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topic 50132p1

Salt Spray Test -- ASTM B117 Operational Problems


A discussion started in 2003 but continuing through 2019

Differing condensate collection rates between collectors

2003

Q. What could be the problem when the condensate collection is not the same for both collecting vessels? The pressure is 12.5 psi and temp is 95 °F. The one closest to the test specimen and to the vents (vents of dispersion tower) collects three times as much as the one farthest from the test specimen and the vents. The collection is always done at 7:30 in the morning (approximately after 24 hours of operation). The pH and specific gravities are within the limits.

Thank you,

Nila O. Par
- Winnipeg, Manitoba, Canada


2003

A. Nila,

Inconsistent condensate collection can be caused several different ways depending on the type and model of your salt spray cabinet. Some cabinets allow for slight directional adjustments to provide consistent coverage. Another factor could be that the nozzle could be slightly clogged or a particle caught in the orifice which would result in a misdirected fog. A final possibility could be the nozzle air pressure. Too high a pressure and the fog will spread wider, too low and the fog will settle closer to the nozzle. It may be silly, but you also need to make sure your collection vessels are not placed directly under panels or holding devices which may drip and cause errant readings.

Best of Luck,

Ira Donovan, M.S.F.
Kansas City, Missouri


2003

A. Nila -

First I would say that this problem is not unusual. Are you working to ASTM B117 [affil. link to spec at Techstreet] ? One thing you might try is replacing your filter.

Terry Tomt
- Auburn, Washington, USA


2003

A. Nila -

Contact the cabinet manufacturer for suggestions on how to adjust for more even collection rates. Have the following information available: cab temperature, air pressure, humidifying tower temperature, collection rate in each collector. If possible, send them a digital photo. Also, be sure the cabinet is level and properly vented.

Cynthia L. Meade
- Sylvania, Ohio, USA




Concentration of collected solution for salt spray test is too low

March 9, 2008

Q. Dear friend,
I have a question: during salt spray test, the concentration of collected solution is lower than original solution, e.g., the solution I mixed is 5%, but collected solution concentration only about 2%.

What happened to it?

Thanks a lot.

Xie Sophie
- Suzhou, China


March 25, 2008

A. I'm not familiar with any ASTM B117 requirement to run a condensate analysis, but would not necessarily expect the condensate to contain the exact concentration of the bulk solution being aspirated into the (95 °F) tank. You may want to compare your 2% result with the concentration of solution taken from the bottom of the tank and from the "moat" that provides the air-tight seal around the lid.

TRH

Thomas Hanlon
Thomas Hanlon, Materials Engineer
aerospace finishing - East Hartford, Connecticut, USA


March 26, 2008

A. I politely but strongly disagree with Thomas. The analysis only counts on the collected condensate that does NOT drip off of the parts.
If anything, the salt concentration would be expected to be higher in the condensate since the aspiration of the solution would evaporate it.
How are you checking (measuring) the salt concentration?

James Watts
- Navarre, Florida


March 31, 2008

A. Hi

We operate SS chambers per the ASTM and it does indeed require that the collected solution be analyzed for both pH and concentration. You can measure concentration by using specific gravity or by using a salt refractometer. The solution must not have touched any parts and it is not to be taken from the water seal around the lid. There are strict requirements in the ASTM as to how the atomized solution is to be collected.

Thanks,

Terry Tomt
- Auburn, Washington


March, 2008

A. This question intrigued me, so I contacted one of the world's experts on this subject (at a UK salt spray cabinet manufacturer) and this was their reply.

Hello Terry,

The salt solution is mixed with air that has passed through the air saturator, this adds some moisture. The take up of moisture by the air is increased if the air saturator is set to a high temperature. Add to this the fact that the chamber is heated through a base covered in water (to maintain humidity levels) there will be some changes in the concentration of the salt solution.

I would be very surprised if the above would cause the level drop from 5% to 2%.

I would suggest measuring the salt concentration remaining in the salt tank at the end of the test to be sure that the salt dissolved is evenly distributed and that additional water hasn't been added to the tank.

Other than the above, I would suspect a fault with the chamber. Perhaps an overfilling air saturator (causes water to be squirted through the atomizer).

Has the chamber been serviced recently? Are you confident that it is working as it should be?

Kind regards,
Martin

This seems to be a very good explanation as it points to several causes that could contribute to the problem and that are worthy of investigation.

Terry

Terry Hickling
Birmingham, United Kingdom



Our chamber rusts the test parts in too few hours

September 29, 2008

Q. We are just starting up salt fog testing to ASTM B117 and have found some issues regarding pH and premature rust. We think it's related.

Since we are using mixed bed de-ionizers to make type 4 water, we know that it produces a low pH of about 5.5. Once it has been in the tank with Salt for a while, and once it is atomized in the chamber, we get about 6.2.

Not sure what concentration and acceptable grade of NaOH, and HCl to use for adjusting, so we have just kept the chamber running at 6.2. The problem is our chamber is rusting the specimens prematurely. This is of course in comparison with our platers, and other testing facilities. Does anyone think running the chamber on the lower end of the pH range of 6.2 would affect the test this way?

Also, does anyone know what concentration and grades of the HCl and NaOH we should use? And how much to add?

Steven Sherman
Buyer, Final Inspector - Northvale, New Jersey


October 1, 2008

A. A pH of 6.2 is not that acid.

I'd suggest using a freshly calibrated pH probe, and 0.01 N NaOH to adjust the pH to 7.0, if you think that will help. (I don't think it will make much difference, but it won't hurt.)

Insofar as documentation: buy the 0.01 N NaOH from Fisher Scientific, and write the lot number down in a book ... it's hard for me to see how even the toughest auditor could object.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


October 2, 2008

A. Steve,

This sounds very similar to a problem I had a few years back. I used 0.1N analytical grade NaOH and HCl for adjustment. Rather than trying to add a fixed amount and see what happened I would take a 100 ml sample and adjust in the Lab and then multiply up to the reservoir size for the addition. In my particular case it was normally found to require about 50-100 ml of 0.1N NaOH in 120 liters of solution. Once adjusted I would retest the pH of the reservoir and ensure it was between the 6.0-7.0 ^ 6.5-7.2 required by the specification.

By the way, this was related to premature failure of chromate conversion coated samples of 2024 Aluminum.

Brian Terry
Aerospace - Yeovil, Somerset, UK


October 2, 2008

A. Steve,

Isn't the pH on fallout required to be 6.5 to 7.2?

And yes, I would think that a low pH will affect your results.

We use 0.1N reagent grade NaOH or acid to adjust. Make small additions

Terry Tomt
- Auburn, Washington


November 15, 2008

A. You must maintain your collection pH between 6.5 - 7.2 if you wish to perform testing per ASTM B117 (and also avoid false failures and audit findings). Is the sample exposed to open air for any period of time prior to measuring the pH? If so, it may be possible that the solution is absorbing carbon dioxide from air and the pH is decreasing accordingly.

Another question: does your pH meter automatically compensate for temperature differences? If the meter is assuming 77 °F, but your sample is 95 °F, there will be enough error to make you believe you are out of tolerance.

As mentioned before, increase your salt solution with 0.1N NaOH prior to introduction into your chamber. You want to target the higher end of the tolerance since pH of the collected fog will almost always be lower than your salt solution. Also measure with a fresh calibration and a suitable pH electrode/meter. We prefer to calibrate prior to each use.

Terry Lycans
- Dayton, Ohio, USA


November 19, 2008

thumbs up signThe fallout is indeed required to be 6.5-7.2. I think I may be getting my ASTM mixed up with ISO 9227 [affil. link to spec at Techstreet] for the make up. One of the problems of trying to run a salt spray to multiple specifications!

If there is a continued problem with low pH as collected, the ASTM does allow you to boil the sample for a period to remove the dissolved carbon dioxide. I have tried this before and it does work, but has always felt as if I was fudging the results. Preferable to adjust your reservoir to obtain the correct collected pH.

Brian Terry
Aerospace - Yeovil, Somerset, UK



Specific gravity readings are rising during ASTM B-117 salt spray testing

December 22, 2010

Q. I am having trouble keeping the specific gravity in range, it always seems to be a little high. I use a premixed 5% salt solution, testing the solution before use I get a S.G. of about 1.035 straight out of the drum. After I test the collections I am getting S.G. of 1.045 to 1.050. Could anyone give me an idea of what might be causing the S.G. to raise during the testing?

Shaun Dickenson
Quality Tech. - Frankfort, Indiana, USA


December 23, 2010

A. That is because of the atomization of the solution: some of the moisture and only a bit of the salt goes out the vent.
I always made up my salt solution on the low side so that the condensed salt solution was on spec.
Carbon dioxide caused me a bit of pain in controlling the pH of the collected solution. It required adjustment a couple times a week.

James Watts
- Navarre, Florida



Effect of unbalanced pH Level on Salt Spray Test

March 1, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

I'm looking for an answer on the effect of unbalanced pH Level during salt spray testing.
As you know ASTM B117 [affil. link to spec at Techstreet] requires the collected Salt solution be within pH Level of 6.5 to 7.2, but what if we don't monitor the pH Level of our Salt Spray Testing ... is there a significant effect on our specimen?
We just follow the 5% NaCl mixture solution.

Also, what are different types of Failure or Effect of Salt Spray testing considering all types of specimen? Is there such thing as reference on how to identify the type of Failure or Effect of Salt Spray. I'm still new with Salt Spray Testing and I'm not familiar with other kinds of Failure ... All I know is Red Corrosion or Rust.
I'm even confused between white corrosion and Calcium deposits.

Please advise.
Thanks!

Jem Bernardino
Quality engineer - NSW Australia



A. Hi Jem. We appended your inquiry to an earlier thread which should offer you some insights. See the subheading "Our chamber rusts the test parts in too few hours" above. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


March 4, 2011

A. Hi Jem,

You really need to tell us what you are testing, both base materials and coatings. At the moment it sounds like you are testing on steel, possibly zinc or zinc alloy plated steel?

Anyway the failure to monitor the pH means that you cannot claim to be testing in accordance with ASTM B117. The specification requires that you keep a daily log of the pH from the collectors. So regardless of the effects of pH you need to monitor it anyway.

Brian Terry
Aerospace - Yeovil, Somerset, UK


March 8, 2011

A. Hi Jem.

1. The corrosion behavior of different platings on different substrates in acidic or alkaline environment are different. Therefore, it is imperative that you maintain pH at 6.5 ~ 7.2 (ASTM B117) to consistently achieve and interpret salt spray results.

2. Interpretation of pass/failure of SST will depend on the standard that the plated part has to adhere to. There is no one reference or standard that covers all. As an example, the mention of white rust and red rust suggests zinc plating on steel substrate. If you are plating to ASTM B633 [affil. link to spec at Techstreet] ( Standard specification for electrodeposited coatings of zinc on Iron or steel ), it states:

7.4 Corrosion resistance - Zinc coatings with type II and III treatments shall show neither corrosion products of zinc ( white rust - emphasis mine ) nor basis metal corrosion products ( red rust - emphasis mine ) at the end of the test period, as shown below, when tested by continuous exposure to salt spray in accordance to 10.3 .
The appearance of corrosion products visible to the unaided eye at normal reading distance shall be cause for rejection except that white corrosion products at the edges of specimens shall not constitute failure.
Corrosion Resistance Requirement
    Types        Test Period, hours
II 96
III 12
SK Cheah
- Penang, Malaysia


January 10, 2012

thumbs up signThank you for the advice. I am now maintaining the pH Level of the collected solutions and already identified the best pH reading for the Salt Solution in order to have a reading of pH 6.5-7.2 for the collected solution.

Jem Bernardino [returning]
- NSW Australia


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