C Hopper's life span...
Guys, the truth of the matter is, a covered hopper will be progressively "demoted" as the car ages. Brand new covered hoppers of course will be used for grain service, and this will include the areas of food processing, for Kelloggs, General Mills, etc, as well as export, and then maybe at the end of that era for cattle feed for Agway and Blue Seal Feeds and such. Then, comes the first demotion, when the car can no longer be considered "sterile" for food consumption products if you will, and it may start being used for fertilizers, wood pellets, or other bulk commodities. At the end of the cars life, the car gets demoted to one more stage in this neck of the woods, and that's road salt. Even now, I see old MILW Road, CNW, MP, UP, as well as other roads being used one last time... the next thing these cars will see after this is the cutting torch!...where they will cut it up for recycling at the steel mills. I think it's kinda neat to excercise this drama in the hobby....having "shiny" new cars for your grain elevators, and yet going to the extreme of some good ole "rust buckets" for the NE salt business..... As far as the ordeal of three pockets vs four pockets is extremely marketing design between the car builders and the railroads themselves, in hopes of answering to market demands. UP had a series of four pocket covered hoppers built, but returned to the three pocket in the next car building contract. Cylindrical covered hoppers have been built for various roads....three pocket, four pocket, even SIX pockets; GN owned a bunch of six pocket...and to the best of my recollection went directly into the dairy feed busness. CP still owns a bunch of four pocket, and they are still in use in the cement industry being loaded at Glen Falls NY and Jolliet Quebec. But it does seem like the design of the two bays have been exclusively for cement, regardless of ACF or ribside....just my 2 cents worth....