It only needs to be replaced if it's old brittle and cracked. So look at the ends and all over to see if air could escape. If it looks like it can leak air, then replace it. Also you'll just need to find where it's disconnected and simply put it back on.. Flame trap isn't difficult at all. And if you really want to start learning how to repair your Volvo, this is a great place to start.

You'll need a nice shop light to see in there, and possible a long nosed pliers. Although, it's completely possible to do this without any tools. Get a repair manual like Haynes, Chilton or Bentley. It'll tell you how. Also here's a diagram from IPD that should help..

http://www.ipdusa.com/products/5317/104083-flame-trap-kit

Once you finish that, "Noobeee" you'll officially be a DIY Volvo mechanic.

Also when you're finished, start up your car and look for leaks, also listen for a "whistling" sound. That's air escaping. A sound vacuum system should be pretty much silent. It's a closed loop that aids in helping the engine breathe. You'll have max power and better gas mileage with that nice and secure. Anytime there's a leak, it could also mess up your front windshield defrost. So be aware of that too, but that's a different post. Good luck!