and flow rates of both also... Thin stringers should be deposited as opposed to weaving the bead layer deposit...
Cleaning each layer should be done carefully no matter the thickness of the base/parent metal.
Here's a more specific paper regarding recommended welding practices for use on 2205 duplex from ""Sandvik" which will help you some...
It's titles: "Welding practice for Sandvik Duplex Stainless steels SAF 2304, SAF 2205 and SAF 2507." Here's the link:
http://www.sandvik.com/sandvik/0140/internet/se01280.nsf/0/ecd132de31b33bd085256bd5006d666b/$FILE/Welding%20Practice%20for%20Sandvik%20Duplex.pdfRefer to page 6 for the recommended percentages of N in the shielding gas.
Now Avesta recommends either straight Argon, or Ar+2%N+10-30% He which is different than what Sandvik recommends to use for GTAW shielding their on 2205 Duplex...
Here's the link I'm referring to this .pdf on page 26 of 47:
http://www.engineersaustralia.org.au/shadomx/apps/fms/fmsdownload.cfm?file_uuid=EF9B0598-E8BE-B607-D9A0-96CF65BCB7D6&siteName=ieaustAnd this one from Outokumpu on page 8 in this .pdf as well as the one below it also:
http://www.outokumpu.com/35058.epibrwThis one explains why increasing the amount of N may increase the amount of pores... So, up to 2% N is the maximum amount recommended... Meaning, less than 2% N is also something to consider in order to reduce the amount of pores... More than 2% N will not only increase the amount of pores (porosity) in the weld, but also increase the Wulfram (
tungsten) electrode degradation at a faster rate than normal thus increasing the possibility of Wulfram
inclusions in the weld...
The addition of up to 30% He is suggested in order to increase arc energy, and to increase welding speed considerably (20-30%) also...
Although, I would recommend a trailing shield if He is added to the shielding gas, and is used in a mechanized/automated application to limit the exposure of the still cooling weld surface area from being contaminated with gases that could become entrapped from the no longer shielded atmosphere...
Finally, the purity level of the Argon being used should be 99.995% or better especially when combining with the other elements to make up the shielding gas...
The backing gas can be either straight Ar or better yet, a mixture of 90% N and 10% H for certain applications, or straight N instead if one is concerned about Hydrogen absorption, and no amount whatsoever of H should be used in the shielding gas mix...
The amount of oxygen content in the shielding & backing gas should be below 0.25% or 2500 ppm (Parts Per Million)...
I don't agree with this amount... I would go even further to reduce the residual Oxygen on the root side to 0.0030% or 30ppm's.
The data is found on page 8 of 20 in this .pdf:
http://www.avestawelding.com/3756.epibrw Look for shielding gas recommendations on page 3 of 4 in this .pdf from Techalloy:
http://www.techalloy.com/_assets/brochure_duplex.pdfNow, I don't know for sure if this will be helpful for you or not because you haven't given us enough background info on your project but, you may also want to consider reviewing this .pdf as well covering "Qualification of welding procedures for duplex stainless steels." Here's the link:
http://www.complianceonline.com/images/supportpages/500768/sample_0402-29.pdfHere is one of my favorite .pdf's regarding the best practices used in welding Duplex stainless steel and is from Stainless Steel World, and is written by
3 engineers from Fluor Canada... Refer to pages 58 & 59 in the .pdf:
http://www.kcicms.com/pdf/factfiles/duplex/SSW_DEC07_fluor_LR.pdf?resourceId=15This one is from Stainless Steel World also... Refer to "4.4 Gases" on page 6 of 10 in the .pdf:
http://www.kcicms.com/pdf/factfiles/duplex/DA2_032.pdf?resourceId=14Keep in mind also that when welding DSS such as 2205, the heat input must be controlled as well as the interpass temperature...
So for GTAW of SAF 2205: 0.5 to 2.5 KJ/mm is the recommended heat input, and the interpass temps should not exceed 200 degrees C.
Here's a very good Power point presentation by Sandvik from WPSAmerica.com and, refer to slides 21 of 44 to 26 of 44 as well as all of the other slides also:
http://www.wpsamerica.com/library/Welding%20Duplex%20Stainless%20Steel.pptThis from Avesta Polarit/Outokumpu, titled "STAINLESS STEELS Their properties and their suitability for welding."
Look for pages 4 (6 of 11) and, page 6 (8 of 11) for both shielding & backing gas advice and Weld Defects/Practical Advice for GTAW of DSS SAF 2205:
http://www.outokumpu.com/applications/upload/pubs_113155252.pdfThis one is from Rolled Alloys... Refer to page 8 (10 of 16) for GTAW parameters:
http://www.rolledalloys.com/trcdocs/corrosion/RA2205Bul1071.pdfThis Power point presentation in .pdf form has a very funny ending
:
http://www.steeltank.com/Portals/0/docs/Grocki%20Duplex.pdfThis one is from Arc Machines International (AMI)... Scroll down to
1/4 inch diameter 2205 duplex, and read the shielding gas combinations used
and the conclusions of each mix... You need to also read the paragraph titled
"Penetration Enhancing Flux":
http://www.arcmachines.com/applications/butt-welding-filler-material/duplex-stainless-steel-tubing This one is from BOC Australia, and I would refer you to page 9 of 12 in the .pdf:
https://boc.com.au/boc_sp/downloads/gas_brochures/BOC_216521_Gas_shielded_ArcWelding_of_Duplex_Steels_BrochureAUS.pdfThis one is from the IMOA (International Molybdenum Association). Refer to page 48 of 56 in the .pdf:
http://www.steeltank.com/LinkClick.aspx?fileticket=8bPs5I0gTfw%3D&tabid=95Finally, here's the Avesta Welding Manual... Refer to pages 78 & 92:
http://www.kskct.cz/images/materialy/en/avesta.pdfWell, that's about it for me... So I hope this will give you enough ammo to convince whoever it is that needs convincing regarding welding practices of Duplex Stainless steels.
Respectfully,
Henry
