We have to make a seal weld between the Duplex tubes of a tube-shield exchanger and the Carbon Steel plate. The material of our tubes is an UNS S31803 (SAF 2205) duplex stainless steel and our plate material is an A105.
Our problems are centered in the selection of the correct filler metal (if it is necessary), and the procedure to follow. We know that is not recomended to preheat the DSS but we are concerned about the possible apparition of cracks in the ZAC or in the seam.
Thanks
Mariano
The suppliers of the duplex material will suggest an alloy of their manufacture for example welding 2205 to carbon steel would have a suggestion of 2209 for a filler metal.
I would strongly suggest you compare alloy 625 ( E/ER-NiCrMo-3) and the suggested filler for the ups and downs of each including cost and availability.
Ni based alloys typically over options and advantages.
Have a great day
Dirk
By -
Date 03-31-2001 19:13
The advice that was given, to speak to the suppliers (Sanvik) is obviously good advice. My personal experience with welding SAF2205 tubes to C/Steel tubesheets has shown that using 2209 filler works well. There is however just a small warning. If you plot the consumables, and the typical dilutions that you can expect, you will see that the first run will result in a material with a certain amount of Martensite present. This can result in problems, especially if you have hydrogen present.
Using a 312 filler tends to get you out of the martensite region, and might be a good choice. (I have also used this in the past.)
Another warning: Most welders prefer to do an autogenous root pass in tube to tubesheet welds. Welding these materials together without filler will definately result in a great deal of martensite formation. You should therfore always make sure that your weld prep allows the addition of filler for both runs. (Assuming that you are going to deposit two runs.)
I hope this helps
Niekie Jooste
Sasolburg
South Africa
By -
Date 03-31-2001 20:19
I tried to post an answer before, but it seems to have dissapeared. We may end up with two similar answers now.
My past experience, welding alloy 2205 to C/Steel shows that using 2209 filler will work. You may however end up with relatively high levels of martensite being present. This can lead to problems if you have too high a dilution of the C/steel into the weld puddle.
Another option is to use 312 filler. This tends to take you out of the martensite region.
A Warning: Many welders prefer to weld the first run of a tube to tubesheet weld autogenously. This would be a bad idea with this combination of materials. You must therefore ensure that your weld prep is adequate to allow the addition of filler metal.
I hope this helps.
Niekie Jooste
Sasolburg
South Africa
