What are the proper procedures for introducing a new tortoise in your collection ?

That would depend on CB or WC, adult, subadult or hatchling. Adding to a collection I'm assuming is adding to an existing group or starting a new one?
I think each addition you make needs to be evaluted on an animal by animal basis and will be different everytime.
That being said a quarantine period is a must, from a month for CB hatchlings to 6 months for WC adults. I always take care of new additions last as that means there is less of a chance of spreading something to one of my existing animals.

Danny

I would like to add to that...don't put different species together. And don't put hatchlings with adults.
Patsy

That brings to mind another story!! (lol)

I have two species of Manouria and I have them separate. The Manouria emys emsy doesn't get as big as the Manouria emys phayrei, so when I bought a hatchling Mep from Vic Morgan about 10 years ago, I put it in with the Mee. This year Vicmorgan is big enough to go in with the Mep, so I tried just putting her in there. Bad choice! My largest Mep gal is 65lbs and the boss of the enclosure. She pushed and bit and fought with poor little Vicmorgan (about 25lbs) until the poor little thing just stayed in a corner and never moved. So I had a brainstorm!! In the Mee enclosure I have 6 10 year old male Mee/Mep intergrades who are all slightly smaller than Vicmorgan. I put them ALL in the Mep pen. There were too many newcomers for the old grouch to mess with, and she eventually left them all alone. After about a week I put all of the intergrades back in their own pen, leaving Vicmorgan in with the big girls, and she's been part of the group ever since.

So, after a period of quarantine, you just have to play it by ear. If you have fighting that doesn't abate, you have to be inventive and figure something else out!! This worked for me.

Yvonne