Salt spray test failure, no cause identified

[Aerospace1]

Hello, I'll really appreciate your help, in case you have an idea of the cause of our problem or in case we are missing sometingh. Recently we had a failure in the Salt spray test (mil DTL5541F)on coupons passed thru Alodine Process. 5 samples show between 10 and 34 Pits. In the last 5 months we haven't had more than 3 to 5 pits on the SS test. Currently we are controling on our process PH for al rinse tanks (Etch and alodine)and PH for Alodine (600) Tank, Chlorides (etch and alodine tanks), tanks temp, concentration of chemicals, PPMs on rinse and inmersion times. All those paramethers look great, no negative trends or something Out of spec. However, suddenly the Salt Spray test results fail. Are we missing monitoring any other critical parameter/characteristic?

 

[metcoat]

Maybe there’s a problem with the quality of your samples? If all other variables are within normal parameters, maybe the integrity of the samples was compromised in some way prior to the test.

Metal Coatings Corporation - Houston TX

http://www.metcoat.com

 

[boothuk]

Perhap's you should check the cabinets you are running. Do you run an interval clean down on your SS cabinets? How about the purity of the NaCl your buying in? We use analytical grade to ensure no trace of copper is in the salt. You must check the fallout rate of fog, chamber air temp, humidifier temp, conductivity of your distilled or de-ion water. All these could throw out the results your obtaining from your cabinet. Are you outsourcing your samples to a 3rd party or performing in the laboratory?

Perhaps it would be a good idea to do a RRT with an independent laboratory to confirm your equipment is running correctly?

If you need help wwith this I can source a company for you with UKAS accreditation in the UK, we have a Boeing approved cabinet for neutral salt spray.

 

[ChEUND09]

You samples may have smearing and worm like pin holes as a result of the finishing process. Have you checked out your samples under a scope? Also, your cleaning process may be helpful.