Name that corrosion! 3

[FiatfLux]

[apologies up front, it appears the photo link coding is not cooperating. For those bold enough to try the links, please repost them if both time and interest allow.]

This happens to be 4140 low alloy steel. The part imaged serves as the plug at the base of an isostatic press. The sealing surface is not shown, but is the surface opposite the large stain in the first two images.

This being the plug, it is at the bottom of the chamber barrel, and some process fluid [water, lubricant, and some anti-bacterial agent] tends to sit at whiles between cycles.

My wonder, [being the new guy with 'some' isopress experience] I would have expected them to use more lubricant. That said they have not seen such corrosion before. The machine was installed new in July 2013, and even just 1 month ago their was remarkably less corrosion evident.

 

[FiatfLux]

Pertinent images attached here.

Thanks all!

 

[FiatfLux]

A few other observations I'd have made were it not for my passing infatuatuion with linking images...

I am not sure of the composition of the screws, or the washers [possibly of the locking variety] used. All of them look pretty cruddy.

The rod shown in the first image, which I thought was not shown, hah, proceeds away from the plug to several points where various o-rings separate certain process areas. The rod terminates in a threaded tip, which connects the rob/plug assembly to a pneumatically driven plug [, possibly of identical composition,] which strikes a sensor.

That thread snapped. I am now interested in confirming the composition of this latter connection, and looking to see if adhesive was used, and whether any further potential for corrosion existed. As stated above, this machine was installed new last July.

OK, thanks for any and all input. Looking into whether and what preventive maintenance may have introduced contaminants to the reservoir.

Have a good morning.

 

[btrueblood]

Looks like the screws were once zinc-plated steel and are now zinc-oxide coated rust. Wonder if they gave some slight anodic protection to the bare steel, which protection went away when the zinc did.

 

[TomDOT]

Nice filiform corrosion. ("dendrite")

http://www.corrosionclinic.com/types_of_corrosion/filiform_corrosion_underfilm_corrosion.htm

 

[FiatfLux]

Thanks true blood. I could suggest trying to confirm as much, since the new assembly is on order, we can trash the screws/washers and run som icp on them.

I would hope that replacing these every 6 months was in the preventative maintenance schedule, will check.

Thanks again.

 

[FiatfLux]

Thanks as well, TomDOT.

 

[TomDOT]

I also agree on the screws.

And thanks is expressed well with purple stars

 

[Guest102023]

Filiform, and I want to steal your excellent picture!

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[FiatfLux]

Feel free, Brimstormer.

I don't believe the assembly was coated in anyway. One person familiar with the equipment's history did mention a slimy film had been discovered on the interior, so, yea, it figures.

If any clear resolution comes of this, I'll update the thread. Have a fine weekend folks.

 

[MortenA]

I were initially thinking filiform corrosion too - but thats an "under coating" type and i could not see any reference to a coating?

 

[TomDOT]

While filiform is typically under a coating, it can happen in other oxygen-limited environments.