Impact of using SS wire brush over the Inconel welds - any chances of rust spots generation ? 2

[Ratheesh_n]

Dear team,

As we know use of CS wire brush over SS and inconel welds are not preferable as it will lead to contamination and rust spots generation. Similarly what will the impact of using ss wire brush over Inconel welds ?

Weld :- Inconel 625

Regards,

Ratheesh N

 

[Dhurjati Sen]

Use low C (L grade) SS wire brush.

DHURJATI SEN

 

[kingnero]

Do you have this option, and does it really matter?

Our suppliers just mention stainless steel brushes, and look at you if you're from the moon when you ask what kind of stainless they are.
Even with "elevated" C%, or if they were a martensitic stainless steel (as this is cheaper), would it really matter?

 

[EdStainless]

If it is a corrosive environment and you embed bits of 420 (or whatever martensitic grade) into it you would get rust spots.
Would it harm the underlying material? Probably not, if you believe that wire brushing some how helps then you are not trying very hard. When you brush you also embed bits of the oxide scale and Cr depleted metal.

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[Ratheesh_n]

@kingnero
Concern is not the type of stainless steel wire brush used. Concern here is what is the impact if we use SS wire brush on Inconel as iron content is more in the ss compare to Inconel.

 

[Ratheesh_n]

@EdStainless
Thanks.. i would like to add the back ground for this case which will have more clarity on my query.

We have fabricated Inconel spools from our shop and shipped to field with proper preservations. During the site fabrications ,we found rust spots in root side of the weld in parent metal as well as welds (with borescope inspection) .. we have cleaned it(pickling) several time and it was very difficult to remove..

Client claimed we may have used CS wire brushes for clean the welds. But we have dedicated shops for SS and Inconel and there is no chance to use CS wire brush over Inconel. So we were analyzing how the rust spots came. we have used SS wire brushes for cleaning the welds..

query is

1) whether the overcleaning and depletion of chromium layer lead to the generation rust spots (we are regularly doing the Inconel spool works and this is first time we face this issue) ?
2) whether the usage of SS wire brushes having any role in this ?

 

[EdStainless]

Check what material your SS brushes are made of. If it is a 4xx alloy then it could be that.
Or, remember that small flakes of metal will corrode easily, even of 625. If you have smeared and embedded metal then that could be the cause.
They are accusing you of using CS brushes, ask them what their inspector saw at your shop. No impector, then they don't care that much.
We used abrasive flap wheels because they would cut metal and were less likely to embed stuff. And then pickled after falp wheel.

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[EdStainless]

Check what material your SS brushes are made of. If it is a 4xx alloy then it could be that.
Or, remember that small flakes of metal will corrode easily, even of 625. If you have smeared and embedded metal then that could be the cause.
They are accusing you of using CS brushes, ask them what their inspector saw at your shop. No impector, then they don't care that much.
We used abrasive flap wheels because they would cut metal and were less likely to embed stuff. And then pickled after falp wheel.

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P.E. Metallurgy, consulting work welcomed

 

[cap1a79]

The main purpose of acid cleaning includes removal of rust and forming protective oxide film again. If the acid cleaning had been properly carried out, there shouldn't have been any rust present.
While mechanical cleaning like brush is physically to remove impurities (such as weld spatter), acid cleaning is chemically to dissolve contamination including rust.

Hence, check the acid cleaning procedure and whether properly followed at the site.



SiHyoung Lee

 

[EdStainless]

What is removed depends greatly on the acid mixture used.
A simple passivation (cleaning) of nitric acid or mixtures of citric and phosphoric acids will only remove embedded Fe. These will not remove rust, heat tint, scale, or the Cr depleted layer of metal under the oxides.
A pickling using a mixture of Nitric acid and HF will remove all of those things.

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[cap1a79]

Eds, Thanks for the input.

Is the "simple passivation" common? I have never heard the actual case that there is kind of cleaning without removing rust but only for the limited usage.

I appreciate if you share the case when only the "embedded" Fe is to be removed.




SiHyoung Lee

 

[EdStainless]

We would often ship pipe or tube that had been pickled at the mill, and then after installation it was passivated to remove Fe from handling and tools.
Straight 30-45% nitric is often used for this since it is fast (we required 15 min just because we needed a time) and works at room temp.
The citric or citric phosphoric blends work but require heating and take time (an hour at least, depending on temp).


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[Ratheesh_n]

Dear EdStainless,

Some clients specifies to do pickling as per ASTM A 380. But ASTM A 380,its applicable for stainless steel. So its not mandatorily doing by all manufacturers, but following as a recommended one. Client also recommended to follow this whenever the surface contaminations found

any other standards or references for pickling of Inconel items and welds.. and how to select the pickling method from ASTM A 380 based on this Inconel metallurgy

 

[cap1a79]

Generally, the best method for nickel alloy is just mechanical cleaning followed by flashing pickling. However, steel & brass brush must be avoided as small particles of steel & brass can discolor nickel alloy or induce rust.

I believe your case is exactly same as the one described in ASM Metal handbook Volume 5.(Surface Engineering of Nickel and Nickel Alloys )

(Quoted from ASM Metal handbook Vol 5 Surface Engineering of Nickel and Nickel Alloys )
Detection and Removal of Embedded Iron.
During mechanical operations such as rolling to shape or hot pressing, small particles of iron may become so firmly embedded in the surfaces of nickel alloys that they cannot be removed by the cleaning methods normally used for dissolving grease or cutting compounds. Under certain corrosive conditions, such iron particles can initiate local attack.

(Omitted)
A solution of hydrochloric acid and ferric chloride, Formula 12, is used to remove embedded iron. This solution should be used cold and should remain in contact with the metal for only the minimum time required for iron removal, not exceeding 1 h. After the work is removed from the solution, it should be rinsed thoroughly in cold water, then rinsed again in warm water. The detection tests should be repeated to verify the removal of the iron.

Formula 12
HCL 1.16 Sp gr - 1 wt%, 30 ml, ambient temperature
FeCl3 - 1 wt % - 11g, ambient temperature
Water - 1000 ml, ambient temperature

P.S. Next time, do not use steel brush but si carbide or al oxide.





SiHyoung Lee

 

[EdStainless]

Sorry Cap, but I would never use that formula. Any residual could cause serious pitting issues.

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[cap1a79]

Eds, note that my input is based on reliable reference like ASM.

Regarding the formula 12, refer to the below link. You can check it whether true or not. ("Detection and Removal of Embedded Iron.")

https://dl.asminternational.org/han...rface-Engineering-of-Nickel-and-Nickel-Alloys

Meanwhile, regarding the use of nitric acid, it is listed in formula no. 1 as a "pickling method". However, it is not shown in the section of removal of "embedded iron" by the steel brush, which is applicable for the case.

In addition, referring to section of "brushing", you find the below statement.

"They should not be made of steel or brass wire, because small particles from the brush are always "embedded" in the metal during the process. Steel particles rust, and brass particles discolor the nickel alloys."

I hope the above are all clear.

Thank you.









SiHyoung Lee

 

[EdStainless]

Straight nitric (40-45%) is all that we used and it met the requirements for all industries (auto to aerospace).
Detection of free Fe on a surface is tricky.
The best test is not one that people really want to use as it involves HgCN as a reagent.
We would sprat a surface with DI and cover with an absorbent pad to keep it wet.
Give it overnight and look for rust spots.
Or buy some white Head & Shoulders shampoo (It must be the white variety).
Brush it on and then mist with DI to keep it damp.
If blue spots appear you have Fe.
Some H&S is blue because it is made in a plant that still has some steel piping. They dye it a standard color so that each batch looks the same.
The white is made in a plant that is all SS piping.

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[dik]

What is DI?

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

-Dik

 

[EdStainless]

Deionized water, sorry

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P.E. Metallurgy, consulting work welcomed

 

[dik]

Thanks... that distilled or something else? I didn't know.

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

-Dik