What are you trying to verify?  Weld deposit?  Each of the base materials?

We will be varifying weld deposit.I know the requirments for P91 are Cr 8.00 to 9.50 % / Mo .85 to 1.05.
With half of the joint being P22 I wonder if there will be dilution that will lower the values?

Yes, the dilution will lower the values.  As to just how much will depend on the process, joint preparation, position, wall thickness, amperages used, etc.  For example, very high energy processes, like SAW on a square butt joint can lead to high dilution levels, as can processes like GTAW on thin sheet.  

Then you run into the fact that the dilution levels at the surface of a cap pass are often significantly lower than they are at the root or sidewall areas... add in two different base metals, and it's an even bigger bag of worms.

Can you give us some detail as to why you're running PMI on a weld deposit?  Are you trying to verify whether the correct filler material was run on a joint, or is there some other reason?

If you have access to the appropriate PQR this should give the acceptable weld chemistry for PMI carried out during the weld procedure qualification.

Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor
 

It is a client requirment that we verify all alloy field welds with PMI to be performed by a third party.Our subcontract performing the PMI has asked for required values for Cr and Mo.The joint is a v - groove sch.80 welded with GTAW/SMAW process so the SMAW cap is the only part being tested.
I checked the PQR and no PMI was performed at that time.

 

I'd personally give consideration to running a coupon or two equivalent to the joint being examined, and provide them with a range based on a PMI reading taken off of that.  You shouldn't see a huge discrepancy from cap to cap.  How broad you make that range may be dependent on the other consumables you have on site.   

Seems like a pointless exercise in a dissimilar metal weld. Why not just PMI the welding consumables and the parent materials before making the weld?  The welding procedure specification takes care of the rest.  Some organisations do get a bit carried away with PMI!

Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
 

QC12

As a client requirement, the client's PMI procedure (or other document formalising the requirement) should state acceptable chemistry limits for this WPS. If not, then submit a technical query requesting such limits be provided.  

Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor