PMI vs Ferrite Testing 1

[Adilah]

Hi everyone,

What is the purpose of conducting Ferrite Testing if we already conduct PMI? I know Ferrite Testing is used to measured the ferrite in the material and it based on FN, but I thought PMI will also display the Fe composition. Why we cannot use the PMI data to analyse the appropriate FN should a material have, for example DSS.

Sorry for asking, but im totally new in this field and I have been reading about PMI and Ferrite Testing, just confuse what is the exact purpose of each for the industry.

Thank you for reading

Kind regards,
Adilah

 

[metengr]

No, PMI is used as a sorting tool for material composition, ferrite testing determines the ferrite phase content in material, two totally different measurements with different outcomes.

 

[Adilah]

If let say, I conducted PMI on certain pipe and it says it is DSS, and then I conduct ferrite testing on the same pipe? Is it reasonable to conduct the same test on the same pipe?

Thank you for reply Metengr

 

[NBrink]

Ferrite testing is not to confirm composition, just to confirm that the delta-ferrite levels in the metal (usually in the weld) meet target levels.

Too little ferrite, and you could run the risk of hot cracking, too much, and you'll decrease the ductility of the weld, increase susceptibility to sigmatization (not that you'd be using DSS in services that hot), and establish galvanic couples between the base metal and the weld. I'm sure there are other reasons for ferrite testing, but that's what comes to my mind...

Since ferrite levels are impacted by things other than composition, such as cooling rates, heat input, etc. PMI is not an adequate measure to ensure correct ferrite levels (not that PMI is particularly accurate anyhow)

 

[weldstan]

Appropriate ferrite/austenite ratios in the weld are paramount for DSS to provide corrosion resistance; hence, the need to determine ferrite content. PMI simply indicates that you have purchased or installed the right material.

 

[Adilah]

Ok, I think I understand now. Ferrite testing is important especially in weldment area is that correct? Do you guys know what standard to refer if that's the correct FN number for DSS?

 

[weldstan]

It depends on the alloy to be welded but generally it is 40% to 60% ferrite.

 

[1gibson]

"but I thought PMI will also display the Fe composition"

Fe refers to the element iron in this context, it does not mean ferrite.

 

[Adilah]

Ohh, I don't know the difference between two. Ok I now I know where to start searching.

Thank you everyone for the valuable information. I really appreciate it

 

[Adilah]

Thank you all for your help.