First of all, here are the numbers for Hanrahan from the first half compared to the second half:
1st Half Hanrahan: 40.1 IP, 1.34 ERA, .201 BAA, 8 BB, 35 K, 1 HRA
2nd Half Hanrahan: 21.1 IP, 2.11 ERA, .235 BAA, 6 BB, 19 K, 0 HRA
Despite blowing a few saves in the second half, Hanrahan has still been extremely hard to hit. His first half was just ridiculous, and I think a person would have been foolish to think he would keep up the numbers he was posting for a full season. Now let's get to business, here's the pitch f/x for the first half against the second half.
Second Half:
You can tell that the velocity on the fastball is down by .4 miles per hour, which is somewhat substantial. There isn't too much difference in the movement, it actually looks like it improved, if anything. His whiff rates were better in the first half while he was throwing a higher percentage of his pitches for strikes. His control has been suspect in the second half, and his walks are much higher than they were before the all-star break.
I'm not worried about Hanrahan in the slightest bit. If he would have done in the first half what he has done in the second half, he would still have made the all-star team, although he probably wouldn't have been in discussions for the best closer in the league, as he was this year. You aren't going to see a pitcher keep a sub 1.50 ERA for very long, and it's encouraging to see that Hanrahan's stuff hasn't dropped off substantially.
There's no reason to think Hanrahan will be anything but dominant in the 9th inning for years to come in a Pirate uniform.