Crevice Corrosion Caused by a Oil Film ?

[Modey003]

Hello,

Has anybody encountered crevice corrosion caused by moisture trapped underneath a oil film? I imagine it could be possible since the oil would trap the moisture and provide a diffusion barrier for oxygen. Anyone have any input? Thanks

Modey

 

[unclesyd]

Happens all the time on things like equipment put on standby without the proper preparation. There are several mechanisms that can cause corrosion, the worst is when you have oil with a water layer combined with MIC. This combination will destroy a piece of machinery in short time. I have seen nearly all different types and combination of types of corrosion associated with an oil water interface where the oil film traps very small droplets of oil. As you state differential aeration cells play big part in some cases.
If you want something to rust in a humid climate just give it a light coating of lubricating oil.

 

[EdStainless]

This is especially true if you use an oil that dries. A lot of 'gerneral purpose' (non-lubricant) oils contian plenty of Cl and S. So in addition to the differential oxygen issues you also get some more aggresive ions present.

My favorite one is stainless that people mark with paint pens. Many of the dyes are high in Cl, and the paint forms very tight crevices. After the paint is striped you can read the marking because it is oulined with pitting.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[corrosionman]

EdStainless
Marker pens and Stainless steel. 20 something years ago at Sellafield Neuclear power station in U.K. the plant was 75% complete when someone realised what these pens contain. They had 30 miles of pipe with every piece bearing its own reference number clearly marked by a pen.And this area of the plant would be "out of bounds" for 100 yrs when it went live.
They then employed 50 men for 3 months to scrub o.ff every mark with fine sandpaper. I hope they got them all CM

 

[Modey003]

My company is in CT and its been very humid lately. I work as a materials/electrochemical engineer for an electroplating company. We do a lot of R&D work, but to bring in the money we have to resort to our core competency, which is conventional plating.
Here is the reason why I asked my question. A local stamping company (lets call them company A) in the area wanted to silver plate carpenter steel. These parts didn't plate well due to crevice corrosion already on the parts when we recieved them. However, we didn't discover the crevices till after we plated half the order. After the 50 % vol HCl activation dip in our process,the crevices were further deepened.
These parts had oil on them and were sent to us in stagenent air conditions. Keep in mind we have been having crazy weather pattern in the past two months in New England. Going from hot to cold, and so on. Now Company A wants us to buy the base material because they think we screwed it up, but if these crevices were never to begin with this problem would never have happened. I guess this is more of a legal question, but who is liable to pay for the stripping of the plated material. They sent us bad base material, but we didn't carefully inspect the base material before plating. Thank you.

modey

 

[EdStainless]

Forget legality. The reality is that you should suck it up for the stuff that you plated. The original condition isn't your fault, but you should have caught it.
I am sure that you will next time.

My guess is that they were just coated with any old oil, not a corrosion inhibitor. They were probably pitted long before they ever got into your hands. It is just unfortunate that plating is so sensitive to this.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[Modey003]

Just got word back from the customer. Vegitable oil was used during the deep drawing of the parts. 15:1 of water to mineral oil was used during their stripping process. The parts were shipped with the vegitable oil coating the parts. Now we are in the process of trying to get them to either degrease the parts before storage or switch to a different drawing oil.

 

[KnifeKnut]

Long ago, when i worked in fast food, I hated the sheila shine that they wanted us to used on non food contact areas for this very reason, simply because it looked shinier at first. It would trap all the dust from the nearby road and adjacent car wash vaccums pulled inside by the ventilation hoods, and proceed to rust the "protected" stainless surface! Stupid managment.