Part corrosion during Environmental Cycle Testing

[mnelsondcss]

Roadside Assistance Kit submitted for Environmental Cycle Testing - 35 cycles

Aluminum coated PET film, Dynamo flashlight and CCA jumper cables DIN72553-25 corroded. Aluminum coating disintegrated, flashlight inoperable and CCA clamps corroded.

One cycle lasts for 720 min (12 h) and comprises the following temperature
and humidity profiles:

60 min heating phase to +80 °C and 80% rel. humidity,

240 min holding time at +80 °C and 80% rel. humidity,

120 min cooling phase to -40 °C, when freezing point is reached: approx. 30% rel.
humidity, the air humidity remains unregulated as of T < 0 °C
(depending on the system, humidity regulation can also be suspended as of T < 10 °C),

240 min holding time at -40 °C, air humidity remains uncontrolled,

60 min heating phase to +23 °C, rel. humidity is regulated to 30% as of T = 0°C




Was told, possible cause is use of deionized water in chamber. Trying to determine if the corrosion is materials used or the deionized water.

Any suggestions?

 

 
 
 
                         
 



 

[Compositepro]

You are almost certainly getting condensation on your test articles. Your test conditions maybe close to real world or perhaps not. If the relative humidity in the test chamber is truly never above 80% you will not have condensation.
Controlling humidity accurately while changing temperature can be difficult. Good air circulation in the chamber is essential to get uniform conditions.

 

[CoryPad]

There is no reason why deionized water would lead to excessively high corrosion rate.

 

[mnelsondcss]

Definite condensation. 1 week after test completion, paper and fabric content that were in PE bags were still soaked.

Carry bag is comprised of Polyester backed with PVC, EPE foam padding and internal nylon lining.

Initial info from test facility said there were issues with the climate chamber and they gave an interim report at 28 cycles following up with another report after 35 cycles. Following up with facility post testing, they say there were no issues with the test.

Could the interruption in cycles have contributed to the condensation and corrosion?

 

[EdStainless]

Yes, changes in the controls could lead to condensation.
There should not be any items that are wet, since there never should be liquid water in the test.
Was the box closed?
Perhaps the cycle rate was too high to allow the temp/moisture in the box to re-equilibrate during the temp ramps.
You need to review the intentions of the test and the cycles rates used.

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Plymouth Tube

 

[Compositepro]

It is not uncommon for items stored in poorly ventilated containers where humidity and temperature fluctuate over a wide range to experience corrosion due to condensation. Wood or paper in the container can make the problem worse because they will typically contain about 10% moisture. This is why I said that your cycling may actually represent real-word conditions.
Once you get any condensation, it will typically not dry out again due to poor ventilation. More condensation occurs with each cycle and water accumulates. Try cycling your items in well-ventilated container.

It is still possible that the humidity chamber is not working correctly. Just a momentary excursion to 100% RH will cause problems.

 

[mnelsondcss]

Thank you all for your feedback.
The "box" or container is a fabric case which zippers shut. All of the components are being tested as a single unit within the zippered case. There is very little opportunity for ventilation within the case.

I'm quoting the test standard, Purpose of the testing is "to uncover component weaknesses in short-term test with accelerated time effect, not to define general component requirements for continuous operation"
The temperature is to be regulated with a tolerance of ± 2ºC and the relative air humidity with a tolerance of ± 5%. The climatic chamber shall be set to room temperature (23ºC) and 30% rel. humidity before the test specimen is inserted.
The holding times must always be maintained. The heating and cooling phases can be varied according to the performance capability of the climatic chambers used. Deviations shall be specified in the test report.

If the relative humidity was brought to 50% and not 30% within the chamber, would the condensation impact be greater? I've re-read the test report which is identifying the relative humidity at 50%± 5% and not 30%.

We have been told that there were issues within the chamber during testing, but the test lab has not identified what the issues were. We are still trying to get this information.

We are currently running another 35 cycles at a different facility. The new facility is running the same configuration as the one that failed and additional countermeasures, which include silica gel desiccant packets and VpCI ziplock bags.

 

[TomDOT]

All of those "shall" and tolerances on your conditions are pretty meaningless at this point. You know the lab had their chamber screw up, almost certainly it was way out of range on your test conditions for some undetermined period of time. Your results are not for your stated test. Your results are for some undescribed test.

You just don't know the conditions your items were subjected to, only that they were not your test conditions.

The lab should be asked to re-run the test for free.

 

[mnelsondcss]

Restitution for testing is a separate issue, but I agree.

We have never seen corrosion of this magnitude on our parts. We have run this type of test before but for a shorter number cycles with no issues.

Product launch is being delayed as we address the corrosion. Since we must find a solution to a problem we have not been able to identify, we are trying to determine if the materials used in manufacturing our components would ever pass this type of test if run correctly and if there are minimal countermeasures that we could utilize to pass the test if they would not.

We do not believe our Roadside Kit would ever travel from the desert to the artic circle and back under the test conditions, but we are required to meet the test standard.

The knowledge I have gained from the feedback is invaluable to future development. The issues raised will become part of our DFMEA process for our Kits, and the issues of corrosion will become evaluation tools for the individual components utilized in any of out other parts.

 

[EdStainless]

I presume that he bag can breath some.
It may be that in the past the testing was done with much slower ramps because of the test chamber being used.
This may have been enough to minimize the trapping of moisture.
The other possibility is that you have unintentionally changed some of the components (foam?) and created a bigger trap for moisture.

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Plymouth Tube