Measurement Uncertainty for Neutral Salt Spray test to BS EN ISO 9227:2006

[staggerlee]

Hi, first time poster & I hope I'm posting this in the correct forum, otherwise forgive me and mods feel free to move.

Anyway, my problem is I have been with a company for just over a year now and we are going through UKAS accreditation to ISO 17025 and one of the tests we are carrying out is the neutral salt spray test to the above mentioned standard (very much the same as ASTM B117). We had a preliminary visit the other week and the gentlemen from UKAS advised us that we need to carry out uncertainty of measurement (UoM) in accordance with their M003 document.

I have read through the M003 document but I am none the wiser as to what needs taken into consideration for UoM so I am wondering if anyone on here can possibly lend a helping hand?

I understand that everything that gives out a measurement or reading needs to go through the UoM but so far I can only think of; temperature, pH and conductivity of the reservoir solution. Are there others that I am missing?

Also any pointers as to how to carry out the UoM will be very much appreciated.

I look forward to reading your replies (hopefully) and many thanks in advance.

 

[Mikishots]

Re: Uncertainty of Measurement for Neutral Salt Spray test to BS EN ISO 9227:2006

Hi, first time poster & I hope I'm posting this in the correct forum, otherwise forgive me and mods feel free to move.

Anyway, my problem is I have been with a company for just over a year now and we are going through UKAS accreditation to ISO 17025 and one of the tests we are carrying out is the neutral salt spray test to the above mentioned standard (very much the same as ASTM B117). We had a preliminary visit the other week and the gentlemen from UKAS advised us that we need to carry out uncertainty of measurement (UoM) in accordance with their M003 document.

I have read through the M003 document but I am none the wiser as to what needs taken into consideration for UoM so I am wondering if anyone on here can possibly lend a helping hand?

I understand that everything that gives out a measurement or reading needs to go through the UoM but so far I can only think of; temperature, pH and conductivity of the reservoir solution. Are there others that I am missing?

Also any pointers as to how to carry out the UoM will be very much appreciated.

I look forward to reading your replies (hopefully) and many thanks in advance.

You would also need to conduct checks on the fallout solution pH, as the CO2 levels can change (depending on whether or not you pre-boiled or heated the resevoir solution prior to use).

How are you measuring time? How often is the test interrupted?

By resevoir solution, are you referring to the solution held before entry into the chamber, or are you using it to describe the solution at any point in the system? In my suggestion above, reservoir solution is taken to be the solution held prior to atomization.

 

[staggerlee]

Re: Uncertainty of Measurement for Neutral Salt Spray test to BS EN ISO 9227:2006

So the pH of the fallout should be checked too? This shouldn't be a problem as the fall out cylinders are external to the chamber.

Time is measured by the chamber itself also - it's a fully automated chamber that gives digital read outs of time and chamber temperature. The test is interrupted at varying times depending on how long a test we are carrying out - e.g. for a 48 hour test it would perhaps be opened for around 2-5 minutes every 2 or 3 hours to check on the development of white or red rust.

And yeah, the reservoir solution is the external salt spray solution before it is atomised.

Thanks btw

 

[Mikishots]

Re: Uncertainty of Measurement for Neutral Salt Spray test to BS EN ISO 9227:2006

The pH of the fallout is critical - this is the stuff that's actually coming into contact with your DUT. It needs to be at a certain temperature and a certain pH. I'd even venture to say that's it's more important than the pH in the reservoir.

More things to consider: tower temperature, impurity levels in the salt, temperature inside the chamber itself.

I suppose what I'm saying is that it's fine to monitor and measure the resevoir solution, but that solution is "processed" before actually ending up on the part itself - it undergoes chemical changes as well as thermal. The critical measurements are made inside the chamber. The compressed air used to atomize the solution is warmed and humidified, the pH of the solution typically increases upon atomization (if it was simply prepared at room temperature), and the fallout rate and pH need to be measured to ensure that the parts are being exposed adequately.

I've battled with many new environmental chambers in my past (both good and bad) and have been through your scenario more than once. The advantage you have is a degree of automation - the chambers I worked with were purely mechanical and had to be monitored closely (the most recent being an MX9216 from Associated Environmental Systems, a nice little unit). Taking uncertainties into account was a bear.

edit: On a side note, the company I'm currently at just picked up an Ascott unit, very expensive and fancy! Word got out that I've used EC's before, so I think I'm going to be thrown back into that world again for a bit. Dammit, Jim, I'm an aerospace auditor, not a QC Inspector!

 

[staggerlee]

Re: Uncertainty of Measurement for Neutral Salt Spray test to BS EN ISO 9227:2006

Once again many thanks Mikishot (I can see why you're an appreciated member )

Yeah, it's an Ascott 450+XP we have - a very nice piece of equipment but unfortunately my very first experience using a corrosion chamber (hence the uncertainty about using it) but nevertheless I shall take your comments on board and hopefully I can get to the bottom of it before UKAS come back in again in November.

Again, thank you for your prompt replies.