P91+SS316-correct welding sequnce to join

Expert, Pl see the attached sketch which self-explanatory. Require welding procedure if this joint is recommended in P91

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• Young-Sun Seo maybe flow nozzle.

  
  

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  Kannayeram Gnanapandithan yes young.

  
  

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  Alexandru Florea I would give a shot for a PQR like that: Use Ar as backing gas, use induction station for preheat, control of the temperature and PWHT for P91 ( induction will not heat the SS). Preheat at 150 C with 150 C/h , root and hot pass - 141(GTAW) using 308L wire, fill and cap- 111(SMAW) with 308L electrode, interpass temp max 200 C, then decrease the temp to 80-110 C and leave it for 1,5 h, after increase with 150C/h up to 730-750 C and leave it for 1,5 h, then decrease with 150C/h. Regards.

  
  

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  Marius Mihai but how the PWHT heat transfer by conduction to adjacent SS area will be avoided? I have never applied this procedure but it seems to me imposible to avoid heating of SS with this practice. I estimate that if 750C deg is achieved at Root of P91 then at least half of the 308L weld will have the same temperature and then adjacent weld and 316L material may reach 600 C deg and slowly decreasing with the distance. In addition the actual configuration requires either to heat P91 at left and right side simultaneously or in 2 subsequent PWHT therefore at 316L location the either the temmperature will be high or the time is doubled. Also 308L is not recomended for this combination since C from P91 will enrich the dilution area of weld and no more low C therefore senzitization and intergranular corrosion.

  
  

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  Marius Mihai Hi Kanayeram
  having seen the design condition I think you have 2 solutions only:
  1. My solution which I have explained before. For this uou have to co tact piping engineer to calculate if the1.25Cr 0.5Mo or 2.25Cr 1Mo material can have the sufficient creep resistance at design temp/pressure. Then issue a Technical deviation request for not applying PWHT between that Low alloy 16mm thk Cr Mo material and SS316L weld. You have to do some WPQR on it.
  2nd solution is using an apropriate Ni alloy weld less susceptible to sensitization + PWHT as recomended already by others. However I do not realy agree that temperature PWHT of P91 can be reduced too much while increasing time since this is not only for streess releaving but mainly for the purpose of tempering of martensite. For this solution you have to check with piping/process engineers to see if possibility of condensate in the steam line exists. Sorry no time too cgeck B31.1 in details, just give you some ideeas. Hope you ll solve the problem in rhe best way and pls give is feed back. thanks

  
  

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  Marius Mihai the issue with condensate in the steam line is that it accelerate SS corrosion with major conseqyences.

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  Alexandru Florea Of course the temperature for P91 will be controlled at the left and the right - there you put the temp sensors for millivoltmeter. The most similar case in my career was to weld 44,5 x 6,3 mm pipe -GTAW P91 (X10CrMoVNb9-1)+12X18H12T . Operating temperature 545 C and pressure 190 bars. 5 years since then no problem. Please check also the Schaeffler and De Long diagram - you can find a program online. http://migal.co/english/service/welding-stainless-steels/schaeffler-diagram-with-different-base-materials/

  
  

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  Marius Mihai the fact that you control the temperature left and right does not mean the SS will not be seriously heated by the PWHT heat with all the consequences.

  
  

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  James Kelly Harry, exactly WHAT is this new filler by EPRI & who makes it? I'd like to sound like I know what I'm talking about, with respect to such steel-stainless joints.
  
  Seems to me your comments on Relaxation Cracking haven't gotten a lot of attention. I saw these sort of fusion line cracks in otherwise well made welds for decades, at Rolled Alloys. Did not know what they were until the last couple years of working there. Just thought that was how God meant heat resistant alloy weldments to fail.

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  Navin Kothari James - In welding P91 to SS 316, the filler ENiCrFe-2 or 3 or ENiCr-3 is used to stabilized austenitic SS while for P91 uses carbon steel but it requires buttering with Ni alloy. This helps in preventing C migration from SS and also soften up coefficient of thermal expansion of SS. The filler is now made by all welding materials suppliers. Lots of work have been done to prevent pipes and pressure vessels cracking in fossil and nuclear power industries Hope this helps.

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  Kannayeram Gnanapandithan

  As discussion going on the above in another post, We have done as follows
  1. Edge preparation was done on P91
  2. Preheated to 200 deg celsius and maintained till completion of weld
  3. Buttering was done on EP face with ENiCrFe2 with inter pass temp of 200 °C
  4. Post heated and slow cooled
  5. SR was done
  6. NDT carried out and EP prepared again with minimum of 5mm weld metal
  7. These was joined with SS316 with Root &Hot pass by ERNiCr3 and balance ENiCrFe2 and SR done. NDT (UT) was done and no indication, But it is failed, pl see the attachment. What could be reason for this
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