When Should one specify Pickling and passivation?
When Should one specify Pickling and passivation?
(OP)
Dear All
I have many times(Almost always) seen the specification that specify "Pickling and passivation" as a requirement where ever and when ever Austenitic Stainless steel is used.
I wonder whether it is objective to ask for Pickling and passivation so very mechanically in all situations.
Surly there has to be some guideline and some international specification/Standard that give the rules (Or rule of thumb) as to when an item is required to be Pickled and passivated.
Can some give the basis on which one can specify Pickling and passivation.
Regards
I have many times(Almost always) seen the specification that specify "Pickling and passivation" as a requirement where ever and when ever Austenitic Stainless steel is used.
I wonder whether it is objective to ask for Pickling and passivation so very mechanically in all situations.
Surly there has to be some guideline and some international specification/Standard that give the rules (Or rule of thumb) as to when an item is required to be Pickled and passivated.
Can some give the basis on which one can specify Pickling and passivation.
Regards





RE: When Should one specify Pickling and passivation?
RE: When Should one specify Pickling and passivation?
I've never seen a compilation of the rules or guidelines in requiring pickling and passivation. A lot, probably most, of the callouts are based on experience.
Here is a short list of generalities.
The pharmaceutical industry.
High purity chemicals and solvents.
Architectural applications.
Purely esthetic reasons, like appliances.
It is often used as a cleaning procedure.
Cleaning after hot forming, removing mill scale.
Some places where it is called for it really has no effect on the say the corrosion rates. If a process will corrode SS there is no need for P&P except for insuring a high integrity on the initial welds.
There is quite a leeway on ways and means to P&P a SS and again it depends on the results required for a particular set of environmental condition the metal will be exposed to.
I will not get into specifics of determining when and where P&P is needed nor the particular processes but if you are confronting a particular situation that you would like more information about please post it.
RE: When Should one specify Pickling and passivation?
There are some SS Vessels in Chemical injection (MEG) packages and some SS in Water service.
The client spec does not specify. Now as a contractor where all should i specify P & P ?
RE: When Should one specify Pickling and passivation?
RE: When Should one specify Pickling and passivation?
I'm not sure about the reference standard. However, it looks clear surface during visual inspection.
RE: When Should one specify Pickling and passivation?
Blasting, grinding, polishing, cutting, buffing, all should be followed with passivation.
You cannot detect if a surface has been passivated, pickled or electropolioshed with out destructive tests. How a surface looks is no criteria. A surface that has been 'flash EPed' or buffed will look bright, but have very poor corrosion resistance.
ASTM A380 is a good ref. It give a list of possible solutions to use and some basic guides. The only tests mentioned are strictly for free iron on the surface, not stability of passivation.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: When Should one specify Pickling and passivation?
I don't understand why a print would state pickle and passivation in the same note. Normally pickling is used to remove heat treat scale by solublizing the scale/metal in a strong acid bath. Since metal is soluble in the acid bath, it will provide a passive or iron free surface. So, to follow this process with a passivation step does not make sense.
I agree with the reply concerning electropolish. Electropolish will also provide a passive or iron free surface. So, to follow this process with a passivation step would also be redundant.
RE: When Should one specify Pickling and passivation?
We passivate after EP in order to remove any residuals from the EP process. Any other cleaning may damage the passive surface, at least using Nitric acid will assure the maintainance of passivation.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: When Should one specify Pickling and passivation?
Passivating after the EP process is interesting. I believe the residuals that you are refering to is residual acid and not residual iron. Is that correct?
RE: When Should one specify Pickling and passivation?
So Do we need to Passivate a SS Pressure vessel after Pickling or not?
I was under the impression that Pickling and Passivation are twins (when ever Pickling is done Passivation is done, such was my assumption).
Is it a correct assumption?
RE: When Should one specify Pickling and passivation?
You really want a layer that is not too thin, not too thick, very rich in Cr vs Fe, and free from organics (C).
Often pickling leaves a poorly developed passive layer as well, since that is not the goal of the pickling operation.
After EP there are the possiblities of sulfur and phos compounds on the surfaces. These compounds have limited solubilities and don't help the surface chemistry.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: When Should one specify Pickling and passivation?