Ferrite testing on the welds

[Mohsen_81]

Hello all,

Bidder stated in the proposal that Ferrite testing will be carried out only on the welds of duplex spools. Why not for the other spools including SS316 and 304L?

 

[bobjustbob]

The ferrite balance of duplex steels is important to their corrosion resistance. It is less of a concern on the austenitic stainless steels.

Bob

 

[EdStainless]

Both corrosion resistance as well as toughness and cracking resistance.
And it is really the HAZ that has issues.
Stray arc strikes are very bad in duplex for this reason (they end up being high ferrite).
There are standards for this measurement, both AWS and ISO. You need an instrument and standards.
The WPS should also have required A923 low temperature impact testing, and the pipe should be bought with requirement also.
Here is a primer for everything duplex:

https://www.imoa.info/download_files/stainless-steel/Duplex_Stainless_Steel_3rd_Edition.pdf

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[bobjustbob]

With cast grades such as CD3MN we had difficulty with the ferrite of the weld itself. All of our repairs were solution annealed so the HAZ tended to be less of an issue. The 2209 filler did not respond the same way as the CD3MN. I think we ended up going to a super duplex filler to meet the NACE requirements.

Bob

 

[dik]

From an earlier posting on SS welding; can Head and Shoulders White be used to test for ferrite?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EdStainless]

No, the H&S will help detect surface Fe contamination.
The ferrite measurement must be done either by micros (point count, destructive) or magnetically (requires reference samples).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[bobjustbob]

What ASTM standard is the Head and Shoulders white in?

We used a Fischer feritscope or a sevren gauge. The sevren gauge is handy if you have the correct references in the kit.

Bob

 

[dik]

From another thread, I understand it will detect the presence of ferrite(maybe just Fe, and not ferrite) in a SS weld... and being a curious data packrat, I was just curious. Seems to be a handy little test, but have't had a chance to check it out... I did, however, pick up a bottle of the stuff to try.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EdStainless]

The H&S isn't in a standard. It works because the active ingredient in H&S forms a complex with Fe and turns blue.
We used it when we had to test very large surfaces. Applied it with a mop and kept it damp by misting with DI water.
The other simpel free Fe test is to cover the surface with something absorbent (disposable diaper material works great) and dampen with DI water. It will take a couple of days but any free Fe will rust in the 100% humidity environment.

To test duplex alloys with a Severin gauge you need calibrated duplex samples, the standard FN calibration is way off.
In fact even with a Fereitscope you need duplex samples, FN curves do not fit well.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

Thanks for the info...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[weldstan]

It was not uncommon some years ago to have 308(L) and 316(L) deposited weld metal checked in cryogenic applications.

 

[EdStainless]

Yes Stan, both Cryo and high purity often require ferrite checks on austenitic alloys.
A Severin Gauge is real handy for these.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[MagBen]

Severin Gauge is simply test the relative magnetic permeability. It cannot distinguish ferrite from martensitic. For wrought austenitic SS (often full annealed), ferromagnetism is often gained by martensitic phase, less likely by ferrite. while in cast grades, magnetism is mainly from ferrite.

 

[EdStainless]

In annealed SS you can get rid of the martensite and will only be left with delta ferrite, it it was under annealed or welded afterwards.
In cold worked SS you cannot tell them apart magnetically, well at least not with a Severin.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed