These test methods for cleanliness evaluation are found in ASTM A-380. However, I will summarize them below:
1- Visual Inspection - is performed under white light with no magnification, and observation of the surface should show no evidence of paint, oil, grease, welding slag, dirt, metal or abrasive particles, rust, staining, or other gross contaminants. The criteria should be determined by the level of quality required for the cleanliness of the surface.
2- Wipe Test - Rub the surface (generally one square foot of surface area) with a clean room, lint free wipe (with or without alcohol) with moderate pressure and inspect the wipe for contamination. Depending on the surface finish and the cleanliness quality required for the product contact surface, the wipe should be light in color from residue. Dark staining from mechanical polishing debris or other surface contamination can be observed and analyzed , if desired. If organic residue is suspected, use a black light to test for fluoresence.
3-UV Light - Use a Black light to illuminate the surface in the absence of white light (dark room or restricted lighting) and observe surface for fluorescence. Typical organic contaminants will fluoresce
4- Water Break Free test - used for components or small parts; Dip or spray surface of component with deionized water and look for a surface that sheets the water instead of forming droplets.
References for exact test methodology are contained in ASTM A-380 and associated documents. The acceptance criteria for these methods can be established based on surface cleanliness requirements to meet the quality level required for you specific conditions or needs. I hope this helps.
MIL. STD.-1330D is a much more stringent requirement than CGA G-4.1.
MIL STD 1330D has specification requirements that cover not only cleanliness levels, but specific chemistries to be used, condition of the cleaning process, and variances based on gas or requirements.
In general, cleaning to meet CGA G-4.1 would not meet MIL. STD. 1330D; the reverse would be true; however, in that meeting MIL STD. 1330D would in most cases, meet CGA G-4.1 requirements.
If you would like a specific item to item comparison, I could furnish it, if desired. DOC
We are having a bracket made from 321 stainless and our drawing calls out for passivation per AMS 2700. This spec gives options for testing the corrosion resistance. 1) Humidity, 2) Water Immersion OR (if permitted by purchaser) 3) Salt Spray.
The manufacturer is asking us if salt spray is OK to use. I see that salt spray only takes 2 hrs to perform while humidity requires 23 hrs. Is the salt spray a less stringent test? Could you please discuss the differences so that I can make an informed decision.
The salt spray test is a very aggressive test, as the chlorides are corrosive to the surface of austenitic stainless steels. That is why they only require a two hour contact time. The intent for all of these tests is to see if there is any free iron (iron metal inclusions or iron particles imbedded onto the surface).
The humidity or water immersion tests are slowly reactive with the iron defects on the surface, requiring the additional time to show evidence of free iron.
From a surface damage perspective, I would recommend the water immersion or humidity test, since little or no corrosion will occur to the stainless steel, only a reaction with free iron will occur. Chlorides are difficult to remove from microscopic cracks in the surface and can remain to produce chloride stress cracking if the surface is subjected to higher temperatures 250 F. or higher.
From an economics standpoint, the salt spray test is quick and effective. The potential for future corrosion relies on the quality of the rinsing and the conditions with which the component is subjected.
We routinely use salt spray or salt water immersion testing on samples to prove corrosion resistance and typically for 24 hours or longer. This testing is a good method to show quality of passive film that is formed by differnt passivation methods. This testing is done on samples that are not to be used or placed into service. Otherwise, we would repassivate after any salt testing and process through a rigorous rinsing procedure.
Citrisurf 2050 is a commercially available citric acid based passivation fluid. When used under proper conditions, it will perform well when compared to nitric acid. The passivation efficacy of any citric acid based product including 2050, is very dependent upon temperature and time of contact; for example, must be used at temperatures of 60 degrees C. or higher (80 C. best, ambient condition is ineffective) and contact time of 1 hour minimum, (3 hours best, 10 minutes ineffective). Astro Pak utilizes our UltraPass CN passivation solution and has shown it to be superior to comparable nitric acid or other citric acid processes.
Use of gelled passivation products, such as 2210, for weld areas are equally effective as nitric acid when properly applied. Brushing of the contact surface during application, as well as maintaining its liquidified state, for a minimum of 1 hour is critical in the performance of these types of products.
Results from our statistically valid testing was published in 2008 to validate the effectiveness of our UltraPass CN Gel passivation process for welds.
Please review the article on our website.
Citirsurf 2050 is a citric acid based passivation fluid for austenitic stainless steels. It and other citric acid based passivation fluids are effective when used under the proper conditions, including temperature, concentration and contact time. Astro Pak has shown that citric based passivation processes must be used at temperatures of 60 degrees C. or above (80 C. best), and for a minimum of 1 hour (3 hours best), to equal the results of nitric acid on 316L. Our UltraPass CN process attains superior results to citric or nitric acid processes when used at the optimum conditions suggested above.
Citrisurf 2210 and other gelled citric acid weld pastes or passivation fluids are effective for spot or weld passivation, if used properly. Brushing of the surface weld area during processing and contact times of 1 hour minimum will produce passivated welds equal to or better that nitric acid passivation.
Astro Pak published a technical paper in 2008, on weld passivation that shows statistically valid results for gel passivation with our UltraPass CN gel, in comparison to nitric acid and other processes. Please review this paper on our website.
We routinely are permitted to dispose of citric acid based passivation solutions into the sanitary sewer in many of our facilities and project sites. You will need to run a metals analysis on the waste stream to determine the chromium, nickel and other heavy metals content of the waste. Depending on the levels of metals in the waste and the local regulators restrictions, you can generally get a permit to dispose of citric passivation waste into the POTW or other sanitary sewer provider. We are typically below 1.0 ppm levels for each of the heavy metals.
We maintain clean passivation solutions and do not allow the metals content to reach permit limit levels. If you are in a production application you will have to monitor the solution for metals and stay below the permit levels. We change out our solutions within a one to two week period or generally after each major batch of processing.
Cleaning and passivation of stainless steel downstream of the ozone injection point provides the benefit of enhanced corrosion protection. Welding of stainless steel leaves a high iron surface in the weld area and creates active potential corrosion sites. Especially in the area immediately downstream of the ozone injection, the unreacted ozone in water will oxidize the surface iron and lead to an elevated corrosion rate at the weld areas.
Typical CGA G-4.1 cleaning requirements are based on safety concerns for removal of hydrocarbon from equipment and piping surfaces to eliminate the possibility of an internal fire (explosion). This is obviously not applicable to the piping containing water; however, any weld in stainless steel requires passivation to reform the passive film and correct the damage caused by welding.
By the way, can you disclose which water treatment plant you are referring?
We are processing ASTM A487 grade CA6NM, class A, 400 series stainless castings. The question after blasting is in what order should we process? Pickle, machine and then passivate or machine, pickle and passivate?
Normally we recommend that you machine first, then pickle and passivate.
However; if you are trying to remove surface contamination prior to machining, then your original order could be effective.
The reason we machine first, then pickle is because during machining, cold work or micro-crystalline deformation occurs at the surface. Pickling can help remove this damaged layer prior to passivation.
I am having a new purified water tank built as part of a contract in a pharmaceutical plant. I have puchased several controls for level, pressure, etc that will be installed in the tank. Should I have these controls (316L diaphragm-type to fit on nozzles with tri-clamp ferules on tank) passivated separately and then install them afterwards, or should I have them installed first and then passivate the tank with the controls at the same time?
I have a couple Laboratory Reports from STERIS suggesting that there CIP200 acid rinse formula is an effective Derouge and Passivation agent. Do you have any experience with the use of CIP200 for Derouge. I recently tried using CIP200 to derouge a 316L Media Hold tank without much success. I recirculated a 20% by volume solution of CIP200 at 80C for a total of 8 hours and didnt see a tremendous amount of improvement on the rouge. The entire tank started with a bonzish looking rouge coat. Its the worst case of rouge I have seen. After the two 4 hour derouge cycles there were some signs of derouge on the floor and walls of the tank. However, I expected to make a bigger dent than what was observed. Any suggestions.
CIP 200 is a phosphoric acid blend derouging/passivation solution that is effective on light rouge, but often will not remove heavy or certain types of rouge. You may need to process for longer periods of time ( 8 to 24 hours ) when using phosphoric acid (CIP 200). There are other derouging products on the market that utilize stronger organic acids (sulfamic, oxalic and others); however, the surface finish may be affected with some of these products. We use propritary blends of organic acids to remove rouges like you describe. If Astro Pak can help you, give us a call.
Control components are generally passivated individually and installed after passivation of the vessel. The components can be passivated after installation, if they are not sensitive to acids, bases or high conductivity fluids. When passivated as a component and they are sensitive to chemical treatment, the external or fluid contact surfaces can be separated from the chemically sensitive careas and passivated.
Is there a spec for gas (Nitrogen) particulate cleanliness, as opposed to a spec for tubing surface cleanliness? I want to specify that gas at the delivery point must be clean per X, where X says how many particles of a certain size, per a volume. Presumably I’d verify adherence to the spec by flowing a volume of gas through a millipore filter, then counting particles.
The particulate cleanliness of gases can be classified with IEST-STD-CC1246D. The specification verifies the quantaties of particles per 0.1 cubic meter volume. You can use a laser particle counter to measure the particles (perferred), or you could use a filter assembly and count particles under a micrpscope, if the gas is relatively clean. Gases are often specified for use by a chemical analysis to determine hydrocarbon, moisture, condensible oils and gases, and total particulate mass (i.e breathing air, oxygen, and others by CGA specifications).
I have a lay-person question regarding stainless steel. I stumbled upon this posting after a thorough internet search for my answer. I hope that you can be of assistance. I purchased a stainless steel water vessel (301 steel) to brew a fermented probiotic drink. Just like any fermentation process, it must specifically be brewed in stainless steel or it runs the risk of leaching metals from other types of containers. I went out of my way to order this entirely stainless steel vessel and last night, after my tea has been brewing for 1 month, I noticed black residue building up around the top of the vessel. This area has been exposed to the fermented tea. I am concerned that this black residue is corrosion of the vessel, and that it is not in fact made from stainless steel. I purchased the vessel on a reputable US website, and it was made by a company called “Zebra” in Thailand( http://www.zebra-head.com/index.asp ). I recognize that this is a rather atypical question for your posting, but frankly, I value your opinion. Is this black residue remnant of the production process and benign? (I did thoroughly wash the vessel with soap, water and rinsed with distilled vinegar prior to brewing) If so, is it toxic and how to do remove it? Or should I send this thing back to Thailand because I was duped into believing it was stainless steel?
WE need to passivate a 5000 gallon 316ss clad vessel so as to prepare it for the production of rubber compound used in the fuel of the shuttle boosters. The problemis there is pitting corrosion on the top and bottom head with exposed mild steel in some of the pits. How can we passivate this reactor without excessivwly damaging the shell?
There are a series of methods to measure cleanliness of surfaces for plastics, including the following:
1. Visual Inspection - Inspect for stains, particles, fibers or oil films.
2. Particle Count - Measure surface particulate contamination by rinsing the surface of components or parts with solvent, filter and count the number of particles and size per 100 ml rinsed on 1 square foot of surface area.
3. Non Volatile Residue - Measure the organic contamination by rinsing the surface with a solvent (100 to 500 ml/square foot) and heating to dryness measuring the mg/100ml of residue or per square foot rinsed.
I do not know of a specification for cleanliness of medical devices; however, typical FDA requirements are no visible particles and less than 1 ppm contamination. The typical cleanliness specification to meet that requirement would be Mil Standard 1246C - level 100 A. This would mean no particles at 100 microns or larger and organic residue less than 1 ppm.
A 316 clad surface with pits or porosity can be passivated with citric acid blends; however, the pits will likely not be cleaned or passivated. The 316 surfaces can be passivated, but the corrosion in the pits and of the iron shell will continue to escalate depending upon the corrosive conditions within the vessel. Iron oxide will continue to bleed from the pits or porosity.
Nitric acid should not be used, since nitric acid will aggressively attack the iron in the carbon steel shell at the pits.
The black residue is probably one of the following:
1. Biofilm - To test, scrape a sample of the black residue and place it on a petri/agar plate and place in warm, protected environment and see if the bacteria grows.
2. Iron oxide - Scrape a sample of the residue and place in glass container and put a small amount of muriatic acid (pool acid and water) with water (1:1) and see if it dissolves.
3. Caustic Cleaning - Scrape a sample of the residue and place in glass container and put a small amount of caustic solution (sodium hydroxide - 5% by weight) and see if it dissolves or disperses.
If it is a product of corrosion, then the acid (muriatic will dissolve it. In this case, the 301 stainless steel (if it really is 301) is not resistant enough for your process. You could remove the corrosion product (magnetite iron oxide) with phosphoric acid heated to 180 degrees F.
If it is a biologic residue, then identification of the bacteria or bioburden would be suggested. Caustic cleaner will likely be required to remove the residue.
Neither of these residues are toxic; however, they should not be occurring in a clean and passivated stainless steel vessel. The process you used to prep the tank seems good and would have eliminated the bacteria and cleaned the surface.
Now, I assume your process is between ambient and 45 degrees C. or 115 degrees F. If the surface will not wipe clean and appears pitted, or you see a plated surface or peeling (chrome plated, not stainless steel) and the black will not clean up with phosphoric acid, I would return it. I have seen plated surfaces being sold as stainless steel.
Contact us again with results from your testing,
The general concensus in the pharma industry is for derouging and passivation of water systems is typically 2 years. The reality is that it depends upon the temperature and conditions of the system and what quality level for particulates and metals content that is required by the process or product. It is easy enough to monitor and mesaure the particulates (iron oxides) generated by the system (from 5 to 50 microns) and the level of metals in the critical utility fluids (in ppb). The hotter the system is maintained and the more stringent the requirements, the more often the system must be cleaned, derouged and passivated.
In our experience, 50% or so of systems are cleaned and passivated annually and the rest are cleaned, derouged and passivated every 2 to 5 years.
We fabricate 304L and 316L tanks for the waste water industry and have cleaned the entire surface of these open topped tanks by bead blasting and application of a clear coat paint outside and inside to a depth of two feet.Recently, the firm we are fabricating for is asking that these entire tanks to be passivated to ASTM A380 code D and after this process still perform the bead blast and clearcoat application. This raises two questions: as these are large 120″ x 138″ x 270″ tanks and they can’t be dipped as no one has the facilities the unload and rotate a 19,000# tank does bead blasting and wipping before clearcoat application acheive the same required condition as ASTM 380? Why would our customer specify the blast and clear coat after chemical passivation, doesn’t this negate the first phase, or eliminate it all together. I know this passivation requirement is due to stringent specification being written for west coast states, say California.
Bead blasting followed by clear coating will remove surface contamination and then protect the surface with the coating. Passivation will chemically remove the contamination and form a passive film to protect the surface from corrosion. Bead blasting will likely reduce the passive film protective layer and the surface should be passivated after blasting.
You are correct in assuming that the passivation of the surface will be compromised by the bead blasting. The proper order for the process should be bead blasting, cleaning, passivation and then clear coating. That woould provide all of the benefits of each process and provide a corrosion resistant surface over the entire surface and additional protection for the areas that are clear coated.
Bead Blasting will reduce the effectiveness of the passive film depending upon the amount of surface removed and the entrapment of debris during the process. It would be recommended to wipe clean before bead blasting and then clean and passivate after bead blasting to ensure a clean and passivated surface. Any mechanical finishing technique should preceed passivation and the surface should be tested for particulate entrapment (microscopic entrapping of particles by processes that bend over the surface peaks onto the surface in its attempt to polish the surface).
I work for a Chemical Processing Job Shop that processes a wide variety of aerospace hardware for various customers. Passivation of stainles steel that meets the requirements of AMS2700 is one of the simpler services we provide. Recently we have been recieving a lot of parts that refuse to pass the copper sulfate test after passivation. These parts are carefully cleaned and passivated, some have even been processed multiple times, and still they fail. We have both a room temp Nitric acid solution and a hot dichromate/nitric solution.
Typically we have the most problems with 15-5PH CRESS, from particular customers. We are beginning to wonder about the quality of the steel being used. The hardware is generally too valuable to destuctively analyse and to large for most surface analysis equipment. We are not privy to our customers material certifications. We don’t want to offend customers, but we don’t want to bang our heads against a wall either. Any reccomendations?
I have an order for 27 filters that require to be oxygen cleaned, dried, packaged and stored in accordance with MIL-STD-1330D. The filters are Norman Equipment from Bridgeview,Il., part #412G-05VE, I am asking them now if they can meet these requirements but what if they cannot? Is there a place that can do this kind of packaging for me?
Precision cleaning and packaging to Mil Std 1330 D is a service we provide. Cleaning to oxygen service standards requires a validated process and documentation system which is the basis of precision cleaning service companies.
Doc: We are trying to remove microscopic rust stains/marks from SS tools such as sissors & forceps. We have tried soaking them in citric acid solutions for 15 -30 minutes but have found them only mildly successful at removing the rust and passivating the SS. What do you suggest?
If you are using a citric acid solution, then you will likely need to heat the solution from 60 - 80C. and soak or agitate for 1 to 2 hours. Other chemistries are available such as phosphoric acid which will remove the slight amount of iron stains. Depending on the severity of rust, different strengths of cleaners may be required.
We have some 17-4ph cylinders which have already been passivated. We noticed there are scratches in the bore which has a very fine finish. If we ball hone the scratches from the bore, do we need to re-passivate?
The passive oxide film is only a few molecular layers thick. When you hone, sand or polish the surface, you will have disrupted or removed the passive film and I would suggest cleaning the surface of particulates from the finishing process aand then passivate to insure the proper formation of the passive film where it was removed.
I am trying to help a customer in the biomedical implant industry with a passivation process control task. They want to automate the control of the Nitric acid in the passivation tanks so they do not have to rely on operators to titrate or make additions. Adding the Nitric is not a problem but have you found any reliable (validatable) means of measuring specific gravity on-line at the process? If so can you recommend any equipment vendors that supply this type of device?
I do not have a source for validated equipment that will measure density (specific gravity) on-line. More important than density, would be dissolved iron concentration of the solution. The process conditions to reach a passive state on the surface will be affected by acid strength and iron concentration as both are critical factors or essential variables in control of the process to be validatable.
We have a part made from AERMET 100 alloy (C .23%,Ni 11.1%,Co 13.4%,Cr 3.1%,Mo 1.2%,Fe balance. The drawing for the part specifies passivation to ASTM A 967. Vendors for the part in recent years (started the parts in 1990) were certifying to Nitric 1 (mildest passivation), which involves 20 to 25% by volume nitric acid and 2.5% by weight of sodium dichromate. Immersion is for 20 minutes and temperature is 120 to 130˚F.
The current vendor for the parts is telling me that the parts are not passing salt spray (per ASTM-B-117).
I called Carpenter Steel to get advice on passivation of AERMET 100 and the metallurgist is sayig that AERMET 100 cannot be passivated, since it has such a high iron content and not enough chrome content. He is saying that passivation needs at least 16% chrome.
Since I have been receiving these parts since 1990 with certification that they are passivated to ASTM A-967 and salt spray tested to ASTM B-117, I am now needing to talk to a passivation expert as to whether AERMET 100 is in fact a material that can be passivated or not.
Does AstroPak have experience passivating AERMET 100? If so, is ASTM A-967 Nitric 1 ok to specify and are there any pre-treatment requirements that should be performed?
I would tend to agree with Carpenter since the concentration of iron is high and the chromium content is low, even with higher nickel and cobalt content; chromium contents below 14% are usually difficult to passivate. We have not had any specific experience with AERMET 100, but other types of similar alloys are best passivated with nitric acid at the lower concentrations, with or without dichromate. It is unlikely that you can remove enough iron from the surface to pasivate the surface or pass a stringent salt spray test, however some high cobalt / nickel alloys will pass a salt spray test, depending upon the iron concentration at the surface. Pretreatment should require proper cleaning of the surface with an alkaline cleaner, prior to nitric passivation with nitric acid.
I would like your opinion of using crystal simple green for the cleaning of divers breathing gas hoses and components. Also could it be substituted for NOC (Navy Oxygen Cleaner). We are working on saturation diving systems that support the oil and gas industry offshore where thereis no availability of a classed clean room.
304 exposed to oxygen < 400C leads to FeO which then oxidizes to Fe2O3 as the top layer. Underneath is Cr2O3. The statement “Essentially, passivation is the removal of free iron from the surface of the steel” - is this referring to the Fe2O3 layer or Fe contaminants?
Simple Green is an accepted cleaner for generic oxygen
cleaning service per CGA G-4.1; however, it would not directly replace NOC in typical governmental regulated specifications. Breathing air specifications often designate the cleaner with no substitutions; but if the specification is simply to meet Grade D breathing air for instance, use of Simple Green probably would allow for passing of the gas testing requirements.
Good question. The industry uses the term “free iron” and it generally refers to metallic iron contamination on the surface ( i.e. iron metal particles, iron segregation in welding, or iron contamination from dust). At Astro Pak, we regard all forms of iron / iron oxide on the surface as contamination and believe it should be removed. Or simply, it is iron contamination, whether it is called “free” iron or rouge/rust or iron oxide.
hi, I have a problem in citric acid passivation
I am using laser mark max power 100 Thelesis brand. After i do laser marking on my stainless steel which already bead blasted, i immerse it in the citric acid tank for passivation.
Somehow the laser mark fade even after 5 minute for temperature of 66 degrees.
What can I do to maintain the laser mark after citric passivation?
Can you send me a procedure that your company would use if we need to clean an INCOLOY 800 piping systems to the requirements of CGA 4.1? The criteria for this system will be after installation the piping system is free of all contaiminates such as oil, grease, iron, weld slag, particles, metal chips, dirt, or copper residule. The cleaning solutions also cannot conatin any phosphate or boron.
I am looking for advice on the passivation of large 316 stainless steel structural elements. Our current project includes a 60′ x 40′ stainless steel framed cantilever deck and two stainless circular stairs. The architect wants the dull media blasted surface appearance. The project is on the beach and wwe are looking for a site applied process that will keep the surface looking consistent long term.
Laser marks are visible due to the iron oxide and carbon that is generated during the laser etching process. During the passivation proces, the iron oxide is being removed, therefore the laser mark lightens in color. It is a compromize as to the darkness of the laser mark and the level of passivation attained. Have you been passing the copper sulfate passivation test after the citric passivation process? Validation testing of the passivation process should include passivity testing and the conditions of passivation can be adjusted to optimize the color of the laser mark and level of passivity attained at the mark. We wrote a technical paper on this subject at you can find it on our website.
Passivation of 316 structures subjected to salt air conditions can be passivated on site with a variety of gel passivation techniques. The surface will likely need future treatment as the corrosion resistance of 316 stainless steel to chloride attack is not permanent. Chlorides attack 316 stainless steel and will require derouging or acid cleaning followed by passivation on a periodic basis, dependant upon the conditions to which the surface is subjected.
We’ve been having a problem with some 17-4 PH SS parts which are turned, wire EDM’d, EP’d, satin finished (mechanical), laser etched, and passivated. The laser and passivate processes are validated for this material, but these parts are exhibiting rust “blooming” (rouge?)on lasered areas after a 30 minute autoclave steam cycle. If I wipe the rust away using fingers, it won’t return on the next cycle, but if I wipe with alcohol, it does return. What could be causing this rusting? If we try passivating again, the laser etch is removed. What can we do with these parts?
Passivation of laser etched surfaces is complicated. If you passivate too well and remove all iron / iron oxide from the surface, you lose the darkness and color of the laser etch and the mark will be removed. If you don’t passivate it well enough, then the lasr mark will rust. The rust is coming from the poorly passivated laser mark; and without removing enough iron from the mark during passivation, the iron will oxidize and turn to rust. When you wipe with your fingers, you smear the surface with oils from the skin and it temporarily protects the surface, but when the rust is removed with an alcohol wipe, the surface contains a clean iron rich surface which will rust in a steam cycle. There are a few factors that affect laser marks and ones ability to passivate the surface, leaving the mark intact and relatively passive.
The factors are:
1. Conditions of laser mark formation, energy level and time of etch.
2. Passivation chemistry and conditions - concentration of the solution, time and temperature of contact
3. Chemistry of surface and chromium to iron ratio versus depth (AES - Auger analysis)
4. Conditions of corrosion and test method - the level of passivation required to delay corrosion under the conditions of use.
5. Validation of the above factors based on significant testing and design of the process to create an acceptable surface.
The passivation of laser marks on 17-4 or other (martensitic) stainless steel surfaces require significant research and design to match the specific surface requirements that must be attained to maintain a passive state as well as the integrity of the laser mark. We wrote a technical paper on this subject and I will forward a copy to you, or you can find it on this website.
Thanks for the quick answer, Doc… An outside supplier made the parts, and apparently did not passivate properly. Is there a simple way for us to re-passivate these? Is it reasonable to try to use our nitric acid setup and just try different submersion times until we achieve good results? Is an autoclave (275F, 30 min) steam cycle a good test to determine passivity?
One of my customers has an indoor swimming pool with a stainless steel gutter. The gutter is most likely 304L staimless steel, 12 gauge. It is only 20 years old. Typically, we would passivate a new gutter with nitric acid followed by rinsing with pool water. Is a newer process available? I have heard of using sodium hydroxide and citric acid prior to the nitric.
Which way is up?
The first question is what is the current condition of the gutter? If it is showing signs of corrosion or rust, you must first remove the rust and corrosion products with a derouging solution like phosphoric acid. To answer your question, the use of caustic as a cleaner is common today, as well as the use of citric acid blends for passivation; however citric acid is not very effective for passivation at ambient conditions. Caustic cleaning followed by nitric acid passivation is still the best for ambient conditions of passivating austenitic stainless steels. In your case, removal of all rust stains or corrosion is critical prior to passivation, or the corrosion will continue.
We have experience in forged, heat treated 17-4 medical devices and other critical surface applications, but not much in casting surface treatment. This alloy is generally low in chromium at the surface (less than 1.0 chromium to iron ratio) and requires optimization of process to insure good surface passivation. We have successfully passivated 17-4 with either citric acid chelant blends or nitric acid solutions. Surface testing for corrosion resistance is important to insure process verification and validation of the process design.
A few comments: First, 12% chromium is at the lowest level of potentailly maintaining a passive surface, plus castings are the weakest formers of passive film. Citric acid processes will rarely passivate these kind of surfaces, while nitric acid is the best choice, if there is enough chromium at the surface. We have not tested this specific alloy; however, I would try the standard ASTM A-380 nitric passivation (at 25-40% nitric at ambient for 30 to 60 minutes) on a blank sample of the alloy. You will have an answer very quickly if the surface turns black, or reacts readily, then the formation of the passive film is not adequate to treat with a passivation acid. Maybe somebody else out there has already tested this alloy, and can answer your inquiry with personal experience. If you need someone to test a coupon for you, please contact our local representative.
At our facility, a 1000′ oxygen line to an ebeam welder was installed using off the shelf 2″ stainless steel pipe with press-fit (mechanical crimp) fittings-nothing was properly prepped before installation. Now we are scrambling to figure out how to clean the pipe. What is the best method to ensure that this pipe is safe and clean. Also, do you think mechanical joints will create future problems due to dirt and etc. being trapped at the joints? Thank You.
Oxygen cleaning to CGA G-4.1 is a minimum requirement for low pressure oxygen gas systems. Liquid oxygen storage systems and high pressure oxygen gas systems require even higher levels of quality control for cleanliness and testing prior to certification and use. I assume that this is a low pressure gas system and not a liquid or high pressure oxygen gas system. A couple of comments: All components in an oxygen system must be designed for oxygen service and certified cleaned, including valves, gauges and other items in the system. Systems of this size are gernerally built with pre-cleaned for oxygen service tubing and then installed clean or alkaline cleaned, rinsed and dried. In your case, a few problems arise. Mechanical joints must be clean prior to assembly, since cleaning of the joint is not possible after assembly. Any combustible material or particles can be a danger. Particles that enter the gas flow, pose a danger to causing a spark and igniting any organics or combustible material within the system. Dirty joints pose both of these potential problems. As the system is operated, these contaminants can exit the joint due to expansion/contraction, presure fluctuations, moisture or corrosion. The system can be cleaned properly after assembly if the joints are clean and pose no significant entrapment area. Drying of the system after alkaline cleaning and rinsing is a critical part of the process and requires a contractor or yourself to make sure the system meets a dew point of near that of the oxygen gas. The proper alkaline cleaning agent is also important, and the Compressed Gas Association (CGA) has a list of recommended cleaning agents (not the only potential quality cleaners, but a good view of acceptable oxygen service cleaners). Certification of the system can be completed by testing for organic contamination with a solvent (like IPA) and measure the Non-Volatile Residue (NVR) or black light inspection of equipment/ large bore piping. Drying of the system after testing and proof of removal of all organics with a Photo Ionization Detector (PID meter) or proper gas sampling and testing is also critical.
A properly designed and cleaned oxygen system is critical to avoid an explosion. If you have ever seen the results of an oxygen system explosion from a dirty non-certified valve, or system, you would understand the importance of meeting the appropriate cleanliness criteria for oxygen systems.
The rod holders on my boat are beginning to develop surface corrosion. I don’t know the specific alloy they are made of but appear to be highly polished stainless steel. The corrosion drips and stains the boat gelcoat. Any suggestions on how to treat them in order to save them or is it more trouble or expense than replacing them? Any passivation or comparable treatment that can be done by a non-professional?
The use of vapor degreasing is best to remove organic residues that are tightly adhered to the surface or require solvent to remove. Alkaline spray cleaning is generally very efffective at removal of particulates and organic residues. So, depending on the substrate and residue that needs to be removed, both may be effective, but size of the component may assist in the decision.
When passivating parts after laser marking, should the copper sulfate be directly applied to the laser marking? I would assume yes to verify that the area where the marking was performed had a passive layer again.
We have been refered to your company as the experts in cleaning.
Further the comment was that we needed 5% citric acid but with a pH of 2.4, is this a normal pH for this acid at that concentration or would you be using a buffered mix?
The laser mark is the most critical surface area to insure complete passivation while maintaining the legibility or clarity of the mark. Copper sulfate test solution should be applied directly on the mark to test the level of passivation attained.
Passivation in a clean room requires additional care to eliminate chemical dust, fumes and any emmisions that could affect the purity of the cleanroom environment. The process of passivating has no specific restrictions for operations within a cleanroom. Doc
After any finishing operation, the surface should be wiped clean with an alkaline cleaning solution, rinsed with DI water and then passivated. Finishing operations like swirl sanding of the surface will damage or remove the passive film and expose the alloy at the surface. The alloy contains 70 percent iron and 20 percent chromium, so oxidation of the surface in air will produce an oxide film that is mostly iron oxide or it will rust. Passivation removes that iron from the surface and leaves the chromium at the surface to form a quality passive film.
Also, wipe the surface with a clean white cloth to visually see if the debris from sanding/polishing has been removed. The wipe cleaning of the surface is critical, since the fine particles of stainless steel from sanding or finishing of the surface will corrode and form an orange film on the surface if not removed.
We are a Stainless Steel Fabricator/installer for the pharmaceutical Industry in Canada. everytime we get our products passivated, the C of C claims that the process has been “Passivated to ASTM A380 norm”. I cannot find this standard anywhere without having to purchase it! Is there anywhere I can view the ASTM A380 this?
We have noticed some white staining in a droplet pattern at the bottom of a 316 stainless steel tank. General location is beneath a sprayball. Not removable with convential CIP using 85 degree C WFI, and most recently with phosphoric acid. Have you had any experience with white discoloration of 316 stainless? Tank is used to contain non-corrosive mild pH liquids.
White discoloration is generally associated with one of three conditions:
a. Pitting on the surface from corrosion.
b. Silica deposits on the surface
c. Water spotting/deposits from low purity water (calcium compounds).
These three conditions are treated using one of two methods. The first method is mechanical polishing of the surface and is used for condition a. and b. Pits or silica deposits are best removed with mechanical polishing followed by passivation. If the deposit is water based, like carbonates, phosphoric acid should remove the stain or deposit, as well as light levels of metal oxides (rouge).
Since you have already tried the phosphoric acid method, I suspect it is one of the conditions that requires mechanical polishing for removal. Do you use chloride compounds to clean and/or sanitize the vessel? Could the spray ball and its supply line contain chloride solutions that were not adequately rinsed, prior to an inactive condition that allows the vessel to dry or remain static for a period of time? Droplets of chloride containing solutions could possibly cause the corrosion that you are viewing. Just some thoughts on the cause.
Acid washing with 5% nitric acid will not affect the surface finish of an EP’d surface. I would say that the ability of 5% nitric acid to passivate the surface is limited. Under the listed conditions, ASTM A-380 or A-967 requires a concentration of a minimum of 20% nitric acid. 5% nitric acid may be sufficient to clean an EP’d surface, but not likely to improve the passive film on the surface. It certainly won’t damage the surface finish.
We are modifying an existing drum chute for a pharmaceutical plant used to dispense product into a tablet press. My question is, after the modified chute is passivated, will it have a uniform finish or will the modified portion have a different appearance than the original? The material is 316L polished ss for the new and orginal portion of the chute but, the original portion has been previously passivated and in use for about a year. If it will not have a uniform finish, is there a process you know of that will accomplish this?
Passivation does not materially affect the surface finish. It may appear slightly more uniform or cleaner, but will not affect the “shine” of the surface. Only mechanical polishing or electropolishing of the surface will dramatically affect the surface finish and appearance. If the two surfaces are finished at the same Ra or surface roughness and grit pattern, they should look the same. If the two surfaces do not appear similar at this point, passivation will not measureably reduce that difference. The mechanical polisher/fabricator should match the two surface finish levels to make them appear the same.
I have a project with exterior exposed stainless steel. The steel is 2205 and the finish specification identifies passivation, electropolishing and bead blasting but does not define a specific order of processes. I would think that bead blasting last would compromize the electropolishing. Is that correct ? Do you have a recomendation of a specific order or are you aware of a publication that would address this ?
The order to perform those requirements is as follows:
1. Bead Blast the surface to remove any gross residue and created any desired surface finish profile.
2. Electropolish the surface to remove any surface damage and polish the surface to a smooth condition
3. Passivate the surface to establish the final corrosion resistance to the highest level.
This order of processing is critical to provide the best surface finish possible with this series of requirements.
Doc, i am buffing stainless steel where muratic acid has discolored the metal to a yellow color. I buffed the surface and brought it back to new but am concerned that the yellowing will return. Have you any advice for dealing with muratic acid and stainless steel.
Thanks for the opportunity to pick your brain. I’d like to piggy back on Ken Altman’s comment from last week regarding the 2205.
We agree that the ideal finish would be BB, EP and then Passivate, however it seems there is concern by the architect that this sequence may lead to a “shinier” finish than desired.
Do you think an alternative sequence of electropolish first, then passivation followed lastly by the bead blasting could be acceptable method? Will the bead blasting last “ruin” the passive nature of the material ?
Discoloration of the surface the surface is caused by corrosion from the chloride solution. You could remove the discoloration by treating the surface with a derouging solution, like phosphoric acid or other proprietary blends of acids, followed by passivation with either nitric or citric acid blends. The problem with hydrochloric acid is that it will continue to attack the surface and produce the yellow color (iron oxide) from corrosion. Passivation of the surface is only effective at slowing down the process for a relatively short time period, as austenitic stainless stels are not resistant to chlorides, especially acid chlorides.
The bead blasting of the surface will damage the passive layer - only 3 to 4 molecular layers thick. I would passivate after attaining the desired surface finish with bead blasting. Passivation will not change the appearance of the surface, since it only affects the top few molecular layers and does not visibly affect the final surface physical appearance.
For 304 stainless steel, citric acid based chemistries are most easily compliant with the RoHS requirements. nitric acid passivation could also be designed to meet RoHS if used under proper conditions. The 400 series alloys are a little different, in that some can be treated properly with citric acid based chemistries, but they must be individually tested to make sure the surface iron concentration is low enough the form a chromium rich layer instead of iron oxide (black smut). nitric acid may be the only choice for many of the 400 series alloys. Both processes can meet the ASTM A-380/A-967 requirements.
Should I specify nitric acid clean or citric acid clean for 303 SST without use of non-rohs sodium dichromate here.so what is the best way to spcify on the drawing.
If I have note like “Passivate as per ASTM A967, citric 2″ will give me enough passivation (corrosion resistance) to pass saltspray test as per ASTM B117?
Thanks Doc. They are asking for electropolishing to be done in conjunction with the passivation, so it’s my understanding that this combined Passivate + EP process with therefore change the physical appearance.
In other words, doing Bead blasting first, then followed by Passivate + EP will probably lead to a shiny appearance (due to the bead blasting), whereas holding off on BB until the end of the process (although not as desirable and functional, due to the reasons you mentioned) will provide a matte finish.
I suppose one option would be to do a post-passivation of the parts after the entire process is completed.
It is quite common to accept Electropolishing as a Passivation method, since it is completed in phosphoric acid, but the quality of the Passivation with EP is not as high as either nitric acid or citric acid chelant processes. So, your choice is to EP the surface prior to bead blasting and test the surface in its final condition, or perform the final passivation after bead blasting to attain the most corrosion resistant state possible.
So the question is, How important is the corrosion resistance of the surface? That would be a decision with the Owner; if corrosion resistance is important then the cost for final Passivation will be worth it. There will be no difference in physical appearance of the surface, with or without Passivation.
Specific gravity can be an indication of acid concentration and iron or other soluble metals concentration. These two factors affect the ability of the solution to clean/passivate stainless steels as well as leave cleaning or manufacturing residues. Acid concentration and iron concentration should actually be measured (by titration or other method) to insure they are within the specification limits of ASTM A-380, or you written protocol.
Daryl L. Roll, P.E.
As Astro Pak's Chief Technology Officer, Mr. Roll serves as the primary senior technical advisor for corrosion, surface chemistry and stainless steel passivation. With over 30 years of experience in chemical processing, Daryl has been published in MICRO, UltraPure Water Journal and Chemical Engineering for his papers on passivation and rouge control. He is a participant on the ASME BPE Subcommittees for Surface Finish and Materials of Construction requirements and a leading contributor for the Rouge and Passivation Task Groups. Mr. Roll holds a B.A. in Chemistry and Earth Science from the California State University of Fullerton and a Professional Engineer's license from the State of California.