Have you ever noticed that many day-to-day things seem to get divided into two opposing camps?  Things like asking what’s the best computer quickly become the PC versus Mac debate.  Phones? iPhone versus Android.  So, passivation?  Yup, nitric versus citric.

There are real advantages to each nitric and citric passivation, but that is a topic for other FAQ’s because once you pick one you still have several choices to make.  Choices like: which standard do I use? which method do I choose?

There are two primary standards that address passivation. The SAE Aerospace “Passivation of Corrosion Resistant Steels” (AMS2700) and the ASTM “Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts” (A 967).

Each allows for citric or nitric and each allows for several options within each citric and nitric.  So what’s the difference? Each standard is copyrighted (and protected) and has to be purchased from the publishing agency, so getting into a lot of detail is not allowed. But here’s a short version of the differences in the various methods:

Concentration of the specific acid – each method varies based on how concentrated the citric or nitric acid is – and in the case of nitric if the nitric acid is used alone or with sodium dichromate.

Temperature of the bath – again, each method specifies a temperature range that must be maintained for the duration of the passivation bath.

Time – the length of time a part must remain within the passivation solution is spelled out as well.

What seems complicated becomes really simple.  The standards spell out the concentration, the temperature and the time.   Each method simply varies one or more of those three items.

 

Within the medical device world there is a need to validate the passivation process.  But what does that mean, and how does that work?

Validation is the process of insuring that the passivation process you use will reproduce repeatable and predictable results every time a batch of parts is run through the process. By validating the process you are able to forego subjecting every part to testing to prove that it is properly passivated.

Typically you will here the validation process broken down into three distinct parts: the IQ, the OQ and the PQ.  Let’s look at each part.

The IQ or Installation Qualification is the first part.  It is developed by describing the machine – what is it? what does it do? etc. It also looks at what the components on the machine are, gauges, switches, PLC, etc.  It provides a description of the machine and its parts – what is it and how does it work?

The OQ or Operational Qualification is the second part. It essentially help you verify the IQ – does the machine operate as it is supposed to?  Do the components do what they are designed to do? etc. – does everything work as intended?

The PQ or Process Qualification is the third part. If the IQ is the theory of how things SHOULD operate and the OQ is the practice of how things DO operate, then the PQ defines how CONSISTENTLY the machine operates.  You create a DOE (Design of Experiments) that tests the equipment at the top end and bottom end of allowable ranges and run parts to verify the results across the entire range of the variables. Now when the machine operates within the specified range of time, temperature and/or acidic concentration you know that your parts will meet the specs.