P-22 to Carbon Dissimilar weld.

[VAWELDER]

We have a dissimilar weld to make,P-22(2-1/4) to carbon steel.Suggested was to butter carbon with P-11(1-1/4) then weld to P-22.Is that correct?It sounded like a downgrade.If you qualified procedure could you weld P-22 direct to carbon.

 

[pipewelder1999]

I think there are many "Opinions" on this. As far as a "Downgrade" goes, apply the "weakest link in the chain" principle. I have seen boiler contractors weld this with various grades of filler metal from ER70S-x and up. There are many variables to consider and hopefully a more educated response will come up.

Good day Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[Metalguy]

Easy-use carbon steel electrodes/wire, but preheat and PWHT for the P22.

 

[sayee1]

Various specifications and codes specify various consumables for dissimilar welding. You can use consumables meeting properties of lower grade or upper grade or with properties in between those for the two grades of base metal. You did not specify what consumable the client is asking to be used for welding the buttered portion to the P22. I presume it is also 2 1/4 Cr 1/2 Mo type.
The client specs is finally binding but we need to understand if there is a technical reason for his asking for the buttering. If you qualify a PQR meeting all the spec requirements welding P22 to cs directly you would be within code but there are hardly any tests you would be carrying out for the creep properties, I don't exactly remember now, maybe tommorow I can reply exactly the reason for your clients asking for this buttering. There is a reason for that. Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[ijzer]

The welding is not the problem. You can weld P22 to Cs with CS filler as well as P22 filler.
The problem is the PWHT. If the dissimilar weld is heattreated at the P22 required temperature you could impair the properties of the CS.
The solution would be : butter the P22 with P11 filler , PWHT , weld the CS to the P11 butter layer and PWHT at a lower temperature.

 

[GRoberts]

I agree with ijzer, with the additional note that as long as the buttering is thick enough that the HAZ from the joining weld does not impinge on the P22 base metal (usually 3/16" - 1/4" mimimum thickness), you may be able to omit the second PHWT depending on your application/governing codes/etc. if you butter with a CS or 1/2 Mo (e.g. 7018-A1) weld metal.

 

[ijzer]

I agree with GRoberts with respect to the buttering thickness , we use min. 6 mm.
Buttering with CS or C-1/2 Mo , i.s.o. 1 1/4 Cr-1/2 Mo is not adviced because again the PWHT at P22 required temperature could impair the CS or C-1/2Mo filler metal properties.

 

[sayee1]

The PWHT temperature can be reduced by using buttering as described by GRoberts or Ijzer above. But the PWHT cannot be eliminated after the welding of the joint unless weld metal is of the austenitic or inconel type as per my understanding. The PWHT not only relieves the stresses in the weld and reduces the hardness in the HAZ(That is why most welding engineers would ask for a PWHT temperature to be maintained lower than the tempering temperature of Q&T steels), but also reduces the chances of HIC by allowing the hydrogen in weld metal to diffuse out. Also, the hardenability of the Cr Mo alloyed steels being higher than normal carbon steels, even less than 19mm(the limiting thickness for cs above which PWHT required as per B31.3)nominal weld thickness requires PWHT. The PWHT in ASME VIII or B31.3 is based on the P No of the base material and the nominal thickness of the weld. In that case would using a different weld metal composition like E70XX-A1 type allow for PWHT to be avoided? Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[GRoberts]

As I stated earlier, the elimination of PWHT depends on the situation/governing code/etc. There are many applications that are not governed by any code at all, and many countries do not use ASME codes. VAWELDER did not state which if any code he was working to unless I missed it, so I was just covering all the options. As far as CS or 1/2 Mo filler degrading under PWHT conditions for P22 material, it depends on what properties are required and what temperatures are used to PWHT the P22 weld. We have tested 1/2 Mo welds that met the properties required after PWHT at P22 type temperatures. Some codes (military in particular) allow the PHWT temperature to be adjusted so that the more important properties are maintained.

As can be seen, one of the most important things for VAWELDER to know is what codes/specifications he is working to and what is allowed.

 

[Weldmedic]

My company WPS covers P5A to 5A,4,3 or 1 with ER90s-B3 GTAW 2pass and fill SMAW with E9018-B3
Preheat 400
Final PWHT 1250F 2 hours
Per ASME IX you need to have PQRs to cover your WPS so be careful.
In my opinion buttering is not necessary. WHat is the thickness? If you are working to B31.1 and the weld is less than .500 thick you can delete the PWHT requirement (if you qualify it that way)
Section 1 allows exemtion if less than 4" nominal diam, less than 5/8" thick and I think less than .15 carbon. hmm better check that out though(im quoting from memory) its in the material pwht charts some other factors too but its all in there.
Write back and tell us what the outcome was.....

Steve

 

[ijzer]

Qualifying a PQR to ASME IX does only proof that you made a sound weld with the given parameters. It does not automatically means that the used welding method/fillermetal /PWHT ,is suitable for any application.

 

[sayee1]

I agree with Ijzer, the tests spelt out in ASME Section IX would hardly test the welded joint for the application. That is why so many additional requirements like J Factor, X factor with step cooling, (I think these are HT embrittlement parameters), HT tensile testing, impact testing ( A question for the experts- Ijzer, pipewelder, GRoberts--- If LA steels are meant for HT, why call for impact tests @ sub zero temperatures?) are being spelt out in various specifications. Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[ijzer]

Thick wall Low alloys e.g. 2 1/4 Cr -1/2Mo steels are tested at low temperatures to find out where the shift from ductile to brittle is(transition temperatre). After long term operation the material becomes more brittle so the transition temperature moves up to a higher temperature.you still want to be safe at that higher temperature.
This embrittlement is some how simulated in a step cooling test.

 

[sayee1]

Ijzer is close to the answer, the reason is though the materials are predominantly used for their creep resisitance properties and hence one would hardly expect any Ductile to brittle transition at these temeperatures. But as the Mo increases, the chances of temper embrittlement increases and even at high temperatures these materials tend to get embrittled. Like Ijzer said, this is tested by carrying out impact tests at various temperatures to plot the curve without PWHT and do it again after PWHT and check the shift in the impact curves. The PWHT here to simulate actual usage conditions would demand a long cycle PWHT with many intermittent cooling and heating up. To avoid this what is actually carried out is a step cooling method where the material is cooled to various temeperatures and held at these temperatures for periods ranging from a hour to 120 hrs. This defines the X factor and in addition J factor is the formula based on the chemistry(the tramp elements) B, Arsenic, Antimony are a few, which increase the tendency to temper embrittlement. Note that I have come across these tests only for the 2 1/4 CR 1Mo types and not the other LAHT steels. Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!