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"Zinc plating thickness vs. salt spray resistance"


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June 27, 2016

Q. Hi,
I wanted to confirm the steps for salt spray test. My customer has randomly picked up a bolt from a lot that we had supplied and sent for salt spray test. There might be chances of problems in material handling which might lead to the bolt not passing the salt spray test. Do we have to give an altogether different part taken from the plater and submit the same to the customer for salt spray test purpose?

Shrikant Soni
fasteners - Pune,Maharashtra, India
^

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2004

affil. link
Zinc Plating
by Herb Geduld
from Abe Books
or





affil. link
Corrosion Tests and Standards, Application & Interpretation
from Abe Books
or

June 2016

A. Hi Shrikant. You should be plating to some particular specification, and that specification will usually dictate the procedures for sample size and sample selection. Good luck and get back to us with the spec if you wish.

Although some plating shops feel that it's easier to not have to abide by any particular specification, if you are not plating to a specification you are constantly exposed to a contract dispute because there are no grounds by which to claim whether the plating is satisfactory or not.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



November 24, 2016

Q. Our company did Zinc Plating on CRCA Test panels and performed Salt spray Test of on it.

Technical Details :

1) We did Zinc Plating on panels as per ISO 2081-Fe/Zn12/A.

2) SST specification : Neutral salt spray corrosion resistance of zinc plus chromate conversion coatings before basis metal corrosion (red rust) begins shall be equal to or more than 120Hrs.

After Testing we get the test results and we observed black spots, black staining and white rust on both sides of 1 test panel out of 3. Remaining 2 test panels found OK.

So by observing above whether plating panels passed or failed in SST?

3) Also report does not have any conclusions like panels are passed or failed in SST. For same point,we made contact to our Salt Spray Testing Lab, they want "Criteria" to pass or fail the test.

We already told lab that please proceed as per astmb117, ISO 2081, ISO 10289 Clause 6.1 & 6.2 ...

So is this sufficient for conducting SST and giving conclusion?

Please give answer.

RutuRaj Patole
Design & Development Engineer - Kolhapur, Maharashtra, India
^


January 2017

A. Hi RutuRaj. ASTM B117 is a specification for how to run a salt spray test and what features are required of the test cabinet. It will not tell you what constitutes passing and failing.

Sorry that I don't have a copy of ISO 2081 at hand, but it may tell you what constitutes passing and failing, what lot/sample sizes to use, etc. Usually, black spots or discoloration are not considered failure, but white rust is.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
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How do I properly specify zinc clear, yellow, or black chromate for 96 hrs ss protection on steel alloys?

January 4, 2017

Q. 1) I believe the following will get what I need for the yellow or black chromate, but is this the proper formatting?
ZINC PLATE YELLOW (or black) AND BAKE, RoHS, Fe/Zn13, TYPE VI, SC3, PER ASTM B 633 (NO HEXAVALENT CHROMIUM), 96 HOUR SALT SPRAY MINIMUM.
2) Clear is Type V, but according to Table 2 in B633 that only provides 72 hrs. But how come Table 2 can identify the level of protection when a specified service condition is not taken into account? Will the specification of SC3 give me that or can I specify SC4 give 96 hours protection?
3) Would I use the same specification for ductile iron? If I need to specify the particular zinc and aluminum alloys to be able to answer this question, I can provide that.
4) Are the colors actually a sealer or just a dye?
5) In what cases would want to specify a chromate conversion or is that the same?

Scott Brown
product engineer - Portland, Oregon, USA
^


January 2017

A. Hi Scott.
1. That sounds okay to me.
2. Service condition and thickness of plating are related: SC3 (severe) requires 13 microns of plating as you imply. But the salt spray hours you mention are before white rust, and that is a function of the chromate conversion coating, not the thickness of the zinc plating.
3. You could probably use the same spec for ductile iron substrates, but the spec reads "... on iron and steel", so you can't use it for aluminum or zinc substrates.
4. Where the colors come from is an interesting question, the answer to which varies as the years go by. Hexavalent chromium is yellowish, so until a decade ago or so, yellow was just the color that chromate conversion coatings were. Most 'thin film' trivalent chromates are clear, so dye is sometimes used where yellow is required. Most thin film chromates use a 'sealer' after them. My understanding is that the 'thick film' trivalent chromates are yellow and don't use a subsequent 'sealer'. But trivalent chromating is so heavily proprietary that it's hard to offer clear cut answers.
5. The chromate conversion coating is the source of the coloration, and zinc plating is invariably chromate conversion coated.

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
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January 12, 2017

Q. Dear Sir,

We have been taking trials of Acid Zinc Plating and trivalent Blue Passivation with top coat on Low carbon steel components. The area of the component is 0.5 dm2. The component is just simply a Bush. SST requirement for this component is 48 hrs without black spots. We have tried external commercial platers also. They are also unable to meet 48 hours of SST. We are trying in-house to achieve the result but unfortunately white rust is forming within 24 hrs. How to overcome this issue? How to achieve the results of 48 hours? Customer is very particular about Trivalent Blue passivation.

Most of the failure samples reveal white rust formation on the HCD area. The plating time is 25 minutes (9 to 12 micron thickness) with 8 pcs and passivation time is 30 secs and top coat time is 15 secs. We have checked the chromating film deposition. It was found to be 50 to 62 nm. When we increase the timing, the corners of the Bush has started stripping in the passivation solution. That is the reason why, we are unable to increase the passivation timing. Kindly request you to provide me the suitable solution. We are under tremendous pressure to take a output and show a consistent result.

MUTHU SWAMY
- chennai, TAMIL NADU, INDIA
^



Zinc plating is failing 96 hour salt spray. Will a higher carbon substrate help?

February 23, 2017

Q. Sir,
For zinc plating we are conducting Neutral salt spray test for each batch as per ISO 9227 [affil. link to spec at Techstreet]. For each batch test is passed for 48 hours. If I check 6 month old zinc plated product is there any chances of getting white rust for same salt spray test for 48 hours?

KIRAN SOLONKAE
- BANGALORE, INDIA
^



April 25, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Thanks very much for the response on letter 35197 Ted.
I have another query. We are currently using EN1A steel material. The equivalent is AISI 1213. This is a low carbon steel, with carbon 0.07 to 0.15%. We carried out salt spray testing for components made with this steel, plated with FeZn8 CrIII and found that it had developed brown rust within 96 hours.

We are also debating whether moving to a slightly higher carbon content steel will increase the affinity to Zn plating and thus improve corrosion resistance. Information regarding this would be highly appreciated.

Mihir Bajekal
- Mysore India
^


April 2017

A. Hi Mihir. No, a higher carbon steel will not deter the rusting, and will only make the plating somewhat more difficult.

Repeating from an earlier comment on the thread which we added your inquiry to: You will pass the 96 hour salt spray test "if the substrate was properly mechanically prepared; and it was properly cleaned and activated; and it was properly zinc plated; and it was properly trivalent chromated with a proprietary chromate and the topcoat recommended by the supplier; and the shape of the component is such that it can get proper plating coverage, and the process is under control."

Luck and Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
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finishing.com - Pine Beach, New Jersey
^


April 26, 2017

thumbs up signThank you Ted for your comments. Appreciate it. I will check with my supplier team and review their process of plating.

Mihir Bajekal [returning]
Triton Valves Ltd. - Mysore India
^


April 27, 2017

? Hi,

Can you tell us what type of zinc solution you use? Is it acid, cyanide or alkaline? Also the chromate you use. This will help to give you a answer on your question.

Regards

Anders Sundman
Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika, Sweden

^



May 11, 2017

Q. Hi,
We are facing rusting issue in few of our plated parts which are directly exposed to sunlight and rain. We are specifying Zinc coating of 12 microns. How much of salt spray test requirement we should communicate to Supplier to avoid this?

Deepak Bathla
- Chandigarh, Punjab, india
^


May 2017

A. Hi Deepak. Although 96 hours would be a good answer, remember that salt spray testing is for the purpose of keeping the process under control, not predicting real-world life. So, what is your evidence that 12 microns would be enough if the process were under good control?

In other words, are you sure that the plated parts which rusted are seeing the same exposure conditions as the parts which didn't? Are you sure that your exposure conditions are not "very severe" (requiring 25 microns of plating)? Is there any exposure to road salt, lawn fertilizer, pressure treated wood, or other chemicals? Is the problem red rust or white rust? Thanks!

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
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^


May 11, 2017

Q. The machine is parked in open weather that is exposed to sunlight, Rain and other environmental degradation factors.

Deepak Bathla [returning]
- Chandigarh,Punjab , india
^


May 2017

A. Hi again, Deepak. Due to the very close timing, it's not clear to me whether your reply was in response to my posting or just coincided with it. But I think the ball is still in your court :-)

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



Trivalent or hexavalent chromate for more salt spray hours?

February 5, 2018

Q. Which type of plating is comparatively stronger to salt spray testing, Trivalent or Hexavalent?

Jayant Kurundkar
Robertshaw controls Pvt. Ltd. - Pune, India
^


February 2018

A. Hi Jayant. If you read literature from 30 years ago, it will say that hexavalent is much better, which it was. But today's modern proprietary trivalent chromates are at least the equal of hexavalent chromates in salt spray testing.

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



February 16, 2018

Q. I seem to be struggling to get any information on how long zinc plating itself not including passivate lasts in salt spray to red rust. Is there any general information out there for it? E.g., 25 microns lasts "x amount" of hours to red rust?

Many thanks in advance

Andrew

Andrew Hopkins
- United Kingdom
^


February 2018

A. Hi Andrew. For my own part, in a career of 50 years in electroplating, I don't recall even once seeing zinc electroplating which wasn't chromated, but Tom Rochester suggests that you look at ASTM B695 [affil. link to spec at Techstreet]. Good luck.

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
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^



Salt spray test for Hydrogen De embrittled part

March 1, 2018

Q. Will Hydrogen De embrittled part withstand the Salt spray test of 144 hours with Zinc yellow passivation. Coating thickness of 8 microns.

Anand Shanmugam
- Coimbatore, India
^


simultaneous March 1, 2018

A. The best answer to this question can be obtained experimentally. If the article, prior to de-embrittlement, would have passed these requirements and has a trivalent passivate, then it would likely pass after de-embrittlement as well. If it has a hexavalent passivate, and just barely passed before salt spray, it would likely fail. But facts trounce theory and opinion.

tom_rochester
Tom Rochester Plating Systems & Technologies, Inc.  


supporting advertiser
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March 2, 2018

A. Hi Anand,

If you need to bake after the chromate, it depends on the last. If the part has 8 microns, I think you can't have white corrosion before 72 hours to assure 144 hours of corrosion resistance.

There are some high thickness chromates in the market that could make up to 120 hours without white corrosion in a salt spray chamber after hydrogen de-embrittlement.

I think that if the color needs to be the SAME every batch and every part, you won't get what you want. If you want even color, you won't find a chromate you can bake. If you want to be "slightly yellow", I think you can achieve that with a high thickness (trivalent) chromate available in the market.

You can always do this: PLATE-BAKE-(ACTIVATE)-PLATE AGAIN (doesn't need to be much time, 2 microns over the first layer is enough)-CHROMATE
With that process you assure de-embrittlement and have active zinc to apply the chromate and assure the corrosion resistance.

Hope you solve this issue! Best regards,

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina
^



March 11, 2018

Q. In Internal salt spray testing we have found red rust in 144 hours in respect to [required] 264 hours.
Plating type - Zinc plating with yellow passivation.
Plating thickness observed -- 9 micron on same batch part in respect to requirement of 12 micron minimum.
Testing condition - As per ISO 9227 -2012
Part Type - M10 -Screw
Photo & test Reports - Refer below

So can you please share the probable causes of above issue, accordingly I am planning to visit at supplier to validate the same.

Regards,

Ansh Mishra
- Bawal Haryana, India
^

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March 2018

A. Hi Ansh. I think the failed thickness check rather than the failed salt spray test is the heart of this matter!

If the screws are supposed to be plated to 12 micron thickness, but the supplier is not plating them for a long enough time to achieve that requirement, something is very wrong and must be fixed before you can proceed. The vendor perhaps justifies theirself by believing that your spec is incorrect or poorly written ... and they may be right or wrong. But whether they agree to plate to your spec or you agree to change the spec, STEP 1 is that the plating thickness must conform to the spec; if it doesn't, all else is simply nonsense :-)

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^


March 14, 2018

A. Hi Ansh. As Ted said, first verify why the bolts have less thickness than specified. It could be that your supplier didn't know the spec (it wouldn't be my first), mistakes in plating time or current, low zinc/low anode surface, low bath conductivity (potassium/ammonia?)...

Not knowing your supplier, you can make many assumptions, but what you have is a part not meeting your spec (12 microns minimum, 264 hour of SST without corrosion of base metal). Go with that and listen to what they say :)

Best of luck!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina
^



February 5, 2019

Q. Hello. Can we achieve 480 Hrs of salt spray life with 8 Micron coating thickness?
If yes, with which process?
Kindly guide.

Pankaj Kumbhare
Rishi Laser Ltd - Pune, Maharashtra, India
^


February 2019

A. Hi Pankaj. I doubt it. But at the least, 480 hours sounds equivalent to very severe exposure (25 microns) rather than moderate (8 microns) exposure. Can you tell us what spec you intend to evaluate the salt spray life according to, and give us some background info rather than a hypothetical? Thanks.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^


February 18, 2019

Q. Hello Mr Mooney.
Thanks a lot for your reply. Actually we had an inquiry from our customer who is dealing in aerial work platforms which are working in environment with moderate salinity & expecting a life cycle of 5 to 15 years (C4). Customer is specifying Zn-Ni plating and 8 Micron plating thickness.
Our supplier is confident of achieving it, I just want to confirm it.

Pankaj Kumbhare [returning]
Rishi Laser Ltd - Pune, Maharashtra, India
^


February 2019
30106ext

A. Hi again Pankaj. Thanks for the additional info. The other people on this thread have been discussing zinc plating; zinc-nickel plating is a different process and is much more corrosion resistant. On topic 28851, Asif Nurie asserts that 500-1000 hours is possible, but some other posters reported failure within that time frame. The way to confirm the ability to comply is to plate sample parts and test them for 480 hours, then evaluate them in accord with some specific specification.

The problem remains that the results will depend not only on the plating process but on the shape of the part, its substrate material, its surface finish, etc. To "teach to the test", trying to design to salt spray hours instead of real life is tough; to try to do so while ignoring the actual parts is impossible. Good luck.

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



April 13, 2019

Q. if we deposit 1 micron thickness on parts then How much life will achieve?

Umesh W [last name deleted for privacy by Editor]
QA - Aurangabad, Maharashtra, India
^


Ed. note: No abstract questions
Please, please, pretty please!!

April 2019

A. Probably zero, cousin Umesh. I've never heard of anyone trying to use only 1 micron of zinc plating. 5 microns is specified for "mild" service conditions.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^


June 15, 2019

A. Hi Umesh,

I'm not sure what life 1 micron will achieve but your business life expectancy with your customer will be zilch if he finds out you were asking..  :)

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind
supporting advertiser 
Bengaluru, India

Saify Ind
^



June 28, 2019

Q. I have a customer that is requiring a Zinc Black .0005" plating. My question is does .0005" provide more corrosion protection than .0002?

Andy Hanks
Fastener Distribution - Erie Pennsylvania
^


June 2019

A. Hi Andy. Yes! .0002" (5 microns) is for "mild" service per ASTM B633 [affil. link to spec at Techstreet] and related specs, and .0005" (13 microns) is for "severe" service. (.0003" is for "moderate" service and .0010" is for "very severe" service).

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



June 28, 2019

Q. Hi I am from a metal stamping company in Malaysia.
I have a customer making snow tire chain wear plates using Boron Steel from SABB Boron 22. After stamping it goes thru Oil Quenching + Blue Zinc Plating (did not specified thickness) + Tempering.
Is it possible to achieve "No white rust after 200 hours in 5% NaCl atmosphere pr salt test standards ISO 9227 [affil. link to spec at Techstreet].
Regards,
Lawrence

Lawrence CHOONG
Y&L Metal components Sdn Bhd - Balakong Malaysia
^


July 2019

A. Hi Lawrence. If you can plate them, you should be able to get 200 hours with a good chromate conversion coating. But I think you might want "clear" rather than "blue", and I'm not sure you will be able to plate oil quenched parts unless you have a very good cleaning cycle. Further, this application sounds like "very severe" service", such that zinc plating thickness should be specified rather than being satisfied simply with a white rust salt spray test. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



August 1, 2019

Q. We want coated brackets with zinc. Brackets can be welded or bolted, generally L shaped. We require brackets for severe environment conditions. So I want to ask about the thickness of coating and salt spray test durations for white and red rust, we should prefer?

Dhanaj Singh Panwar
- Bhopal, India
^


August 2019

A. Hi Dhanaj. Per ASTM633 and some related industry standards, "severe" service should have 13 microns, 'very severe' (bold atmospheres, cleaners, saline solutions, denting, scratching and abrasion) 25 microns. It seems to me that automotive and some others tend to use alloy platings like zinc-nickel of the next thicker thickness instead (8 microns of alloy plating for the severe stuff and 5 microns for the moderate).

192 or 200 hours to white rust seems to be pretty typical. As for red rust, I'd concentrate on the thickness rather than the hours to red rust since salt spray testing tells us little to nothing about real-life endurance of zinc coatings because the corrosion mechanism is fundamentally different.

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



August 22, 2019

Q. My question is: is there any relation ship between plating thickness (any type) and salt spray hours or any other factor also contribute for salt spray hours.

sateesh .n
nash - bangalore, karnataka, India
^


August 2019

A. Hi Sateesh. You are asking an extremely broad abstract question which is probably more appropriate for a book than for a brief public forum response :-)

The short answer is, no, the salt spray resistance is generally not directly proportional to the thickness. In zinc and zinc alloy plating the quality of the chromate conversion coating is probably a bigger factor in salt spray resistance than the thickness of the zinc plating. But zinc is anodic to iron so there is at least some degree of proportionality between plating thickness and salt spray hours because the zinc plating will gradually dissolve.

In other types of plating, where the plating layer is cathodic to the substrate, such as nickel plating on steel, the 'porosity' of the plating is far more important than the thickness because corrosion begins as soon as the salt solution reaches the steel substrate. As a general rule, increasing the thickness of the plating probably decreases the porosity, but a properly applied fairly thin plating layer may be less porous than a poorly applied thicker layer.

Please introduce yourself and your particular situation; people can usually help you with a specific problem but, much as they might wish to, they cannot condense a lifetime of experience into a couple of paragraphs for you :-)

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



September 25, 2019

Q. Our client want that surface treatment MFZn2-C and SST required 240 Hrs. Is it possible? If yes, what is the procedure?

Jamal Yousuf
- Karachi, Sindh, Pakistan
^


September 2019

A. Hi Jamal. What company or international standards body are you referring to with that spec? Different automobile companies have specs that may use similar abbreviations and which look sort of the same but which are not the same specs. In some specs the number after MFZn is thickness in microns, but I'm sure that's not the case here; it's perhaps a Honda spec and means exposure class 2.

Under ideal conditions, yes, a well controlled zinc plating process can probably deliver 240 hours, quite possibly more. Does the specification mention 240 hours or is that only mentioned on the drawing? Thanks.

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



WSS-M1P85-B2 zinc plating is failing 120 hour salt spray

October 28, 2019

Q. Hello, Jason here from the automotive sector.
I have a door hinge of stamped steel (EN 10149-2-S420MC) that is treated per WSS-M1P85-B2 (electrolytic zinc 8µm thin film passivate).
I am seeing red rust around 50-60 hours; spec is 120 hours.
The film build using electrometer is above requirement at ~13µm. Documentation from the supplier is good.
I'm traveling to the plater to [investigate] root cause. What should I be looking for?
My plan is to review the spec and process with the plater. Then place parts in the salt spray chamber (marked) and watch them on-site for three days.
Any insight would be appreciated.

Jason Naffziger
Advanced Quality Engineer - Auburn Hills, Michigan (USA)
^


October 2019

A. Hi Jason. I think you should try to track one batch of parts from the receiving dock to the salt spray cabinet. Very often the flow sheets, no matter how carefully written, don't describe what really happens. "Walking the line" often immediately reveals what is wrong ("No good decision was ever made from a swivel chair" -- General George S. Patton).

Some thoughts: The spec probably calls for no "white rust" until 120 hours, let alone "red rust". The high salt spray hours bragged about by the process vendors always apply to ideal shaped parts and after excellent mechanical preparation. Has the plater made any comments about "design for plating"? Are the hinges properly deburred? Are these "hinges" pre-assembled, such that capillary action may mean that acids are drawn in from early process steps are carried through the process? Is there a particular area on the hinge which rusts first? Has the plater recently changed chromate suppliers?

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



November 14, 2019

Q. We have bung inserts made from EN19 steel and our supplier provides trivalent coating of 9-11 microns thickness. The bung inserts are exposed to hard water and we see rusting on finished components after use as well as when stored at 40% RH. Does the grade of steel make any difference for trivalent coating? If we change steel to IS 20162 (hot rolled structural steel)? Or should we go for Ni-Cr plating? The bung comes in contact with propane gas.

Pradeep Kamat
Composite LPG Cylinders - Mumbai, India
^



December 16, 2019

Q. As far as the Zinc spec. ASTM B633 [affil. link to spec at Techstreet] Type III SC 3 (FE/ZN 13) is concerned, what Does the SC mean?

Raymond Haase
- Hauppauge, New York USA
^


December 2019

A. Hi Raymond. SC 3 means Service Condition 3, "Severe Service", and requires 13 microns of plating thickness.

Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^



August 9, 2020

Q. Hi Anyone please clarify me about, Salt spray acceptance criteria. We have done Zinc plating coupon 96 hrs salt spray test. Got result with no rust, but coating peels off. We found on some surfaces the coating was completely removed. Can we accept it?

Guhan Veeramani
- UAE Abu Dhabi
^


August 2020

A. Hi Guhan. You ask "Can we accept it?" but you haven't introduced yourself :-(

- If you are the purchaser, sure, you can accept it if you wish, although I wouldn't.
- If you are a testing lab, I think due diligence and product stewardship demands that you do your best to convince the client to not accept the parts.
- If you are the plating shop, I think you must admit that the components are NOT satisfactorily plated.

What usually actually answers most questions is the plating specification. Someone should have, and possibly did, write or reference a specific plating specification for the plating contract. Please give us that specification or specification number and we can probably point to a specific line which defines such plating as unsatisfactory. Good luck!

Luck & Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
^


November 23, 2020

Q. Sir
I am Guhan and working as a Quality supervisor at Oil field manufacture company. We are doing now ELECTRODEPOSITED ZINC PLATING ON CARBON AND LOW ALLOY STEELS validation process and currently doing salt spray test (96 hrs). We had sample coupon with minimum 8 Micron (Zinc plating thickness) at before salt spray test stage. And after salt spray test we got good surface without any rusting formed. But Zinc thickness fell into the 6.2 Microns. Can we accept it? Is Zinc thickness also a consideration to have acceptance?

Guhan Veeramani [returning]
- Abu Dhabi
^


November 2020

A. Hi Guhan. The part is probably satisfactory; you are probably not supposed to recheck minimum thickness after an accelerated corrosion test, but again we must ask for a specification or specification number before anyone can say for sure whether the part is satisfactory. For example, you say "without any rusting", but do you mean red rust or are you including white rust ... and which one does the spec say you must resist for 96 hours? Salt water isn't terribly abrasive so it's hard to imagine losing 1.8 µm of plating without generating any white rust. And does the spec actually say that testing one sample part is enough, or might it demand a specific sampling plan? You cannot assert that the quality meets the requirements without a specification number telling you what those quality requirements are.

If you received just a vague requirement like "8 µ Zn + yellow chromate, must pass 96 hour salt spray", then you should pick a spec or write a spec that answers such questions because without it you cannot have quality assurance. For example, what happens if you're out sick next week and your replacement views things differently?

Luck & Regards,

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Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
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^


November 24, 2020

Q. Adding to above my question, Electrodeposited zinc plating on carbon and low alloy steels in accordance with the latest revision of ASTM B633 [affil. link to spec at Techstreet] and Salt Spray Test per ASTM B117 [affil. link to spec at Techstreet] for a minimum of 96 hours and sample coupon we selected 3 ea

guhan veeramani [returning]
- Abu Dhabi
^



January 6, 2021

Q. Hi to all,

I am Gopinath working as a head of quality dept. in metal shop field. We are making wire mesh cable tray with mild steel base and finish of electro zinc plating Fe/Zn12. It is complete alkaline base zinc plating, blue passivation (Trivalent).

After complete electro zinc plating finishing we did Salt spray on samples for test 550 hrs as per ASTM B117 [affil. link to spec at Techstreet] . Here our question is: sample passed 550 hrs SST without any white rust or red rust; only observed black stain marks on the sample.
We have checked mass of zinc coating of the sample the result is 15 microns. How did this material pass SST at 550 hrs sample have only 15 microns?
Our sample is 4.5mm dia wiremesh

GOPINATH HARICHANDRAN
- THANE maharastra, India
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January 2021

A. Hi Gopinath. That does seem like outstanding performance, but I guess the answer is that you did a good job of applying a very good trivalent chromate and sealer onto a very good zinc plating layer on a very well prepared substrate. But as for "only 15 microns" that is not thin zinc plating, it's more than enough for 'severe' service.

If you are trying to imply a suspicion that the salt spray test was conducted incorrectly, please try to be a bit more explicit and specific. Thanks.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
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