PMI on weld 1

[smart143]

I used ER316L filler wire for welding of 4" sch 80 piping ,PMI is required on weld metal so I carried the same & found that %Mo is 1.2 to 1.3 only. When I carried the PMI on same batch filler wire %Mo found is 2.04 which is just meeting the requirement.
Why PMI value are less in weld .will code allow such variation?
Any code reference will help?

 

[SJones]

PMI = positive material identification. It does not mean 'accurate verification of compliance with chemical composition requirements of a specification'. If the parent material and the weld filler have been verified as austenitic stainless steel of a nominal composition, and that's what you said you were going to weld, then you have complied with the ethos of PMI. If the specification has a requirement that the deposited weld metal must meet specific chemical composition requirements, using PMI equipment will not be appropriate for this application. What did the specification require?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[metengr]

I don't see a problem. PMI as mentioned above uses x-ray fluorescence and Mo is one of the alloy elements that has a primary peak similar to another alloy element. This means the alloy analyzer can detect the presence of Mo qualitatively. So, there will be variation between a standard chemical analysis and one using PMI.

Some of the newer hand held alloy analyzers have increased accuracy based on increased dwell time.

 

[stanweld]

When using XRF analyzers, the capabilities of the instrument used vary from manufacturer to manufacturer and analytical mode chosen. As metengr stated, some XRF analyzers provide greater accuracy with longer dwell times. Also XRF measures only the first few atomic layers at the surface.

XRF is not the only PMI analytical mode. I have had occasion to use portable, light emitting, spectroscopic analyzers that provide extrodinarily accurate elemental analysis and have verified that analysis with laboratory analytical instruments.

 

[smart143]

thanks to All,
specification only calls for PMI on PM & weld no other limits specified so it looks fine to me now