Tinplate Can Corrosion Pinholes

We have a problem with a customer product which is developing pinhole leaks fairly quickly. Product is an ammonia/alcohol/90% deionized water mixture, ph ~ 8.0, filled into sealed tinplate steel cans. Within 3 weeks they develop pinhole leaks near the bottoms of the cans and at the seams. There is no "detinning" visible in the leakers when opened up. Normal non-leaking cans have the dark grey detinned appearance. The last set leaked after only 17 days...

We pull 15-20 in. vacuum before crimping the cans. It is blamed we are not pulling enough vacuum and there is air left in the cans which promotes the corrosion. Another opinion is that the tinplate is thinner than years ago and more likely to have tiny pits which are rapidly attacked and corrode. Any comments, suggstions? - H.Pol Sixe, Toronto

 

[lgspe99]

I would have to say that the problem is caused by the thinning of the tin coating in the areas near the seams and the bottom crimp. The metal is "stretched" in the crimping process to make the seam and attach the bottom and in doing so it causes the coating to thin and cause holidays in the coating.